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Old 09-14-2013, 05:46 PM   #1
City: wrightsville Beach NC
Country: USA
Join Date: Sep 2013
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Smile advice on older mainship w Yanmar power

Looking at 79 Mainship with 250 HP 2010 Yanmar, Things to look for during survey ?
What should this boat cruise at ? Feul burn ?

Welcome any advice Thanks

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Old 09-15-2013, 08:27 AM   #2
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City: Maryland
Country: USA
Vessel Model: 42' Sportfish
Join Date: Aug 2013
Posts: 4,798
Mainship built their original 34s with Perkins approx 210 hp and the DD 8.2T (220-hp IIRC). 250-hp should be quite acceptable.

Ours was an '87 Mainship III with DD. Cruise was about 8-9 kts, 10-12 possible for a while if necessary, 14 was WOT if I remember right... Cheap to run at 8-9 kts, but I don't remember specifics.

I recently made up a list of my own thoughts about mods I might consider if we still had that boat today -- we really liked it -- and could post that if it would help.


South River, Chesapeake Bay
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Old 09-15-2013, 05:54 PM   #3
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City: Litchfield, Ct/Punta Gorda, Fl
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I don't know which Yanmar engine that you have. It could be a 4LH (not likely), a 6LP or a 6LY. The later two would be good choices. Post your specific model and we can comment appropriately.

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Old 09-17-2013, 09:56 AM   #4
City: LI or Fla
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Yea 250hp is unual number to me, the 4 banger LH was 240, and was a great one, I believe discontinued in 2010, the LP was 260 or 315, I believe the 260 was discontinued also before then, which leads to the BY, which is 220 or 260, I would say the BY has not been the prize of the Yanmar fleet.
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Old 09-17-2013, 10:10 AM   #5
Country: CANADA
Vessel Name: SUMMER II
Vessel Model: 34 MAINSHIP
Join Date: Sep 2013
Posts: 10
Our 34 has a Perkins 165hp, cruises at 8knts and burns 1.7 gph. Get your surveyor to check the deck including the cockpit for moisture.

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Old 09-17-2013, 03:31 PM   #6
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The original power for a 1979 Mainship 34 was a Perkins T6.354 at 160 HP.
It would cruise at 9 knots probably doing 2.5 gph. Top end was around 10.5 or 11 knots.

With a 250 HP modern diesel the boat should be able to cruise at 14 to 14.5 knots and top out at 16 to 16.5 You'll obviously burn more fuel at that cruise speed BUT at 9 knots or less it will be MORE efficient than the original power was at that speed.

250 HP is just about right in my opinion for that hull and boat model. Fast enough to get you there when you want, yet extremely efficient when you choose.

(I owned a 78 Mainship 34 ran the original Perkins for 9 years then repowered it with a 270 Cummins so I know the scoop first hand).

Jay Leonard
Attitude Adjustment
40 Albin
Mystic,Ct. /New Port Richey,Fl
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