Outboards on gas (propane) ?

alystra · 29 June 2006, 22:54

Just wonder if anyone here uses gas (not American petrol) to fuel their outboards. Is it possible/practical? Is it feasable in a RIB (Thinking of tank weights etc.)? I have a round trip of 32 miles to the nearest petrol station. The thought of getting a cylinder of propane from the marina is appealing.

My engine's a thirsty six year old Merc 90 4stroke. I think it has carburettors, rather than fuel injection :-(. At 3000 revs. it seems to use more fuel than a 250hp Verado, and that's glum. Would think gas would be cheaper, but don't know. Anyone got any info?

I wonder if one can retro fit fuel injection? - (OK, OK. I don't know much about engines, but I know a lot about other things.)

Cheers, Tony

Matt · 29 June 2006, 23:31

At larger flow rates the bottle can cool off, losing pressure causing the engine to run lean.

Hugh Jardon · 29 June 2006, 23:45

i would put it in for a service if not been done for a while as it should not use too much fuel, what sort of figures are you getting?

fit fuel injection if carbed now......probably too expensive

fit gas conversion.....probably too expensive as cars cost 2k ish i believe

Quote:

Originally Posted by alystra

Just wonder if anyone here uses gas (not American petrol) to fuel their outboards. Is it possible/practical? Is it feasable in a RIB (Thinking of tank weights etc.)? I have a round trip of 32 miles to the nearest petrol station. The thought of getting a cylinder of propane from the marina is appealing.

My engine's a thirsty six year old Merc 90 4stroke. I think it has carburettors, rather than fuel injection :-(. At 3000 revs. it seems to use more fuel than a 250hp Verado, and that's glum. Would think gas would be cheaper, but don't know. Anyone got any info?

I wonder if one can retro fit fuel injection? - (OK, OK. I don't know much about engines, but I know a lot about other things.)

Cheers, Tony

Kernow Buoy · 30 June 2006, 07:05

Alystra
yes it can be done, but not easily, the main part of an lpg system is the vaporizer which is about 6" in diameter and 3" deep, quite where that would fit under a cowling I can't think. If your a reasonable mechanic you can buy a self fit system for a car for about £750 complete, lpg is currently about 40p litre so there is a big saving to be made once the purchase cost has been absorbed.A friend of mine was considering this but couldn't get insurance once converted.

Rogue Wave · 30 June 2006, 07:19

IT's not realy a goer with an outboard but holds up a little better with an inboard. It's a shame really as more economy and less emision woulld be a good thing.

It is my understanding that the calorific content of LPG is about 15% lower than than of petrol which means you don't get as much bang (less power) and therefore more fuel volume used (bigger tanks). however if your specific circumstances dicate you go LPG but you may well be disapointed.

The local harbourmasters ran some LPG outboards on their boats for a year or so but removed them after a while!

Kernow Buoy · 30 June 2006, 08:53

Quote:

Originally Posted by Rogue Wave

IT's not realy a goer with an outboard but holds up a little better with an inboard. It's a shame really as more economy and less emision woulld be a good thing.

It is my understanding that the calorific content of LPG is about 15% lower than than of petrol which means you don't get as much bang (less power) and therefore more fuel volume used (bigger tanks). however if your specific circumstances dicate you go LPG but you may well be disapointed.

The local harbourmasters ran some LPG outboards on their boats for a year or so but removed them after a while!

True if you do a straight conversion without adjusting your timing, lpg is a higher octane (118?) fuel than petrol so the timing needs advancing to make best use, my LR is fitted with an advance/retard amp that adjusts the timing when I flick from petrol to lpg, new lpg systems should be as good as petrol.

Matt · 30 June 2006, 09:00

You really need closed cooling and "auto" (ie higher temp) thermostats to make it work. The vaporisers need a hot water supply to keep the gas as a gas - which on outboards, with low cooling temps and high fuel flows is very difficult to do.

Poly · 30 June 2006, 09:15

I think Alystra is planning to run this on standard "gas cylinders", e.g. calor gas type cylinders. Is that possible?

I would have thought for the cost of upgrade to LPG (with uncertainty, risk, etc) that upgrading the boat to a diesel - available at the marina would be a possibility?

Neil

Turbodiesel · 30 June 2006, 14:49

We (Barrus) sell Mariners already running on LPG and Petrol Dual fuel Outboards, with factory warranty!!

joakimhansson · 30 June 2006, 15:01

Why not try biopower (etanol or e85). That give you on a saab 150 turbo engine, 180 hp if you drive it on bio, etanol or e85.

alystra · 30 June 2006, 17:15

Well, thanks to all who've commented so far. Consensus seems to be that any conversion is going to cost a fair amount and cause me some headaches. I'll probably never recoup the investment.

Engine was serviced (major) 18 months ago by Mercury service agent in Glasgow. Only run about 20 hours since then. Oils changed, plugs checked, filters checked and replaced, greased, etc. this season. No fuel flow meter so have to rely on dip stick after each trip to measure consumption. Figures so far are :-

3500 rpm 23 knts 12 lph 7.2 mpg
3100 rpm 20 knts 11.3 lph 7.1 mpg

Only 8 hours running time, so far, so figures could change. All measures in light airs and no swell to speak of. Just me on board and 90 litres of fuel to start with. How do the figures compare?

The pipedream had been to buy a cylinder of propane and decant contents into a fitted tank on the RIB.

The manual uses half a page warning of dire consequences (for the engine) of using alcohol in the petrol. I think it's possible to make bio diesel in the back garden from old cooking oil. Not sure about bio petrol. If possible, it's bound to be illegal.

Hasn't there been a thread somewhere about adding parrafin or kerosene to the petrol? I wonder what that does to the engine?

Cheers, Tony