Hippocampus
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Don just make sure you’re not under powered agree over ain’t a biggie.
Big HP vs Small HP
- Thread starter Don L
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If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
I would "assume" that if original engines it isn't underpowered really.
Guess that could make an ass out of me
rslifkin
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It depends. Some of the SD trawlers out there could be considered underpowered in the sense that the hull could easily make use of more power (and it might be useful if you were running through challenging inlets frequently, for example). But for primarily running at 7 kts, they're not underpowered.
mvweebles
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Agreed. What would really suck is buying a boat with largish twins but they are not big enough to get past the hull-speed barrier. It happens. I'm pretty skeptical of most builders- few are experienced mariners so tend to be a bit opportunistic in what they install.
Personal experience: (1) A Bayliner 3288 with a pair of Hino 135s would not get on step with 4 people aboard which means displacement or plowing a helluva wake. (2) I recall a Marine Trader that was close to 50-feet and loaded that was a handful with twin Lehman 120s, perhaps due to being in liveaboard trim. (3) Finally, a near infamous example was the early Nordhavn Coastal Pilot 35s that were designed to plane but were too heavy right out of the gate.
mvweebles
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Yep. Plenty. Won't plane the boat - maybe 12 kts. But assuming adequate rudder size, plenty to keep the boat maneuverable.
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rslifkin
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For running at typical trawler speeds, it's plenty. As mentioned, it's not enough to get a 42 footer on plane (I'd expect a top speed in the 12 - 14 kt range depending on hull shape and weight with that power). So in some situations you might be able to take advantage of more power, but assuming the rudders are adequately sized, etc. you probably don't really need more.
Last Tango
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My Perkins TE6.354’s get 2.4 GPM AT 7 Kts on a 42’ Ocean Yacht. Awesome engines. 43 years old now. Hope to make another mini loop here next year
Last Tango
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darkside
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I really hope that is 2.4NMPG
Nomad Willy
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Almost universally a small engine running fairly close to full power will be most efficient (gas engines included) probably because they have relatively less capacity to act as a heat sink. Most heat lost through the exhaust system, cylinder walls and all other parts of the engine heated by combustion will lower the efficiency.
Big engines w big cylinders and engine surface area are best at radiating heat and are thus less efficient.
So smaller engines are more efficient.
Big engines running at low output have (relatively cool) cylinder walls but make so little power a higher percentage of heat goes by by into the engine compartment and thus outside the boat. Heat lost. Any heat lost is power lost and efficiency lost.
Big engines w big cylinders and engine surface area are best at radiating heat and are thus less efficient.
So smaller engines are more efficient.
Big engines running at low output have (relatively cool) cylinder walls but make so little power a higher percentage of heat goes by by into the engine compartment and thus outside the boat. Heat lost. Any heat lost is power lost and efficiency lost.
Nomad Willy
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Depends on the hull type.
42’ typical rec trawler w 320hp may be over-powered.
42’ FD rec trawler w 320hp would definitely be over-powered.
Hippocampus
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we are 42’ and have 540hp. At 17-18kts and WOT we are at 100% load. Think if we had more hp we could go even faster.
Glad we don’t have more hp. Could not deal with the fuel bill.
Glad we don’t have more hp. Could not deal with the fuel bill.
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Nomad Willy
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Hip,
Yup, you sure could if your hull bottom was close to straight or straight and your boat wasn’t too heavy. Heavy and curvy bottoms don’t go fast unless there’re really long and close to straight aft.
You’ve just got 500hp more than my old Willard.
Yup, you sure could if your hull bottom was close to straight or straight and your boat wasn’t too heavy. Heavy and curvy bottoms don’t go fast unless there’re really long and close to straight aft.
You’ve just got 500hp more than my old Willard.
Could you share the designer of your boat?
I'm interested in purchasing a set of study plans...
Thank You!
rslifkin
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My 38 footer has 680hp total. Fast cruise is 17-18 kts, estimated to use about 400hp total. Flat out it'll do about 25 kts. At 6.5 - 7 kts we're likely using 40 hp or so, making the boat rather overpowered at that speed. But the ability to cruise steadily on plane is nice at times. Would be better if we had diesels (would carry less fuel economy penalty at low speeds in exchange for having the extra power).
