DW
I am late to this thread, and may be repeating what earlier posters have said, though I am usually the odd man out on this subject.
I bought this boat in 1994 and re-powered in 2000. My boat is about the age of yours, similar style, and I suspect from what I have seen of your posts here that our cruising style is similar.
My Re-power was from Volvo TMD40s, 145hp, to Volvo TAMD41s, 200hp. In the re-power, I first left the original props on, so the only change was the newer generation engines.
After the repower, my cruising speed increased by a knot and my fuel consumption/mile decreased by almost 10%, due to the more efficient engine design. My mechanic, who had suggested the change, thought that I could get still better fuel economy if I re-pitched the props to reduce the cruising rpm.
When I had 4" of pitch added, my cruising rpm dropped 500rpm or so and I gained a further 5% approx in fuel efficiency.
Naturally I NEVER run these engines at rated WOT.
If I had a planing boat, I would pay more attention to "overpropping", oh, wait, I have a 40 Honda on my dinghy. It reaches 25 knots and 5500 rpm at WOT, so I do have that experience. On a big boat like that, I would pay close attention to what rpm is reached at WOT, but when my best speed is around 8 knots, on a boat that would need 2000 hp to plane, driven by 1/5 of that, I am happier to overprop and save fuel in the process. I am also of the belief that the longevity av a diesel engine is measured best by its fuel consumption, so anything that improves fuel efficiency is good.
If there was ever a hint that underloading was occurring, surely that would have become clear within the 23 years since my "overpropping" experiment began.
I am late to this thread, and may be repeating what earlier posters have said, though I am usually the odd man out on this subject.
I bought this boat in 1994 and re-powered in 2000. My boat is about the age of yours, similar style, and I suspect from what I have seen of your posts here that our cruising style is similar.
My Re-power was from Volvo TMD40s, 145hp, to Volvo TAMD41s, 200hp. In the re-power, I first left the original props on, so the only change was the newer generation engines.
After the repower, my cruising speed increased by a knot and my fuel consumption/mile decreased by almost 10%, due to the more efficient engine design. My mechanic, who had suggested the change, thought that I could get still better fuel economy if I re-pitched the props to reduce the cruising rpm.
When I had 4" of pitch added, my cruising rpm dropped 500rpm or so and I gained a further 5% approx in fuel efficiency.
Naturally I NEVER run these engines at rated WOT.
If I had a planing boat, I would pay more attention to "overpropping", oh, wait, I have a 40 Honda on my dinghy. It reaches 25 knots and 5500 rpm at WOT, so I do have that experience. On a big boat like that, I would pay close attention to what rpm is reached at WOT, but when my best speed is around 8 knots, on a boat that would need 2000 hp to plane, driven by 1/5 of that, I am happier to overprop and save fuel in the process. I am also of the belief that the longevity av a diesel engine is measured best by its fuel consumption, so anything that improves fuel efficiency is good.
If there was ever a hint that underloading was occurring, surely that would have become clear within the 23 years since my "overpropping" experiment began.
