what size of fuel tank?

[gshaw]

Yes I know if all depends on so many things but I am looking at a few pointers based on experience please,

70hp 2 stroke outboard (1977), 17ft cathedral hull 536 Shetland

what size of fuel tank should I fit (bigger the better within reason) and any sort of fuel usage figures from similar set-up ? I want to get the tank ordered soon to let me fit it. Thanks.

 

[rivonia]

You are spot on...The biggest that you can fit in the space available as long as it does not effect the balance when full as Diesel does weigh a lot.

Peter

 

[NorthUp]

Consider fitting two (or more) smaller standard outboard tanks-
alternative fuel source if contaminated
'reserve' fuel, obvious when you have reached half fuel
easier to keep track of oil mixing, tank at a time
may be easier for refueling if you have to transport them
easier to balance the boat both at sea and on trailer, far less 'free surface effect, i.e no fuel slopping about in a half empty tank.
Just change over fuel lines, you dont even have to stop the engine.

 

[gshaw]

You are spot on...The biggest that you can fit in the space available as long as it does not effect the balance when full as Diesel does weigh a lot.

Peter

I used to rally cars and we had baffled tanks to stop or reduce the slop of fuel affecting the balance/handling. Are baffled tanks available for boats? Some where filled with a sort of foam to also stop slop (and help in fire) I like the idea of two small tanks but would prefer a balancing system of pipes to avoid one sided weight, OK that would do away with some of the advantages of the two tanks but if gauged fully not a big issue. Would not a large flat tank design be better so that fuel weight was kept as low as possible?

Still no idea as to consumption Vs size Vs distance. What sort of fuel figures do you guys get?

 

[NorthUp]

consumption

Well, 150HP V6 Johnson on a 6m rib, laden for long distance, averaged a litre a mile at cruising speed of 34 knots.
Flat out hurt- 60 litres/hour at 49 knots!

I had a fixed tank of 120 litres, and standard 5 gallon tank for reserve, and when required a selection of jerry cans..
managed to burn a lot before the prices went through the roof, now burn in a year what I used in an afternoon- became a WAFI!

If you are having a tank built, it will be easy to incorporate baffles, but if possible leave an access hatch for cleaning the inside eventually.

 

[Matata]

Fuel consumption figures. We have a 120 two stroke out board and in a typical five hour day we go through 50 litres. Thats cruising, water skiing, idling , picnicing, pottering. My lad he has a 40 horse two stroke and in a similar day would get through 20 litres. Hope this helps. Nik

 

[JohnTH]

The SG of diesel is about 0.86 Rivonia. It may not run a two stroke out board engine but I agree with you, the biggest tank to fit the space available.

73s de

Johnth

 

[prv]

I used to rally cars and we had baffled tanks to stop or reduce the slop of fuel affecting the balance/handling. Are baffled tanks available for boats?

All TekTanks tanks are baffled as standard.

Pete

 

[William_H]

Fuel tank for O/b

I think most boats like you describe around here (and there are a lot of them) would use the off the shelf 20 litre tanks. They can be bought in plastic or steel. Plastic are far longer lived due no rust. As already suggested you have multiple tanks and just change over the fuel hose. These are very convenient to remove for refilling or cleaning. I think you can get bigger plastic fuel tanks but of course they are heavier to remove. I use a 10litre but that is for a tiny o/b but the tank has given long life, far longer than a steel one.
Due to fire danger you should be careful about carrying too much fuel. good luck olewill

 

[Ceejay]

That's a pretty old engine, so will use more fuel than today's models. I had a 70hp Mercury bought back in 1978 and it consumed about 4 gallons an hour at cruising speeds on my Solar Corsair. The Corsair was a similar craft to the Shetland, but had a deep vee hull, so took more power to get on the plane. The up side was that it could ride rougher seas more comfortably. The cathedral hull of your boat should slip along more easily and use a bit less fuel. I used to travel from Oban to Coll not infrequently and on that sort of trip 4 gallons per hour was the norm. From a safety point of view I would use proper outboard fuel tanks, as many as you need and can afford to buy and fill. The point already made about using separate tanks to aid trimming the boat is a good one.
CJ