Sealing a Mast Head and Rivets :: Catamaran Sailboats at TheBeachcats.com

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Sealing a Mast Head and Rivets

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leeboweffect

Rank: Mate

Registered: Apr 22, 2015

Last visit: May 21, 2023

Posts: 484
Posted: Aug 18, 2016 - 12:21 PM

dmgbear55I doubt those are necessary for a mast head casting. They are going to be very hard to pull with a standard riveter and require a steel mandrel rivet that is going to rust and stain. I think they may be more appropriate somewhere where the part is getting worked around very hard, like a Hobie frame member, rudders or something like that. They would also not help where the rivet hole is not completely round. Here is the link and info on these:

http://www.murrays.com/19-5020.html

I think in the case of the mast head that taking care with some silicone application would be better. If you use these you need to coat the jacket with something to isolate the stainless from the aluminum mast.

Totally disagree with this. The casings are very thin SS (13/64" OD, 3/16" ID) and conform very easily to whatever the mandrel pulls them into. As Murrays states, their primary purpose is to prevent water and/or air from leaking through the center of the rivet where the mandrel runs. Further, you can use monel rivets with SS mandrels to virtually eliminate corrosion.

http://www.murrays.com/19-5022.html

On a mast I use 3M 4200 to seal the casings and rivets:

http://multimedia.3m.com/mws/media/891179O/3m-marine-fast-cure-general-purpose-adhesive-sealant-4200fc.pdf

If you want a water tight, air tight assembly, use the casings.

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Hobie 16 (3 formerly)
MacGregor 25 (formerly)
Chrysler Dagger 14 (formerly)
NACRA 5.0 (currently)
High Point, NC
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Edchris177

Rank: Chief

Registered: Nov 26, 2009

Last visit: Aug 10, 2024

Posts: 2531
Posted: Aug 19, 2016 - 12:21 AM

QuoteI gotta add, the stress on the mast base when stepping is going to be severe.

The Hobie is quite different, this is not an issue with the legacy Nacra. The base is a plug that goes a decent distance into the extrusion. The plug has a flange that bottoms against the end of the extrusion.
When I took apart a busted 5.2 to save the base as a spare, it was only held by 2 AL rivets from the factory. One is at the very front,the other goes through a cheek block for the downhaul.
TNELL's boat is the same as mine, looks like this;

Edited by Edchris177 on Aug 19, 2016 - 01:10 AM.

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Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--
Edchris177

Rank: Chief

Registered: Nov 26, 2009

Last visit: Aug 10, 2024

Posts: 2531
Posted: Aug 19, 2016 - 12:46 AM

QuoteI was just about to take my mast head off the other day and re-seal it. Got new rivets and everything. Then I realized that there are rivet CASINGS that should probably be used which I didn't have. The rivet goes inside the casing thus eliminating the hole. Murrays has them.

I guess the whole point of this thread was sealing the masthead. Depending on how each particular boat addresses the masthead, I would use different solutions.
The OP wanted to know about legacy Nacra. For those, I think it is overkill to remove the masthead/base, unless there is a good amount of visible corrosion. They are stuck in the extrusion pretty good, with a couple of AL rivets,(with no casing), just to make sure they can't fall out.
Wipe the joint with acetone, smear a thin bead of marine silicone around it, plus a dab on each rivet to seal the hole. Dab each rivet at the hound, diamond tangs, & any cheek blocks at the bottom.
Go sailing. Five years later, inspect, & repeat if necessary.
I drilled a bottom rivet head out of the 5.0,(same extrusion, same top/base), on a hot day, to replace a cheek block with a broken sheave. When I punched the rivet body through, a whoosh of air came out. The mast was sealed quite tightly, using only the 5 minute fix described. If you're into make work projects, have at 'er, but I'd rather sail.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--
tnell

Rank: Mate

Registered: Apr 15, 2004

Last visit: Jan 13, 2023

Posts: 358
Posted: Aug 19, 2016 - 04:31 PM

I smeared some silicone today. I'm pretty sure it's good to go. Edchris, you know those bearing tangs on the inside of the hulls under the beam used to locate the dolphin striker? One of mine has a loose rivet and has a gap behind it. I siliconed it up real good so it's not leaking, but do you know if there is any backup inside the glass on those rivets. I'm inclined to just leaved it alone since it's not structural.

