dive compressor...?

[CharlesM]

Hello All

About 8 years ago I was on a far and wide ranging dive trip. Indonesia, Australia, Solomons, Red Sea etc.

While in the Solomons I saw a cruiser (I think 35') and that was when I decided the way to do my diving was by boat. I initiated a 5 year plan. Well, the plan has thus far extended to 8 years, but at last I have the boat. It also morphed from simply a means to an end (independant dive platform) to a lifestyle wish.

But the diving was the initial seed, and I think still an important part to it all.

QUESTION. Does anyone have dive compressors on board, and if so - what should I look for / look out for? I have a generator and a large 24V battery bank on board. I do not want a petrol driven compressor, and dont think a third diesel engine is the way to go so will most likely go for an electrical compressor.

Will the generator handle the starting load of the compressor, or would an alternator on the engine (72 hp) sort it out?

Anyy heads up would be appreciated.

Cheers
Charles

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16 days.... /forums/images/graemlins/grin.gif

 

[Scubafill]

As a scuba instructor you will understand the need to locate the inlet in clean air away from any exhausts etc.

I think you may have a problem getting an electric compressor as most are land based setups which require three phase electricity.

We have a couple of 240v compressors in our club but replacements will require 3 phase.

Have a look on divernet,com and use the forums in there to discuss the pro's and con's

Phil

 

[pappaecho]

I am aware of a boat based compressor in Fethiye in Turkey.. the reason it sticks in my mind is that the safety valve failed, and the bottle exploded. Unfortunately, a visitor diver returned to the boat to collect his kit, and lost a leg (and other bits ) in the explosion. I am sure this was a diesel driven compressor and I seem to remember it was the size of a 6 cylinder engine.. the boat is was on was 70 ft, but I think it would be cumbersome and heavy in a boat the size of yours

 

[cameronke]

Single phase to three phase inverters are available from (among many) Lenze

Hope this helps

Regards
Cameron

 

[kandoma]

I have a Bauer (Honda petrol engine) divecompressor on my Fisher 30. There is enough space in the engineroom to transport it. To fill the tanks, I run the compressor in the cockpit.
Currently, I'm installing a hydraulic (running off the main engine at 2000 rpm)) operated 7 kw generator to power my oven and the compressor. (380 Volt 3 Phase)

My problem with diving off the boat is of different nature: I'm unable to carry a sufficent big tender with the necessary 20 hp outboard. We have been unable to go to any good places with our rigid dinghy and the 2 hp Yamaha. We also had a 2.75m inflatable on board, but we lacked the 9hp outboard. We almost did not make it back against the wind from Klein Bonair to Bonair.

When we sailed along the Brother Islands in the Red Sea, our heart almost broke. There was no safe way to go diving on our own. Are you leaving your boat on anchor on a remote place, dive down, encounter a strong current ??? .......
My personal opinion: the dinghy must be minimum 3.70m long to carry 2 persons with equipment.

We met a boat who did use a Bauer compressor with a 230 Volt single phase motor. He generated the 230 Volts with a modified alternator off the main engine. The generator had the required 2kw of power, but he had trouble to start the compressor due to the big starting current needed.

Peter

 

[CharlesM]

Hi Kandoma

Yes, the thought of diving and not being able to get back to the boat has certainly entered my mind. I guess that will just have to be taken into account on a case by case basis. For example, I will not dive the Tiran straits without someone in a tender above us, but perhaps some costal dives where there is a minimal current.. I do appreciate your feelings about the brothers - the diving out there is just amazing.

Anyway, regard9ing the compressor. I have found in my searches reference to a compressor without an motor and using the engine to drive the compressor.

Also, I have found on ebay a cheap compressor with a filter attached to it to produce clean air - I am not sure about the safety of this. Does a compressor need to be specifically rated as breathable air, with the others producing dirty air?

Petrol might be the simplest, but I am concerned about the explosive fumes.

Regards
Charles

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16 days... /forums/images/graemlins/grin.gif

 

[kandoma]

I operated my Bauer for a while directly connected by belt to the main engine. This setup was not too good. The engine room gets very hot in summer plus the 2 kw heat generated by the compressor is too much. It takes forever to fill a 12 Liter tank, if the air around the compressor is 40+ C°.

I have seen sometimes in developing countries, "professionals" using a standard off the shelf air compressor (10 bar) with a separate oil absorber/ air filter and a long hose. You can buy now new filter elements, that also completly eliminate water from your breathing air.

In the states, they have sold for many years 12 volt operated rubber inner rings with a small compressor inside. But there is a 10 meter limit.

Generally, if you need to fill your tanks ( 200 bar), there is to my knowledge no way to do it below 2 kw power.

The fumes off the Honda is no problem at all. The fresh air for the compressor is taken 2 meter above deck level with an ordinary hose. At anchor....ok?

Peter

 

[stephenmartin]

Have you considered keeping a bank of J cylinders on board and topping up dive cylinders when needed....and filling the bank up at night whilst moored up....

