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model 10 · 11-09-2016, 08:33

[QUOTE=SV gypsy spirit;2210520]
Let's assume the bottom is clean, a 37ft not overly loaded down cruising boat, with a clean, 3-blade prop with the correct pitch.

How could it be the correct pitch if it's turning to many rpm? Some 108 engines need to turn up so they can reach 50 HP. A 36hp rated Perkins makes full power at a much lower rpm.

SV gypsy spirit · 11-09-2016, 08:48

Quote:

Originally Posted by Guy

How could it be the correct pitch if it's turning to many rpm?

It's not turning too many rpm, I am actively revving it up to say 2800. I can't get over 3200 in gear though. I understand that a bigger prop or a different pitch would not allow the engine to rev up more while delivering more thrust in lower rpm scales.

I am just wondering why I seem to have to rev up (way) higher than a year or two ago to reach the same speeds with the same prop. As said, I got 5-6 knots with 2000 rpm, now I need 2500 - 2800 to get up this same speed. On 3100 rpm, I can get to 7.5 - 8 kts. This just doesn't seem right.

Quote:

Some 108 engines need to turn up so they can reach 50 HP. A 36hp rated Perkins makes full power at a much lower rpm.

I wouldn't even assume my boat would "need" the full 50 hp to get to speed X. It's a 37 foot modified fin keel boat after all. Jeez, I got her to 4.5 knots easy with a dinghy tug tied alongside, with a 15 hp outboard.

model 10 · 11-09-2016, 10:08

Quote:

Originally Posted by SV gypsy spirit

I wouldn't even assume my boat would "need" the full 50 hp to get to speed X. It's a 37 foot modified fin keel boat after all. Jeez, I got her to 4.5 knots easy with a dinghy tug tied alongside, with a 15 hp outboard.

One of the other sailors here kept a very accurate fuel log for his boat with a Perkins. He averaged only about 10 hp worth of fuel per hour in a boat your size.

SV gypsy spirit · 28-12-2016, 06:21

After a while Away From Boat and then other projects, I am back at the engine issue.

For those that didn't read the whole thing: My 37ft sailboats Perkins 4108 returned black fuel. Since then, I changed the fuel hoses and filters and ran it ~5 hours off a 5 gallon jug with new fresh clean yellow fuel, with the pickup and the return line into this jug as a test.

Yesterday I had to remove and thus look at this jug. The fuel again is pretty black.

Other posters directed me towards the injector pump as a possible oil-into-fuel leak (rear seal/gasket), since on my engine the lift pump has been removed and is ruled out.

Before I take it off, is there any other suggestion or idea what could cause this?
Many thanks,
Daniel

zeehag · 28-12-2016, 06:31

rebuild your lift and injector pumps. mine was black return before the runaway. beware and repair now not after the runaway. one person singing along with dion and belmonts is enough.