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.

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?

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.

RickyB said:

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.

Click to expand...

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.

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.

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.

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?

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.

Using a photo tach, check accuracy of onboard tachs.

Thanks for the reminder. I have a nice one. Thanks.

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.

Thank you. I didn't know that. I've been doing a lot of learning lately.

"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.

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.

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.

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.

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.

By the way. Looks like you found yourself a really nice boat. A Big Congratulations. Have Fun with Her.

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.

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.

You're so right. I'll trust what Perkins says the most.

RB

Props move boats. Keep in mind Perkins did not prop the vessel, they built the motive power. Re-read Ski's post #16 for sea trial RPMs to keep in mind.

Did you get the manuals and check maintenance recommended vs performed? Don't forget the after coolers are due for servicing, not cheap and if done by the wrong guy could prove fateful.

Be careful about what the engine manufacturer's say. They are motivated to satisfy customers by telling them to run the engine all day at 200 rpm off of top. This is often too much for best life. And they are very unlikely to pay a warranty claim during the first two years of warranty. It is only after a 1,000 hours or more that you see the effects of high load.


If that engine is rated for its maximum hp at 2,500 rpm, then I would cruise it at 2,100 rpm or less. But also think about what your sea trial tells you. If the boat is still struggling to get over the hump at 2,100 rpm then you can't plane. You have to run less. Hp requrements at the hump is very high and hard on engines.


I would want to be on a clean plane at 1,900 so I can cruise at 200 rpm more. If you have to cruise too close to the hump then a head sea will drop you off and it will take lots of hp to get back up.


All of the foregoing assumes that this is a planning hull.


David

RickyB,
Note the continous rated rpm is predicated on the engine being propped to rated max power rpm. Engine load is what we need not to exceed ... not rpm. Within limits of course. It is assumed you are propped right to make use of the continous rpm rating. If you're overpropped even 100rpm your assumed continous rpm will probably be more than 100 rpm less than the manufacturer's specs.
So rated continous rpm is only valid if you can reach max rated rpm or slightly more.

djmarchand said:

Be careful about what the engine manufacturer's say. They are motivated to satisfy customers by telling them to run the engine all day at 200 rpm off of top. This is often too much for best life. And they are very unlikely to pay a warranty claim during the first two years of warranty. It is only after a 1,000 hours or more that you see the effects of high load.

Click to expand...

The support group of engine manufacturers is motivated to have the engines last as long as possible, as trouble free as possible. I don't understand your feeling that they have some motivation to give bad information. I've also found engine manuals to sometimes have recommendations spelled out. If one wants to be extra cautious, the way to be so is to take their break in recommendations (those after the first very few hours but before the next threshold) and use those always.

Engine manufacturers have no incentive to cause damage to their own engines.

There is nothing complicated on this issue. First, have the engines been maintained properly. Second, is the vessel propped correctly. Third, will the vessel remain comfortably on plane at 2050 to 2200 RPM.

BandB said:

The support group of engine manufacturers is motivated to have the engines last as long as possible, as trouble free as possible. I don't understand your feeling that they have some motivation to give bad information. I've also found engine manuals to sometimes have recommendations spelled out. If one wants to be extra cautious, the way to be so is to take their break in recommendations (those after the first very few hours but before the next threshold) and use those always.

Engine manufacturers have no incentive to cause damage to their own engines.

Click to expand...

Don't put too much faith into manufacturer's tech manuals. I used to write them and there was a strong incentive to just copy stuff from earlier versions even though the system changed. Make changes and you get all sorts of extra scrutiny.

I see examples of this in some engine manuals: Manual covers a certain engine with many hp ratings. Same "200rpm off the top" is there for a low rated natural or mild turbo engine. New super hot engine comes out and manual has zero changes. Same "200 off the top", or whatever. Even though engine guys cringe at that.

Ski in NC said:

Don't put too much faith into manufacturer's tech manuals. I used to write them and there was a strong incentive to just copy stuff from earlier versions even though the system changed. Make changes and you get all sorts of extra scrutiny.

