The Right Way to Run a Diesel

[psneeld]

Originally Posted by TeddyDiver

You are guessing wrong.. another thing is that today there's not much for small or sailing vessels, and the Norwegian manufacturer doesn't answer a simple quote which pisses me of..

While a bit out of date...this NA supported my "guess"

Controllable Pitch Propellers


This guy too - The big down side to a controllable pitch prop is the cost. Hundested; Hundested Propeller controllable pitch propellers, is renown for some of the best controllable pitch props so got a quote from McGowan Marine Inc. 1-508 990-1114 stevegow@aol.com, on a new system for a 70ft motor sailor is $66,913 plus shipping. Needless to say I am no longer looking a new Hundested drive systems.

Here's a comment like I was thinking.... The engineering concept of a CP is grand but the costs would be way high for a small diesel.

50hp is 2 gph ,(with the finest engine at flank) gaining 20% efficiency will take a long time to recoupe $5000 in expenses for the CP.

Perhaps Rob White had the better idea, a prop system that allowed a rapid and easy no tool ,prop change , so the prop can suit the expected conditions.

So maybe my "guess" is better than your's...care to prove me wrong????

[dennisail]

I think a CPP is a great idea. I believe a company made a small engine and CPP unit for sailboats under 40". The pitch could also be set to feather mode. These are out of production but are highly sought after by people in the know. I forgot who it was now that made them. I found the thread again here. Worth a read. http://www.boatdesign.net/forums/pro...oat-35702.html Saab still makes them. The cost for a new build would be worth it probably, but not for a retrofit.

Also a passenger car diesel might make say 100hp but to cruise it only needs about 5hp to maintain speed. The thing is load is always changing and high throttle is used for accelerating. I'm sure if it was run at 5hp continuously there would be problems.

[Nicholson58]

Originally Posted by S/V Antares

There are many "Types" of diesels out there. Older, heavy slow turning to newer lightweight hi rpm types. The lighter one like the Yanmars, Kobota and Mitsubishi based units under 100 hp do not do well at low rpm with hi load. They really need to get rpm to make HP. Lugging them will cause issues like carbon in the rings and compression loss. My rule of thumb your cruising speed should be about 70 -75 % of Max RPM. My max RPM is 3600 where it is prop to but I cruise at about 2500-2600. I think it is a good practice to run the throttles up to max rpm for a few minutes every 10 or 20 hours.

I have worked on large diesels that max out at 200 - 300 rpm and are the size of a bus. Things are much different with the new small displacement low mass engines we see in boats these days.

Ours is a 1983 Westerbeke 6-cyl; 115 HP with a 2:1 reduction to a Hundested 3-blade 24 inch variable pitch prop. Displacement is 55,000. We run around 1000 to 1200 rpm and make about 7 to 8 knots depending on sea and wind. Glycol temperature hits abour 185 F. I can flatten the prop and crank up the rpm but it will over heat.

[Oceansailor]

Running the engine on light load during the brak in period will result in glazing on the cylinder wall due to low temp.

After the engine is broken in it is less damaging to run it on light loads. But no doubt it is better to run the engine on 70-75 % load if possible. A compromise is to run it harder 10 minutes every 3 hour just to clean out carbon from turbo and exhaust.

[dennisail]

I have a yammar 50 in my 40 foot boat. Its a great engine. Max RPM is somewhere like 3600. So its certainly a high revving type. Slow revving engines have their advantages but also disadvantages. The slow revving engine will last longer, but the high revving one will be much smaller capacity for the same power and it will weigh much less and cost much less to buy.

I only have a 2 blade prop but I can cruise at 1.8L per hour at 1600rpm @ 5 to 5.5 knots. Since that is about an average passage making sailing speed (and wind is free) I don't see the point in motoring much faster and depleting my limited and expensive diesel reserves. Every now and then I will gradually increase the revs to max to blast any carbon out to prevent glazing. This seems to work as I get some smoke which clears as I increase load.

[charliehows]

actually it doesnt really matter how you run them, unless you have a particular knack for buggering up engines. What matters is how you maintain them, oil changes, anodes, filters timely repairs etc. Poor maintenance is what causes 99% of boat engine problems. Most engines will adapt to how they are used over time. Heres a simple foolproof secret to keeping old engines going pretty much for ever - change the oil frequently - yeah thats all...

[stillbuilding]

Originally Posted by charliehows

actually it doesnt really matter how you run them, unless you have a particular knack for buggering up engines. What matters is how you maintain them, oil changes, anodes, filters timely repairs etc. Poor maintenance is what causes 99% of boat engine problems. Most engines will adapt to how they are used over time. Heres a simple foolproof secret to keeping old engines going pretty much for ever - change the oil frequently - yeah thats all...

Charlie, a few really good diesel mechanic have given me similar advice ie that is OK to run them lightly for longer periods with occasional high load to clean out. But does not seem to be a widely held view.

