Proper outboard shaft length

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aspaziani
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Joined: Thu Apr 26, 2018 2:23 pm

Proper outboard shaft length

#1 Post by aspaziani » Fri Apr 27, 2018 8:29 am

Hello Everyone,

Long time lurker first time poster. I've had my 24' 2 log, pontoon for a few years now and just got a new to me 70hp Johnson, i believe its a 20" shaft, but see attached picture and correct me if I'm wrong. I used it all last year with no real issue except for the fact that I can never get my bow out of the water and at WOT its ventilating, doesn't matter if its just me or fully loaded. I always keep it trimmed all the way down to keep it deeper in the water otherwise it will ventilate at lower speeds. But I'm always plowing into the water, perhaps because I'm trimmed down, and if I run into any waves at high speed I usually get a good amount of water over the bow. I understand that I should match my shaft length with the length of my transom which is 20". My cavitation plate is about half way down my pontoons,I'm also told it should be at or below them. I attached a picture of my motor and a picture of my transom, any advice is appreciated.
motor measurement_scaled.jpg
motor measurement_scaled.jpg (131.46 KiB) Viewed 1739 times
8848.jpeg
8848.jpeg (75.69 KiB) Viewed 1739 times

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rbtnt
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Re: Proper outboard shaft length

#2 Post by rbtnt » Fri Apr 27, 2018 9:28 pm

Here is how to measure your engine shaft length and diagram shows a good starting point for engine height.
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transom.jpg
transom.jpg (48.96 KiB) Viewed 1722 times
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