What RPM should I run my boat at?

[jasonmiddlebrooks]

Posted this in another section but figured I would post it here also....

This is probably a loaded question but lets assume just running from point a to point b, not worried about top speed but what is best for the engine. Lets assume calm waters too.

My setup is a Bayliner 2052 Capri Cuddy, Mercruiser 4.3L (262) 185HP, Alpha 1 Gen 2 sterndrive, 19 pitch 3 blade prop. WOT is rated at 4400-4800 RPM.

The other weekend I was running 33-34MPH (not GPS measured) at 4100RPMs.

I assume it is not wise to run the boat at WOT all the time so I am looking for a general rule as to what is the ideal RPMs to run at when running 10-20 miles up and down the lake.

Is there a % of WOT one should run at to get the best life out of your engine? I know inboard/outboard are different than outboards so lets focus on inboard/outboards.

Thanks for any advice/criticism.

 

[Bondo]

Re: What RPM should I run my boat at?

I am looking for a general rule as to what is the ideal RPMs to run at when running 10-20 miles up and down the lake.

Ayuh,... The usual Sweet Spot is 3200/ 3500rpms on Most hulls.... Conditions allowing of course....

 

[jimbo3123]

Re: What RPM should I run my boat at?

It's always been my understanding that the most efficient speed is the lowest speed that allows you to stay up on plane. The exact speed depends on the boat and how it's loaded and trimmed.

 

[QC]

Re: What RPM should I run my boat at?

Not usually true ^^^^^^^ The problem is the low limit of planing speeds still has a lot of boat in the water and is typically comparably inefficient. Generally speaking, from all of the test data I have seen, Bondo's input is pretty close. There are a few that show best economy at 3000 and even a few at 4000, but 3500 is often a sweet spot. The fact is that this really isn't about the engine's preference, much more about the hull . . .

 

[HT32BSX115]

Re: What RPM should I run my boat at?

It's always been my understanding that the most efficient speed is the lowest speed that allows you to stay up on plane. The exact speed depends on the boat and how it's loaded and trimmed.

That might be true for some boats..... You'll only know if you have a fuel flow indicator. so you can calculate miles/gallon. lowest mpg is the most efficient speed. (on-plane that is)

I have this one:

Mine doesn't read in mi/gal yet because I have not wired my GPS to the NMEA2000 network so it only reads in gallons per hour.

At 30 mph (about 2800 rpm), I get about 10 gal/hr (3 mi/gal)

At 45 mph, I burn 15 gal/hr (3mi/gal) slower & faster it's a little worse.

Most sterndrive engines will last the longest and be most efficient if you run them no higher than 3000-3500 RPM for continuous cruise.

You should only run at WOT once in a while and for very short periods of time. Running at WOT will tell you if you're propped correctly because you should be in the range you mentioned above (and for good holeshot you should be at the top of the WOT-RPM range)

If you're at the bottom of the range (@WOT) you might get a couple of MPH faster but your hole-shot will suffer. (you might not even be able to pull a skier out of the water with a lot of people in the boat)


Cheers,

Rick