Hello,

I have three mast that are not air tight. Two are Prindle 18s the other is a Prindle 15.
On one of the Prindle 18s the rivets were pulled 2/3 out from the mast stepping plate. So, I have removed the rivets, stepping plate and the mast base.

I was thinking of filling in the holes with JB Weld.
Question 1
If there is something better than JB Weld please advise. If JB Weld is the right way to go which JB Weld product should be used?
Before I removed the stepping plate and base I submerged all the mast, lots of bubbles from rivets. I am thinking of replacing all rivets. I read a few threads on rivets. Some suggested using Monel rivets, Bulb Tite Blind Rivets. I searched Monel Rivets and found Dome Heads, Large Flange and different sizes.
Question 2
If I use Monel Rivets should I use Dome Heads or the Large Flange?
Question 4
What size should I use or do I use different size for Mast tang, mast base, mast head, cheek block, and diamond tangs?
Question 5
What sealing material is best for mast head, mast base and all tangs?
Question 6
Do I use the same material in question 5 for the center of the rivets or are Monel Rivets self sealing?

Thanks for your assistance,
Greg

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Prindle 18 w/ wings, Prindle 16, Prindle 15, current
Hobie 16 in rebuild
2 Hobie 18 past
NACRA 5.2 past

Saint Cloud, Florida
member Lake Eustis Sail Club
http://www.lakeeustissailingclub.org
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You want Monel rivets. They are highly corrosion resistant. Every rivet on Prindles (and NACRAs) is Monel.
Seal them with silicone.

Your Prindle uses rivets rated as MSP 6-32 all over. Only the length varies.
Translation: Monel rivet body, Stainless Steel mandrel, Pan head.

Look here for an explanation of rivet sizes:
https://www.thebeachcats.…388&g2_imageViewsIndex=1

You can vary the diameter bigger if your holes are enlarged instead of using JB Weld. Murray's sells an aluminum "shell" that goes over the rivet and seals it off, requiring a slightly bigger hole (which you already may have)
You can also get them longer.

You should try to seal the existing rivets in place with silicone before removing them all.

What kind of rivet gun do you have? You need a beefy one. Mine is driven by an air compressor, but you can use a manual one that has compound leverage, especially if you are doing a lot of rivets. Using a smaller rivet tool will not give you properly set rivets, waste your time and money, and you will have replaced strongly set rivets with weaker ones. Don't be fooled by how many rivets hold a piece on. Once one rivet pops, the others will follow like a zipper- sometimes rapidly.

There are a few places on your cats where the use of the rivet is not structural (beam end caps) and you could use an aluminum rivet. Don't. Aluminum rivets react poorly with all the metals on your cats (especially in salt water), and are weak. Don't even buy aluminum rivets that you could use on your cat, so that you won't be able to accidently use them.

My $0.02.

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Sheet In!
Bob
_/)_____/)_/)____/)____/)_____/)/)__________/)__
Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
AZ Multihull Fleet 42 member
(Way) Past Commodore of Prindle Fleet 14
Arizona, USA
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I agree that Monel are preferred in high shear load applications, but a whole lot of beachcats have aluminum in a lot of low load applications and IMHO they are fine. They are inexpensive, easy to pull with a hand rivet tool and easily replaced when needed. Pulling Monel rivets requires a more substantial rivet tool. I would also advise that sealing rivets with silicone is adequate, the only trick is to remember that you are not just sealing the mandrel hole, but the area under the rivet head which is easy to do.

Here is a video I did when I was working on my mast: https://www.youtube.com/watch?v=dMqKhR1qNyY&t=21s

I can think of no reason to use JB Weld in any part of sealing a rivet or even trying to plug a hole with it. The aluminum may bond to the material for a while, but thermal cycling, stress and a bunch of other reasons I can think of make this a poor choice. Even if you don't intend to use the hole again for retention of a part, simply fill the hole with another rivet and silicone around it to seal it up.

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dg
NACRA 5.2 #400
This End Up
Original owner since 1975
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You need to seal more than the rivets
I also seal around the mast tang, mast base, mast head and any other place that may have a through mast fitting. If you are wondering why I would seal the mast base or boom fitting, have your boat turtle and these fitting are under water.
I also replace the front rivet at the mast base with a self tapping screw and silicone it. So I can check to see if there is any water in the mast if I happen to flip.

Question: how common are mast head plugs? to seal the mast head from the inside? I'm too lazy to take my mast head off and check, but I'm sure it's more effective than just sealing the mast head edges.

Hullflyer, I agree you need to carefully seal more than just the rivets themselves, tangs are a good example of an area that needs special attention. I think the video covers some of that. What I think also is important is all the holes in the bottom of the mast (actually every hole in the mast is important). Water intrusion comes from rain and humidity too, so can be very nefarious at finding ways into the mast over time. I also advocate for having a hole in the base of the mast that is covered with adhesive aluminum foil. From time to time just pull the foil tape off and let the water that invaded the mast drain back out. This is particularly important with my old 5.2 because it still has the original impossible to seal mast spreaders. I think when I stripped my mast bare there were something like 50+ rivets in it, so lots of places to seal up.

As to sealing the masthead and mast base at least with the Nacra castings they were easy to seal up after having removed them and cleaned them up. Simply coat the inside of the mast and reinstall the castings. The silicone from the original installation of these castings was still very sound when I removed the castings. Not being exposed to UV probably explains that after 40 years. The retaining rivets had been resealed several times over the years.

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dg
NACRA 5.2 #400
This End Up
Original owner since 1975
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Does anyone provide for a removable plug of some kind to allow an upright mast to be drained? I also need to seal a mast, and recall following a capsize that the mast was draining from a hole near the base.

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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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Quote

lso replace the front rivet at the mast base with a self tapping screw and silicone it. So I can check to see if there is any water in the mast if I happen to flip.

Hull flier provided a great solution for this -
"also replace the front rivet at the mast base with a self tapping screw and silicone it. So I can check to see if there is any water in the mast if I happen to flip."

Great idea, thanks!

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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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