Mast Hardware, Fine Thread or Standard?

[s/v Jedi]

@James: The boom is much weaker thus needs reinforcement. You basically used a very large bracket on the outside, spreading the load much like an internal reinforcement but it isn't really a reinforcement because you are only pulling from the bottom of the boom. An internal reinforcement is a piece of boom profile cut open length-wise and the ends shaped so that it's longer on the bottom than on the top to prevent stress risers. You pull where the bolts are so each is a stress riser. It looks very substantial though so I wouldn't worry (just take it off after a couple of years of hard use to check the boom under the bracket).
For the mast fitting: indeed, so there must be machine screws there, not rivets. But the mast is very strong at it's back because of the track and thicker wall (so longer thread contact).
How did you do the attachment for the sheet and reefing lines on the boom?

@delmarray: I agree but good charts should already list different drill sizes for different materials or at least thread-depth plus advise on required depth for each material.
Course thread: yes, but I meant that the course thread on metric is just a little finer than on US fasteners of similar diameter. When you go to bigger diameter screws like for rope clutches, the US thread gets so course that you might not even get a full turn of thread in the thin mast.

@rtbates: TefGel is one of those modern products that really makes difference. But it is also a lubricant meaning that even a little vibration can loosen the screws in the mast. So I prefer to use a medium thread locker instead, like Permatex Blue. This also gives insulation, although not at the level of TefGel.

ciao!
Nick.

[s/v Jedi]

Originally Posted by James S

Thanks Nick....I would love to have copied yours but you don’t post any pictures!

Can you see it here?


(click on it to get to the album where you can zoom)
cheers,
Nick.

[s/v Jedi]

And, looking at my own photo, I see something else that everybody should fasten to their boom: a knife!

A divers knife is perfect but replace the rubber leg-straps with webbing/velcro because the rubber straps don't last with UV... I know and luckily found the knife on deck instead of overboard ;-)

@James: you can also see some of the rivets holding the reinforcement inside the boom for the vang attachment.

cheers,
Nick.

[David M]

I have threaded plenty of stainless into aluminum. Definitely use coarse threads. One more thing, use Tef-Gel to stop water from penetrating between the two dissimilar metals. This will do two things. If will stop the corrosion which means you will have a stronger connection plus it will allow you to remove the screw if you ever need to. In my opinion, Tef-Gel is far superior to Lanocoat or NeverSeize. Ask any rigger in a boat yard who has been around for many years that has had to remove seized stainless in aluminum. Tef-Gel is like a god send to them.

[hpeer]

I know that this is an oldish thread but it seems there is quite a bit of experience here.

Our mast has mast head fittings for three halyards going forward. But only the center one is use for the furling. So I want to add one halyard on each side.

I have the exit gates, but have not yet screwed up the courage to hole the mast.

I also have two Spinlock clutches I want to install above the wInches. Now these clutches are to take 5/16" by 18 thread screws. OK, no problem. But the clutch base is flat, not curved. The clutches are 69mm wide, a little under three inches so there is some noticeable wobble due to the curve of the mast.

My first thought was to make up a mast pad out of some (cut down) channel and flat plate bent to the shape of the mast. I will weld the cut down channel to the curved plate.

I will use Klik Rivet threaded inserts and 5/16 -18 screws to hold the base to the mast and tap the clutches to the pad (top of channel.) This will spread the load out and should make a nice installation.

Am I over thinking this? Should I just screw the clutches to the mast and not worry about the curve?

Alternatively I could cut the channel down so that the center is almost touching the mast and use some longer screws to go into the mast.

I kinda think the klik rivits will be stronger than taping the mast, but they will likely not be completely in-line with the holes in the clutch making it very difficlut to thread.

Your thoughts please.

[Cheechako]

Generally always coarse thread in aluminum. Although if you are tapping 5/16 into aluminum that is likely 3/16 thick...I would think fine thread would be nice.

[s/v Jedi]

hpeer,

This is why often a couple of single-clutches are used instead of the blocks with multiple clutches in one unit.

In your case I would shape a piece of King Starboard and use it just like a "washer/spacer".

ciao!
Nick.