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Old 05-19-2016, 10:07 PM   #1
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Cruise rpm's on Perkins Sabre M300TI?

Can someone help me out how to find cruising rpm's on Perkins Sabre M300TI?
On boatdiesel.com it shows 2500 rpm's max. I don't want to push these engines. Thank you.
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Old 05-19-2016, 11:56 PM   #2
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The PS manual in front of me agrees with boat diesel for 2500 as max. This does not mean 2500 for cruise RPM however. What is your application?
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Old 05-20-2016, 12:37 AM   #3
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You're so right. I'm want to find out what manufacturer says is max cruise rpm's. I'm in the process of buying a 38' cabin cruiser repowed 8 years ago with the M300TI's. They still look new with 160 hrs on them. I am not a speedster & don't want to work them hard.
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Old 05-20-2016, 01:10 AM   #4
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Quote:
Originally Posted by RickyB View Post
You're so right. I'm want to find out what manufacturer says is max cruise rpm's. I'm in the process of buying a 38' cabin cruiser repowed 8 years ago with the M300TI's. They still look new with 160 hrs on them. I am not a speedster & don't want to work them hard.
Insure the vessel is propped correctly, book maintenance is performed, after coolers serviced and EGTs monitored. The manuals are hopefully part of tthe boat literature.

BTW, how have the engines and boat been stored? 20 hours per year is abusive if they just sat around untended. There is a yearly maintenance schedule when hours not achieved. Great engines if they've not suffered from underuse.
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Old 05-20-2016, 06:49 AM   #5
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Start with cruising at 1800RPM and see if the boat is making a huge stern wave,

Be sure at 1800 you can advance the throttle and see 2100 RPM, then go back to 1800.

The best way to find a cruise speed is to create a graph of GPS speed VS RPM.

Say every 200 rpm up to full tilt.

You will easily see an speed where more RPM gives almost nothing extra in speed.

There you are.
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Old 05-20-2016, 08:56 AM   #6
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Thank you all for the information. I did not know about the rpm vs speed graph. Since it is a planing hull I'm very familiar with the stern wake when it gets on plane.
From what I understand if max is 2500 rpm then during sea trials it should achieve that at wide open throttle since the boat is out of water now with clean hull. Thank you again gentlemen.
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Old 05-20-2016, 09:13 AM   #7
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You say "max" cruising rpm.
The manufacturer has a max continous rpm (not rpms) for that specific engine. If you are propped to at least rated power rpm (2500 in your case (or preferably 50rpm above)) and as sunchaser pointed out your engine is well maintained the continious max rpm stated by the manufacturer is what you're looking for. That should be fine for days on end but you must be able to attain rated rpm at WOT (wide open throttle). I'm guessing the continious rated rpm is about 2200 but I don't know. What is your WOT rpm?
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Old 05-20-2016, 02:47 PM   #8
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I have not had boat in water yet. It is suppose to go in the 31st. Sea trials will be then or next day. I will make sure it hits 2500 rpm. I think they are governed so I don't know if it would go to 2550 rpm even in neutral. The boat is being surveyed as I type this.
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Old 05-20-2016, 03:45 PM   #9
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Using a photo tach, check accuracy of onboard tachs.
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Old 05-20-2016, 09:06 PM   #10
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Thanks for the reminder. I have a nice one. Thanks.
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Old 05-20-2016, 10:03 PM   #11
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RickyB,
Assuming it is rated for power at 2500rpm the govonor should limit rpm to about 100 to 300rpm above rated rpm. So 2550rpm should be attainable if the prop and gear allows it.
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Old 05-20-2016, 10:06 PM   #12
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Thank you. I didn't know that. I've been doing a lot of learning lately.
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Old 05-21-2016, 07:59 AM   #13
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"That should be fine for days on end"

For an industrial sourced motor , perhaps.

For this style motor I would get in writing the allowed loads and time limits.
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Old 05-21-2016, 08:14 AM   #14
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Greetings,
Mr. RB. I do NOT know that motor at all but I would guess that an acceptable "cruise" RPM wouldn't be much above 1800 RPM to assure a long life. I have this gut feeling that running 2200 RPM for "days on end" would not be prudent. All caveats mentioned, (prop size and maintenance etc.) apply.
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Old 05-21-2016, 08:49 AM   #15
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RB

If you peruse boat diesel you will find many data sheets discussing duty cycle for this industrial engine. Particularly under the Cat banner since they still make and sell it AKA 3056. Same assembly line, same parts bin but a different paint booth.

Get a fuel curve and you'll note 80% load is 7.5 to 9 gph dependent upon propping. To be safe, operate it per the PS 225 TI or Cat 3056 TI specs. The 300 version has one nice thing, bigger cooling system to accommodate higher rate fuel system.

But again, nil use and sitting around for all these years. How and where was it stored? Was the oil changed annually? Be careful and good luck.
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Old 05-21-2016, 10:12 AM   #16
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If engine hp is matched well to the boat, it should get to a planing attitude at maybe 1800-2000 rpm, and be planed nicely at like 2100- 2200. Then when at full power, scoot nicely and reach 2550.

The problem with many cruising boats is that they often put too low of hp engines in considering what the boat needs to plane. In that case boat will not plane until like 2300 and still be just barely over the hump. For the boat to run nicely planed, you basically need to run at full power. In that case the boat is underpowered and should be considered a trawler!!!

So give it a test run after you splash, and see what category you are in.
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Old 05-22-2016, 08:03 AM   #17
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OR of course you can lighten ship.

Take EVERYTHING out of the boat , every draw , every locker , and decide how much you like "Stuff" vs how fast you want to travel.

The sail racers take it to the extreme with only allowing a toothpaste tube with enough contents to last the race , but that's the idea for speed.
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Old 05-30-2016, 09:03 AM   #18
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By the way. Looks like you found yourself a really nice boat. A Big Congratulations. Have Fun with Her.
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Old 05-30-2016, 10:40 PM   #19
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I go on sea trials tomorrow. I'll watch boat get launched & marina manager that maintains it will run through the systems before & during sea trials. Looking forward to it.
Boat was in inside storage each winter & well maintained very well. Keep you posted.
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Old 05-31-2016, 12:03 AM   #20
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As to cruise RPM and speeds and loads for running, I'd get a manual and if it wasn't clear then call and speak to Perkins. They should have the best answer.
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