Smaller engine swop

[davea]

Hi there
I currently have an AQ211A V8 running a 290 duo prop, pushing a planing 2 ton boat. I get plenty of performance from this set up, but the fuel consumption is stupid, I get about 1 mile to the gallon, I live in the UK, the fuel is ?5 per gallon(?6 from a marina) thats about $7.50.
I was wondering if I could do an engine change and still keep my same leg?.
I would like to go down to a V6 if possible, I think the new v6 pumps out around 190hp.
If this swop can be done will the fuel savings be much?.
Currently I have a top speed of about 30 knts, But the boat feels happiest at around 20 kts. so I really don't mind having a lower top speed.
Thanks
Dave

 

[45Auto]

Re: Smaller engine swop

Don't be surprised if changing to a smaller engine doesn't get you any better fuel mileage. Boat size and weight is a MUCH more dominant factor than engine size. It takes a given amount of power (thus fuel flow) to push your boat at 20 knots. Little motor at full power or bigger motor at partial power are going to be real close to the same fuel flow. Look at some tests on the same boat with different size engines. They all get the same mileage as long as they're going the same speed.

Of course, a bigger engine at Wide Open Throttle gets worse mileage than a smaller one, but the boat is moving faster. You pay for that speed. Power required to push a boat through the water goes up exponentially as you go faster.

Your best bet would probably be to get a smaller boat with a smaller engine.

 

[Bondo]

Re: Smaller engine swop

Don't be surprised if changing to a smaller engine doesn't get you any better fuel mileage.

Ayuh,.... Agreed...

 

[davea]

Re: Smaller engine swop

I dont think that is quite true, My neighbour has the same boat running a volvo 3.0 gl, He uses almost half the fuel I use.
we did a comparision test both running the same speeds,

 

[45Auto]

Re: Smaller engine swop

So a Volvo 3.0 puts out the same amount of power as your engine on half the amount of fuel? Sounds like a compression test and/or tune-up may be your best investment .....

 

[davea]

Re: Smaller engine swop

You misunderstand me, not made myself clear, my boat will run flat out to 31kts, His boat runs flat out to 23 kts.
If we travel at like for like speed, my boat uses a lot more fuel that his.