5 mph increase dreaming

[rjr]

Would love to obtain 5 mph increase in cruising speed. I know it would be difficult if not impossible. We have a 440 MY with CAT 3126s rated at 420 hp each, ZF transmissions with a 2.9:1 ratio and 30x33 propellers.

We can reach 15 mph at 2250 RPMs.

Is there any way to obtain a speed increase without excessive drive train wear and to do it economically?

[buster53]

Assuming your engines are running in tip top form and you have it propped correctly, about the only thing you can do...make sure your bottom and running gear stay squeaky clean and do anything you can to reduce as much weight as possible. Got a lot of junk onboard you rarely if ever use...get rid of it. No need to keep your fuel and water tanks topped off. Only have enough for your current needs.
4-500 lbs of less weight won't do much, but any increase in speed is better than none at all.

[buster53]

Source of the post
We can reach 15 mph at 2250 RPMs.

Is there any way to obtain a speed increase without excessive drive train wear and to do it economically?

What's your engines recommended WOT and are you getting that? 2250 sounds pretty low. A little more speed may get the boat up on a better plane and actually give you more MPG's

[Midnightsun]

I believe top end on those is 2800 and recommended cruise is 2400-2500. That being said you really need to see if you are propped correctly before doing anything else. Can you obtain 2800 rpm at wot?

[rjr]

Thanks for the input. WOT is 2800, did obtain that during sea trial. I'm hesitant to run at 2400 since that is about 85% of the capacity. How is correct propping determined?

[Midnightsun]

If you attain 2800 at WOT you have correct propping. I have read on boat diesel that 85% is an appropriate RPM to run diesels all day long.

[km1125]

15 sounds way too low for that combo of engine/boat. I do think you just need to nudge the throttles a bit more and let it get fully up on top of the water. What speed were you at when you did the WOT test?

I'll be that boat cruises at just north off 22 at the real cruise rpm.

[rjr]

Looked at my notes from sea trial. Like a doofus, I didn't record speed. Will try 2400 (next year) and see what I get.

Mechanic mentioned flashing the engines. I checked with local CAT dealer - waiting to hear back. Anyone know about this?

Thanx.

[waybomb]

Please don't add horsepower or change the power curves.

The best thing you can do is clean the bottom, remove the junk from they boat, make sure your engines are tuned, make sure the props are correct for your engine fuel is good, filters are clean, and the boat trimmed correctly.

You add horsepower, you'll need different props, your fuel usage will go up, and engine life will decrease.

For example, a 350 hp 454 could go a couple thousand hours before failure.
Taking that 454, make it a 572 cubic inch engine, add a blower and make 900 horsepower, you better at least do a top end rebuild every 100 hours.
Take it to 1350 horsepower and you get allot of practice taking that engine apart every 35-50 hours.

[Viper]

Source of the post Please don't add horsepower or change the power curves.

The best thing you can do is clean the bottom, remove the junk from they boat, make sure your engines are tuned, make sure the props are correct for your engine fuel is good, filters are clean, and the boat trimmed correctly.

You add horsepower, you'll need different props, your fuel usage will go up, and engine life will decrease.

For example, a 350 hp 454 could go a couple thousand hours before failure.
Taking that 454, make it a 572 cubic inch engine, add a blower and make 900 horsepower, you better at least do a top end rebuild every 100 hours.
Take it to 1350 horsepower and you get allot of practice taking that engine apart every 35-50 hours.

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