Long shaft, short transom

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deadkitty
Posts: 73
Joined: 17 Jul 2012, 00:42
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Location: Portland oregon

Long shaft, short transom

Post by deadkitty »

I just picked up a merc 9.9, thought it was a short shaft at the time of purchase (clist). Dude said it was, I didn't bring a tape measure. Anyway, so now my cavitation plate is a good 3-5 inches below my hull. I'm chugging and can tell motor is not getting up to full rpms. I have seen many posts and full transom replacements and offsetbrackets as solutions. To do it "proper" is seemingly a couple hundred bucks and/or a large amount of time cost.

So my question is this, is this dude crazy?

https://m.youtube.com/watch?v=AvXwllgchs4

Seems like a simple, cost effective, quick solution. If it's not viable, why not? He never had a follow up video, so no proof of concept...

This pic is with a 1" piece of wood spacer at the bracket, trim is one notch up. Definitely too low still.
[ external image ]


Also, hydrofoil, once motor is proper height, yay or nay?

Weldorthemagnificent
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Joined: 12 Mar 2017, 12:09
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Long shaft, short transom

Post by Weldorthemagnificent »

Can make a transom higher with a couple pieces of aluminum, 1/4" thick is good. And a piece of wood in between. Bolt it through the transom and hang the motor on. Make your aluminum plates double your height below existing. For example, if you are planning to raise 4", make the plates at least 12" so that 8" is below the existing transom. If you can spare a few bucks, have your top and top 4" of the sides capped and welded to make one solid unit. I've seen this done and works fine.
As for the hydrofoil, I am a fan of them. Helps plane faster, allows slower planing speeds and is more forgiving with weight distribution.


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Ttexastom
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Joined: 20 Feb 2017, 13:18
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Location: Danielsville georgia

Long shaft, short transom

Post by Ttexastom »

Love those hydrofoils. Ran one on three different motors. Always fast to blast off in bass tournsments. Make ride better too!!
2011 15 ft alumacraft, 16hp go-devil
1984 24 ft party barge 70 hp johnson

surfman
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Joined: 29 Dec 2011, 17:29
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Long shaft, short transom

Post by surfman »

I would only use the hydrofoil if you need it, otherwise they work good.
the YouTube fix does not look kosher, not enough bracing but, that is a small motor, a 9.9 as a lot more torque. Maybe if you braced it all the way down and on both sides you could get away with it.

turbotodd
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Long shaft, short transom

Post by turbotodd »

Use a jack plate. Or make one, but you'll have to lift it up pretty high to get the 5" of lift to make a 20" motor fit a 15" transom. I am making one and might try it later in the fall. 4 pieces of angle aluminum, some plywood laminated, SS hardware, etc. Real easy to make.

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beetlespin
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Location: Central New Jersey

Long shaft, short transom

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earl60446
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Joined: 17 Dec 2010, 12:15
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Location: Kankakee County, IL

Long shaft, short transom

Post by earl60446 »

Lots of people have done it and it works. Seems to me like the youtube guy did a poor job engineering his.
He could have run the board all the way across the transom.
He could have used the struts on both sides of the transom.
He could have run the struts lower and used 2 bolts on each strut thru the transom.
Tim
16ft 1989 Fisher SV-2 w 1988 48hp SPL Johnson "CIGAR BARGE"
(engine looks like a wreck but runs great)
Used to have 1972 14ft Lund w 1977 15hp Mariner
(engine looked great but always ran marginal)
XLINE SPORTSMANS CLUB

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Buckethead
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Joined: 15 Jul 2012, 22:18
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Location: Union, MO.

Long shaft, short transom

Post by Buckethead »

I did it with heavy wall 1-1/2" aluminum angle and a fresh cut white oak board from a sawmill. I had to extend my short transom 5" to fit a 50hp short shaft jet. It worked perfectly. I extended the angle from the bottom on the transom on the inside with 2 1/2" stainless steel bolts/nuts. I've since sold the jet unit and have a short shaft Yamaha prop motor on there now. I saved my transom extension in case I decide to go jet again.

deadkitty
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Joined: 17 Jul 2012, 00:42
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Location: Portland oregon

Long shaft, short transom

Post by deadkitty »

Thanks guys so much. So... yeah... did a bunch more research and found out mercury short shafts are 18" , lol so that explains the extra depth. I put a 2x2" underneath as a spacer and it'll work fine for now. I will likely put something more permanent in later, ala many of your great suggestions.


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ericman
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Joined: 02 Jun 2013, 10:26
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Long shaft, short transom

Post by ericman »

This was a short transom that I turned into a long transom.
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RaisedByWolves
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Location: Bucks county PA.

Long shaft, short transom

Post by RaisedByWolves »

deadkitty wrote:Thanks guys so much. So... yeah... did a bunch more research and found out mercury short shafts are 18" , lol so that explains the extra depth. I put a 2x2" underneath as a spacer and it'll work fine for now. I will likely put something more permanent in later, ala many of your great suggestions.


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Im redoing my rotted transom and I bought oak plywood to raise the transom to fit my $50 CL longshaft 25hp evenrude. The transom is 20" but the engine is 22" which Im not sure if thats normal or what.

I plan on sandwiching two identical pieces of ply into a truncated pyramid shape which I figure will be stronger than if I used a 2" spacer on top of the new transom. The two plys will be glued and sealed with polyester resin.

Later if I go with a different engine with a shorter shaft length I can easily cut it down to meet whatever needs.
Sailbad the Sinner

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