Dumb Q's on DIY dive compressors

[AndyEss]

I'm with Nani Kai on this one - mistakes with high pressure are often lead to fatalities. 3000 psi compressed air is a totally different animal from a 3000 psi Hydraulic system. Hydraulic oil is relatively incompressible - remove whatever is keeping it under pressure, and you have a big oily mess to clean up. Remove the confining element from high pressure air - and you have the nearest thing to a dynamite blast. Buy something commercial that the manufacturer had to get liability insurance on to sell his product.
Harbor freight sells cheapo oil-less compressors for hookah bottom cleaning, hull inspection diving. Buy the extended warranty.

[1oldbuzzard]

first, let me say that the person who went on the rant is right on the money. Kudos there.

For over 35 years I lived and worked in the scuba business all over the world. I am certified to work on most dive regulators and equipment and 5 different brands of compressors. I was a scuba instructor for over 40 years. I think I am an expert.

Scuba is the way to go if you want to do something other than right around the boat. However there are a couple of units made with a diaphragm oil free compressor that float on the water as you swim. Typically they have a pull start gasoline engine. Usually they will supply air to 2 divers to about 30ish feet. I had one for years and it is safe and simple. Although no filter system.

If you want to fill tanks, the cfm output of your system dictates the fill time. Most tanks these days operate at 3,000 psi. I think you can still find tanks that are rated lower. The pressure is not the issue. Its the volume. 72 cubic feet is still the same at 3,000 psi as at any lower or higher pressure and it is the volume that gives the dive time influenced by the time at depth. I wont go into the amount f air in a tank vs dive time because I have seen a dive tank last 15 minutes on a person that would last me over an hour. Many, many factors control dive time.

Filters are a big issue. The air you breathe must be clean, dry and oil free. ANY oil in the air will coat the alveoli in your lungs causing lymphoid pneumonia. Look it up.

Moisture in a compressor between stages will destroy the valves in the compressor so you will need a compressor with moisture filters between stages. Unless you have one of the single stage diaphragm compressors. They are usually only good for 30ish feet. But most life in the ocean is actually in the top 15 feet. You want to go deeper, you will need tanks.

As for the power supply for a compressor, you can use anything you want as long as the combustion exhaust is reliably downwind from the intake. I know of 2 live aboard dive charter boats who have their compressors on a drive shaft to their main engine. One has a belt drive on the main engine to a manual clutch. Start your main, push the lever, the compressor runs. Voila. You dont need a separate power supply. One is in line on the main drive shaft.

Are you aware of the no decompression limits of diving?

As an alternative think about just renting tanks wherever you go. You can have all the other gear but dont buy your own tanks. Of course you will need to be a certified diver to rent tanks or have tours filled. But no compressor, no storage problems and no maintainance. A scuba tank will require a yearly visual inspection and sticker and periodic hydrostatic inspection or no one will fill them.

I hope I have given you usefull information. I have over 5,000 dives. If you are not certified, do so. Believe me, there are really things you need to know before you can dive safely. Im 71 and still doing it. Living and cruising on my 32' sailboat.

[billknny]

I spent much time and mental energy thinking about how to equip my boat with dive gear. I ended up with a commercial floating, gasoline powered hookah. That does not mean that that decision is best for everybody, but it has worked well for me.

I am strictly a no decompression diver, so limiting myself to <60 feet is my normal dive protocol, and not a problem, even though my hookah is capable of two divers to >80 feet.

It is easy, simple, reliable. I can load it on the dinghy and go where ever I like. Less storage space and weight than a compressor and tanks. Overall, a good choice for my full time cruising lifestyle.

[jlcnuke]

I'm still interested in hearing what compressor people filling tanks are using on their boats. I'm still learning about sailing and cruising, but as I love diving (currently only AOW certified) and I'm pretty decent with mechanical systems (having been trained as a nuclear mechanic and spending 12 years doing that in the Navy) so I'm confident I can understand and maintain pretty much any system on a boat, including life support systems.

The pros and cons of commercially available, or tested alternatives, systems greatly interests me. Especially as I really don't like the limitations and potential problems of the hookah systems at depths anywhere close to recreational limits.

