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PostPosted: Sun Jan 29, 2023 5:42 pm 
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Joined: Sun Jan 29, 2023 4:39 pm
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Hi,

I am helping a friend who purchased my old (mid 80's) H16 and has an issue with the rudder gudgeon attachment and I need some knowledge to help her out.

I recently changed out the lower rudder gudgeon due cracking, some of the S/S attach screws were bent, they were very tight, I was reasonably confident they came out without causing secondary damage. New parts ordered and refitted all 4 screws were lubricated but still had some drag to screw in all the way, one screw started to strip when home so I stopped at that point, I guess that one is ~30% of its original integrity.

Her first sail in light conditions and that complete gudgeon pulled all 4 screws out, this baffles me, I have a solid enough mechanical background yet didn't pick anything odd bar the one starting to strip, the other 3 felt like they screwed home securely.

Unfortunately we don't have the old bent screws to compare for length, the new ones are ~ 1" in length and sold in a packet of 20 with the comment that they are a universal screws for the H16. However, I have a gut feeling the ones that came out were longer and I am wondering whether when refitting I was screwing through flock or some other medium in there giving feel of screwing into thread but never actually engaged the thread due shorter screws.

My questions are, what is on the inside of the transom, I assume some sort of glassed in backing plate with captured nylock S/S nuts or similar. How long are the correct screws? are the female threads open at the back end? can they be tapped successfully. I would rather not pull one of the other gudgeon screws to compare length, what ain't broke and sleeping dogs and all that.

Is there a known failure mode in here (saltwater use). To my thinking if they were the correct length then we have an issue that might mean cutting an access hole in the rear top deck, I can do this work and have done this sort of thing on composite aircraft.

If anyone has a photo of what's in there that would be brilliant, otherwise just a description will do.

Thanks in advance, Mick


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PostPosted: Mon Jan 30, 2023 10:41 am 
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Site Rank - Old Salt

Joined: Mon May 09, 2005 10:25 am
Posts: 4176
Location: Jersey Shore
The gudgeon screws thread into an aluminum plate that is bonded inside the hull and tapped with a #12 thread. It is very common for the screws to seize into the plate, especially if the boat was sailed in salt water. Once the screws seize, they can either break off or strip out when trying to remove them.

The transom is the thickest part of the hull because the fiberglass is thick back there and in addition to the aluminum plate, there may also be wood core there too. If the screws you used were too short, it’s possible that you were only threading into the fiberglass and not engaging the aluminum plate, although I would think 1” screws should be long enough (sorry, I don’t know the Hobie screw length spec offhand).

You have a couple options. If you think the screws were too short, buy some longer ones. You should be able to crank down on them firmly if they’re properly engaged in the aluminum. If the aluminum plate is stripped, then you can either drill out the gudgeon and plate and tap to the next larger screw size (1/4”-20) and use larger screws, or you can cut an access hole in the deck and thru-bolt the gudgeon using longer screws, nuts, and washers. The challenge with thru-bolting is that the back of the hull can be a tight spot to reach your hand into and use tools.

sm


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PostPosted: Mon Jan 30, 2023 4:31 pm 
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Site Rank - Deck Hand

Joined: Sun Jan 29, 2023 4:39 pm
Posts: 2
Thanks SRM.

That has given me the knowledge I need, I'll tap to M16 (metric here) if I discover the plate has turned to oxide at the screw holes I'll cut a hole in the top deck for access and run through bolts, hopefully dig up a hatched well insert to place in the access hole, win win then.

Thanks again.


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PostPosted: Mon Feb 13, 2023 6:49 am 
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Joined: Mon May 24, 2004 10:33 am
Posts: 686
Location: Clinton, Mississippi
And use some Tefgel, Lanacote, or other such goo for dissimilar metals when replacing the gudgeon bolts (and just about everything else on the boat, your house, your car.....)

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Jerome Vaughan
Hobie 16


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