150 PSI, oil less pancake compressor from sears. Only a 2 stage regulator is needed due to the low pressure of the output, 50 feet of hose, running off of a 1500 inverter. Always have air and it runs as long as needed, no filling of high pressure tanks. Do not have room for them anyway. We are not into diving, so this fits our needs at a reasonable cost. It is also neat to be attached to the boat by the hose. (Hose being up graded to that related to specific breathing needs at this time.) While under the hull you can hear the unit cycling on and off so are able to monitor what is happening above. We are never below 5' with it.
The compressor is permanently stored below, and is never used while the engine is operating.
This setup has been used by a diver friend of ours in this area for boat owner service for the last 10 years or so, and ours is an exact copy of his, except that it can also be used when away from the dock.
Very interesting setup! Being able to stay down, even in shallow water is very handy. It's a boat, after all, and at times stuff happens - rope around the shaft or whatever.
Not sure the air quality is suitable for prolonged diving, but sure sounds good. Especially because being electric, it does not produce fumes to be drawn into the compressor and sent below. Do make sure there is ample fresh air without any type of fume at the air intake, under the pressure of water your lungs will absorb more fumes, just like beer under pressure absorbs more CO2.
Very nifty, practical, and affordable setup, I like it a lot. Thanks for the extra description.
On further thought, I would not be afraid to go to 20 ft. with it. Just pinch you nose and try to exhale out of it, that should equalize the pressure in your sinuses and ears so there will not be any pain. Don't ignore pain, just clear it. If you have a cold it might not work, or perhaps when coming up you will feel pain or numbness in the front teeth, but that will clear with time and swallowing.