The propeller has several parameters to be considered,
but two in particular: its diameter and its pitch.
The pitch is the distance that a propeller with no
slippage would advance in one full turn. These two
parameters are usually expressed in inches and as
"(diameter) x (pitch)". Thus, an "8 x 7" propeller
would have a diameter of 8 inches and a pitch of 7 inches.
The diameter is determined by the HP of the motor and
the need to minimize drag particularly in sailboats
when operating on sail.
The pitch, on the other hand, is a function of the
maximum hull speed of the boat and the recommended
operating RPM of the engine at maximum throttle. A
pitch below optimal will cause the motor to deliver
less than its maximum power at maximum throttle while
a pitch above optimal will cause the motor to operate
below its intended RPM which [in an outboard] will foul spark-plugs and
fail to charge the batteries. It will also cause
the boat to accelerate to maximum speed even at low
throttle. This makes difficult the maneuvering of the
boat at low speeds, which can only be attained by
bursts of power at low throttle interspersed between
intervals in neutral.
Ideally, at maximum throttle the boat should reach
maximum speed and the pitch * RPM (prop) should be
covering the same distance as the hull speed - or a
fraction above it due to slippage of the propeller.
Terrific article by Greg Jones in Feb 2004 issue of Blue Water Sailing magazine
Seahawk's "Feathering, Folding or Fixed ?"
Folding or feathering prop can get jammed in an odd position if
a line gets tangled into it (or barnacles grow in the
wrong places). Unlike a tangle in a fixed prop,
you could end up with no forward and/or no reverse.
Folding or feathering props require lubrication at some interval, from every 6 months
to every 2 years. Usually requires a haul-out, but some can be lubricated
in the water.
From Alan Lewis on The Live-Aboard List
In spite of all the positive reasons for choosing a feathering prop (vs.
folding) -- including more speed under sail and better performance in
reverse -- I just encountered a serious drawback. A few weeks ago I picked
up a 20' length of nylon rope on my Maxprop which, unlike pot warp which
usually stops the engine, shredded and lodged between the blades. The prop
continued to spin and stripped the gears in the propellor, rendering the MaxProp
useless. Fortunately I was able to sail to my home port and get hauled. It
appears that the prop may be unrepairable and will need to be replaced. I
am seriously reconsidering getting another MaxProp in favor of a return to a
conventional fixed blade. It is nearly impossible to replace a MaxProp in
the water, making emergency repairs unlikely. Furthermore, I had to shorten
the shaft to accommodation the end cap on the MaxProp which leaves room for
only a single shaft nut to hold on a conventional prop (which means I should
also replace the [two year old] shaft).
From Justin on Cruising World
Some boats with an aperture don't have the space for a feathering
or folding propeller. With a traditional feathering propeller you
have to be careful that the extra length of the hub doesn't cause
the blades (or hub) to hit the rudder, and with an Autoprop you have
to make sure your shaft is long enough that the blades don't hit
your keel (or whatever is supporting your shaft) when you are
powering in reverse. Twouldn't be fun to spend all that dough and
then find out a fixed-blade is the only thing that will fit on your boat.
From John / Truelove on IRBS live-aboard mailing list:
I installed a 20" 3-blade Martec Autostream S stainless feathering wheel last
spring. Some advantages over the Max-prop (which I also considered): 2/3 the
price; greasing and pitch adjustment for ahead and astern can be done without
hauling; reasonably-priced replacement zinc is retained by one fitting. I
asked Martec to ship the wheel with the pitch set to equal my 20" x 14"
3-blade, and they were "spot-on."
There is a huge difference with the new prop vs the old fixed 3-blade.
Despite the fact that the astern pitch is much less (on purpose) than the
ahead, the stopping power is much greater and the prop "walk" reduced to
almost nil. ...
From Jon Eisberg on Cruising World
I just installed an Autoprop [6 months ago], and am very pleased with its performance ...
I had come from a conventional two-blade, and the reduction in vibration was
considerable - not to mention the achievement of hull speed at a reduced RPM ...
The mechanical complexity of these things is, of course, a concern ... I made a couple
of very minor modifications to my installation - for example, I didn't care for
the original setscrew arrangement which locked that shaft nut in place,
so I added a large lock washer under the lock nut itself, and changed to a
longer setscrew with lock washers which would put a positive pressure on the
lock nut itself ... And I didn't like the nylon bolts for attaching the zinc, so
I switched off to stainless ones ...
The only thing I find takes a bit of getting used to with an Autoprop is the
initially disconcerting "clunk" you notice when first engaging a gear,
and the blades "snap" into position ... There's a bit of a learning curve with
close maneuvering with a feathering prop - I find you have to occasionally give
a slight burst of RPM to really "set" the blades in their proper orientation,
but none of this is any big deal ... And, the Autoprop - at least on my boat - has
reduced the initial degree of prop walk in reverse significantly ...
Of course, as with any piece of gear this complex - you'd be a fool not to keep
a simple fixed-blade backup tucked away somewhere aboard. And, by the way,
most conventional prop pullers are unlikely to fit an Autoprop properly - mine
required just a bit of modification, easily done.
From Dan Blanchard on the WorldCruising mailing list
I installed a three-blade Autoprop on our 40' Brewer sloop "Augusta" two
years ago. The power train includes a 46 HP Westerbeke diesel with a Hurth
V-drive, the auto-prop has a 19" diameter. The performance figures below
were taken with much of our heavy cruising supplies off the boat, around
23,000 lbs. I have noted the following improvements in performance under
New max. 2600 RPM, 7.9 knots
Old max. 2600 RPM, 7.1 knots
Old cruise speed at 2450 RPM 6.5 knots
New cruise speed at 2250 RPM 6.5 knots
I have seen no real change backing our boat down, she never pulled hard to
port with the old fixed three-blade either so I guess there was not a lot of
room for improvement here. I have noticed a considerable increase in
emergency backing power, I can stop the boat in half the distance of our old
I am very pleased with the performance of this prop. I wish I had installed
one prior to our Seattle-Sydney cruise a few years ago. I could have saved a
lot of fuel and wear and tear on the engine given the lower cruise RPM. It
is surprising how this prop performs at lower RPMs on flat water. At 1500
RPM we can poke along at 5 knots as long as there is no head sea. I can't
help but think how nice this would have been on one leg of our last cruise
that had us becalmed north of the Cook's for three days.
