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I have a broken prop strut on my Chaser 29. Where in heavens name does a guy find that part?  It got welded once but it didn't last long. 

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Also, why did it break? Takes a lot of force to break one of those things - serious misalignment for a long time?

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2 hours ago, SloopJonB said:

Also, why did it break? Takes a lot of force to break one of those things - serious misalignment for a long time?

I had one broken for me when the mechanic tried to push the cutless bearing out with the shaft in place. They had a machinist duplicate the old one in stainless.

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42 minutes ago, Diamond Jim said:

Some bronze foundries can use the old one as pattern for a replacement.

The new part will shrink and be a little smaller that way - 1% to 2%.

Probably not enough to matter.

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On some regatta boats  , when you wind up the backstay  , the boat bends like a Banana

the drive train gear doesn’t bend 

this  causes a pinch that can knock a few hundred rpms off , stress the  Engine mounts , wear out the cuttles bearing  , and fatigue the strut 

Ease the backstay  before motoring 

 

 

 

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Old bronze struts can break due to galvanic corrosion, the warning sign is a pinkish color.  My '70s boat has a strut design which is quite thin and many sister boats in the 770 boat production run have had their strut break due to corrosion.  Due to  the way the strut is imbedded into the hull it's a several thousand dollar+ repair.

Cheap insurance is to mount two button zincs on the strut, and scrupulously maintain them.  The shaft zinc doesn't protect the strut because the cutlass gland insulates the strut from the shaft.

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30 minutes ago, axolotl said:

Old bronze struts can break due to galvanic corrosion, the warning sign is a pinkish color.  My '70s boat has a strut design which is quite thin and many sister boats in the 770 boat production run have had their strut break due to corrosion.  Due to  the way the strut is imbedded into the hull it's a several thousand dollar+ repair.

Cheap insurance is to mount two button zincs on the strut, and scrupulously maintain them.  The shaft zinc doesn't protect the strut because the cutlass gland insulates the strut from the shaft.

Exactly what I did. 

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  • 4 weeks later...
On 5/9/2021 at 4:03 PM, Diamond Jim said:

Some bronze foundries can use the old one as pattern for a replacement.

PT Foundry estimated $1100-1200 if they had a pattern close to start with, more if they had to make one off my strut.

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On 5/9/2021 at 2:19 PM, Ishmael said:

I had one broken for me when the mechanic tried to push the cutless bearing out with the shaft in place. They had a machinist duplicate the old one in stainless.

I'm making one from SS 316.  Just a couple hundred for the metal and a few hours grinding it out, Fabricator is welding it up. 

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On 5/10/2021 at 4:08 AM, slug zitski said:

On some regatta boats  , when you wind up the backstay  , the boat bends like a Banana

the drive train gear doesn’t bend 

this  causes a pinch that can knock a few hundred rpms off , stress the  Engine mounts , wear out the cuttles bearing  , and fatigue the strut 

Ease the backstay  before motoring 

 

 

 

This probably explains why the new owner of a soveral33 in our harbor broke his after the last guy managed 30 yr intact. I had not considered how bendy a boat could get but this makes sense. 

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2 minutes ago, crankcall said:

This probably explains why the new owner of a soveral33 in our harbor broke his after the last guy managed 30 yr intact. I had not considered how bendy a boat could get but this makes sense. 

A few years ago , taking a beating while  motoring into an English Channel gale , the boat was bending ...rpm up and down ...

the strut held , but we broke the aft engine mounts 

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13 hours ago, SockeyeUS119 said:

'm making one from SS 316.  Just a couple hundred for the metal and a few hours grinding it out, Fabricator is welding it up

I made a strut from carbon fiber. Probably $50 in materials in it. Cut a slightly oversized hole in the bottom and glassed it to the inside of the hull with some foam and glass ribs. 

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8 minutes ago, Zonker said:

I made a strut from carbon fiber. Probably $50 in materials in it. Cut a slightly oversized hole in the bottom and glassed it to the inside of the hull with some foam and glass ribs. 

Hey Zonk, isn't that risky if something happens to your shaft? When I replaced my strut, the shipwright intentionally put small fasteners through the hull before fairing so they would shear off and not tear a hole in the bottom; to use a fuse analogy.

Maybe we both overthought this though.

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  • 2 weeks later...

Well, I screwed up and didn't take any photos. we built a stainless strut and with about an hour of scraping the bog on the tidal grid I got it lined up pretty well. I get a second shot when I get to haul out. My biggest worry it the brass sleeve on the cutless bearing against the stainless strut. Not sure how to deal with that. They make cutless bearings with fiber sleeves but not in my size.

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On 6/8/2021 at 1:19 PM, Ron Swanson said:

Hey Zonk, isn't that risky if something happens to your shaft? When I replaced my strut, the shipwright intentionally put small fasteners through the hull before fairing so they would shear off and not tear a hole in the bottom; to use a fuse analogy.

No worse than bolts tearing out a big washer or backing pad through the hull.

In my case the strut was into a stern locker that was w.t. the rest of the hull. So even if it filled with water it wouldn't have mattered. Lots to be said for w.t. bulkheads.

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On 6/21/2021 at 2:57 AM, Caecilian said:

For a low hp yacht just make one in carbon, same size as your original. 50 bucks is about right.

How are you with dealing with the galvanic issue that the carbon introduces, would think it might be hard on the bearing/sleeve? 

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