Re: RIVETS PULLING OUT!

JBlumhorst@aol.com
Mon, 27 Sep 1999 22:38:03 EDT


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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In a message dated 9/27/99 4:47:51 PM Pacific Daylight Time, hapilife@efn.org
writes:

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> West Wight Potter Website at URL
> http://www.lesbois.com/wwpotter/
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> The rivets holding the eyes on my mast where the shrouds attach are
> pulling out!!!! How do I fix this? It's an HMS 1988 p-15.
>
> I just chipped my gelcoat too and decided that after 5 months in the water
> straight it was time for me to clean up and check everything...good thing
> I noticed the rivets...wouldn't have been fun getting dismasted !
> Ken Silverman, p-15 "vegan Lorax"
>

Ken,

The problem with attaching the shrouds with rivets is that they are under
tensile strain (as well as shear strain), meaning that they're being pulled
out along the axis of the rivet. Rivets don't hold well that way.

There were a few years when Joe Edward was making the boats that the shrouds
were attached with pop rivets. The original HMS company used thru bolts and
tangs and all the P15 's and P19s from International Marine have them too.

The best way to attach shrouds is:(1) Attach strouds to tangs with double
forks. A fork is a gadget that has a fork on each end with a clevis pin
between the forks. You attach the tang to one end of the fork and the shroud
to the other (2) attach the tangs to the mast with a thru-bolt (with washers
and nylon locknuts)

You don't absolultely need to use forks to attach the shrouds to the tangs.
You can swage the shrouds directly onto the tangs, with a stainless steel
thimble set inside the loop. But the forks make it easier to take them on or
off or to replace.

You can see pictures of tangs at the Dwyer Mast website www.dwyermast.com.
Just go to masts, select one, and look at the accessories at the bottom of
the page. Tangs are flat stainless steel plates about 1" x 3"; they have
holes in both ends; they are bent about 20 degrees so that when one end is
attached to the mast, the other end points down at the chainplates in your
hull.

Even better than just a thru bolt is a thru-bolt with an aluminum compression
tube around it. Example: say I use a 1/4" bolt for attaching the tangs to
the mast. I get a short piece of aluminum tube with a 1/4" inner diameter
and a 3/8" outer diameter. I drill a 3/8" hole in both sides of the mast,
slip in the tube, and then trim the tube so it's flush with the mast on both
sides. Then I assembe the tangs on the mast, putting the bolt thru the
sleeve. This way, I can tighten the bolts with no fear of putting a crink in
the mast, and I don't have galvanic corrosion occurring between the mast and
the stainless steel bolt.

The tangs on a thru bolt with a compression tube are good method for attachng
shrouds because (1) it won't pull out, (2) the tangs can swivel as the mast
flexes so there's no point loading of forces, and (3) the tube will last 5-10
years before it gets corroded and it's better to replace the tube than to
have a big hole from galvanic corrosion in your mast.

That's how I refitted the tangs and shrouds on my P19. (And, BTW, when I
removed the existing thru-bolt that didn't have a sleeve, there was noticable
enlargement of the original hole from galvanic corrosion) That's also how I
attached the bail for the boom vang, with a compression post.

But, for my boat, I'm a little compulsive about these matters, and since
tangs and forks are the time-tested way to do it, that's how I do things.

If you have any questions, email me back. My boat is out being totally
re-wired (found a GREAT guy to do it!) , so I can't get a picture of a
compression tube, or forks or tangs until Wednesday or Thursday.

Best,
Judy
1985 P19 #266 "Redwing"
SF Bay, CA