Thank you professor, you are definitely a "gold mine" to all of us!!
May I add a further request? Would it be possible to add a fuel consumption curve in reference to the rpm or power for the commercial application of the 4108?
I beleive that this is also an important factor to be considered when choosing a cruising speed. (The noise being also one!!!)
Kind regards.
Philippe 41/022

Dear Philippe
The most reliable consumption curve for your yacht is achieved if you measure at least six about equally spaced rpm/speed readings in the normal cruising range, including full throttle.
Could you pls confirm what your high idling rpm is? (Full throttle in neutral gear)

Suggest that hull number, engine type, reduction gear ratio, propeller type, diameter, pitch, number of blades be mentioned on the diagram, unless you prefer not to have this shown.
Kind regards
Lars

Dear Professor,

One more question, but not necessarily the last one!

I have read that diesels like to be run up to full throttle to avoid glazing of the cylinder walls.  If we use the 3380 max rpm setting recommended in the commercial setup, does this have any negative effect on this issue?

Thanks,

Chris

Thank you professor. This question is definetely attracting a crowd!
I need to check all the points you mention, knowing for the time being that we cruise at around 2100/2200 RPM which gives around 5 to 5,5 Knts, and takes around 3 to 3.2 litres/hour.
Not sure whether we get 3000rpm or 4000 high idling rpm.
The propeller is a Max Prop, allowing around 3000rpm for maximum throttle, but there is some smoke, not sure about boat speed.
Boat is a 41, hull nb 22.
Need to check all this when sailing: I will then come back to you with detailed numbers.
In the meantime here is another question:Is adjusting the high idling rpm a complicated matter or does it simply need to adjust the right screw on the injection pump? (Using Perkins instruction leaflet)
Kind regards.
Philippe

Engine is a Perkins 4108, forgot to mention.
Philippe 41/022

... and transmission is original Borg Warner Velvet Drive expected to be 2.1 to 1 ratio.
Philippe 41/022

Chris
In order to avoid glazing the engine should be loaded, and high idling is not loading it very much. I believe the intention of engine manual texts is to ensure that the rpms are varied enough for new engines while running them in, and particularly aim at avoiding too low loads. It is clearly pointed out that marine engines need to be loaded.
For a 3000 rpm engine using 2000 rpm loads it to about 30%, and it i advisable to stay above this if fuel saving is not the main issue.
Kind regards
Lars


Dear Philippe
Adjusting high idling rpms is done with one screw, and normally this screw has been sealed by the engine manufacturer. The seal may still be there. It is assumed that there is no engine warranty any more, and you could therefore change the setting of this screw.
Kind regards
Lars

Dear Lars,

Thank you for your reply.  I understand your answer; my question was not well articulated.  I should have said "running the engine at full throttle UNDER LOAD."  My last boat had a 5 cylander marinized Mercedes Benz truck engine that had a max rpm of 4400 under load.  I typically ran this engine up to full speed for at least 10 minutes if I ran the engine for around 2 hours or more.  I assume that when I set the high end of the injection pump to 3380, running the engine at 3000 rpms under load will avoid the glazing problem.

I already know this is true since you would not recommend doing this otherwise!  I wander if you recommend using the procedure I outlined above?

With warm regards,

Chris

Dear Chris
It was mentioned earlier that marine engine manufacturers recommend that at least 25% load is used on average if the engine should stay clean. This number may vary between manufacturers. Pls note that this does not mean 25% of the max rpm, but 63% of it according to the propeller curve. See the curves on this thread.

With your 4400 rpm engine the recommended cruising rpm then was 2800, and provided you used this or more the full speed cleaning may not have been necessary.

If you used lower cruising rpms the cleaning operation was probably necessary. Did you notice some black smoke from the exhaust when advancing the throttle? If so the collected soot was blown out, but this type of smoking should stop fairly soon, indicating when the engine is clean.

If smoking at full throttle persists and does not stop this indicates that the engine is overloaded, and usually the cooling water temperature tends to rise also.

To conclude - provided you use at least 2000 rpm when cruising with the 3000 rpm max setting for the Perkins, full throttle cleaning should not be required. The recommendation is, however, to try a few times and see if some soot is blown out.
The above assumes that the propeller is matched to the engine power and rpm.
Kind regards
Lars

Dear Professor,

Thank you.  I always learn from you when i ask questions.  With regard to my last engine, yes, I ran it around 2800-3000 rpms and yes i did get black smoke initially when at full throttle but that lasted seconds and then the engine ran smoothly.  Seems like this was an unnecessary but exciting step - one could really feel the power of that engine!

You may have read in a previous note that I have taken the fuel tank out so it will be at least 1-2 weeks before i can measure the rpms at the shaft to determine the reverse gear ratio.  Of course, when i do, I will ask for more help!

With warm regards,

Chris

Dear All,

I was able to run the pick-up and return lines to a Gerry can and measure the rpms of the engine and the shaft; I purchased a $15 (delivered) digital meter and it worked flawlessly and easily.

Unfortunately for me, I have the 1.52:1 reduction gear and, as suspected, does not work well with the boat nor the prop.  So, in email correspondence with the Professor, and calls to Transatlantic Diesel In Richmond, VA, it looks like I will be replacing both my reverse Gear and the propeller.  The Professor recommends Flexofold from Denmark so that's the type of prop I will be purchasing.

I need to make a few additional measurements for the Professor and then we (he) will determine which reverse gear (1.91:1 or 2.52:1) and which propeller to purchase.  These measurements need the boat on the hard - waiting patiently for the yard!

I will report back.

Chris