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Shaft length and my transom height

post #1 of 12
Thread Starter 
Hi All,



I have ordered the Honda 50HP EFI, but I noticed that the sales person ordered the "long-shaft" version. I talked to the service guy, and he said that the engine comes in a short-shaft (15''), long-shaft (20''), extra-long shaft (25''), etc.



I have fairly low freeboard on my boat and the transom height is 20''. Does a 20'' shaft on an engine translate to a transom of 20''? Where is the shaft measured from on an outboard?
post #2 of 12
Measure from the top of your transom to the bottom of your keel. If it is 15" to 17" you'll need a "short shaft" outboard. If it is from 20" to 22" you'll need a "long shaft" outboard. Tohatsu/Nissan outboard shafts are measured from the bottom of the engine mounting clamp bracket to the cavitation plate (large fin above propeller) on the lower unit - see diagram below. Generally most boats need either a short or long shaft although some boats require a 25" "ultra-long shaft" outboard. Below is a diagram on how to measure your transom for proper shaft length. NOTE: ANY OTHER MEASUREMENT OTHER THAN THE ONE DISPLAYED BELOW WILL BE USELESS INFORMATION.

For normal operation your engine's cavitation plate should be even with the bottom of the hull. A gap of 1-2" in either direction is acceptable and considered normal. If you are still unsure as to which shaft length your boat needs contact your hull's manufacturer. Your outboard owner's manual will also contain more information on shaft length and proper installation
post #3 of 12
Thread Starter 
I think that I am perfect. The old engine is 20'' and the transom is 20''. So the term "long" shaft should really be "nominal" shaft
post #4 of 12
Quote:
Originally Posted by FlyByNight View Post
I think that I am perfect. The old engine is 20'' and the transom is 20''. So the term "long" shaft should really be "nominal" shaft


You are good to go Andrew.
post #5 of 12
What shaft length do you use if your transom measure 18 or 19 inches or do boat mfgs make sure they dont.
post #6 of 12
Quote:
Originally Posted by Charleston View Post
What shaft length do you use if your transom measure 18 or 19 inches or do boat mfgs make sure they dont.



The extra holes in the mount are for raising the motor if you need to.
post #7 of 12
Rather than start a whole new thread I thought I would post my question in this one which partially but not completely answers what I am trying to figure out.

I just came into a new, heavily build small wooden skiff. I am painting it and stuff and looking around for an older 2stroke. The transom is 23" so I am trying to figure out if a long shaft, which is what I have been hunting for, would be right. Or if I should be looking for an extra long shaft? Or if I should be considering cutting down the transom to exactly 20"?



Another way of posing my question - Is it better to have the cavitation plate a little above the bottom of the boat or below?



I have included a picture of her. Not because I think it will generally help answer my query. But I just really dig her on account of her toughness and old school charm.



Thanks for any help advice or insights.

Bob
525
post #8 of 12
are there motor mount holes drilled yet? I would very much try and get a stand-off bracket. that will allow you up or down movement. You COULD use an extra-long shaft, but unless you are buying new, that will be VERY hard to come by in small power. I wouldn't cut that pretty transom up, but bolt something to the transom, that you can then bolt the motor to, and not have to worry about messing with the boat.

something like this:




They are calling it a fixed jack plate.
post #9 of 12
Thanks for the help Chief. I have a question about the bracket. If I bracket the motor lower won't the tiller be too low for the transom?
post #10 of 12
I don't think that a bracket on a small wooden boat like that is worth it. You would be much better off taking your time laying out a nice cut line and cutting the transom down to 20". It will look like it was supposed to be that way. IMO the bracket will ruin the look of a boat like that.
post #11 of 12
Cutting the transom will ruin the look and reduce stern freeboard , considering the hondas are not lightweights...
post #12 of 12
I'm thinking about just getting a long shaft and just seeing how it works. If I need to in the future I can adjust the transom hight. The only other option is a Johnson Sail Master that is on CL. It has a 25" shaft but I think the price is way out of line for what I was hoping to spend.
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