Attaching hardware to boom

[sjs]

I am replacing a single line reefing system with slab reefing and plan to screw or rivet two padeyes, two blocks and two cleats to the boom. I have marked the locations for the hardware and think I have this part right. The boat is a Catalina 270.

However,I have not done this before and would appreciate any advice on attaching the gear. I understand I need some barrier between the stainless steel and the aluminum.

I have a few specific questions. Are rivets better than screws, or vica versa? The current hardware uses screws for some, and rivets for others.

Also, I was told to be careful with tap and die on the soft aluminum boom and go a size larger because it can gall when cutting the hole. This was a professional giving me free advice but he was busy and I did not want to take advantage of his kindness so I did not waste his time with any questions. I do not understand what he meant. Is it the screw that should be larger than the hole?

Any other info is appreciated.

[jim lee]

Maybe you don't need to put padeyes on the boom?

I have slab reefing with no padeyes on the boom. (35' boat) On mine, the end of the boom has some sheeves(sp?) in it. Kinda' like a mast head.

With this system the reefline goes down the inside of the boom, out the end, up to the cringle, down to and around the boom, then pokes thrugh a hole in the foot of the sail and ties to itself.

Now, if you don't have any sheeves (I do wonder how that's spelled) on the end of your boom, my wonderful plan won't work and you'll have to add one anyway.

In that case, I'd use rivets.

-jim lee

[Chuck Baier]

sjs, I have had the aluminum pop rivets fail on a block on the boom. They corrode on the inside where you can't see them then let go under load. You should try to gasket the stainless hardware where ever you can and use tef-gel or a similar product on all stainless fasteners on the spars. This will also allow you to remove them when you need to.

[BC Mike]

I would use 3/16 stainless rivets. The no block idea can work if the main sheet is not in the way. The way I have seen it done. There is a line exiting the rear of the boom. Pull the line, put a small pulley on the line, pass the end of the line through the reef point in the sail and down the opposite side, under the boom and tie the end to the pulley. Now when you pull the line tight it will bring the sail down and out. Use the second line in the boom for the second reef and the first line for the third reef if need be. You do not need a pully you can loop the exiting line with a bowline but it will not slide as well.
BC Mike C

[delmarrey]

The thicknes of the metal is not enough for threading. If you can get your hands inside, I'd recommend putting screws backed up with a washer and a nylock nut inside, otherwise use rivets and the tuf-gel as Chuck mentioned.

And that was bad advise on the drill and tap. If any thing you would want to go to a 85% thread on aluminum. Which would be even a smaller drill than standard (70%) When tapping alum. you want to use a cutting lubricant like solvent or kerosene.

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[tenknots]

The use of aluminum rivets will prevent some galvanic corrosion between metals on the boom - though the aluminum is not identical, it's better than stainless. You can buy teflon sheets and cut to shape to place between the boom and fitting - tef-gel is great for where dissimilar metals meet, but can be washed off over time. I'd still use it for the rivets.

[sjs]

Thank you folks. Lots of different viewpoints to think about, which is just what I asked for. Hope to have this done this weekend, if the weather allows.

[Alan Wheeler]

Yep, lot's of good advice and I will throw more into the pot.
Firstly, if you use rivets, Monel is the material of choice. It is high strength, low corrosion with both SST and Alloy. IF you use a blind rivet, then ensure you have a SST shaft thingy. That is so the head remaining in the Rivet won't rust. IF you use an open Rivet, that shaft thingy will most likely be nickel plated. So you need to punch the head back out when it breaks off.
SST Rivets are the next choice, but can corrode in the alloy, if Salt water can get to them. Stay away from Alloy rivets, the just aren't strong enough if in a high load situation. You could use them in a load load.
Threading should only be used when the load is not in a direct pull. Side pull or low loading is OK. Same with screws. In high load and direct pull situations, you always need a nut and washer on the back. A good size rivet will outperform a thread or screw.
The next thing is the fixing and insulation of the Fitting. Place a thick smear of an adhesive sealant, such as Seka Flex or similar product onto it. This will ensure a good bond other than just the Rivets, and also isolation from the two metals and water can't get between the surfaces. Then when it is all fixed in place, wipe the thing down with a thinners or some solvant to wipe away excess sealant to make it all look tidy.
When drilling, cutting or tapping Alloy, use WD40 as a cutting fluid. It doesn't require much, but it does require it often.

[Talbot]

beat me to it Wheels.

Monel is always the rivet of choice for attaching items to booms and masts.

Aluminium is noit strong enough
Use Stainless only if you are happy to replace mast/boom fairly soon when corrosion has eaten its way through the spar!