YachtForums.Com - View Single Post - Will slowing down damage larger diesel engines

Kniffin · 03-12-2008, 10:09 PM

Well, the responses so far bring up some interesting issues. I think that we all agree that operating temperature is critical to healthy engine life, as is a proper break-in. I have heard that synthetic oil usage in diesel engines is desirable as well (after break-in). By the way, the article about 4 stroke gas engine break-in is quite interesting. What do the manufacturers concur on proper diesel break-in? All I have heard about this subject is to vary throttle without too much high end operation - with proper temps and loading, then a prompt oil change at recommended interval.

We all know that proper loading is critical to diesel engine health - but typically on larger yachts, props need to be "sized" to fit the load and rpm requirements of each boat, thus often subjecting the boat to undue break-in stress. And even though I claim no background expertise in prop design, my observation is that there is some "black magic" involved in attaining the best design (often at owner expense) for acheiving decent performance throughout the low, mid and upper ranges of cruising - with the measuring stick often being able to obtain 100% load at full recommended rpm. Even so, I have seen dramatic improvements (and the other way around) by switching prop styles and blade counts with the same rpm's attained.

Some, if not most yachts also have different operating characteristics at different weight loads, with the props sized to slightly "overrev" when light in order to compensate for heavier loads when the props get loaded. So, if a boat with higher power goes slower, should it carry two sets of props - one used for slower operation with heavy fuel loads. would variable pitch props or composite props (with a pitch adjustment) be a good idea?

And what about the turbo?- I have heard that operating a boat without the turbo boost can sometimes foul things up. Would the concept of going WOT at the end of the cruising day be applicable and desirable for engine health?

Finally, we sometimes figure that single screw operating on twin screw boats can help with range goals, provided that transmission cooling is achieved - but often the prop drag and the need to compensate the rudders counteracts the intended fuel savings.

I am interested to hear input on these issues.

03-12-2008, 10:09 PM	#5
Kniffin Registered User Join Date: Jul 2007 Location: Fort Lauderdale, Florida Posts: 8	Well, the responses so far bring up some interesting issues. I think that we all agree that operating temperature is critical to healthy engine life, as is a proper break-in. I have heard that synthetic oil usage in diesel engines is desirable as well (after break-in). By the way, the article about 4 stroke gas engine break-in is quite interesting. What do the manufacturers concur on proper diesel break-in? All I have heard about this subject is to vary throttle without too much high end operation - with proper temps and loading, then a prompt oil change at recommended interval. We all know that proper loading is critical to diesel engine health - but typically on larger yachts, props need to be "sized" to fit the load and rpm requirements of each boat, thus often subjecting the boat to undue break-in stress. And even though I claim no background expertise in prop design, my observation is that there is some "black magic" involved in attaining the best design (often at owner expense) for acheiving decent performance throughout the low, mid and upper ranges of cruising - with the measuring stick often being able to obtain 100% load at full recommended rpm. Even so, I have seen dramatic improvements (and the other way around) by switching prop styles and blade counts with the same rpm's attained. Some, if not most yachts also have different operating characteristics at different weight loads, with the props sized to slightly "overrev" when light in order to compensate for heavier loads when the props get loaded. So, if a boat with higher power goes slower, should it carry two sets of props - one used for slower operation with heavy fuel loads. would variable pitch props or composite props (with a pitch adjustment) be a good idea? And what about the turbo?- I have heard that operating a boat without the turbo boost can sometimes foul things up. Would the concept of going WOT at the end of the cruising day be applicable and desirable for engine health? Finally, we sometimes figure that single screw operating on twin screw boats can help with range goals, provided that transmission cooling is achieved - but often the prop drag and the need to compensate the rudders counteracts the intended fuel savings. I am interested to hear input on these issues.