Best fuel economy

[dpmulvey]

If any of you are going to enlarge your trim tabs, consider adding a hull extension to it. I did with mine and don't even need to use the tabs to get on plane.

Before

and after

Interesting.....

How did you attach it to the hull bottom?

 

[aerobat77]

a typical planing hull with a gas engine will actually reach is best mpg at no wake speed nearly idle ;-)

 

[Creekwood]

Frank is absolutely right as I have two of those lovely engines in my boat. At 3200 RPM on a long run I wonder if there is a leak as the engines drink in the fuel!!!! But at 3000 RPM all is well and they sip it. So I enjoy the cruise at 3000 RPM at about 20-21 knots. But at 3200 RPM I do get a 24 knot cruise, but that consumption reduces my miles per gallon.

To the original poster you have to look at the ratio of miles traveled over gallons consumed to get mile per gallon. That is your best indicator of a good cruise for your boat.

I know that over 3500 the secondaries re full open, but on my 330, I think that about 3400 they are not fully open and the fuel burn is OK. That puts me right at 29-30 mph (25 knots) I have done reasonably long on plane cruises at that speed and I am quite sure that is the sweet spot. Now I have all chain rode (200ft) which puts a bit more weight up front and levels the boat nicely without much tab. Maybe that is my difference. In any event, I don't worry about fuel usage. Up here in Canada, our season is short. The more it burns, the more I am using it - and that's all good by me.

 

[aerobat77]

You forgot to say general speaking.....

oh - you are right

well, you are as a general thumb of rule spot on with your 3500 rpm,s . the exact value may vary a little dependant on the engine installed ( carb , efi , mpi ? ) , the driveratio , proppitch, hulldesign ( what is the minimum speed where the boat is fully on plane ? ) and more. but it starts to be hairsplitting.

there are two sweet spots : 1) go slow at no wake speed 2) the lowest speed where the boat planes without being forced with full trim tabs etc to do so.

keep away from transient speeds ( bow up, massive stern wakes) and from going WOT.

best !

 

[Do Over]

Missed this thread somehow.......good stuff......not for technical purposes but as a perfect example of how most forum threads on the ol worldwideweb go...generally speaking of course.

Notice the copious use of .... to represent actually conversation.

I'm gonna go look at fuel usage tables now :grin: