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  Short shaft motor on 1979 13-ft

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Author Topic:   Short shaft motor on 1979 13-ft
MikeC posted 08-10-2001 02:20 PM ET (US)   Profile for MikeC   Send Email to MikeC  
Will 15-inch shaft motors work on the 1979 13 footers? I just picked up a mint 1979 13 footer with a long shaft OMC 35 hp motor. I have a 2000 Tohatsu 50-HP 15-inch that was blueprinted with Boysen reeds and Wiseco pistons. I would love to put that motor on my 13. What do you think, will it work?
Peter posted 08-10-2001 03:43 PM ET (US)     Profile for Peter  Send Email to Peter     
No. The motor will cavitate. Unless it was modified, your '79 13' has a 20" transom. You'd have to cut a notch in the transom. I wouldn't do it.
MikeC posted 08-10-2001 06:31 PM ET (US)     Profile for MikeC  Send Email to MikeC     
Are you speaking from experience or are you going by the Whaler brochure? I realize that it's a 20-inch transom, but I have raced many boats with 20-inch transoms and had to jack the motor way up to get it to perform. I was just wondering if anyone has tried it.
Peter posted 08-10-2001 09:05 PM ET (US)     Profile for Peter  Send Email to Peter     
I've never run a 15" on a 13' but I have trimmed the 35 out and it will cavitate. While the 13 is quick, I don't believe it is a performance hull. Give it a try, see what happens and let us know.
Sam Collins posted 08-10-2001 09:16 PM ET (US)     Profile for Sam Collins  Send Email to Sam Collins     
Look at page 28 In cetacea at Clark Roberts 13' Alert....
MikeC posted 08-10-2001 10:04 PM ET (US)     Profile for MikeC  Send Email to MikeC     
Cavitation is easily fixed with a good cupped stainless semicleaver prop. I think I just might give it a shot. I am not looking to make a raceboat out of it, I just want to have a little more power on hand. This motor I have only has about 5 hrs on it so I would hate to go buy a new motor for the Whaler.
Clark Roberts posted 08-11-2001 01:46 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Mike, I know I have already e-mailed you but will repeat the unofficial "rule of thumb" regarding set-back. Generally goes like this: back one inch, up a half inch... so to make up the approx 5" you may have to bracket the engine back about 10". Since the 13 has a very "steep" transom angle you may get away with 8" back. Mount the set-back bracket in position of normal outboard mounting. I use a T&H manual jack plate (THmarine.com)with about 8" set-back on my 21 with 135 Merc Opti and it's jacked up about 4" ... runs great with no cavitation on hard accel but some breaking loose if I turn too sharply without tucking engine under a bit. You will need nerves of steel to run that 13 with a blue printed 50hp Tohatsu. Those engines seem to be really strong in stock form anyway... remember that the fiberglas Boyntsen reeds are sacrificial and will wear out! You will be able to tell when they begin to sluff off and loose their bounce! Good thing about them is that they will blow through if broken and will not ruin the engine...Happy Whalin'.. Clark ... The Old Man and the Sea
jimh posted 08-12-2001 08:39 AM ET (US)     Profile for jimh  Send Email to jimh     
If you actually do install the engine, by all means post some performance measurements for the boat. They should make interesting reading.
Bigshot posted 08-13-2001 01:00 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I would do as Clark says and get a plate. Do not think you would get away without it.
MikeC posted 08-13-2001 08:35 PM ET (US)     Profile for MikeC  Send Email to MikeC     
I think I will just sell that motor,I dont want to add any brackets to the boat.I want it to look as origanal as possible.I may just get a new 40 hp Tohatsu 20 inch.I really like those Tohatsu motors.The 50D I have will turn a 18 pitch prop at 7000 RPM :)

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