As I recall, the prop was expensive, around $2,800 for the whole thing.
From Doug Sterrett on the
WorldCruising mailing list
I got a tip from
Downwind Marine in San Diego about the zincs for my Autoprop: Drill a hole
(3/8" - 1/2") in the center of the zinc. This will allow the zinc to
corrode more evenly and will extend the life of the zinc without
sacrificing functionality. Also paint the inside of the bolt holes where
the shafts of the bolts would contact the zinc metal. This will prevent
the zinc from prematurely corroding where it is attached and falling
off. So says Downwind Marine and they sell a lot of these.
Use conductive grease between zinc and shaft to make better contact.
From JeanneP on Cruiser Log Forums
We put an Autoprop feathering prop on SV Watermelon to reduce the vibration and pressure
on the transmission more than to increase speed.
Although we had slightly less prop walk with the feathering prop, we lost almost a
knot of motoring speed in forward, and reversing required a bit more initial power
to get the blades to reverse.
I did not notice any improvement in weather helm with our changing to the feathering prop.
As we got better at trimming our sails, most importantly reefing earlier, the weather helm eased significantly.
When we sold Watermelon in Singapore, we agreed to take the new owner out for several
days to help him become accustomed to the boat. Because we felt the feathering prop
required more skill than this owner possessed (he was a complete sailing novice when he
bought the 'Melon), we put the original fixed prop back on the boat.
Peter and I were both surprised at the faster motoring speed with the fixed prop,
and the quicker response when the boat was put into reverse. I had forgotten what we
gave up to get that little bit of extra sailing speed and reduced vibration.
We had one frightening episode that I think was due to the feathering prop.
Rather than relate it here, it's in our log for Papua New Guinea
the 2nd and 3rd paragraphs.
It was an Autoprop, made in Australia, that was installed in St Martin by the Aussie
riggers there (absolutely fantastic sailors, those guys!). Peter says he doesn't think
he'd install another of that make, though changes to the design were made several
times while we owned ours and it was a better prop by the time we removed it than when we first installed it.
I should also add that since the winds in the Caribbean are so strong and reliable,
we did not use our engine very much at all in the four and a half years that we
sailed there (we probably used about 50 gallons of diesel per year). The feathering prop
was far more useful there, and in our long passages in the S. Pacific, than once
we arrived in SE Asia where there wasn't much wind at all and motoring was more important.
From Richard on SailNet's Gulfstar mailing list
Folding prop ... forget it.
We were heading into our slip and guess what ... It never engaged in reverse
and we crashed into the dock. Need I say more?
From James Moran on the Yacht-L mailing list
We recently had a customer install an Autoprop on his yacht. Based on his
experience, we probably won't be recommending them again. Maneuvering with
them can be pretty difficult. It takes a fair amount of RPM to get the
blades to pitch, especially if you want reverse when the boat is moving
forward or vice-versa. At low engine speeds, it doesn't develop much
It has the feeling of an automatic transmission with a slipping torque
converter. The engine revs for a while, then the boat starts to respond.
We like Max-Props. They develop excellent thrust in forward and reverse.
The VIP models allow one to adjust the pitch with the boat in the water, but
we do a pretty good job of getting the pitch settings correct before the
boat is launched so the Classics are what usually get installed on our
From Jane McKelvie on The Live-Aboard List
We have two Max Props on our 50' catamaran that are powered by two Volvo
Penta MD40 engines. We are very happy with the performance of the props but
there are a few things you should take into account:
1) Max Props (ours anyway) have to be removed from the shaft with a special
tool (one-off purchase).
2) Max Props come off in several pieces which then have to be replaced very
precisely to get the correct pitch.
3) After six years of working with the props we are now able to remove one,
clean it up, grease it, and replace it in two hours.
4) Check out the anodes that you need for the props - we have to buy special
anodes and unfortunately the one between the s-drive and the prop is a cone
which can only be replaced by removing the prop.
5) As a result of all the fiddling about we feel we would not happily/easily
be able to remove/replace the props under water. There are too many pieces
to lose. We also have rope cutters to add to the pieces!
Despite this we have never changed our minds and returned to fixed-blade
From Steven Dubnoff on The Live-Aboard List
I just went though the same choice this year. Everyone I talked to (my
mechanic, and those with similar boats) advised me to get the
Maxprop. I bought one and have been very happy.
Recently another Nauticat owner made the other choice and bought an
Autoprop which he says vibrates like mad. They have been also known to drop
The Maxprop is expensive and you really have to watch the zincs. I had
mine put on by a yard where they knew what they were doing. It did not
Pyacht.com has them at 10% off list all the time. They will get a
recommendation from PYI for you (PYI will support you anyway).
From Ron Rogers on The Live-Aboard List
I've owned a Maxprop and was very satisfied. It improved reverse
tremendously, and reduced prop walk. However, there was a small loss in
top-end speed. Be sure to pay attention to zincs and try to get the one that
allows you to adjust pitch underwater and grease underwater. You may find
that you can improve on the factory recommended pitch setting by trial and
A friend of mine purchased the Autoprop and noted improved performance in
all aspects, HOWEVER, the blades became loose. In consultation with
Autoprop, they advised him that their propeller requires a haul every six
months to repack it! They fixed it anyway, but he did not purchase an
Autoprop for his new boat.
From Luke Curtis on SailNet's Gulfstar mailing list
We have a three-blade Max Prop on our Gulfstar Sailmaster 39. Great performance under sail
compared with our old fixed Michigan (+ 1/3 to 1/2 knot) plus much better
backing ability under power.
Like many other Max Prop owners, we have been plagued with short zinc life.
In addition to the 63M zinc on the prop, we carry a shaft zinc as well. We
need to replace the 63M every three months.
Part of the issue with the Max Prop zinc life is the design as the three
attachment points are at the bottom of the cone and wear through quickly,
tossing off the balance of the zinc. Also, we have a hot marina which doesn't
At the Seattle boat Show, the PYI folks gave us the following tips to
prolong zinc life:
- Clean and rough up both the zinc and prop surfaces prior to replacement
(suggest same on shaft zincs as well).
- Put conductive grease around base of zinc.
- Apply bottom paint to zinc around the screw hole areas.
- Use an O-ring on the screws to reduce conductivity between the
- Use locktite on the screws to keep them in position.
PYI says this should extend the 63M zinc life by 50-100%.
From natanzon on SFSailing:
I am using a 3-blade Max-Prop. It is set for 18" X 13" for a Volvo 50 HP Sail Drive.
I like the use of the prop. I had it set at first for 18" X 12" and
after a year when pulling the boat changed the pitch.
One real problem with the Max-Prop is parts and grease
that you need for it. If you need to
replace the zinc every year or other year and you
need to pump the prop full of a special liquidy
grease you may be finding it hard to get. The factory
is willing to mail it, but will not accept
credit cards use for payments, only bank transfers,
so that easily it can cost over $120.
From Alan Lewis on SailNet's Gulfstar mailing list
I installed a three-blade Max-Prop on my Gulfstar 41 this spring, and it
has performed flawlessly. It was easy to install myself; I was a little
intimidated by the need to cut off an inch from my shaft, but it worked
out well. I gained at least 0.5 knots under power, and about the same
under sail. I especially noticed an improvement in light-air conditions
(always nice for a '41 which isn't known for its light-air abilities).
From Don / Allied Mistress 39 on Latitudes and Attitudes Cruisers Forum:
I have a Maxprop on my full-keel boat, with wide "deadwood" ahead
of the prop aperture, very similar to the Morgan OI.
It works very well; adds 1/2 to 3/4 knot under sail and
provides good handling in reverse.
From Philip Lange on World-Cruising mailing list
We had a Max Prop on our Searunner 37. Twelve years of 'on the
move' cruising and the only problem I had was after I backed into a rock
with it. (Got it straightened out in VZ and it worked just fine.) Sent it
off after ten years to have it tightened up. Found the guys there to be
fast and reasonable. When I got the prop back it was like new.
Boat always backed well.
From Grandma Rosalie on World-Cruising mailing list
We have replaced our fixed prop (3 blade) with a MaxProp, and I think
it has been money well spent. The shaft no longer sounds like a
freeway at full speed when we are under sail. Other CSY owners have
also put MaxProps onto their boats and they've been happy with them.
We did a short test sailing with the engine on but in neutral (to run
the refrigeration) and the prop free-wheeling, and then with the
engine off and the prop feathered and figure that we gained about a
half knot in speed.
It does take a little bit of time to learn to make the prop feather.
Other people in the group have put on the AutoProp which I think is a
folding prop, and they also were happy with it. They also did test
runs with the old prop first, and then with the AutoProp. We got the
MaxProp because it was less expensive.
From Lynn Ogden on World-Cruising mailing list
None are as efficient as a fixed two- or three-blade prop. They cost a lot of money. They require
more maintenance than a fixed prop, and some expensive replacement components. For me, I think
they are a waste of money - unless you race a lot. Further, having a component with a lot of moving
parts that can foul or break under the boat, under water, that you can't see or repair without a
diver or a haulout or extra spare parts isn't for me.
From Bryan Genez on World-Cruising mailing list
Simple is always good (KISS), but every so often, simple can be improved.
Feathering props are one of those improvements. They *are* more efficient
than fixed props in reverse. They *are* robustly made, and rarely, if ever,
fail. Maintenance might involve five minutes per year to add grease ... not
exactly a back-breaker. The winches on your sailboat are more fragile and
require more maintenance than the feathering prop. Further, they can be
adjusted by the owner to most efficient pitch, depending upon your cruising
RPM. Some - like the Autostream - can be adjusted while the boat is in the water.
A feathering prop will probably add one-half knot of speed over a fixed and
locked prop. That's 12 miles/day or two hours/day of cruising time. A
fixed-blade prop will be more efficient when you're moving forward under
power. Definitely a benefit if you prefer motoring to sailing.
I've had a three-blade Max-Prop for 18+ years. I never race. I'd
cheerfully "waste" my money on another, if I were to purchase a new cruising boat.
From Lynn Ogden on World-Cruising mailing list
I don't know about you, but I spend very
little time in reverse to warrant a +/- $2000 prop that "backs up" well. Likewise, 12 miles a day
aren't worth $2000 to me either.
In Annapolis many years ago I went sailing with a friend who had to
dive over the side to scrape the growth off his folding prop before he could get out of the
marina. To me that would be a back-breaker. ... one barnacle in the wrong place can render a
feathering/folding prop inoperable and unusable; a fixed prop would have its efficency reduced, but
would still work.
From Bryan Genez on World-Cruising mailing list
I haven't experienced anything close to this. While barnacles are quite
strong, the forces against a feathering prop are stronger (in my
experience). A barnacle that interfered with the action of a feathering
prop would be broken off.
As recently as last year, I had fouling so severe on my prop that I had a
diver clean it. I hadn't used the boat until the end of the year, and the
Chesapeake barnacles had free rein to grow at will. But prior to the
cleaning, the blades rotated properly; the problem was that the water flow
across the blades was so turbulent that the prop lost about half its
efficiency. It was exactly comparable to the losses experienced by a
fixed-blade prop with barnacle growth.
