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Old 03 January 2012, 14:44   #1
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Transom / Shaft Length

Hi , can anyone advise ?
my transom height is 22.8 inches , can i get away with a 21 inch shaft motor without cutting the transom down . Rib is a RC 585 , motor i'm looking at is a 115 4s Mariner.
Thanks
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Old 03 January 2012, 14:47   #2
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I'd get a 25inch shaft and mount it 2 inches high.

Potentially being 1.8 inches too high means you may end up needing to cut down the transom. That's lot of work and the transom may not like it compared to mounting a longer shaft a few bolt holes down (raising it).
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Old 03 January 2012, 16:51   #3
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I'd run a long shaft.
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Old 03 January 2012, 18:24   #4
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I use to run my etec about 2" above the bottom of the transom. However E-tecs like to be mounted fairly high so this was fine.

I would ask Ribcraft as they know their hull better than anyone and will be able to advise you.
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Old 03 January 2012, 18:27   #5
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Quote:
Originally Posted by chewy View Post
I'd run a long shaft.
What is that in the UK?
Over here its:
15" = short
20" = long
25" = XL

but various companies are making all sorts of intermediate lengths depending on the motor and HP so I don't know what to call a 17.5" shaft.
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Old 03 January 2012, 18:33   #6
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thats a little annoying , was hoping for a "well it was ok on mine" kind of answer ! any fabrication guys got any ideas , i think the transom was cut down already and was probably a long shaft ( 25 inch) to begin with .
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Old 03 January 2012, 18:38   #7
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Quote:
Originally Posted by captnjack View Post
What is that in the UK?
Over here its:
15" = short
20" = long
25" = XL

but various companies are making all shorts of intermediate lengths depending on the motor and HP so I don't know what to call a 17.5" shaft.
12" = short (race motors)
15" = standard (commonly referred to as short shaft)
20" = long
25" = extra long (XL)
30" = ultra long

The 17.5"/18" tend to be called mid-shaft.
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Old 03 January 2012, 18:40   #8
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I'd run a long shaft.
So would I, but keep an eye on the water pressure and check for prop slip when testing.
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Old 03 January 2012, 18:46   #9
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Quote:
Originally Posted by Downhilldai View Post
12" = short (race motors)
15" = standard (commonly referred to as short shaft)
20" = long
25" = extra long (XL)
30" = ultra long

The 17.5"/18" tend to be called mid-shaft.
Thanks I don't think I've ever seen a 12" shaft in a US catalog or showroom. Otherwise we're the same. I just forgot about 30" ones which are rare, at least on RIBs here.
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Old 04 January 2012, 04:46   #10
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Mine's a 25" leg on a 25" transom - I'm pretty sure the engine it not resting on the top either, I expect you're right on the edge as does't the anti ventilation plate want to be a couple of inched higher than the very bottom of the hull?
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Old 04 January 2012, 10:29   #11
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Thomas , thanks for the pic. I spoke to Ribcraft and they think a 20" will be ok . I think the extra weight ( 170kg) of a 4 stroke may help , originally these boats were made with a lighter 2 stroke in mind ( mines a 1999 and says max hp 125 ) . I was planning to push the console forward a bit to balance. Think i'll try it and see and if the transom needs to come down an inch then so be it. Ribcraft said watch out for back wash , i'm always pretty mindfull of this and have seen a "collar" type of thing elsewhere on the forum , made by " Biffer" i think so should be avoidable. Got any other tips while i'm still in build mode ??
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Old 04 January 2012, 11:29   #12
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Mines a Ribtec, I was warned before I got mine that the low transom was an issue, turned out mine was full height and needed the long leg so back wash is not an issue on mine. Mine is back heavy though and the bow does stick up quite a lot, though the Merc is a lighter engine than others, I suffered a little from chine walking but stuck another anchor and more chain in the locker and it really helped.
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Old 05 January 2012, 06:43   #13
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been advised by my local mariner dealer that if it's not a fit i can get a mariner extension kit and it won't affect the warranty, happier now i have a couple of options
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