Most economical cruising speed

[kgarguilo]

carver_fuel_economy.jpg

[/quote]

km1125, that is a cool graph, what program generated it?

[km1125]

Source of the post

carver_fuel_economy.jpg

km1125, that is a cool graph, what program generated it?

Just MS Excel. I just added a calc for MPG based on the other numbers.

[karenunger615]

Would like to see this graph, if possible.
Karen

[MyPleasure]

Wow, we got a little off topic, but all information is valuable that’s for sure. I found that the big blocks are sure more fuel hungry than the small blocks that’s for sure! We love our 36 Carver aft cabin, but we should have kept our 4207 with the 375hp Cats.
We we’re just on our friend’s 3488 Bayliner for happy hour, and the Bayliner has no room on it compared to our 36 Carver. Carver may not be in a class like an OA or a GB, but we love them! They are so comfortable and roomy compared to just about any other make of boat, I will stick to Carver anytime, no matter what that David guy says!

[MyPleasure]

Hey Bud37, yes they are definitely the marine version Edelbrock carb, should be for the price! The exact same model as the port engine. It has worked out very nicely compared to the old Holley that came from the factory.

[MyPleasure]

We just got back from our favourite anchorage yesterday, and I did find quite a difference in fuel consumption this trip.
It’s about 10 nautical miles to the anchorage, but last trip we averaged about 1,800 RPM with gave us 8 1/2 - 9 knots, this trip we cruised at 1,500 RPM at 7 1/2 - 8 + knots. Just in the last trip, we saved almost $100 in fuel cost. That is of course planning our trips after the right tide change.
That old theory of travelling at or near hull speed gets the engines better fuel economy seems all right to me!

[MyPleasure]

Hi KM 1125, does your 406 have big block gas engines? If so, are they the 496 Crusaders? You’re 406 gets better fuel mileage than our 3607 with the Volvo 454’s, that’s for sure. Maybe it’s because of the longer hull, and the better fuel injected engines.
At 1800 rpm, our engines use about 6 1/2 GPH each. We brought the boat up from Portland, Oregon, we ran at 2400 rpm up the coast, and my flowscans registered snout 12 gph for each engine. Of course I probably ran at the wrong rpm for fuel economy, but we had the trip planned at a certain speed, so economy went right out the window!

[km1125]

Source of the post Hi KM 1125, does your 406 have big block gas engines? If so, are they the 496 Crusaders? You’re 406 gets better fuel mileage than our 3607 with the Volvo 454’s, that’s for sure. Maybe it’s because of the longer hull, and the better fuel injected engines.
At 1800 rpm, our engines use about 6 1/2 GPH each. We brought the boat up from Portland, Oregon, we ran at 2400 rpm up the coast, and my flowscans registered snout 12 gph for each engine. Of course I probably ran at the wrong rpm for fuel economy, but we had the trip planned at a certain speed, so economy went right out the window!

That's not my data. I just graphed kgarguilo's data he collected from his boat.

You really need to make sure the engine is running correctly before changing other things (like props). I wonder if your engines were running rich or have issues with ignition timing which would cause a loss of the rated power for the engine. It still could start and run really good, just consume a lot more fuel for the power that it produces.

If the carbs and ignition system are correct, then you won't get much more performance or economy just by going to fuel injection. You have to do a lot more changes and also have a lot more feedback from the engine to be able to reliably generate more power with a given amount of fuel. Most marine engines (especially anything over 10 years old) don't have those capabilities, so those fuel injection and ignition systems can only result in very marginal improvements. They can't push the 'limits' of the block because a small thing wrong would lead to big problems quickly, so they need to be pretty conservative or they're reliability numbers tank.