Diving, especially
from a cruising sailboat.
         Please send any comments to me.

This page updated: January 2011

How Stuff Works's "How SCUBA Works"

Personal SCUBA gear:

From Dave on the WorldCruising mailing list:
For the two of us we carry:

4 tanks, I use more air than my wife so I have Super 80's and she has 2 aluminum 72's. Get aluminum tanks, they are so much lighter aboard. Tanks are strapped into foam racks in the aft lazarette about 1 foot from the stern platform. Our sailboat has a reverse transom, something we felt was necessary for our diving.

Tank boots, thick neoprene boots that protect the topsides and deck.

Hose kink protectors at the high-pressure fitting. I prefer European tank fittings to American but this isn't a big deal.

When you buy ask the dive shop to show you how to do basic maintenance on the regulator. We both have two regulators on our octopus for a back-up.

I carry a 2 cu ft. Spare Air. A tiny tank and regulator that is great for just jumping overboard for a minute or two.

We both have thin skins and shorties. Even in the Caribbean a long dive can get chilly.

We have a lobster stick for catching them and a net bag with float to keep them away from us. Not a good idea to trail your catch close by - sharks etc.

Both booted and non-booted fins allow us to pull on a pair quickly to dive on the anchor.

Dive Compressor is an electric Bauer II Yachtsman. I am told by a professional compressor service person Bauer is the best there is. Made in Germany but sold worldwide. This is all stainless steel compressor, 3 stage, and fills an 80 cu. ft. tank in 20 minutes from empty. We do not have a cascade. Electric drive, 110V powered by our genset. The fill hose runs aft to the lazarette so the tanks can be filled in their racks. I have a set of spare valves, belts etc. for the compressor but have never needed them. I also carry several cartridges which are good for about 200 fills depending on the air supply. Ours is very, very clean.

Extra snorkels. Somehow they seem to disappear.

Mask with a little magnifier glued onto the lens for looking at teeny tiny stuff when down. Also works well in a driving rain or storm.

From Steve Strand on WorldCruising mailing list:
We have had lots of problems with aluminum tanks cracking at the neck and corroding internally. Steel tanks seem to give heavy users fewer problems. It is a tough call, but there are lots of really old steel tanks around and I have thrown away quite a number of aluminum ones.

From Jan Bruggeman on the WorldCruising mailing list:
1) aluminium bottles: Here in Belgium (and I'm afraid in the rest of Europe) very difficult to obtain and to get approved, due to regulations I think. ... Weight is not really an argument, for the lighter your bottles, the more lead you have to take with you. The total weight remains the same, on board as well as while diving. And positive buoyant bottles are an annoyance when you do decompression dives ...

2) Tank boots are to let the tanks stand upright. This should be avoided at any moment, especially on a boat, and so it is better to leave them off. You'll have less problems with un-noticed rust forming as well. And it only is an annoyance when refilling, when sometimes the leads are too short to fill bottles lying down. But this is an issue for diving centres, who teach you to never let stand bottles, but force you to do so when refilling ...

3) ladders, getting back on board: my trick: prepare your gear (jacket attached to bottle, regulators fitted and bottle open), blow up your jacket, tie the lot to a rope ATTACHED TO THE BOAT ;-) , throw everything overboard, jump overboard only dressed in suit, basic gear and lead belt, put your gear on in the water, detach the rope (even this I've seen people forget it, funny !) and dive. When surfacing: follow reverse order. A point of discussion is whether to leave on your weight belt while stepping on board, or to take it off. I prefer the latter. Note: this method is not "general practice" on well-equipped diving boats, but is for me the best solution when you're only two divers diving from a boat which is not primarily meant as a diving platform. Doing it this way lets you dive from any boat that has a (even simple) means to get back on board. On my boat I don't even need a ladder ...
From Dave on the WorldCruising mailing list:
Jan, I purchased 2 of my aluminum tanks in Munich, Germany last spring. They are approved.