[billknny]

A full blown tested, commercial unit from Bauer, or Brownies, or any number of others runs $2500-$3000.

I am SURE you could spend a LOT of time assembling the parts for a bit less... but unless you know exactly what you are doing, and your time is really cheap, is it really worth it? I am guessing if you really knew what you were doing, you wouldn't be asking the internet how to do it.

We are talking about your LUNGS here. Last I checked you only get one pair.

[jlcnuke]

Originally Posted by billknny

A full blown tested, commercial unit from Bauer, or Brownies, or any number of others runs $2500-$3000.

I am SURE you could spend a LOT of time assembling the parts for a bit less... but unless you know exactly what you are doing, and your time is really cheap, is it really worth it? I am guessing if you really knew what you were doing, you wouldn't be asking the internet how to do it.

We are talking about your LUNGS here. Last I checked you only get one pair.

I built an electric smoker with PID controller for about 1/2 the cost of the equivalent commercially available unit. However, I'd spent time with the parts needed before. I haven't even looked at commercial compressor systems much less their parts to have any idea what is available at this point. I'm sure I could figure something out if I tried, but asking what others have already done is a pretty easy and simple research methods...

[clownfishsydney]

We run our Bauer Junior II that we have owned for 17 years. We just change it over to a petrol 4 stroke Honda engine from its electrical one before we head off sailing. Fills two tanks from 100 bar to 220 bar (about 3,300 psi) in under 40 minutes. It does take up a bit of space, we store it in a stainless container under the main dining table.

Despite what one poster said, it is not that noisy and you can really only hear it if you are downwind of us (I have checked).

As to why hookah units are limited to shallow depths, this is because a lot more power and larger compressor is needed to push air deeper and more importantly, as most people using are untrained, for safety reasons.

[jlcnuke]

Originally Posted by clownfishsydney

We run our Bauer Junior II that we have owned for 17 years. We just change it over to a petrol 4 stroke Honda engine from its electrical one before we head off sailing. Fills two tanks from 100 bar to 220 bar (about 3,300 psi) in under 40 minutes. It does take up a bit of space, we store it in a stainless container under the main dining table.

Despite what one poster said, it is not that noisy and you can really only hear it if you are downwind of us (I have checked).

As to why hookah units are limited to shallow depths, this is because a lot more power and larger compressor is needed to push air deeper and more importantly, as most people using are untrained, for safety reasons.

Thanks.

[Lepke]

I have a lot of compressors on boats and a lot of dive trips, too. The issue is how long do you want to sit and watch your tank fill? How many people will be diving, too. I've been on recreational trips where the only compressor was gas driven and we had a full time guy just barely keeping ahead of the divers. About 20 minutes a tank.
The best, timely setup is an diesel driven compressor. Better still is a tank farm that allows quick refills.

[Nani Kai]

Originally Posted by jlcnuke

What compressor setup did you go with?

Right now I am in between boats so don't have a compressor set up. My wife and I hope to have a Leopard 44 or a Lagoon 440 in the VIs this November. (We are going to St. Lucia in mid-March to look at 3 prospects). We plan on doing limited charters for 2-3 seasons and then head out to points unknown. In between charters we will be re-fitting for cruising. While in the Caribbean we will probably not have a compressor as air is pretty easy to come by. When we do install a compressor I will probably go with the Bauer Junior II-EY1/115/230VAC electric, 3 stage, 2.9 cfm. I have used them in remote locations before for weeks at a time. They are reliable, easy to set up and maintain, have a relatively small footprint, not too heavy and are workhorses. I will also probably install soft start hardware to reduce the initial load on the genny. My current plan is to install it in one of the coffin berths. This puts weight forward which I'm not overjoyed about but the space is there, it's far forward of any diesel exhaust and I should be able to put adequate sound proofing in place without creating excessive heat retention. I will probably install a larger hatch on deck over the compressor so that when in operation the hatch can be opened for better air circulation. I thought about running high pressure lines back to the stern for filling in the tank racks but will probably not go to all that trouble and expense. The Junior II also comes in a diesel or gasoline version but I won't have them on my boat. Exhaust gases are too much of a headache and gasoline is too volatile. As far as diving without a compressor see my next post to follow.