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Old 20 January 2015, 14:40   #1
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Using a 20" Long Shaft Outboard on a 15" Transom

I know using a short shaft motor on a 20" transom will have its obvious implication of the engine not getting water to cool itself with the boat on plane, but what of using a long shaft motor on a shorter transom? I didn't know until now that the Futura uses a long shaft engine, but most inflatables take a short shaft. The Futura is what I'm eyeing, but if i got a smaller inflatable alongside it for solo outings and wanted to not buy a second engine, could I mount a long shaft and not run into any major problems? Is there some sort transom adapter that'd make it work? My only worry with trying to adapt the transom to properly accommodate it is changing the fulcrum at which the thrust acts on the transom, possibly leading to premature failure or a total, sudden structural failure.
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Old 20 January 2015, 17:50   #2
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It'll be slow due to the extra drag, probably spray a bunch of water over the transom back into the boat too.
We built up a transom to take a long shaft once, worked ok but was only a 15hp outboard. Not sure if i'd want to do it with a bigger engine.
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Old 20 January 2015, 18:59   #3
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Quote:
Originally Posted by simmons0 View Post
It'll be slow due to the extra drag, probably spray a bunch of water over the transom back into the boat too.
We built up a transom to take a long shaft once, worked ok but was only a 15hp outboard. Not sure if i'd want to do it with a bigger engine.
Built up the transom??? How does one do that? I'm by no means looking for a massive engine though, probably 20 HP.
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Old 21 January 2015, 00:17   #4
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Originally Posted by kestrel452 View Post
Built up the transom??? How does one do that? I'm by no means looking for a massive engine though, probably 20 HP.
Do a search in the SIB forum. Lots of posts about it. Essentially, you add material to the top of the transom to adjust motor height. Not sure if you could do 5" though.

jky
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Old 23 January 2015, 09:16   #5
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PROVIDING you have a metal two layer floor: If five inches, run two 14-16 inch diagonal metal tubes from near top of transom to floor (3/4 or 1/2" ss screws that will go NO deeper than the top layer of of the allum floor) Use 1" wood screws on the top of metal tube to transom. This will secure the transom to handle more stress. Or you could remove the rear metal floor panel, drill and use two carriage bolts for the metal transom tube supports (preferred method).
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