Fuel consumptions

[wayneakp]

Hi

This is gonna be another silly I guess but anyway:

Has anyone ever come across any tables or even a rule of thumb regarding average fuel consumption for various engines on boats. Looking around there seems to be lots of choice but the last thing I want to would be to look at a boat that I could not afford to fuel. Is it always the simple case that the bigger the engine the worse the economy or is there a point at which the size of the engines match the weight of the boat in such a way as to give better economy than smaller ones - if you see what I mean?

rgds

Wayne

[senator]

Hi Wayne, What is fuel economy?

The reality is boats use tons, if it is old it will use tons more and if you want to go fast you can add a few more tons.

Trouble is that the size of the engines is only part of the equation, hull design is a major factor as is the decision to go with shafts or drives but everything is a compromise.

If you want to go fast then a planning hull is the only sensible way, semi displacement will burn lots more trying to push through the water to get to the same speed.

If you want to go slow then a displacement hull will give you great fuel economy and a very roly ride.

If you are looking for something in the middle semi displacement gives you a more stable displacement boat and a whole range of speeds that a planing hull can not sensibly deliver, giving you the chance to maximise fuel efficiency to match your required cruising speed complete with a decent turn of speed should it be needed.

Drives will save you 20% in fuel as long as you trim them properly but the money you save will probably be spent on maintenance, you just gain space in the boat and more speed per horse power.

Engines only use fuel per HP so a bigger engine running at lower revs can be more economical than a small engine screaming like mad.

Single engine, semi displacement is probably the most sensible option but at the age that I buy boats I see having 2 engines as a major advantage, think if you are buying new it may be a harder decision.

Best thing to do is find boats you like then find fuel economy figures for the boat, it is possible to obtain engine burn figures for most popular engines but to be meaningful you need to know what speed a given RPM will produce.

Also worth considering that fuel burn is only part of the cost, it is the one you notice when you pull up at the pumps but taken as a percentage of your boating spend over the year it is likely to be relatively small so any savings have to be taken in context.

With Clanny I take the view that buying 17 year old boats puts you squarely in the possible engine rebuild category and I can totally replace Clanny's petrols for a fraction of the cost of rebuilding the equivalent diesels. This gives me serious comfort factor as a diesel rebuild could take me out of boating for at least a year if not for life, a petrol replacement smarts but it is manageable.

If you are going to do upto 50 sea hours a year it probably wont make any difference what boat you buy, over that and you need to start to think carefully about all the factors.

Ian

[Guest]

I know you luv your oil guzzlers but if economy is important now and in the future sail power has to be a contender. Get yourself a nice dutch motor sailer, loads of room below and miles of noice free exploring. purrfect.

[senator]

Thanks smelly, I forgot to add that if you don't want to go where you would have liked to have gone and you are not too fussed about when you get where you didn't want to go then there is always sail.

[Antares_9]

I'm happy, these D4s seem to run on vapours, must put some more in soon though.

[Guest]

This gives me serious comfort factor as a diesel rebuild could take me out of boating for at least a year if not for life, a petrol replacement smarts but it is manageable.

not if you deploy volvo pentaman