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 Post subject: RE-FITTING THE MAST
PostPosted: Mon Jun 24, 2013 7:03 am 
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Joined: Fri Jun 21, 2013 8:08 pm
Posts: 2
Hi folks,

New to the forum and to Hobies. Finding a great deal of knowledge here. I have purchased a '98 Hobie 16 with the black annodised mast. Having noticed corrosion around the cheek block, have decided to strip all the fittings from the mast to assess and found minor corrosion beneath the tang and retainer at the top. My questions are what should be done to treat the existing corrosion? and what should I use to put everything back together i.e. marine grade silicone sealant or an anti-electrolysis compound such as Duralac (not sure if this is a sealant also). I have removed the foam plugs and aluminium plates to gain inside access, also which I will reseal. What is the recommended practice for rivets etc?

Thanks.


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 Post subject: Re: RE-FITTING THE MAST
PostPosted: Mon Jul 01, 2013 6:41 pm 
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Joined: Sun Mar 17, 2013 10:55 am
Posts: 4
Location: Cleveland, Ohio
Hey, I have an '81 H16 and I was planning to redo all the hardware on the mast this past winter. I looked at all the rivets carefully and they seemed to be in good condition so all I did was drill out the rivets for the top and bottom castings so I could remove them and take a look inside.

Among other things, the H16 mast needs to float and so it needs to be watertight. When you replace the foam plugs and the aluminum plates make sure the aluminum plates are sealed in the mast. Then make sure that all the rivets between those two plates are watertight.

If you redo any rivets between the plates you will need a anti-electrolysis compound (Duralac is an excellent choice I hear) and some "rivet caps" (one "rivet cap" for each rivet). To replace the retainer, first put some anti-electrolysis compound on the outside of the rivet caps, put the rivet caps in the holes on the mast for the retainer, line up the retainer over the rivet caps and rivet it onto the mast.

A few points:

In general, corrosion on aluminum forms a barrier against more corrosion, so unless you are going to paint over where you cleaned off the corrosion, don't clean off all the corrosion!!

Use a sealant for the aluminum plates inside the mast, but use an anti-electrolysis compound for rivet caps.

Don't use any glue on the top and bottom castings when you put them back on the mast. Two rivets on the top and what is it 5? on the bottom is plenty.

Don't use aluminum rivets. Use stainless steel or monel rivets. Monel is stronger, you will get less corrosion with monel, but you will need a bigger, better, stronger, rivet gun to do monel rivets. You will (unless, of course, you are Chuck Norris)

Nick624


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 Post subject: Re: RE-FITTING THE MAST
PostPosted: Mon Jul 01, 2013 7:41 pm 
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Joined: Sun Jun 21, 2009 7:32 am
Posts: 287
When drilling out rivets, follow these directions:

Use the same size diameter as the rivets (3/16"), new cobalt drill bit.

Keep the drill bit for only this job, and stick the sharp end in a little piece of extruded Styrofoam to store in your toolbox.

Only drill into the rivet head a slight bit to form a seat for a 3/16" pin punch. The pin punch also needs to be one that hasn't been used for other purposes than pushing a 3/16" pin. The cobalt bit will cut quickly. Don't swing the drill around to wallow out the head of the rivet. The rivet is a lot harder than the aluminum under it, and I've seen many holes in the aluminum enlarged by this technique. You only need to drill into the rivet head the thickness of the head. With the sharp bit, it only takes a few revolutions, so if you are using a variable speed drill, you don't need to rev it up. That cuts through the rivet almost completely and leaves a good seat for the pin punch.

If you drill the head all the way off, there's an almost certain chance you have also carved out some of the aluminum.

Place the pin punch in the newly formed little hole, and tap lightly with a hammer. It doesn't take much of a lick at all, and the punch finishes cutting the rivet, pushing the stem into the mast. You can't get away from ending up with parts of the rivet inside the mast anyway, so don't worry about that.

This leaves the hole in the mast in the best possible state to have maximum strength for the new rivet.

If the rivet head spins when you first apply the drill bit, hold it under one side with a woodworking chisel, doing your best not to scratch the mast. It doesn't take much pressure from a sharp chisel to keep it from spinning.

I always cringe when I see someone wallowing a rivet head off by swinging the drill round and round. I've replaced many thousands of stainless rivets on Hobies this way.


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 Post subject: Re: re-fitting the mast
PostPosted: Tue Jul 02, 2013 8:19 pm 
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Joined: Fri Jun 21, 2013 8:08 pm
Posts: 2
Thanks to Nick and Tom for the detailed info and tooling advice, much appreciated.


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