From Philip Lange on World-Cruising mailing list
Sometimes that extra half knot gets you into the harbor before dark. A
half knot on a five-knot boat is a 10% increase in speed. If your boat is
faster, you will most likely have a proportional increase in
speed. Twelve miles a day on a thirty-day passage is 360 miles. You get
where you are going three days sooner.
On a faster boat it is a safety feature. Turbulence from a fixed wheel
causes the rudder to loose its "bite".
I had my three-blade Max Prop for 12 years and did not have any problem
with it that was related to its being a feathering prop.
There is a world of difference between a folding and a feathering prop. No
one should talk about them as if they are interchangeable. I have
experience with both and don't have much good to say about the two-blade
folder I had. Folders are usually much less expensive and can be easily
found secondhand for very little. I would not consider any that did not
have the blades geared together. The Gori propeller is one that does. They
make a three-blade folder. They are not cheap. No folder backs as well as a
Feathering props are rare on the used market. I remember seeing a well-used
Max Prop at the BAM in Annapolis. It went for over half the new price.
From Gregg O'Malley on SailNet's Gulfstar mailing list
I had a Martec on my Catalina; not in the same league with Max Prop.
From Fred Fraim on The Live-Aboard List
I would not give up my Martec
folder. With the Martec I can steer just as well in reverse as in forward. ...
From Nick on Cruising World
Two or three years ago we put a Martec Autostream feathering prop on our Catalina 42.
The Martec and Max are similar design - I took the Martec because it was $400
less. It replaced the 18" 3-blade.
Regarding speed increase, there was a slight improvement.
Bob and Rick have an identical boat and in the past we could sail a long
time with almost identical speeds. With the new prop we gained about
0.1 kt at 6-7 kts to weather. Without a head to head match race we'd
never notice the speed increase. They've since put on an Autoprop so
we no longer have the upper hand. Back to luck and skill in that order.
The most noticeable improvement is in helm reponse and rudder effectiveness.
The feathered prop doesn't disrupt the water flow over the rudder nearly
as much as the fixed prop so we have noticably less weather helm.
The improvement was pretty dramatic. Keep in mind our boat has the stubby
square rudder the Catalina put on the 42's in the earlier years.
This may not have been as important with the new, deeper rudder.
Under power it isn't as smooth as the fixed prop. I think this is due to
the compromised blade shape. I noticed this the first couple of times out
but have since gotten used to the slight vibration and don't think about
it anymore. You can't set the pitch the same as for a fixed prop.
The fixed pitch was 13". Translating that to the degree setting would
have resulted in way too little pitch. Martec gave us an initial recommendation
which turned out to be too little pitch. When summer came I spent an afternoon
diving/adjusting and testing. After about 3 tries I finally got it where I wanted.
The Martec is very easy to adjust in the water. Performance in reverse is
very good with almost no prop-walk. Sometimes this isn't a totally good thing
since the prop walk can be used to help pivot the boat in a tight spot.
Sometimes, though, you want to swing the other way so the lack of prop walk is a good thing.
I can't compare performance of the Max v.s. the Martec since we haven't done
a head to head. The Max does have greater blade area which may be a benefit.
Same for durability and resistance to damage. The Max is bronze, the Martec
stainless steel. There are arguments for and against each.
I'd do it again. Might consider the Max the next time because of the larger blades.
From Charlie Stillman on Cruising World
I had a three-blade maxprop on a previous boat and it was fantastic
compared with the old two-blade Martec prop. By jingo, the
Maxprop worked great EVERY time in reverse!
Here's the problem I have with Maxprops. Look at the blade shape.
They are shaped like paddles. Now look at most fixed three-blade props.
They have more of a foil shape. They are optimized for moving a boat
through the water. The Maxprop is a compromise between feathered
profile and engaged profile. They are mechanically complex and
require regular maintenance.
The Flexofold prop folks have test data claiming greater efficiency
*and* tied for lowest drag compared with the competition.
(Such data could be cooked
of course, and tank tests may not be same as real world.
BTW, Maxprop claims 96% efficiency compared with a regular prop.
Evidence?) Flexofold blades look more like those of a regular
fixed prop to me than Maxprop blades. That would fit with claims
by Flexofold for greater efficiency and less likelihood to cavitate.
One Maxprop advantage is you can change the pitch.
There are many satisfied Maxprop users. I just think there are better
cheaper alternatives. We were skeptical when we heard about
Flexofold props, based on our experience with Martecs.
But we found that Flexofold props have awesome stopping power.
I ran into an HR43 friend at Armchair Sailor yesterday. He had
had problems with his Gori and was replacing it with a Flexofold.
Flexofold zincs cost $30 apiece. THAT is a problem.
I have no room for a shaft zinc. Gotta get a zinc fish to help at the dock!
Propellors are a case of: there may be more than one right answer.
Getting size and pitch right is critical.
From Gary Elder:
Considering the design of your boat [beamy shoal-draft full-keel motor-sailer]
and its intended use [liveaboard cruising], I would not do
it. Many times, I've had to try to help West Marine customers sort out various
problems with folding and feathering props. One of the better feathering
props has a major problem with electrolysis, but the manufacturer won't
admit it - always blames it on the boat owner, but it's always the prop that
causes it. I don't think you will see much improvement in performance - with your boat - by
changing to a folding or feathering prop.
... MaxProp. Today I was able to talk to one of the 'unfortunates' who purchased one of
these things. He is really pissed. He paid about $2K for it, spent about
that much again trying to troubleshoot the electrolysis problems, and the
only performance improvement he can notice is that it will stop a little
quicker when he puts it in reverse.
