Gaff swivel broken -- again

[Aldebaran_III]

I wonder if anyone else had this problem on an HC or Suncat?

About 3 years ago, when the boat was only a couple of years old, the universal joint between the gaff and the mast broke whilst sailing. It also badly bent the ears on the gaff uphaul slide, where the universal joint attaches. I figured it was now weakened so I ordered the whole gaff to mast swivel and slide assembly.

Now it just happened again! The ears on the gaff uphaul slide looked OK, so I reckoned I could just replace the universal joint. The original is just bent and drilled from stainless steel sheet and doesn't seem very strong. So I decided to make one out of solid aluminum.
This has worked out fine, but I'm just worried that the weak point is now the ears on the gaff uphaul slide where the UJ is pinned to the slide.

Not sure if this is just a weak design or if I'm doing something that accelerates this failure.

Cheers, Derek

[bruce]

Derek, your block design looks great. I'd keep it lubricated to limit corrosion and galling. It would be interesting to see photos of the assembled gooseneck, and evidence of stress and wear on the other components. It's interesting how focused the force was in your case. That one flap took a lot of abuse, otherwise the part looks OK.

Jim in TC started a good thread on the SC list about the throat gooseneck. His boat came with a heavily damaged universal joint. Some good input there that might be useful.
http://cpyoa.geekworkshosting.com/forum/index.php?topic=10938.0

Com-Pac lists the sliding gaff gooseneck assembly on the SC and PC as the same part. The HC part is different, I'd guess because the spar dimensions differ, but it looks similar and they're all made by Dwyer. Dwyer offers the components separately, so you don't have to buy the whole assembly. For example, the SC equivalent of the part that broke on your gooseneck is available for $5.65. I'm not sure what boom profile is used for the HC gaff.
https://www.dwyermast.com/families.asp?cat1ID=30&cat1Name=Booms
 

[Aldebaran_III]

Hi Bruce, thanks for all that very useful info. So far, everything looks good, but I'll keep a close eye on it.
The pins and block are coated with Tef-Gel which both lubricates and prevents electrolysis between the stainless steel and aluminum. It's long lasting and doesn't wash off easily in the rain.
Cheers, Derek

[bruce]

I agree, Tef-Gel is great stuff.

I was curious what extrusions Com-Pac uses on their catboats so I contacted Dwyer. On the HC, the mast is DM-450, the boom DM-375, and the gaff is DM-2. Looks like your slide would be DH 354-1L. Click image for a parts diagram.
https://www.dwyermast.com/items.asp?cat1ID=30&cat1Name=Booms&familyID=4&familyName=DM%2D2+Boom