Replacing riveted hardware?

I need to replace the main downhaul block and the jib traveler cam cleats on my 1981 H16. The existing parts are riveted to the mast/crossbar. After drilling out the existing rivets, what is the best practice? I'll try to go nice with the removal, but if the existing holes end up oversized or the new parts don't align with the existing holes what's the proper fix? I'm thinking I can just move the new part a 1/4-3/8" or so from the old spot and drill new holes.

But do I need to fill-in the old existing holes in the mast and crossbar? What's the best way to do that?

1) Use cobalt drill bits. You are much less likely to spin a rivet with a sharp cobalt bit than a soon to be dull HSS bit.
2) Use the same drill size as the rivet. After drilling out the first you may find that the rivet is in a sleeve, in which case you may use the same size as the sleeve.
3) Once the rivet head falls off use a hammer and a punch to knock out the rest.

If the holes are still good.
4) install new rivets (and sleeves if present before, or if desired) and hardware. Use a beefy rivet gun as the small one-hand squeeze style won't pull stainless. Dip rivets (or sleeves) in caulk and pull while wet.

If the holes are toast and you want to move the hardware.
4a) If it won't cause an interference issue, drill the holes out to the next size larger and install a caulk dipped aluminum rivet into the hole.
4b) If it will interfere, fill the holes with Marine Tex (grey) or a similar epoxy putty.
5) Drill and install hardware with new rivets (and sleeves if desired). Dip rivets (or sleeves) in caulk and pull while wet.

Things to keep in mind:
Keep the mast water tight. All old holes should be filled. All rivets or sleeves should be dipped in caulk before inserting them. If you don't use sleeves be sure to push a little caulk into the end of the rivet after installation.

If you drill new holes, move the holes by 3x the diameter of the hole, measured center to center.

If you reuse holes that had sleeves, use sleeves when reinstalling. Hobie PN# 8011291
Hobie uses rivet sleeves to prevent water from leaking through the center of a rivet. More caulk works too.

Thanks for the detailed info...

I have the rivet sleeves for the downhaul block I'm replacing on the mast. The new lance cleats for the jib traveler came with small screws and the existing are riveted. Do I need to keep the crossbar water tight too?

As far as filling any old, unused holes, I happen to work at a metal fab shop, would a quick hit with a tig welder and some AL rod do the trick? Could I then drill new holes closer than 3xDia? What type AL rod would I need?

Don't drill all the way through the rivet head, and there is Much less of a chance to enlarge the hole. Using a sharp, Cobalt bit, same size as rivet, just drill into the head a little bit.

Then, using a good Pin Punch the size of the rivet (typically 3/16) punch the rivet barrel through. If a light tap won't cut the rivet, drill it a hair deeper. You don't want to have to hit the punch hard, or it can deform the aluminum. It doesn't take many tries to see how deep to drill the seat for the punch.

I've changed thousands of rivets on Hobies, and this method won't enlarge a hole, if it's not already corroded.

I cringe when I see people drilling out a rivet, and wallowing the drill bit around to make sure they're cutting the head off.

A sharp drill bit definitely makes all the difference. I almost never use a drill bit the same size as the rivet. Doing so risks oversizing the hole. Generally, I use a drill that is roughly the same size or only slightly smaller than the rivet head diameter - like a 1/4” drill. Drill carefully and the drill bit will just take the head off the rivet. Once the head spins off, use a pin punch to drive the remaining shank into the part. If all goes right, the drill never touches the aluminum part and the hole doesn’t get enlarged.

If the holes in the new part are only slightly off, use a small round file to open up or slot the hole in the fitting. If the holes are way off, then relocate and drill new holes if that’s an option. Install a rivet in the old hole to seal it. Use Tefgel grease to reduce galvanic corrosion of the mating parts.

sm

Sure. Be quick. Welding on aluminum is always dicy. A great weld with no heat treat weakens the part by 25%. Dump too much heat in and you can drop the strength by up to 75%. (these values are for 6061T6). That said, the bottom of the mast is not highly stressed and your welds are small, so no worries.

The 3 diameter spacing is a rough rule, feel free to violate it if you don't need the full strength of the material being riveted. If your welds are good you can go closer, or even overlap.

That said, if corrosion isn't an issue none of this will matter as you will be able to reuse the holes.

I use JB Weld on old, unused holes....would avoid welding if at all possible.

_________________
Jerome Vaughan
Hobie 16

Great, I'm lucky to have someone that'll fix me right up.

As far as drill bits and drilling stainless anything, my company buys bits by the 100s, in the smaller sizes, they're considered disposable, I just always use a brand new bit for stainless.