The boat is a Pacific Seacraft 34, which like your boat doesn't go to
weather very well (but better than yours), and like yours, doesn't have a
bottom that will let it perform really well. It is, however, a very
His performance improvement under sail alone is so unremarkable that he
can't tell any difference between the MaxProp and his old three-blade prop.
He has been able to get the MaxProp folks to admit that the speed increase
using their prop is usually measured in tenths of a knot. If you are a
racer one tenth of a knot is important; if you are a cruiser it's nothing.
His advice? Spend it on a new 150 jib and some rig improvements. My
perception of that is that you will still have a MOTORsailor; the basic
design of the hull and rig will never let it be a motorSAILOR.
[Another guy,] who used to work for Morgan and Gulfstar,
said there are "a hundred other things to spend $2K on that will help
you more than a MaxProp".
From tsenator on Cruising World
I've had the Autoprop for 2 years now and I am very happy with it,
but I agree it might not be for
everyone. I suspect that most Autoprop or Maxprop
users will say theirs is best. Who will admit
that they made a $2000 bad choice?
My take on it:
Autoprop - a lot more efficient under power
and especially motor-sailing since the
prop always finds it's own best pitch. Sort of like an
automatic transmission. Good speed gain
under sail with the feathering. Some early users might
have had an issue with the right size
Autoprop, I think with years of experince they have gotten
really good with specing the sizes. You
probably won't go wrong with their recommendation
if you have a popular boat, as they've already
gone through the trial and error to find the right size.
Some owners also might have an issue with
clearance from the strut or other geometry depending on
your boat, this is because the blades will
swing all the way forward and cover a wider area
to swing into reverse. Also remember these props
are really not as good for smaller boats as the hub
size needs to be a certain size no matter what,
and if your blades are small then naturally
the blade size to the hub size is a smaller ratio. The
other thing is that these are very heavy props and
you should go to stainless steel shaft as
bronze doesn't have the stiffness needed.
(Trust me on this; I know.)
Maxprop - slightly less drag under sail because
the blades are flat rather than cupped like the
Autoprop. Good motoring power compared to standard prop,
but not quite as good as Autoprop except
perhaps at full power. Since the pitch can only be
adjusted for max efficiency at full power, the
efficiency at part-throttle or motorsailing will
be less. Because you have to adjust the pitch
yourself, some owners report having a diver make
several dives and adjustments before they are
happy with the pitch. This seems to be trying the
recommended setting and then trial and error to
get it perfect. Probably not that great a deal
unless you are a perfectionist and it is only done once.
If I was a racer, I would absolutely lean towards the Maxprop,
especially nice is that they have a
2-blade option not available on the Autoprop.
For some cruisers, I think the Autoprop has some
real benefits. Especially the efficiency of
motorsailing, it's amazing, when I have the engine
running at just idle, and I am motorsailing it
feels like the boat goes into turbo mode. I always pick
up a few knots of speed and much more than
I ever did with my 3-blade at the same RPM's.
Also I have noticed a drastic increase in fuel
economy, where I used to get about .8 Gal/hour,
I now am rarely above about .6 Gal/hour. So the fuel economy
alone with limited fuel on a long distance cruiser
might really help. BUT if I was a full time
cruiser and cruised with an Autoprop, I would
definitely carry a spare fixed-blade prop and an
autoprop prop-puller, because, you never know,
it "is" a mechanical device and there "is" a small
chance of a problem. But the service from the Autoprop
people have been very good and I have heard
mostly good things about them. They will make things right for you.
So why did I finally decide on the Autoprop? I will
not argue about sailing drag -- especially
when racing a boat. The other folding props will
be much better for drag, no question about it
(especially is very light air) -- But I just cruise
and go gunkholing and besides it is WAY
better with drag than my previous 3-blade prop.
(Autoprop has 85% less drag than a 3-blade fixed
-- Folding Prop has 95% less drag than a 3-blade fixed.)
Cruisers tend to motorsail when the winds are light.
They don't want to pull the sails down
completely but want to get where they are going.
Reaching hull speed at low RPM's while
motorsailing can be done with the Autoprop due to the
automatic variable-pitched prop. The blades
will increase their pitch due to the assist
from sailing and create thrust over all RPM's. This
will increase your speed and cut hours off a voyage.
But one of the main reasons I got the Autoprop is
the amount of power in reverse. Most of the
props and, yes, especially the fixed ones are very
inefficient in reverse. There is NOTHING better
(nothing less than putting on a reverse-turned
fixed propeller) than the Autoprop in reverse. The
Autoprop is designed to produce the same lift
and thrust in forward and reverse.
You might ask why I care so much about power in
reverse, well, like I said above, I like to go
cruising and gunkholing. And, well, the places
I like tend to go into shoal a bit and have *very*
thin water under my keel. So if I touch bottom,
the Autoprop is by far the most powerful propeller
your boat can have to "un-ground" itself ...
I look at it as part of my "Tow Insurance" ...
From Andy Anderson on The Live-Aboard List
Re: Autoprop variable pitch propeller:
We have owned a 1977 P365 for about 8 years now. When we first bought her the
previous owner had installed a folding prop, I don't know why but presume for
more boat speed. We used it for the first season and found that the boat
would not back up! Thus, we took the folding prop off at winter haul out and put
the original 17X10 fixed 3-blade back on.
From Bob Perry on Cruising World
I have a Gori on my own boat and I like it a lot.
I have had it for eight years without a problem.
From bernie on Cruising World
Have a Gori on my HR. I like the two-speed option ... but
still think that the Max-Prop is better.
From Jeff H on cruisersforum.com
I had a Gori prop on my last boat. The props were not terribly reliable
(the polyurethane connection between the hub and the shaft socket failed
several times, and a hinge pin failed once as well) and the factory support
was far worse than awful. I would never buy a Gori prop again and would
consider it a deal-breaker on a larger boat if it required one.
