Mast Exit Block Replacement

[IanA22]

Hi, first time on here. Looking for some advice.

I've recently bought a 1987 Catalina 22. In the UK. Yes, UK, really. Not a 'Jaguar'. A Cat22.

She's in pretty good shape but there's a few replacements needed. One of the first has me a bit stumped as I'm new to this. I need to replace the exit block for the in-mast halyard at the foot of the mast. The plastic wheel is falling apart and the block itself is only held on by two screws not four.
The good news is that the Cat-Direct site sells replacements. I pasted a screenshot of a a new one from their site below. Then, below that is the current one I need to replace.

current old block:-

My question to you wise Cat22 people : is this just a case of unscrew and re-screw the new block into the same holes? What type of screw - self tapping or any stainless steel? Or are the existing holes unusable because they've been screwed into already?

Any advice to a newbie really appreciated. How would you fix the new block on?


Thanks!
Ian

 

[Justin_NSA]

You may have to go larger if the holes are stripped out. I imagine that is why two are missing.
It might be possible to get a locknut inside for a machine screw but it's hard to tell.
That may be the saddest looking sheave I have seen.

 

[AaronD]

...is this just a case of unscrew and re-screw the new block into the same holes? What type of screw - self tapping or any stainless steel? Or are the existing holes unusable because they've been screwed into already?
...

You can go with any of 3 types:
1) Stainless steel machine screws (316 stainless if you can find it - boltdepot.com and mcmaster.com here in the US, but you might need to look for other sources in the UK). Use Tef-gel or equivalent to isolate the SS from the aluminum.
2) Stainless sheet metal screws. They'll bite into aluminum OK. But the sharp point inside the mast can catch wires and lines. Not my preferred method. If you do use these, again, use Tef-gel.
3) Rivets: Aluminum or SS, either should work. I think for this use case, aluminum rivets might be my choice. Especially because your existing holes look to be stripped out - you can go up a size in rivet and mount in the same cutout. Tef-gel is still a good idea, this time to isolate the aluminum rivet from the SS block hardware.

See a couple good sources from @thinwater:
* Stainless Steel Bolt Specifications
* Screw/bolt size question
He's done lots of lab testing with fasteners of various sorts.

Hope that helps

 

[jamieFL]

I agree with Aaron's 3rd choice. I've worked with aluminum for years and rivets work real well and won't fall out later. I'd go with aluminum rivets and make sure you are putting your rivets in a nice round hole in good aluminum.

 

[IanA22]

Thanks all, brilliant advice. I’ll start looking into rivets, seems like that has the most votes.

 

[AaronD]

Thanks all, brilliant advice. I’ll start looking into rivets, seems like that has the most votes.

I should have said that I originally shied away from rivets, as they seemed totally permanent. But aluminum rivets drill out easily, so they're not as permanent as I had thought. Good choice.