Although you may certainly share a different view I prefer the alloy bottles due to weight aboard and when above water. Handling the extra kilos of steel on deck is always a problem on a heaving deck. Of course when in the water who cares whether it is steel, aluminum or whatever.

On the extra weight or lead in the water, I dive with only 2 lbs ~ 1 kilo and my wife requires about 4 lbs ~ 2 kilos. This is in the Caribbean with warm water and little buoyancy from thick wet suits. I would agree with you if we were wearing thick suits. We find most people are wearing way too much weight usually brought on by their prior experiences in cold, cold water with thick, thick suits. I have seen 18 lbs with no suit. People have to pump up their BC to near max just to gain equilibrium. IMHO the argument to use steel over aluminum to put you on the bottom doesn't weight in.

Air compressor:

From John Dunsmoor:
[Re: should I get an air compressor for the boat ?]

I think most sailors do as we did, you carry a couple tanks and your gear but for the most part you free-dive. It is simpler and most of the good stuff is within twenty feet. Saving SCUBA for chores and the few times you are some place where the diving is worth the effort and cost.

Compressors are expensive, don't like the corrosive live-aboard environment much better than most mechanical expensive equipment. So that rare time you do use it, it refuses to work.

So I would never suggest adding a compressor to a boat unless you are going diving constantly.

We carried two full tanks and I think fifty percent of our use was using the compressed air for other reasons. I had all kind of gadgets on the boat, air nozzles, paint sprayer and such.

From Lew Hodgett on the IRBS live-aboard mailing list:
If you want pneumatic tools on board, then why not also have the correct equipment to support them such as a small, say 5-10 gallon, ASME certified vessel along with an engine-driven air compressor such as those used by every 18 wheeler operating on the highway? ...

Re: SCUBA tank air compressor on board, from SE on rec.boats.cruising newsgroup:
If you dive, you have to have one. As far as I'm concerned, not an optional piece of equipment. ...


Forget running it off your inverter, not a chance, it'll barely run off a 5 kw generator. If you don't have a generator, you have to either get a gas or diesel compressor, or run it off your engine (either direct drive or hydraulics, both expensive). ...


I have a Bauer U10, pretty much the same compressor as the Junior. Only difference is the frame, the pump is the same. I installed a 110 volt, 2 HP motor and run it off a 5 KW generator. I get between 2 and 3 cu ft a minute with the electric motor. When I need faster fills, I take it up on deck and use the gas engine that it came with, the U10 needs no tools to change motors, takes about 30 seconds. Absolutely no way you'll run one off an inverter. Never get it started, forget about it.

Re: SCUBA tank air compressor on board, from Michael Pearce on rec.boats.cruising newsgroup:
I contacted Bauer via email and asked about the power needs of their portable Bauer Junior system. His reply was that a minimum 8 kw genset was required to start and run the system. He said it pulls 90 amps at startup and 17 amps running.

From Compressed Air Specialties:
> I am about to buy a 40-foot or so sailboat to live on.
> If possible, I'd like to run a SCUBA compressor with a belt-driven
> power take-off from the boat's main diesel engine.
> Is this possible, is it easy to install, what compressor could I buy,
> what RPM would that compressor need to be run at, and approximately
> how much would it cost ? I'd be doing recreational diving, so I'd
> probably be filling 4 tanks a week most of the time, maybe 12 tanks a week
> when I have guests.
> I'd really like to avoid adding another engine to the boat, so I don't
> want to buy a self-contained portable unit if possible.

We get this request quite often. It is not the easiest feat to accomplish.

First, Bauer will not sell a compressor block only. They only sell the packages with the compressor, motor and filtration. Plus, when you drive a compressor directly from your diesel, this voids the warranty.

Second, you need to take into account how you will engage/disengage the compressor, drain the condensate drains, change the oil/filters, and run the compressor at a constant rpm.

Third, the compression of air from ambient to 5000 psi creates heat, thus the compressor needs adequate cooling. Being next to your diesel engine is not the best place for cooling.

I am by no means saying that this cannot be done. But, taking everything into account, it is difficult.

> Is Bauer the only game in town ?
> Does anyone else sell a "compressor block" ?