Getting back to the original question, my boat made a very distinct 'thunk thunk'
at speed. I had been concerned that it was a problem with the Martec prop and had
it rebuilt and the noise did not go away. This spring I replaced the cutless bearing
and it is amazing how much quieter the engine and drive train became. The thunk thunk is gone.
Also, it turns out not all
props are made the same. Many folding props are actually made so that they are
more efficient in motoring in the forward direction than a fixed prop because
they do not have to have the compromised shape to reduce drag when sailing.
Like many things in sailing, the improved efficiency in forward sometimes results
in a reduced efficiency in reverse. Autoprop claims a higher efficiency than
other props because the pitch changes with load. That said, I have come across
some negative comments on the Autoprop when used in rough conditions.
From haffiman37 on the Sailing mailing list
A year ago I replaced my original Radice 2-blade prop with a Gori
16,5 x 12 x 3 on my Janneau SO37 2002 model. The main attraction was
the advantage of the "overdrive" function that would, if worked, give
me an extra range of approx 20%. Quite interesting as I am going for
quite a trip later this year: Norway to Malaysia through the Panama
Canal and Pacific.
The propeller was calculated by Gori who was given
all info on the boat. However approx 150 RPM was missing when testing
on "empty" boat. Next shock came when I lifted the boat after one
year at sea: severe galvanic corrosion, beyond repair as stated by
Gori. The original factory-mounted anode was of course gone. The
original Radice had no signs of corrosion after 14 months and exactly
the same conditions. No shorepower hookup etc. The boat is always
moored with battery-switches off.
However Gori denied any
responsibility whatsoever both for corrosion and even for the wrong
prop calculation. Instead they claimed 150 RPM below required RPM
was "bulls eye", and corrosion a result of neglected maintenance,
(change of anode). My opinion is of course quite different, as I claim
that a service-interval of 12 months has to be expected and
calculated when designing the propeller and anode dimension. Not to
forget that the service department of Gori threatened me with a lawsuit
if I went public with this case, giving Gori a bad reputation. No
need to say that buying a Gori 3-blade is not what I recommend if you
are looking for lasting quality and good service!
From Jerry on Cruising World
I have had severe problems with Gori prop (3-blade folding). I have for the second time lost a
blade placing myself, guests, and boat in danger. Both incidents happened with less than 10 hours
on the prop. I returned the prop with their authorization two months ago and have not heard from
them since. I am preparing to take further action.
From Ivars on SailNet's Gulfstar mailing list
Re: folding prop on GS 41 ketch
You need to check the amount of clearance behind the prop to determine
whether a folding prop or a feathering prop will be better suited. Most prop
manufacturers should have data as to which prop will be better suited. A
folding prop needs more space (to fold), whereas with a feathering prop the
blades just rotate into a feathering position. Either one will enhance the
entire sailing experience and is the best bang-for-your-buck performance
enhancement. Typical speed gains under sail are close to 1 knot. At 5
knots that is a 20% speed gain. Performance under power is not affected vs
a fixed prop.
From Bad Matt on Latitudes and Attitudes Cruisers Forum:
A fixed prop is designed to spin forward. Its blades are not properly curved to spin in reverse.
It will work in reverse, just not well, which is why fixed-prop boats usually are
somewhere between bad and useless in reverse (lots of prop-walk usually).
The feathering prop allows the prop blades to be properly aligned when
spinning in reverse, thus making the boat handle better in reverse.
Almost like if you were to take the prop off and put it back on backwards
when going in reverse (at least for the Gori).
Re: which prop:
The Beneteau list has a semi-annual prop war, which usually deteriorates
into the kind of name-calling and childishness one would expect on the Ford vs. Chevy forum.
I think this happens because those who have upgraded (myself included) to a
Gori-Auto-Flex-o-Max-a-Vari-who-the-hell-cares-what prop have found it to
be some of the best money you can possibly spend on a boat (unless it's sinking).
I have a Gori and I absolutely love it and would recommend it again without hesitation.
That said, some portion of that euphoria is simply the handling under power and
substantial increase in speed under sail (like, a knot's worth) that I've observed.
Now, I can't say that any other, or all, of the competitors' products would
or would not provide the same enjoyment. I think I can say this: you will NOT
regret getting a high-tech prop. I don't know that the Gori is necessarily so
superior to the others. In theory, it's curved blades allow it to power better in
reverse than the Max (I buy that, I guess). I've made several people nearly commit
suicide when they saw how easily I get into my slip.
From Jeffrey Kay on Latitudes and Attitudes Cruisers Forum:
I have learned that one of the major differences with the Gori is that it has an "overdrive" feature.
From their website: The "overdrive" is used when motorsailing in fair weather or when
using the engine under sail. The "overdrive" gives the same speed at lower RPMs.
The result is less engine noise, less vibration and better fuel economy.
The function is simple. E.g. when changing from "overdrive" to normal ahead the
shift and throttle control is set in neutral, which allows the propeller to fold.
Then the shift and throttle control is set in forward again.
It sounds a little confusing -- like how do you know if your in overdrive or
not -- but I'd imagine you'd get used to it.
From Bad Matt on Latitudes and Attitudes Cruisers Forum:
You know, I forgot about the overdrive part (boat's on the hard - go figger).
I've used that a couple of times. It's nice. You gotta be serious about it though,
because to get into overdrive, you gotta go backwards, then pop the throttle into
neutral, then forward and you're in overdrive. It is nice when motorsailing though.
I've never had a problem accidentally winding up in OD. It's pretty easy to tell
when you're in OD inadvertently (i.e. no sails helping out) because the engine
will be laboring and won't wind up like normal when throttle is applied.
If you think about it (and this is one of the reasons I don't use OD all THAT much),
putting the prop in OD without the sails helping to move the boat is basically
like having an over-pitched prop, which is overloading the engine.
From Paco PWD on Latitudes and Attitudes Cruisers Forum:
I had all the same issues with the original 18x13 fixed 3 blade prop on my Corbin 39.
