15” shaft on a 20” transom

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
bklake
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Re: 15” shaft on a 20” transom

Post by bklake »

I had a 15hp Evinrude that was pretty easy to convert from 15" to 20". All Evinrude parts. A 5" spacer for the lower, a 20" drive shaft and I had to make a water pick up tube. It took awhile to find and collect the parts but they were out there. I'm not sure if your motor came in a similar configuration but it is worth looking into. There may be a complete lower out there. It isn't any harder than dropping the lower to change the impeller.

This was 15 years ago and the website I used as a guide is long gone. I don't know where to look for info now. Parts diagrams for your motor would be a good place to start.

jbo_c
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Re: 15” shaft on a 20” transom

Post by jbo_c »

Good point, BK. I’m imminently capable of doing that and have a good local source to (probably) get the parts. I should have considered it more.

That’s one reason I like these older Johnnyrudes. I can do most anything that needs doing up to the point of just needing to toss it on the scrap heap. To my knowledge there is no “high-thrust” version pre-mid 70s or I’d probably not be looking to go to a newer engine.

Jbo

bklake
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Re: 15” shaft on a 20” transom

Post by bklake »

Keep all the 15" parts and when it is time to sell the motor, include them so the new owner has options.

Edit: Just a quick peek at parts diagrams, looks like the Jonnyrude 18 and 20hp used a 5" spacer like my old 15. Not sure what year your motor is but boats.net has parts diagrams for many years of these motors. You never said exactly what motor you have but OMC is the only one I know of that was listed as 18hp. My knowledge of these old outboards is pretty limited. I dumped all the knowledge to make room for knowledge of my new Suzuki 9.9B.

jbo_c
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Re: 15” shaft on a 20” transom

Post by jbo_c »

Thanks for the thoughts and ideas. I know 50’s to mid-70’s pretty well mechanically speaking. This one is a 1968 Fastwin. It’s a family “heirloom” so it’s never going anywhere. :)

There’s a huge boat cemetery/junkyard here that I’m sure will turn up the parts I need when I’m ready.

Thanks, again.

Jbo

TomW1
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Re: 15” shaft on a 20” transom

Post by TomW1 »

jbo, on one of Jacques houseboat plans he has a bracket for a small motor. I don't remember which but I'm sure you can find it and ask Jeff to see if he he would send you just that part of the plan. I do not also remember what HP it was rated for. Tom

PS: Found it the HB18.
Last edited by TomW1 on Thu Nov 03, 2022 6:57 pm, edited 3 times in total.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

jbo_c
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Re: 15” shaft on a 20” transom

Post by jbo_c »

You’re right, Tom. Good remembering. I may do just that.

Jbo

fallguy1000
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Re: 15” shaft on a 20” transom

Post by fallguy1000 »

Just make the engine a 20" and thank the contributors you are not spraying water all over.
My boat build is here -------->

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