I dive too

 

[wooslehunter]

Do the sums. As an instructor you'll be able to understand them no problem.

Assume a 12l, 232 bar cylinder at 50 bar after a dive. So you need to add 12 x 182 = 2184l of air. Some of the smaller petrol driven compressors are rated at 3.5cfm - cubic foot per minute. There's 35l per cubic foot so a 3.5cfm compressor would take somewhere around an hour to blow this cylinder.

This compressor would be around 4hp if it was petrol powered or 3kW if electrically powered. If you have a 24v battery bank and draw 3kW from it, you'd be drawing 125A. That's some battery bank + cabling the size of an elephant's whatsit. This is purely theoretical though since I've never seen a compressor operating from 24v. They all operate from mains & most from 3-phase as people have stated.

The point is that even operating a 3.5cfm unit electrically would really take some specialised electrics on a boat & anything smaller isn't really practical.

Go for the petrol model. A friend of mine picked one up in the local "Free Ads" paper for a couple of hundred quid.

Bear in mind two other things as well: oil & filters. Generally the compressors need lubricating with some very special oil - something like Anderol. You can't just use any oil since it will break down and produce toxins. It needs changing regularly. Also be aware that the filtration systems used are pretty special as well and also need changing regularly. You'd typically have an oil filter & a water filter. A typical filter system may only last 30 hours. That's just 30 fills on a 3.5cfm compressor. You'll have to carry stock of oil & filters. The oil & water filters are different.

Still interested? Get loads of data from the compressor manufacturers & then see what you can pick up second hand or buy new if you can afford it.

 

[ean_p]

And then of course you have to keep your cylinders and compressor in test, and find a place where you can dive with no restrictions from the authorieties.........if your still interested have a look at Coltrisub who reputedly make some of the best /smallest portables........

 

[William_H]

A few comments made already bear reiteration. A main boat engine driven compressor would appear to be the answer in terms of power efficiency but the dissipation of heat from the compressor would be a major problem unless you can really ventilate the engine room. (Water cooling would be great) That leaves the portable petrol compressor on deck as the only way to go.
What sort of diving do you do? Do you need a full tank? The last part of the tank fill (high pressure ) is the hardest slowest partt ot complete so if you can make do with half a fill you can save a disproportionate time and energy. Have you noticed how the dive shops who fill tanks always have a bank of cylinders storing the pressure. If you have a full storage tank and you decant into an empty dive tank you take high pressure air and a lot of it becomes lower pressure as it fills the dive tank wasting the energy required to acheive the high pressure. So they start filling your tank from a lower pressure storage tank. They then go on to the next storage tank for another stage of fill. Fimally they use a storage tank at 30 bar to top up your dive tank but only a little of this (precious) high pressure air is used to acheive full pressure. The storage tanks are rotated as they are depleated. The point being (er I duno) obviously a full tank is a lot harder to acheive than half a tank so maybe you should dive with twin or large capacity tanks.
Yes in the dive business air quality is very critical and is tested on a monthly basis. The obvious source of contamination is the oil in the compressor. I have seen hookah compressors run on castor oil as that is edible even if it has effects on the digestive system.
The concept of leaving any boat unattended on the surface is to me horrible I would much rather dive alone and leave my buddy in the boat or tender than leave the tender unattended.
Just a few thoughts PS snorkelling is a lot easier olewill

 

[ongolo]

Hi Charles,

Have you heard of the hooka system? They run a compressor on top and feed you air down on a pipe. Filters are used and a regulator, wreckdiver use this system a lot. It is simpler and and you cannot lose your boat, but you have other restrictions.

It is important that you have good filters, compressors allo leak some oil past the piston and that enters your lung under pressure, not healthy I was told.

A lot of guys who have tried it, never go back to bottles. Have a look at the wreck diving forum.

regards ongolo

 

[wooslehunter]

Everything I dive with is double backed up, especially when diving deep. i.e. main + pony or independant twins. Even then I'm with a buddy and more often than not with top cover as well.

If you look at the incident reports then the primary casue of UK dive incidents is separation from the boat either due to boat problems or divers being lost by their top cover. Next comes people exceeding their capabilities. Way down are incidents caused by genuine accidents. Hindsight is a wonderful thing though.

If you're diving in a remote location with no backup you need to make sure everything's as bullet proof as possible. If you have a surface supply like a hookah, you should still carry a pony for backup if that fails. Otherwise you end up with a free ascent with the associated risks. You then need to make sure you can fill your bail out. Surface demand commercial divers are by law required to carry a bail out in the UK.

Another problem with surface demand is the drag of the line. Ever dived with a surface marker in a current and tried to hold position? Even drifting will cause quite a bit of drag since the bottom current is slower that the mid or top current. The drag of the line is difficult to cope with. Now increase the diameter of the line to tube size. Having said this if you have no top cover, you shouldn't be diving in a current anyway.

A final point is know the risks and plan for what may go wrong. That minimises the risks. You can't get rid of them completely so you have to accept increased risk when diving solo, with no top cover or in a remote location.