Since we got a "J Prop" variable pitch / feathering prop, it's like a different boat,
sailing and motoring. I very highly recommend it.
The blades have the same profile in Forward and Rev.
and the pitch is externally adjustable (even in the water) by indexing a marked dial on the hub.
In case of the J Prop, you can go with the largest
diameter that can fit, as you can easily pitch down if need be.
From Jeffrey Kay on Latitudes and Attitudes Cruisers Forum:
> how much speed under sail does your feathering prop gain you over a fixed?
All things being equal, about a knot.
[1980 Gulfstar 44 CC Sloop]
From Bad Matt on Latitudes and Attitudes Cruisers Forum:
> how much speed under sail does your feathering prop gain you over a fixed?
So, another way to think about it would be that it's about a 15-20% increase in speed. It is extremely noticeable.
From The Barnacle on Latitudes and Attitudes Cruisers Forum:
One comment about gaining 3/4 to 1 knot sailing speed by using a feathering prop
or 2-blade vs 3-blade [2-blade turned to "hide" behind the keel].
Those are VERY optimistic numbers. I've towed buckets,
people, anchors and all types of draggy items while sailing different boats
just to check drag/speed. It takes a lot more area than a prop to slow a 30-40'
sailboat boat down 3/4 to 1 knot. If it does there isn't enough sail out and
you are in ghosting wind conditions.
From John Dunsmoor:
Would not completely agree, the personality of vessels is many times unique.
I can attest that the difference between fixed prop left free to rotate and
not rotate while sailing is negligible. One of the reasons that we always lock
the prop when sailing on our boats. But having sailed with fully feathering
props the difference can be dramatic. We were on a 78 foot Cheoy Lee motorsailer
with huge propellers, they must have been around 30" and the boat would not
tack without cranking up the outboard engine and helping the boat out.
The boat had a lot of sail and really powered along in anything approaching twenty knots.
But between the twenty foot beam and a massive amount of windage it just would not
come through the eye of the wind. The boat was modified to use a set of Max Props,
which feather, and the boat would tack without cranking an engine.
On Ciboney, 400 Beneteau, this is a modern clean underwater design and one time
we lost the prop and had to sail back from the Bahamas without a prop, you
could feel the difference. Everything about the handling of the boat was different,
not spectacularly different but you could tell.
On our little Columbia with or without the motor in the water, large
difference in both handling and speed.
Now the fellow is right about maximum speed potential, if the hull speed of the vessel
is eight knots and you can reach this with a locked three bladed prop in twenty knots
of wind, then the installation of a very expensive feathering prop (and the Max Props
set the Choey Lee owners back a fortune) is not going to change the formula much.
Your hull speed is still going to be eight knots, with a feathering prop you might
be able to achieve hull speed in 15 knots of wind, instead of twenty, who knows.
But the fact is most of our sailing is done in less than twenty knots, and do you
want to be sailing in ten knots of wind at four knots, or five and a half knots.
Twenty four hours the difference is 36 miles, going across the Gulf Stream the
difference would be hours. Four knots is barely enough to beat the current;
the difference between four and six knots is dramatic.
On Magnolia [Gulfstar 44 motor-sailer]: I would think that the change would be dramatic.
You could experiment by pulling your prop and sailing without it for a bit, an awful lot of work.
The personality of the boat would change. At the same time the boat is a bit of a
barge with lots of sail area so maybe the difference would not be so dramatic,
especially once you had some wind. On the other hand a three-bladed Max prop
is going to set you back thousands of dollars. Is half a year's cruising fund worth it ?
One element is how much time you are actually spending moving, which would make a
boat that is sailing only a few days a month less worth the investment than a cruising vessel
that is continually on the move.
Another problem is growth, a fouled prop is a pain, and a fouled feathering prop is more of a pain.
I was on a 65-foot Lancer with Max Props, and one thing that I did not like was the bang
that emanated from changing from forward to reverse. I was sure that we would eventually
shear something, but it never happened. And also there was a time lag when docking
between forward and reverse, which was another queer element that one needed to get used to.
It was only a delivery so I never got used to the idiosyncrasies of the power train on
From 5/1/2000 issue of Practical Sailor
Max-Prop: flat blades so less efficient in forward, better in reverse.
Autoprop: requires less RPM than Max-Prop, but longer to get traction
when starting, more drag and vibration.
From Bruce Clark on Latitudes and Attitudes Cruisers Forum:
I have a Maxprop and am very pleased with it. I have one friend who removed
an Autoprop after one year because he was not pleased with the performance
for some reason. I have heard of a few boats having motor-mount problems
because the Autoprop is so effective in acceleration and reversing.
This would not be a problem with the prop - more of an endorsement.
From Senator on Latitudes and Attitudes Cruisers Forum:
My take on each is this:
Autoprop - probably more efficient under power and especially motor-sailing,
since the prop always finds it's own best pitch. Just as good in forward as reverse.
Sort of like an automatic transmission. Also one of the few/only props that
swivel 180 degrees and can make this claim. If I was a bluewater cruiser
where I might have to get as much efficiency as possible and put as many
miles per gallon while motoring ---- I don't think there is anything better
than the Autoprop at efficiency under varying loads, which happens often
when the motor is needed to cruise. (Autoprop is 25% more efficient
than fixed 3 blades and 30% more than folding.) Good speed gain under
sail only with the feathering, but not as much as with folding props
or the Maxprop. A few users report a little more vibration under power.
(I don't notice it.) Some people also report they have to maneuver at
speeds above slow idle to get the blades to start to grab.
Some people choose to add a little length to the prop shaft with a
"drivesaver" to give more clearance from the strut depending on your boat.
So I say the nod goes to the Autoprop for cruisers.
