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Old 07-15-2017, 08:55 PM   #1
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1977 Marine Trader 40

Hey folks,

New to the forum and new to trawlers.

I'm looking at a 1977 marine trader 40 double cabin. This is our first time in the market for a "livaboard size vessel".

This boat had a survey in 2014. Clearly on page 6 the survey lists the boat hull type to be semi displacement.

It has a single Lehman 120.

Am I missing something here? 30,000 pounds with 120 ponies...This boat seems like it should be a full displacement hull. Right?

My basic understanding of semi vs full is this:

On a semi the engine power is divided both between forward propulsion and lifting the bow. Semi = slightly faster cruising speed at the cost of significantly worse fuel consumption.

On a full displacement 100% of the engine power is spent on forward propulsion. Full = slower speeds but it's the most fuel efficient vessel under power aside from a sailboat.

I'm sure my understanding is elementary so any and all help is greatly appreciated.

Thanks,
Perry
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Old 07-15-2017, 10:53 PM   #2
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You have it pretty much right, and yes, as the owner of a 34 ft boat with similar hull shape and the same engine, I can tell you there is no way I can semi-plane, so that boat won't. The description might be right re the hull shape, but you'd need twins of 300hp plus to meaningfully semi-plane in the vessel you are describing, in my view. Others may differ, but I doubt it.
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Old 07-16-2017, 06:41 AM   #3
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I have 168hp Mercedes in mine. (single) No it doesn't plane or semi-plane but the fuel consumption is fantastic.
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Old 07-16-2017, 08:04 AM   #4
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Wonderful. Thanks for the help! If we purchase I'll post pics for sure.
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Old 07-25-2017, 08:17 AM   #5
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My 41' President with twin FL 120's only dreams of planing or going any faster than 8 kts. But, as Donna mentioned fuel consumption is fantastic at 3 GPH and I carry 700 gallons.
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