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Old 24 June 2022, 22:51   #1
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18 shaft Evinrude 35hp

Hi guys, everyone here is super knowledgeable so I thought I would see if the community could lend a hand. I have a great running early 80s Evinrude 35hp motor with an odd ball short shat that is 18.

Im looking for a RIB to go with it as my old Bombard C4 from the early 80s bit the dust this week. Ive been looking at some different 15.5 boats but they all call for a long shaft. Its frustrating because I cant find transom height in any of the owners manuals.

Would this work on like a 15.5 Zodiac Bombard Typhoon?
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Old 25 June 2022, 16:38   #2
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18" sounds odd for sure. The measurement is usually from the cavitation plate to the yoke or from the water pump to the top of the drive shaft. If it really isn't the 15" or the 20" then I would buy a short shaft transom and build it up. I run a long shaft on my boat that had a short shaft transom. I built a block to complete the height and then made aluminum plates for the front and back of the transom. With several through bolts to hold the motor, the floor plate, transom/floor stiffening gussets, scupper bolt clips and then one through bolt in each corner the transom is most likely stronger now then when it was new.
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Old 25 June 2022, 22:17   #3
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Its easier to cut down a long shaft transom than it is to build up a short shaft. You'll often find long shaft boats are a bit short, 19" instead of 20" in which case you might find the 18" shaft runs fine 1to 1.5" high is often the sweet spot for hight
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Old 29 June 2022, 15:48   #4
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Even easier to just get a jack plate and move the power head up or down to the perfect height...
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Old 29 June 2022, 19:19   #5
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Even easier to just get a jack plate and move the power head up or down to the perfect height...
Your own build up method seems a lot more involved than trimming an inch or two off the top of the transom & resealing the exposed core. He also has the advantage of more freeboard with an 18" transom & he states most boats hes found are 20" transoms. All things considered cutting down a 20" boat may be his easiest option
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Old 29 June 2022, 20:43   #6
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Installing a jack plate is easier than a build up or a trim and allows for maximum flexibility.
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Old 01 July 2022, 20:44   #7
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I’m no expert but I thought a jack plate could only be used to raise a motor. Ie, a long shaft motor to work better on a short shaft transom
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Old 06 July 2022, 20:16   #8
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Yes, long shaft on a short shaft transom would be easier with a jack plate.
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Old 06 July 2022, 22:17   #9
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Im no expert but I thought a jack plate could only be used to raise a motor. Ie, a long shaft motor to work better on a short shaft transom
Yes your right hence the suggestion to cut down a longshaft boat to fit your engine its easy done and the boats are easier to find as you already know. But first off I'd sit it on & see how it looks & maybe try it in the water.
No idea why a Jack plate is being suggested for your purpose
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Old 07 July 2022, 15:23   #10
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Yes your right hence the suggestion to cut down a longshaft boat to fit your engine its easy done and the boats are easier to find as you already know. But first off I'd sit it on & see how it looks & maybe try it in the water.
No idea why a Jack plate is being suggested for your purpose

Funny, I find short shaft transoms readily available all over. Must be a UK thing. The jack plates are pretty darn nice thing to put a boat on plane and trim up to the perfect height. I'm not an ocean boater. I run class V whitewater with these boats along with several friends. Lot of different ways to run ribs.
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Old 07 July 2022, 20:43   #11
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Quote:
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Funny, I find short shaft transoms readily available all over. Must be a UK thing. The jack plates are pretty darn nice thing to put a boat on plane and trim up to the perfect height. I'm not an ocean boater. I run class V whitewater with these boats along with several friends. Lot of different ways to run ribs.
No disrespect to the op but his engine is relatively old & not worth a huge amount of money, probably a similar value to the cost of a manual jack plate, a hydraulic jack plate will cost probably twice the value of his engine. A jack plate realy isnt a cost effective solution to his problem. Some folk would say its ruining the value of his boat to cut the transom but if it gets him on the water then its almost a no cost solution for him. He could also look for a short shaft & build up but if he can only find longs then thats his way to go. If in the future he replaces his engine with a 20" version then it will probably still bolt up to his 18" transom using the lowest bolt holes to keep it up high enough.
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Old 08 July 2022, 22:26   #12
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No disrespect taken. Many of us here on the Colorado River use jack plates. Once on plane you can raise the prop and have greater efficiency. But I don't really care what anyone else does. Cut it down. Built it up. Use a jack plate. I was only offering possibilities.
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Old 11 July 2022, 19:15   #13
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35hp 1978

I have a 1978 35hp Evinrude in a very 1970 slightly glittery beige colour with 70 font lettering and a couple of go faster stripes.

Its on a 4m tiller steer, sit on the tube job. Cheap basic and tons of fun.

Its a thing of beauty, goes like a train and starts first pull every time.

Well done for keeping such a lovely engine going.

They dont make them like they used to.
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