Maxprop - slightly less drag under sail because the blades are flat
rather than cupped like the Autoprop. Good motoring power compared to
standard prop, but not quite as good as Autoprop except perhaps at full power.
Since the pitch can only be adjusted for max efficiency at full power,
the efficiency at part throttle or motor sailing will be less. Because
you have to adjust the pitch yourself, some owners report having a
diver make several dives and adjustments before they are happy with the pitch.
This seems to be trying the recommended setting and then trial and error
to get it perfect. Probably not that great a deal unless you are a perfectionist,
and it is only done once. So I say the nod goes to the Maxprop for racers.
Basically the Autoprop is great for getting the most out of your engine
and at different speeds and ideal for motorsailing. Debatable, but more
generated thrust in forward and reverse. The Maxiprop gets the upper hand
in reducing drag especially in lighter air. (I think when the wind picks
up you won't notice the difference.) I have heard a few times that fuel
consumption is poor with the Maxprop in heavy and hard conditions
With any of these props works with the dealer/factory to make sure the size
and pitch is correct for your boat, engine and transmission type.
In these cases one size does not fit all.
From PhantomSailor on Latitudes and Attitudes Cruisers Forum:
I have an Auto Prop on my 1997 Catalina 42. I just love the propeller.
Moves the boat a 7.2 knots at 2500 RPM with fuel consumption at .73 - .76 GPH.
The engine is a Yanmar 50hp 4JH2E. Stops on a dime and very little prop walk in reverse.
Sailing performance is about the same as my friend's Flexofold 3 blade feathering prop
on an identical boat.
FYI, Autoprop recommends that you put the transmission into forward gear while sailing
to fully feather the blades and to stop rotation. The common practise of putting
the gear shift into reverse will not work with an Autoprop as the blades will
rotate to the reverse position which causes the prop and shaft to rotate in the
reverse direction. Most trannies will allow rotation in the same direction
as the gear shift indicates. I.E. if you have a right hand prop, the prop and
shaft rotates clockwise (looking at the prop from the stern)in forward gear.
With engine shut off, the gear shift in reverse, and sailing forward, the
Autoprop will go to the reverse blade position and the prop will want to
freewheel CCW. The trannie in reverse will allow this because that is
the direction the trannie rotates the shaft in reverse. If you place the
gear shift in forward, the prop still tries to rotate the shaft CCW but
the trannie will not freewheel since CCW is the opposite direction the
trannie drives the shaft with the engine running. Once the prop is
fully feathered, you can return the gear shift to neutral but I seldom
bother. BTW, it takes 3 or 4 knots of boatspeed to fully feather the blades.
However, once feathered, they will stay feathered even if the boat speed drops again.
From article by Greg Jones in Feb 2004 issue of Blue Water Sailing magazine
- Taking spare blades with you is not practical,
as the blades are a carefully matched and balanced set.
Better to carry a fixed prop as a spare.
- Feathering props (and Autoprop) have larger hubs than
the others, and often larger blades to compensate.
- Feathering props (and Autoprop) need annual
greasing (some can be lubricated in the water); folding props
need less maintenance.
- Saildrives have a splined, non-tapered shaft.
USA-built boats have one standard shaft taper.
European-built boats have one of at least four different shaft tapers.
- Feathering props are slightly better for motoring or motor-sailing; folding props
are slightly better for sailing.
From Steve Rust on cruisersforum.com
A couple of additional points from the article in Feb 04 edition of Blue Water Sailing:
Feathering props will generally provide more power in reverse than folding props because
they present the same leading edge whether in forward or reverse. And as stated before,
folding props will generally provide more power in forward due to the more efficent blade shape.
Folding props are superior if reduced drag under sail is your goal with one exception.
If your prop shaft is at a considerable angle from horizontal, then a feathering prop
with independently rotating blades will deliver less drag as each blade can weathercock
to the water flow. Folding or ganged feathering blades will be pulled through the water
at the same angle as the prop shaft. Kiwi Props and Autoprop were two listed as having independent blades.
From delmarrey on cruisersforum.com
I vote for the feathering prop.
I've run both, and the feathering prop really makes a difference.
Once you learn the personality of the feathering prop you'll forget all about the fixed.
They do need to be kept in good shape or they'll vibrate.
From Roy Brown on the Morgan mailing list
I went with the 4-blade Variprop which is probably the most expensive. Once
I installed it I experienced significant shaft vibration as the prop is very
heavy so now my additional expenses are:
1) Haulout to remove variprop and re-install original prop.
2) Install a new shaft - SS to replace the bronze shaft.
3) Install an extra strut mid-shaft since the distance between engine and
prop is extremely long (this is the recommendation of both the marina and
prop manufacturer once I explained the vibration problem).
Re-installing the old prop solved all the problems so I am confident the
shaft and alignment are OK.
The old prop is a LH 18" diameter 20" pitch - the new Variprop is 23" diameter and 19"
pitch. This is the size recommended by the manufacturer for the engine
(Perkins M65) and there is more than enough clearance from the tip of the
blades to hull.
I measured the shaft length and there is 46" inside the boat and 63" outside
and so the additional strut is going outside where the shaft exits the hull.
From Ed Merta on the Morgan mailing list
... you might be getting some vibration from the skeg shadow, which will
change the pressure on the prop blades, as they go behind it. You can also
have this problem with a two-bladed prop.
That is one of the advantages to the three-bladed prop, you always have two
Having purchased a Campbell Sailer myself, I second everything that has been said
and will buy another when I need to. But I was not told that I would be charged for repitching,
and ultimately paid several hundred more to get it right.
Now if they had used my requested pitch (based on Catalina factory recomendation),
rather than their own ideas initially I would expect it to pay for changes, but they (CS)
told me they knew best from experience. The final pitch was exactly what I had asked
for originally (Catalina did know best).
So I would get it in writing who is paying for repitching and the associated costs.
Two repitch's meant pulling the boat three times. Ouch.