No, Bauer is not the only game. There is Max-Air. I just spoke to Andre with Max-Air and they do not sell the block only either.

> If you get this request a lot, maybe it would be lucrative for you to
> design a solution ?

There is no universal "solution". Every boat is different and there are problems that are intrinsic to the goal.

> I don't know how the "constant RPM" requirement could be solved.
> How strict is that requirement ?

Fairly strict. It is not reccommended to run above or below the guidelines of RPM for proper lubrication of the compressor.

I posted this on Yacht-L mailing list:
How could one connect a SCUBA compressor (for filling SCUBA tanks) to a power-takeoff from the main engine of the boat ?

I think you'd need:
1- fan belt from engine to compressor
2- some kind of belt/pulley clutch so the compressor runs only when you want it to
3- keep engine at specific RPM so compressor runs at proper RPM
4- some way to cool the compressor
5- somewhere to buy the compressor and any controls/gauges
6- maybe a water-trough to cool the SCUBA tank being filled

Has anyone done this ? I assume there are easy solutions to #2, but how did you solve #4 and #5 ?
and got these responses: From Jay Jones:
... Depending on compressor size it could take some time to fill a tank (my 4cfm takes over an hour). ...

I've been on lots of dive boats of all sizes 15' to 300' never seen a p.t.o. compressor but don't see any reason it couldn't be rigged.

From Greg Walsh on Cruising World message board:
We have owned two scuba compressors and used each for 1 year aboard two different boats in Mexico and French Polynesia. The first was a gasoline-powered compressor (5 hp Honda engine) bolted on the deck of a 42' steel sailboat. The second, which we currently still own, is an electric-powered Braun Jr, mounted below-deck on a 53' sailboat.

Both compressors have given good service but we greatly prefer the electric compressor. If you have a genset, this is the way to go. You definitely do NOT want to go direct-drive off of the engine. I was advised against this 6 years ago by a dive-boat operator and observed first-hand the result of this type of installation on another boat.

Dive compressors put out a lot of heat and need a very large amount of ventilation to prevent overheating. Sticking them in a confined space with a hot engine is a recipe for failure. The other boat I mentioned had a genset with direct-drive of the scuba compressor mounted in a small space under the chart table. The compressor literally blew up with flying shrapnel etc. Upon post-mortem it was obvious that the failure was due to overheating.

If you don't have the space then I would advise the above-deck gasoline engine powered compressor. We had friends with a Tartan 34 who did a very large amount of diving on a year trip through Mexico and French Polynesia with a gasoline compressor they kept in their cockpit.

If you go the below-decks route, you need to make provisions for draining the condensate. Since its oily and yucky you don't want it draining into the bilge. Standard practice above-decks is to just (somewhat unecologically) blow it into the air. Below decks you need to collect it in some kind of container with an air/oil separator. You have to do this every 15 minutes or so while filling a tank. There are automatic ways to do this but they add some complexity. We have such an automatic arrangement and I can provide info if desired.


The deck-mounted compressor was on our steel boat which featured a raised "poop" deck at the stern. It was a semi-custom mating of a 5 Hp Honda to a Stewart Warner compressor fabricated by a guy associated with a local dive shop. This was in 1995 so I have no idea whether they make them any more.

We used rubber/metal engine mounts to bolt the compressor frame to the deck more or less permanently. Then we had an aluminum box fabricated that was secured to the compressor frame by 4 "quick pins". This made a nice seat underway since the compressor was right next to an existing deck box. Bolting things like this is one of the nice things about a steel boat. The box wasn't watertight on the bottom but did keep even serious spray off the compressor. And the poop deck was high enough that you never got a boarding wave. We sprayed the compressor with Boeshield periodically and didn't have any serious corrosion problems.

