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#1
12-25-2009, 08:32 PM
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new to me
picked up a 1976 ma in really good shape has the teak and everything, its got a omc 90 on it.It had about a 40 gallon belly tank in it and i'd like to put about a 60 gallon.What kind of crusing speed could i expect, or does it need a bigger motor?
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1971 seacraft 20 1976 seacraft ma 
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#2
12-25-2009, 10:09 PM
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Re: new to me
Congradulations and Happy Holidays! 90 horses may be short but I wouldn't replace the tank until you run her. Bigger power will require bigger fuel.
1979 MA 1999 175 OMC and factory 68 gallons!
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#3
12-26-2009, 01:41 AM
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Re: new to me
Fr. Frank is running a 20' tsunami w/ 90 merc. He posted some numbers on it here in the last few months. You should be able to find them using the search feature. Probably under the performance threads.
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Getting home is more important than getting there! Plan accordingly!
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#4
12-27-2009, 10:57 AM
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Re: new to me
I have a 20' Seafari cuddy cabin with a 90hp Mercury Optimax. I cruise at 24 mph, and WOT is about 33-34 mph. I get just a hair over 5 mpg at cruise. My 90 Optimax actually produces 105-110 hp at the propeller.
If you're running a 90* degree CrossFlow OMC outboard, you should cruise at about 23-24 mph at about 3 1/2 mpg, and I would guess a top speed of 28-30 with the right propeller. These motors actually produced about 85-90 hp at the prop. If you're running a later Loop Induction ("Looper") with the VRO system working, I think you should see a slightly better top speed of 30-32, and 3.5 to 4 mpg at cruise, again, with the right prop. The Looper 90 actually produced about 95 hp at the prop. If the VRO system is disabled, your performance will be comparable to the CrossFlow system. As a Marina manager in the early 80's, I rigged many new 20' SeaCrafts with a single 85 hp V4 Evinrude outboard or single 90 hp Mercury 6 cyl. They performed quite well with that power. By far the most common OE power was a 115 hp motor.
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Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes. Fr. Frank says: Jesus liked fishing, too. He even walked on water to get to the boat! Currently without a SeaCraft  (2) Pompano 12' fishing kayaks '73 Cobia 18' prototype "Casting Skiff", 70hp Mercury
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#5
12-29-2009, 10:48 PM
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Re: new to me
yhanks guys,with that information in hand I think i'll put my johnson 150 on it and save the 90 for something smaller
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1971 seacraft 20 1976 seacraft ma
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#6
12-30-2009, 05:08 PM
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Re: new to me
Quote:
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Any way you measure it - dumbass is expensive
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