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Old 03-28-2018, 12:21 AM   #21
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WOT should be about 1 or 2 hundred RPM below rated maximum. WOT at half power setting makes no sense.

Coolant temperature rarely gets above 170 degrees and look at the plate on your gears, its usually rated well above that.
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Old 03-28-2018, 05:24 AM   #22
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Input from a matine engineer to clear something up in the discussion....


"A diesel can be about twice as thermally efficient as a gas engine. That means that for the same horsepower delivered to the shaft a diesel may convert nearly twice as much heat into power than a gas engine. The heat not converted to power in either engine is transferred to the cooling water or surrounding air so if both gas and diesel have the same power output the gas engine may produce nearly twice the heat as a diesel. A transmission has no idea of what is spinning its shafts and the heat it produces is related to the power in vs power out."
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Old 03-28-2018, 05:52 AM   #23
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If the oil leaving the tranny is under 240F with the cooler in the fresh water system , it would work for me.

This boat is like most cruisers, way over powered, so going with the reality of the current installation and operating profile seems safe enough.
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Old 03-28-2018, 07:25 AM   #24
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Quote:
Originally Posted by Xsbank View Post
WOT should be about 1 or 2 hundred RPM below rated maximum. WOT at half power setting makes no sense.
The power installations of many or most trawlers of this vintage make no sense. Oversized engines were installed for marketing reasons and because reduction gears with the proper ratio were expensive and hard to obtain when trawlers suddenly became popular. The boat is seriously under propped so the governer maxes out at about 50% power. The props are the best compromise for the speeds we like to operate at, 7-8 knots, S/L 1.12 - 1.28, 1400 - 1600 RPM, 33-56 HP (18 - 28 each engine).

Going slowly through the long no wake zones of the ICW and harbors would become harder if we added pitch to the props.

When I was designing research vessels like these,

Roger Long Boat Designer and Sailor

Engine suppliers would generally insist on the engine turning within 50 rpm of maximum at WOT if you wanted a guarantee. Modern engines are a lot less forgiving though than the Perkins museum pieces we have.
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Old 03-28-2018, 08:54 AM   #25
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The power installations of many or most trawlers of this vintage make no sense. Oversized engines were installed for marketing reasons and because reduction gears with the proper ratio were expensive and hard to obtain when trawlers suddenly became popular. The boat is seriously under propped so the governer maxes out at about 50% power. The props are the best compromise for the speeds we like to operate at, 7-8 knots, S/L 1.12 - 1.28, 1400 - 1600 RPM, 33-56 HP (18 - 28 each engine).

Going slowly through the long no wake zones of the ICW and harbors would become harder if we added pitch to the props.

When I was designing research vessels like these,

Roger Long Boat Designer and Sailor

Engine suppliers would generally insist on the engine turning within 50 rpm of maximum at WOT if you wanted a guarantee. Modern engines are a lot less forgiving though than the Perkins museum pieces we have.
I suppose you get that "neck snapping acceleration" with that low pitch.

But seriously, I'm going to suppose that 50% power is at a point much more than 50% RPM on the prop curve? And, more to your point; trying to use that unavailable 50% is generally fruitless in a FD trawler, with typically supplied engines.
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