As far as the automatic condensate drain ... Bauer makes a timer/drain unit for their larger 4-stage compressors that the installer of our (3-stage Bauer Jr) incorrectly adapted. It initially sort of worked. However, after we had accumulated about 100 hours of usage, the time to fill a tank became almost double what it should have been (from about 25 mins to 50 mins). It turned out that this was due to the drain valves leaking. They are pneumatically-actuated by an electric timer. The actuation air is intended to be a few hundred PSI and is taken from the 2nd stage on Bauer's 4-stage compressor. However, on the 3-stage Bauer Jr, the 1st stage has only 100 PSI and the 2nd stage has many hundreds of PSI. This is either too little or too much. The installer chose too little and the result was too little pressure to hold the valves closed.

To make a long story short we had the Bauer rep in Hawaii, "Pressure Systems Inc", fabricate a custom mod to this setup that involved some parts from an aircraft landing gear control that made it work correctly given the pressures available. The bottom line is that I'm not sure that there is a stock setup available to meet your needs. However, it really is true that the intermediate and final stages need to be drained that often on the Bauer. On our earlier compressor you could get away with one tank fill (about 25 mins). The old compressor was cleverly arranged so that the act of disconnecting the tank also caused the draining so that you couldn't mess up. On the Bauer, if you don't do the draining there is no backup and bad things will happen.

From Paul Cayley:
One should be fairly careful with any air supply - many "oiless" compressors are teflon lined - and are not filtered and thus unsafe as a breathing air source. ...

Bauer Compressors: Diving

Hookah (Sport Surface-Supplied Air; SSSA) equipment:
From cruiser Paul in Marathon 11/2002:
We got SCUBA-certified and bought the equipment. Once we bought a hookah, we found we always used the hookah and never used the SCUBA equipment (BC's and tanks).

Keene Engineering's "Introduction to Hooka Diving"
Yandina's "How to make your own diving setup"
Sarana's "Make a hookah"
AMDS hookah components

From SSSA article by Robert Rossier in Sept/Oct 1997 issue of "Alert Diver" magazine:

From Rick on Cruising World message board:
A friend owns an Airline hookah rig I use regularly. It's nice but my complaint is it's quite a heavy and awkward piece of equipment to tote around. I like it when the diving will be an all-day event but it's a bit much to mess with for just a quick trip over the side. Without fail, it must be rinsed after EVERY use in salt water. Other than that it requires the normal amount of maintenance (oil changes, etc) as any other engine. The rest is pretty much keeping everything clean and corrosion-free. In all but storm conditions it simply won't get flooded with water, capsize, sink or any other bad stuff. It's pretty robust and very reliable. My complaint is the bulky clumsiness (and the engine noise for those remaining topside).

I have no direct experience with the Brownie Third Lung but, just looking at them, they seem pretty similar. A Honda engine is the biggest part, they are much more durable than a Briggs and Stratton and they both use them. It's hard to say if there is a meaningful difference in the compressors. To my eye the Airline looks a bit more robust, but Brownies are more common so parts may be easier to find.

If they are already SCUBA divers, there's another possibility: for a quick trip over the side I have a Brownie Yacht Tender, really just a long hose (60', though I'd recommend the longest hose you can get) that hooks to a regular SCUBA tank. For scrubbing the bottom, checking the prop or un-sticking an anchor it's great. The tank stays in the storage rack below and the hose just leads outside. It sets up in about 2 minutes. I use it diving sometimes too, though a day of diving makes it more worth donning all the scuba gear. There's really no maintenance and if needed it can be put away without rinsing until it's convienient. I do, of course, have to mess with getting tanks refilled but, for me, that's something I'd be doing anyway. If you don't dive or aren't near a refilling station, choosing the the compressor type may be more reasonable. The cost is an issue, too. The gasoline-powered ones are, what, $2500 at least. A Yacht Tender is about $250 on eBay and the difference would buy a lot of air tanks.

I see the choice as what you want the hassle to be: lugging around SCUBA tanks to be refilled or lugging around a pretty hefty hunk of machinery when diving. I SCUBA dive anyway so the Yacht Tender is my choice.

From JeanneP on Cruising World message board:
For diving on the boat to do work and maintenance, however, we use a homemade hooka built from a 12V truck tire inflator (relatively high pressure, rather low volume), a collecting tank, and hose and regulators.


