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Old 21-03-2015, 16:58   #1
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Full Power Run

I have a 1981 Cheoy Lee Ketch, 41', 12' 6" Beam, 6' Draft, 25 Gross Tons. I read an article by Steve D'Antonio about engines running under full load and reaching maximum power. When you run the boat with the throttle wide open the boat should come up to it's maximum RPMs and not overheat.

Today I filled the boat up with our normal cruising load of full water and fuel tanks and we slowly increased the throttle to full forward and our RPMs came up to 2700, not the 3000 that we had back in San Diego before we left to go cruising. We were towing our 8' Walker Bay dinghy during the test. We cruised for 5 minutes with the throttle wide open. The cooling system functioned as it should, the temperature stayed right around our normal 180 degrees, there was a small creep up to maybe 186 so our cooling system is doing great.

I don't think the dinghy would cause the engine RPMs to not come up to 3000, but maybe there is a prop size mismatch?
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Old 21-03-2015, 17:25   #2
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Re: Full Power Run

Dinghies exert a fair amount of drag. Try holding the painter when you have the throttle on the boat wide open.

Other variables at play--condition of bottom of the boat; condition of the prop. When were these last cleaned?

How does boat speed compare with your last test?
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Old 21-03-2015, 18:42   #3
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Re: Full Power Run

A fully loaded boat can pretty easily decrease max revs by 200 or so, towing a dinghy as well I am not suprized rhat you saw 300 off.

Sounds like everything is parking as expected to be honest.
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Old 21-03-2015, 19:00   #4
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Re: Full Power Run

If you didn't have black smoke coming out the exhaust it sounds good to go.
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Old 21-03-2015, 22:37   #5
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Re: Full Power Run

Boat speed was less than our max, 7.2. Bottom was cleaned last month. Maybe barnacles on the propellor.
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Old 22-03-2015, 10:18   #6
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Re: Full Power Run

Dirty bottom, towing a dink, heavily loaded boat. What did you expect?
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Old 22-03-2015, 20:10   #7
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Re: Full Power Run

The rpm in San Diego doesn't mean anything. What kind of engine is it and what does its manufacturer say is its top rpm?
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Old 22-03-2015, 20:26   #8
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Re: Full Power Run

Don't believe the manufacturers rev counter when sorting out props. You MUST do a real RMP check. I have seen manufacturers units out by as much as 30%! If you want to DIY, you can buy an optical tacho pretty cheaply, but make sure it has a calibration or accuracy cert.
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Old 31-03-2015, 15:38   #9
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Re: Full Power Run

The engine is a Westerbeke 44. It comes up to 3000 RMP (Max RPM according to the manufacturer's literature with the correctly pitched prop)

Got the bottom cleaned today and the diver said he found an oyster on the keel five inches around and the propellor was dirty. Getting underway tomorrow to check out the new performance.

On our last underway the engine only came up to 2400 RPM at full throttle and our boat speed was 4.2 knots max (no current) in flat open water with the dinghy out of the water.
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Old 09-04-2015, 22:40   #10
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Re: Full Power Run

OK. Got underway and headed north out of Nuevo Vallarta. The engine came up to 2900 RPM. After a few days in La Cruz we left to go farther north towards Mazatlan and the engine came up to 3000 RPMs and 7.3 knots. That's a tenth of a knot faster than we've ever gone before, this time out of San Diego bay, in 2 foot ocean swells with zero wind. back to perfect for the rest of our cruise north. Thanks cruisers forum for the input, thread closed.
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