[daddle]

99% of the diesels in the world are running lightly loaded with only intervals of higher power. Most trucks, powerplants, locomotives, farm tractors, construction equipment spend most of their time at powers well below half their maximum. The diesel engines don't mind. Properly maintained they last a long time in all these applications. The nautical world if rife with unfounded superstitions.

Overloading with the wrong propellor is bad ... lugging.

[dennisail]

Originally Posted by daddle

99% of the diesels in the world are running lightly loaded with only intervals of higher power. Most trucks, powerplants, locomotives, farm tractors, construction equipment spend most of their time at powers well below half their maximum. The diesel engines don't mind. Properly maintained they last a long time in all these applications. The nautical world if rife with unfounded superstitions.

I mentioned that point earlier. But all the things you mentioned also get used at high power very regularly under normal operating conditions (so there is no need to be aware of underloading the engine)

If the wind dies there is no operational requirement to load a sailboat engine up (no hills no traffic lights, to picking up 5 tonnes of rocks etc). The usage may just require it to be run at very low revs and power for up to a few days at a time. This is why we need to be careful. Our operational requirements rarely require anywhere neat the full power of the engine. At least this has been my experience in my recent pacific crossing. Thats why I give it a blast every now and then.

Overloading with the wrong propellor is bad ... lugging.

Agree 100% there.

[Thumbs Up]

I think that most sailboat engines go bad from sitting. If you don't take your boat out much, run the engine anyway. Put it in gear, tug on the dock lines. Bring it up to full operating temperature which evaporates any moisture out of the oil. Use it or lose it!

[lancelot9898]

Everybody seems to agree that lugging a diesel is bad, but not sure what lugging means. If the pitch of the prop is set too large then the engine can not achieve its rated rpm at WOT. That is my understanding what the lugging term means. I have a Perkins 4-108 and it's max hp rating is achieved at 3600 rpm. My max prop pitch is set so that I can only achieve 3000 rpm at WOT. I cruise at around 80% of the 3000rpm and only occasionally bring it up to 3000. I do not think that I'm glazing the cylinder walls by operating in this manner.

[svlamorocha]

Originally Posted by Morgan3820

Why should I race the engine before stopping it? I do not understand.

Yanmar says that you should race the engine before stopping it because "to clean the carbon from the cylinders and fuel injection valve". The carbon comes from the 5 minutes of idle to cool down the engine..
I am sure you will find this in your operator´s or service manual, both of which are worth reading...
Cheers
C

[daddle]

Originally Posted by lancelot9898

Everybody seems to agree that lugging a diesel is bad, but not sure what lugging means. If the pitch of the prop is set too large then the engine can not achieve its rated rpm at WOT. That is my understanding what the lugging term means. I have a Perkins 4-108 and it's max hp rating is achieved at 3600 rpm. My max prop pitch is set so that I can only achieve 3000 rpm at WOT. I cruise at around 80% of the 3000rpm and only occasionally bring it up to 3000. I do not think that I'm glazing the cylinder walls by operating in this manner.

That is a common error in understanding the lugging problem. Because of the way propellors load the engine one can be 'lugging' the engine at any RPM, even rather low RPMs. One would have to carefully analyze the engine and propellor power curves to know for sure. If you look at your engine's power curve you may find it should produce say 37hp max at 3600rpm, and 32hp at 2400rpm. The proper gear and propellor for the boat and conditions should use those same powers at those engine speeds.

The propellor that overloads this engine might require 41hp when the engine is at max RPM. The engine cannot produce that power so maximum RPM is never attained. But the surprise is this: That propellor also overloads the engine at 2400rpm because at that RPM the propellor requires 35hp. The engine probably can produce 35hp at 2400rpm, but it is significantly overloaded. It is operating in a way the designers did not design for. It may be producing black smoke, it will certainly be overloading the rod and main bearings. That propellor might even overload the engine at idle speeds, I don't know.

Someday we might get computer controlled injection, in that case the computer can probably make sure the power curve is never exceeded. That trick is beyond the capability of a mechanical injection pump. Until then the manufacturers have come up with a simple test for overloading: the test for attaining max rated RPM with the propellor at typical boat speeds.

[Aloha_float]

I was taught to run my diesel near the high end. I usually stick to 2200 rpm as it is an efficiency issue. Anything above that gets me little to no increase in speed and I start to drink fuel.

I think my engine maxed out is 2600 rpm if I recall correctly.

[Capt Phil]

Beware of the 'one size fits all' idea that is pervading this important thread. Do you think running a MAN or CAT D330 is the same as running a 20 hp Yanmar? How about an old lugger with a top RPM of around 1400 RPM that you could start by hand by throwing the decomp lever and spin the flywheel over by giving it a toss clockwise.
I belive it would be a good idea to check out the manufacturers' suggestions on run-in procedures as well as optimum run rate before applying a bunch of well intended advice and buggering up a perfectly good engine. Just some advice from an old salt... Phil