I see examples of this in some engine manuals: Manual covers a certain engine with many hp ratings. Same "200rpm off the top" is there for a low rated natural or mild turbo engine. New super hot engine comes out and manual has zero changes. Same "200 off the top", or whatever. Even though engine guys cringe at that.

Click to expand...

I've never run across the 200 of the top routine. I also have manuals specific to the engine, not the range. And if I'm not comfortable I'd talk to the service side of the manufacturer, not the sales side. I'm sure some are just as you say, just not the ones I've encountered.

Further to Ski's point above, Yanmar rates ALL of their engines for continuous duty at 200 rpm off of top. Everything from a two cylinder sailboat engine, my 6LY 370 hp turbocharged and after cooled engine and especially the notorious 6LY2 440 hp engine that will quickly self destruct at that rpm are all rated continuously at 200 rpm off of top.

That continuous rating for my engine is 290 hp at 3,100 rpm (3,300 is rated). 290 hp is 55 hp per liter which is about 20 hp higher than what most pros (Tony Athens) recommend for decent engine life. I say decent, because it is a compromise. Best life is probably half of that. OTOH, sportfishermen often run the snot out of their DD TI engines and are happy to get 2,000 hours between rebuilds. But I suspect that we trawler owners expect more engine life than that.

But Yanmar finally got some religion when they issued their propping specs some years ago. Even though my engine is rated at 3,300 rpm they recommend propping it to a minimum of 3,425 rpm. That gives them a 325 rpm hedge against their 3,100 rpm continuous rating. Not enough, but better than 200 rpm.

David

djmarchand said:

Further to Ski's point above, Yanmar rates ALL of their engines for continuous duty at 200 rpm off of top. Everything from a two cylinder sailboat engine, my 6LY 370 hp turbocharged and after cooled engine and especially the notorious 6LY2 440 hp engine that will quickly self destruct at that rpm are all rated continuously at 200 rpm off of top.

That continuous rating for my engine is 290 hp at 3,100 rpm (3,300 is rated). 290 hp is 55 hp per liter which is about 20 hp higher than what most pros (Tony Athens) recommend for decent engine life. I say decent, because it is a compromise. Best life is probably half of that. OTOH, sportfishermen often run the snot out of their DD TI engines and are happy to get 2,000 hours between rebuilds. But I suspect that we trawler owners expect more engine life than that.

But Yanmar finally got some religion when they issued their propping specs some years ago. Even though my engine is rated at 3,300 rpm they recommend propping it to a minimum of 3,425 rpm. That gives them a 325 rpm hedge against their 3,100 rpm continuous rating. Not enough, but better than 200 rpm.

David

Click to expand...

Rating the engine and saying to run it that way constantly are sometimes two different things. Our only Yanmar is on RIB's and while rated at 180 hp is not run at -200 or anything close.

I agree with them grouping engines into manuals the way they do being bad.

Our manual says nothing about running after break-in. It has two break in periods. During the second of those periods (10 to 50 hours), it recommends against extended cruising at low speed, recommends running it primarily at -400 RPM or about 70% load, with 10 minute runs at -200 RPM and 4 to 5 minutes at WOT every 30 minutes.

Now we talked with them as well as others. On a RIB it's certainly not practical to run at 70% load all the time as that's around 30 knots and not the purpose for which we use it. The advise we ended up with which made sense to us (only for our application though) was that after running it 30 minutes at low speed to run it 4 or 5 minutes at 70-80% load. We typically run around at 15 knots or so, some at around 25 knots but then do our 30 knot runs. If we use it for 6 hours or so in a day, we'll typically open it up to WOT for about 2 minutes.

I admit to their guidelines, or lack thereof, not being very useful. They also tend to not even realize that some of their engines are not in trawlers but in boats that only weigh 2400 pounds including the engine.

Regardless, the most hours we have on a Yanmar diesel at this point is about 120 hours so we can't speak as to what kind of durability we might have running as we do.

We don't have props and they will turn at WOT full RPM of 4000. We have no continuous rating on them as they're really not designed for continuous running in our situation.

That said, on every other diesel engine we have whether propulsion or generator we have far better information in the manual plus available from them. That includes MAN, MTU, Cummins (Onan), John Deere (Northern Lights), and Kohler. I can't speak as to anyone beyond that.