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Old 22-06-2013, 19:44   #1
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Stern tube/driveshaft/strut clearances

I'm re-powering a 25 ft. fishing boat that has a 120hp diesel inboard, direct drive system. I'm going to be putting in a 200hp diesel and need some advise. I'm going to a 1 1/2" from a 1 1/4" prop shaft. My fiberglass stern tube is 1 3/4" I.D. That's a close fit, but is there any rule of thumb for minimum clearance? Trying to avoid the huge job of putting in a larger tube, if possible.

Second part is the bronze strut would have to drilled out to 2" I.D. for the new cutlass bearing. The strut is 2 3/8" O.D.,after drilling it out to 2", that would leave 3/16" of thickness. Any rule of thumb on minimum thickness strut tube?

Anyone know where I can find the answers?


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Old 22-06-2013, 20:16   #2
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Re: Stern tube/driveshaft/strut clearances

Be a lot easier with 1 3/8" or 1 5/16 " with monel, you would be all right with this HP and it would be a easy fit with new bearings ect. I sorta feel you will weaken things going out to 1 1/2 without changeing at least strut, but then I always try to make sure things will never give me trouble again !! just my 2 cents

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Old 22-06-2013, 20:29   #3
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Re: Stern tube/driveshaft/strut clearances

You should have at least 1/4" per side of clearance for the stern tube unless it's water injected. Then as long as it doesn't whip and bang the tube it will work.

As for struts, a lot are the same casting with just different size holes bored in them to take what ever bearing is needed.
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Old 23-06-2013, 09:25   #4
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Re: Stern tube/driveshaft/strut clearances

Thx, for the help guys. Its great to have some other objective points of view.
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