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Tim
Collierville (Memphis), TN
Supercat 15--sold :(
Hobie monocat--given
Vanguard 15--traded for...
Nacra 4.5--sold
Nacra 5.7
Hobie 14–sold to make room for...
Supercat 17–sold
--
Edchris177

Rank: Chief

Registered: Nov 26, 2009

Last visit: Aug 10, 2024

Posts: 2531
Posted: Aug 19, 2016 - 11:11 PM

Quotedo you know if there is any backup inside the glass on those rivets. I'm inclined to just leaved it alone since it's not structural.

Have a look at this album of the inside of a 5.2 that we busted.
http://www.thebeachcats.c…pictures?g2_itemId=82844
The 2nd image,(2547), I believe shows one of the rivets that holds that tang. There does not appear to be any backing. The tramp tracks don't use any backing, so I don't think that tang would have any, as it's not structural, the rivets just hold it in place.
I would drill it out, it's AL, & replace this winter. Put a smear of silicone on the back side of the tang & pull a new rivet.
Use a piece of wire with a small hook bent into it at the end, to "feel" how thick the hull material is, & get a rivet that is long enough. I replaced a few tramp track rivets that were pulling out this way. IIRC I used 3/16" diameter x 1/4" long.
Also, for sealing rivets, don't just dab silicone on the center hole. Smear it around the perimeter of the head too. That prevents any leakage getting in under the rivet head. I put a dab on each rivet body when i insert it in the hole.

Edited by Edchris177 on Aug 19, 2016 - 11:16 PM.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--
tnell

Rank: Mate

Registered: Apr 15, 2004

Last visit: Jan 13, 2023

Posts: 358
Posted: Aug 19, 2016 - 11:28 PM

Thanks!

--
Tim
Collierville (Memphis), TN
Supercat 15--sold :(
Hobie monocat--given
Vanguard 15--traded for...
Nacra 4.5--sold
Nacra 5.7
Hobie 14–sold to make room for...
Supercat 17–sold
--
dmgbear55

Rank: Mate

Registered: Jun 22, 2015

Last visit: Jul 06, 2018

Posts: 258
Posted: Aug 20, 2016 - 11:42 AM

Using this wire hook method I was checking the thickness for the shroud plates on the sides of the hulls and found out that the thickness of the glass was not the same up and down the plates, so different length rivets will be required. Then I checked these tramp rail holes and they had some variation too, but not as dramatic. Aluminum rivets are pretty forgiving, so a longer rivet may be the way to go and just let the mandrel accommodate the variations in thickness. Monel rivets on the other hand are not forgiving and the correct length must be used, or the mandrel will break off before the bulge has pulled the rivet tight.

dg

--
dg
NACRA 5.2 #400
This End Up
Original owner since 1975
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tominpa

Rank: Mate

Registered: Jul 29, 2015

Last visit: Dec 12, 2024

Posts: 594
Posted: Aug 20, 2016 - 02:03 PM

Are the original rivets for the tramp rail aluminum?

--
Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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Edchris177

Rank: Chief

Registered: Nov 26, 2009

Last visit: Aug 10, 2024

Posts: 2531
Posted: Aug 20, 2016 - 06:25 PM

QuoteAre the original rivets for the tramp rail aluminum?

Yes, rail is also AL
Doesn't appear to be any backing plate or washers. IIRC they were 3/16" diameter. Using a bent wire to "feel" the depth, i think i needed 1/4" long shanks.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--