We bought the truck tire pump in Australia from Bumpa to Bumpa (?) - didn't cost much, maybe about $15-$25 US. The bottles Peter found in Indonesia - he originally wanted to use a new propane bottle to accumulate the air, but that was expensive, and these bottles were rated for a higher pressure than we needed. We found these in one of those everything-stores (a little food, a little hardware, a couple t-shirts, etc), had no idea what they were for, but they looked as if they'd do the job, so Peter bought them. I think that the Vetus pressure accumulator thingy (for your pressure fresh-water system) would work, but that was horribly expensive compared to these bottles - they're quite small, the reason there are two of them.

The hoses (40') and regulators are standard SCUBA gear - you do not want air forced into your lungs.

Because the tire inflator is high pressure but low volume, this is okay for cleaning the bottom of your boat, but if you exert yourself too much you're going to breathe faster than this little pump can produce. On the other hand, it's really sturdy, already has a cigarette lighter plug, and ours, built in 1996/7 hasn't missed a beat yet.

I might add that the reason that Peter built this was because I got sick of using our dinghy air pump to pump air to him while he cleaned the bottom of the boat - it was easier (for him) than setting up the hookah or any other option. Also: Peter's had to dive on our rudder and prop in the middle of the ocean several times to free our prop from chunks of fish nets or other line, and having this setup, which is ready to go in five minutes, makes it quick and leaves me free to keep watch in case anything went wrong (nothing did, Phew!).

From Rick on Cruising World message board:
You know, for about the same price as a brand-new hookah setup you could get a compressor to refill scuba tanks. An ultra-hardcore diving friend has one on his boat and they work well, though they introduce their own hassles, too.

From Cap'n Jack on Cruising World message board:
We use ours for bottom cleaning mostly. It's a home-assembled rig with an electric 2 HP oilless compressor and tank, a 'T' into two 100' hoses and two hookah regulators (also can be used for just one if desired). Total cost: about $390. We run it from shorepower while dockside, or generator or inverter when away from the dock.

From Rick Koenig on Cruising World message board:
I have a little experience with diving. (Navy salvage diver, though that was -ahem- a few years ago.) I'd consider the surface-supplied air as a good alternative for the casual diver, provided you get basic instruction in diving. You don't need to be certified as a diver for the smaller floating units, most of which I believe go only to 30-40 feet, about 1 atmosphere. You can't get in a lot of trouble at that depth [unless you hold your breath while ascending, or panic, or ...]. Not requiring certification is a plus for the occasional dive over the side for fun or to do some hull work. It's fun at that depth; the light is usually not that great when you're much deeper anyway. (Depends on where you are, of course.)

I think one of these systems would have been great to have during the 6 months of cruising I did recently. Here's the thing as I see it: if I'm over the side with tanks (or surface-supplied air) and I get a little tangled up, it's a minor annoyance. If I'm snorkeling and holding my breath and get tangled, it's a Problem. I am pretty well trained, though not as experienced as some here, certainly not recent, and I think about that every time I snorkel down. "Rule 1 - Do NOT get tangled in anything ..." I had a line around my prop once and it took two of us an hour of up-and-down diving to clear it. With a surface-supplied system I bet I could have done it myself in 5 minutes.

For those taking longer hoses (someone mentioned 100') you really need to be certified. At those depths you need the same training and experience as any other diver. In fact, I would not want to go more than 40' with anything unless my quals were up to date and I had recent experience. Just not worth the risk.

Finally, not to appear critical of anyone's personal preferences or skills, I would recommend against "homemade" systems for the casual or novice user. They just seem to be a risk not worth taking. That is especially true for someone who might read this post and think, "Hey, I can put together my own dive system on a shoestring budget and go down to 75 feet !!" Somebody doing that needs a check-up from the neck-up.

Just my observations. Your mileage may vary. I've been known to be wrong before.

