Seastoke
Well-Known Member
We have 2x perkins sabres 225,s what should be max revs and how much throttle back on long journeys any advice is good .cheers roy
Max revs and cruising revs
- Thread starter Seastoke
- Start date
omega2
Well-Known Member
Get them warm then put the pedal to the metal note your max revs, then run 200 rpm below that figure, "THEY" say!
Latestarter1
Well-Known Member
Rated speed of 225 is 2,500 rpm, and 200 off the top as suggested by Omega is a good continuous number.
dpb
Well-Known Member
Divemaster1
Well-Known Member
NO !!! general rule on medium speed engines... sort of 2600 RPM down to about 2000 RPM WOT.... Leisure hig rev V...s are very different.... even DD stated that their 2300 RPM WOT two stroke engines are recommended to run at no more than 1850 RPM if the run is at 10 hr +... that is a 450 RPM drop...
Seastoke
Well-Known Member
Divemaster sorry i dont understand
oceanfroggie
Well-Known Member
It is a bit of a generalisation but most diesel engines are designed to run continuously at between 75% and 80% of their max power. If your Perkins 225's have max 2500rpm then I would suggest 1900-2000 rpm for long continuous running (ie fast cruising). From memory the 225's were a modification of the original 135hp engines, rebored with turbo added to bring them up to 225 hp. So to generate 225hp at 2500rpm they are working quite hard already. Running at above 80% for prolonged periods may stress older engines more than necessary.
Latestarter1
Well-Known Member
Very engine specific. Working hard, remember 1 lire/cylinder, Perkins Sabre 225 actually only 205 max hp, running 200 off the top pulling way less than 180 hp, easy peasy.
Bore of Phaser block always 100mm same as 6.354, however NA and turbo engines totally unrelated development.
Likewise all Cummins B ratings same displacement, up to 3,000 rpm run 200 off the top continuous.
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Seastoke
Well-Known Member
can you put it in binmans terms please roy
Divemaster1
Well-Known Member
Looks like you should be getting 2500 RPM @ WOT .... run them hard at 2300 RPM (if you acheive 2500).... more relaxed at 2000 - 2100 ...
Seastoke
Well-Known Member
got it .ta
omega2
Well-Known Member
the question was what are max revs and what is best cruising speed, he got his answer. But conditions must dictate, after all we can run at tick over if we please.
Latestarter1
Well-Known Member
I dug out yet another curve for the Perkins Sabre 225, they have changed like the weather over the years.
If we assume 40 degree C fuel and not the fanciful 20 degree data best rated output is 205 hp @ 2,500 rpm on a good day with the wind behind you, which is why Trading Standards went after Perkins Sabre at one time.
200 rpm off the top looks more like 150 hp not 180 as I previously stated and best point on the bsfc curve looks to be between 16/1700 rpm which unsurprisingly is peak torque.
However the accuracy of your tacho cannot be assumed, if you want to be certain check it with an optical hand held tacho.
Seastoke
Well-Known Member
are you saying we should rev at 1700 on long journeys.
ulyden
Well-Known Member
Just a coupe of things. Its the propeller that gives the engine load. Depending on propeller cure that normally is a n^2.5 to n^3 you will get
About 80% load at 92% speed. If engine is rated 225hp at 20 deg fuel or 218hk at 40deg fuel. A bit dependent og fuel pump cooling. The propeller load must be less. Assuming that engine can reach 2500rpm the propeller power must be less than 215hp. Running at2300rpm your power output will be maximum 172hp. This is a lot and normal rules says maximum 90% speed at cruising on pleasure rating. This correspond to 2250rpm and 150-165 depending on propeller curve. This is the same for all engines in a normal boat. Crusing at 80 to 90 % speed is normaly not bad for the engine.
Talking about 200rpm off is stupid not considering engine rated speed.
A high sped engine like mercruiser operating at 4600rpm will have 90% load operating at 4400rpm a larger engine having a rated speed of 1800rpm wil be having 75% power at 200rpm off.
Just one thing. It might be clever to avoid operating points were torque is weak compared to propeller torque. An easy way to detect this area wich is dependent on hull and turbo layout, is to check the engine acceleration. Don't run the engine were acceleration is low. This means that torque reserves is small and temperatures might get high. The boost pressure is always the limiter. Very often this speed is 65-70% of rated speed but can be different depending on turbocharger layout and adding on VTG or Waste gate. I don't think this engine have that.
I don't know about this engines power but i have been to some test beds in GB. Some tolerance on test bed equipment is not surprising.
About 80% load at 92% speed. If engine is rated 225hp at 20 deg fuel or 218hk at 40deg fuel. A bit dependent og fuel pump cooling. The propeller load must be less. Assuming that engine can reach 2500rpm the propeller power must be less than 215hp. Running at2300rpm your power output will be maximum 172hp. This is a lot and normal rules says maximum 90% speed at cruising on pleasure rating. This correspond to 2250rpm and 150-165 depending on propeller curve. This is the same for all engines in a normal boat. Crusing at 80 to 90 % speed is normaly not bad for the engine.
Talking about 200rpm off is stupid not considering engine rated speed.
A high sped engine like mercruiser operating at 4600rpm will have 90% load operating at 4400rpm a larger engine having a rated speed of 1800rpm wil be having 75% power at 200rpm off.
Just one thing. It might be clever to avoid operating points were torque is weak compared to propeller torque. An easy way to detect this area wich is dependent on hull and turbo layout, is to check the engine acceleration. Don't run the engine were acceleration is low. This means that torque reserves is small and temperatures might get high. The boost pressure is always the limiter. Very often this speed is 65-70% of rated speed but can be different depending on turbocharger layout and adding on VTG or Waste gate. I don't think this engine have that.
I don't know about this engines power but i have been to some test beds in GB. Some tolerance on test bed equipment is not surprising.
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Latestarter1
Well-Known Member
What does the boat tell you............