Drilling the Boom

Apr 1, 2016
21
Catalina 22 14735 Lake St Clair, MI
I bought the Cat Direct boom topping lift kit and had a question about the installation. When mounting the new hardware to the boom, should I drill and tap the new holes, or is drilling sufficient? I'll be mounting a small cheek block and a cleat, 4 holes total.
 
Mar 26, 2011
3,399
Corsair F-24 MK I Deale, MD
If you mean can you thread in machine screws without tapping, the answer is no.

If you mean can you use self-tapping screws, the answer is maybe. It depends on the hole count and orientation--Cat direct should know. Blind rivets are generally a much better choice. Also, if there are any wires or ropes inside the spar, self-tapping screws are deadly.

If you can get nuts on the back, that's even better.
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
The hardware should be fine threads to get maximum threads in the metal. Still, though, there might be only three. You might consider pop-rivets or nuts and bolts if you can get into the aft end of the boom. While you're doing the TL, you might consider adding a boom bail to the bottom of the boom with a bolt through the boom. Use the BB to haul people out of the water, or to hang a light, or a baby seat, or awning , or....
 
Apr 1, 2016
21
Catalina 22 14735 Lake St Clair, MI
The kit came with all of the hardware, all stainless screws. The instructions recommended using Tef Gel for corrosion and I do have some of that. I don't expect the topping lift to be carrying much load, more for convenience. You guys still think rivets are a better choice? Backing plate is not an option since I can't access inside the boomIMG_0150.JPG
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Might depend on where on the boom the attachment point is and if it's in sheer or not. Side? Top? Bottom?
 

T_Cat

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Aug 8, 2014
333
Catalina 22 1987 New Design. 14133 "LadyHawke" Modesto CA
I just installed the same kit. I used the supplied screws for installation. If I have a problem down the road I'll rivet them. Everything else on my boom is screwed in place.

Russ
 
May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
I like SS rivnuts you can easily remove the hardware and don't have sharp edges in the extrusion. +1 on tefgel

Les
 
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Mar 20, 2015
3,094
C&C 30 Mk1 Winnipeg
I like SS rivnuts you can easily remove the hardware and don't have sharp edges in the extrusion. +1 on tefgel

Les
+1 rivnuts are great.

In this case I'd probably do what @T-Cat did, and tap threads into the boom and use the supplied fasteners, along with tefgel. If they ever showed signs of failing, I'd make the hole larger and install a rivnut.
 
May 24, 2013
29
Catalina 30 MK III 6444 Marina Del Rey
Your topping lift can come under quite a load if you don't ease it after hoisting the sail. In that case, it is resisting the main sheet blocks. One can even bend a boom that way.....with help from a winch.
 
Oct 18, 2013
20
Catalina 27 Vernon, BC (Okanagan Lake)
Thank you ST. I have a boat that came with a bent boom and I could not figure out how it could have happened. I couldn't believe just using the mainsheet or vang hard could do it because the boom is designed for that.
 
May 16, 2014
2
catalina 30 san diego
As a mechanical engineer the general rule is one diameter thickness per screw. Example
1/4 inch diameter screw, 1/4 inch thickness of material to be drilled and tapped.
 
Mar 26, 2011
3,399
Corsair F-24 MK I Deale, MD
The hardware should be fine threads to get maximum threads in the metal....
Incorrect, in soft metals particularly. Course threads have greater holding capacity per thickness, even if there are fewer. Standard engineering, which you can find on most fastener web sites. I have also tested this with a load cell. Fine threads are for steel and high strength bolts, where then can give better adjustment of clamping force, and slightly higher strength (not because fine threads are better--because the core diameter is greater).

Pop rivets are stronger than tapping in thin materials, below about 0.1 inches. Above that, coarse threads are better.
 
Sep 14, 2014
1,251
Catalina 22 Pensacola, Florida
Actually the real problem with self tapping screws is making the hole the right size and how the thick the mast stock actually is. You can twist a screw right off or not get it to turn if the hole is to small, too large and it just wallows around in it.