AirLine by J. Sink

Rodale's SCUBA Diving



From John Dunsmoor:
Re: snorkeling under boat with extended snorkel tube to the surface:

Try it, you are going to find an amazing amount of effort to draw air as depth increases. It all has to do with our body mechanics, and when we do not have an air pump to move air, we expand the space our lungs take up using the diaphragm. When you put body under pressure then we have to displace water pressure, and not zero ambient air pressure so the difference between what the stomach and diaphragm are working against, in comparison to the surface air pressure is amazing. Just the difference in pressure vs. depth, compared to surface air pressure is dramatic.

[I had mentioned that exhaling into a long tube would not exhaust the bad air out of the tube; it would tend to "oscillate" inside the tube and you breathed in and out.] The travel for bad air is a definite problem, this has to do with tube volume. While one would think that a large bore would be better, the fact is a small tube diameter would allow the two liters of air to completely vent before taking in the next breath. Plus we only use about 20% of the oxygen we take in anyway. Simple solution would be, do not exhaust air out the tube, exhaust the air into the water. If you want to get more sophisticated you could have a double snorkel and valve to exhaust used air.

But you will never get to that point. You will find it very difficult to pull air two feet down. You have to try this.

If you are focused on trying to work something out that does not require air fills, what you need is an oil-less compressor, that has a capacity of one to two cubic feet per minute at about 30 psi. This should provide a continuous stream of air out the end of a tube. Kind of like the Weeki Wachee Mermaids use. Good to ten to twenty feet I would guess.

Diving in Florida:
From Gary Elder:
> Someone said "The gulf waters are shallow and
> provide little to see while diving. There are a few
> shipwrecks and man-made reefs which I have dived, but
> visibility ranges from only 2 feet to at best 10."

Twenty five miles off Marco Island the water depth is about 65'. Off Naples that depth is a little closer to shore. Much of the Keys diving (bayside) is in water less than 12' deep, but the visibility is much better than off Naples. In the Keys there are lots of lobster waiting to be picked up.

There are some shipwrecks and man made reefs that are well-charted, but I have never heard anyone complain about visibility being less than 10', even after a storm. I think 20' is more the norm, better in the Keys. Also, there are approx a half dozen giant towers in the gulf that are accessible to divers ... Good fishing in 60' or so. If memory serves, the northern most tower is at approx the Naples/ Marco latitude about 25NM offshore. They run in a line down towards the Dry Tortugas.

Additionally, there are a couple of 'holes' nearby. One is called the Blue Hole, the other one is called the Black Hole. I think there may be another one, but I'm not sure. These are good places to see giant Jewfish. I'm not sure, but it seems like they may be about 100' deep.

From John Dunsmoor:
> Someone said "The gulf waters are shallow and
> provide little to see while diving. There are a few
> shipwrecks and man-made reefs which I have dived, but
> visibility ranges from only 2 feet to at best 10."

Pretty close, ten thousand acres of flat rock bottom with a little grass. Visibility can be better, twenty miles out you can get pretty nice. But the water is not tropical. No aqua-marine greens and blues like the Atlantic.

Certainly not the diving capital of the world. But then again with the right attitude, I have been talked into and had fun diving, in waters a whole lot less than the Gulf.

More from Gary Elder:
Talked to a dive instructor today who told me that "in the Gulf, from early May thru Sept you can expect to see 60 - 70' visibility, while in the Keys you can expect it to be good all year".

My experience so far (snorkeling):

Avoiding jellyfish stings:

Why I don't SCUBA-dive:

From article by Chris Doyle in 12/2010 issue of Caribbean Compass magazine:
About 16 years ago some island governments started requiring that all diving be done with a local dive shop. The banning of independent diving spread. About half of the English-speaking Eastern Caribbean islands now ban independent diving.


Only a limited number of really good dive spots are easily accessible by dinghy, and for the rest it is much easier to go in a dive shop's boat. ...

Another factor in the islands: where would you have to go for treatment if you got the "bends" ? In 10/2012 a local fishing-diver on Grenada got the bends, and it seems the nearest hyperbaric chambers are in Barbados and St Lucia.

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