So I purchased a very clean 1981 P18 and it has some corrosion on the mast where spreader base and mast horn are located. I was wondering if they drill our rivets and weld a plate or ??. Any information is appreciated on how to go about it.

Some corrosion is normal there, after 35+ years between dissimilar metals. The worst of it is often hidden.

You need to drill the rivets out and see what's under there. IF the horn has a serious corrosion problem, you should check ALL the mast's load-bearing bolts and rivets. The diamond wire hardware and mast step bracket come first to mind.

Show us some Picts. Folks here can recommend repair techniques.

By popping the large castings at the mast top and bottom, you can do a proper inspection inside the mast. Even scope it. Backing plates can be added then, if needed.

I did this while rehabbing my P-18 mast this year. I ended up sanding and clear coating too. Put on all new wires too. And gooped everything to seal the mast.

They all go hand in hand.

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Prindle 18
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So if I do a backing plate would it be riveted in place and I assume a bit larger footprint then the area of repair ?

Riveted, if needed. Backing washers work well in the areas you can reach, like the lower mast.

Likely just new, or larger rivets will work, without a plate.

Welding is not an option.

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Once you drill out these rivets you will have a better understanding of the problem. I agree with nohuhu about going to larger rivets. Make sure to track down a 7/32" cobalt drill bit for drilling the high strength 3/16" rivets that are either Monel or possibly Stainless Steel. For sure have these same kind of rivet when you are putting this back together. Aluminum rivets are not up to the shear or loading forces on these kinds of parts.

Here is the link to the album I created referring to the aluminum parts when I was rebuilding my 5.2. https://www.thebeachcats.…ictures?g2_itemId=123176

One of my big concerns before I rebuilt my boat was that the corrosion may have enlarged the holes in the aluminum mast, but while the area around the holes would be corroded, the actual hole size had not enlarged.

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dg
NACRA 5.2 #400
This End Up
Original owner since 1975
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That's the awesome thread I combed though, before starting my mast restoration. Thanks for documenting all that work so well, DG.

How's the paint job holding up?

Expo - you shouldn't ignore the horn area but the corrosion/ enlargement issue I found was on and inside the lower mast were fresh/salt water ends up collecting (folks often don't think to rinse their masts well after capsizing). Aluminum oxide may attack here most aggressively and it may not be obvious.

The mast step bracket gets lots of high torque stress and theses rivet holes can open up easily. An early indicator.

By comparison, the mast hound, diamond wire tangs, stay adjusters and bow tangs get thousands of twisting/pulling stresses. That may work things loose over time, and also introduce small stress cracks. As best you can, inspect for these too, in all the the standing rigging.

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Thanks for all the helpful information and I will get this taken care of after this season. I am finding that boats like this are worth a lot in parts and just missed a complete boat for $400 that would have had everything I need in replacement parts. If I had the room I would buy up all the old cats.

A little over a week ago I pulled a bronze beam lug through the glass and have just finished that repair. I was not willing to take the boat 100% apart to be able to spray the repair area on the hull, so just rolled and tipped it. The new and old paint areas match perfectly for color, but the rolled and tipped shows the brush marks, which in this small area is not a big deal and isn't very noticeable.

So a year later the dark blue is holding up really well and the jet grey on the mast the same. There are already multiple dings in all of it, but that was expected from the beginning. One thing I have noticed about the dark blue Perfection paint is that it gets really hot in the sun. The old one part paint was not as glossy and that could be why it didn't get so hot.

Heading out this weekend to one of the coolest places on the planet to go sailing, Lake Waldo, Oregon. I will have time to finally to shoot some video of the assembled boat and go over all the things that were done and what this crazy project looks like now. This boat is now 41 years old.

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dg
NACRA 5.2 #400
This End Up
Original owner since 1975
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To follow up on "paint on a beach cat"

my 6.0 is grey emron and awgrip
looks hot (sexy)
feels hot (temp)
every scratch shows white gel-coat underneath (etch a sketch)
stress cracks are forming in the paint coat
added cost and weight (not worth it)
would i ever paint a beachcat knowing what i know now (no way)

MN3, Where are the cracks starting?

I would be more inclined to paint my mast and beams, and found that part of dg's huge restoration project particularly riveting.

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MN3, Where are the cracks starting?

bow tips where the spin bridal attach
bow tips where the furler bridal tangs are
several high stress areas on the deck (i was told there were stress fractures in the gel-coat there pre paint, and the fabricator didn't add glass, only gelcoat so they re-appeared)
one or two spots on deck lids presumably from a trap handle getting stepped on or similar (when the wings were on the boat)

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I would be more inclined to paint my mast and beam

besides added weight - no problems with this



Edited by MN3 on Jul 26, 2017 - 03:36 PM.

On my boat there was very little gel coat left after all the prep sanding. Then using the Awlgrip 545 as the primer really gives the paint something to hang on to. No cracking or chipping anywhere on my boat, just dings and scratches already from who knows what (nothing serious). I sanded off more of the Awlgrip 2000 on my mast and beams then I care to think about. I doubt there is much weight gain from the paint, if there was a gain it was from the surface prep stuff, which in the scheme of paint was a fairly thick coating. On my next project I will only be using the Awlgrip 2000 for the finish coats. The advantage it has over the Perfection is that it can have defects repaired. The Perfection paint does not tolerate being rubbed or buffed, it goes dull and loses the gloss.

One thing I would do for sure now is to use a pressure pot system for all the spraying and not my HVLP setup. The second thing is that I would spray way thinner coats than the manufacturer recommends. They are looking for low VOC, I am looking for a finish that doesn't sag. I am not quitting my retired job to be a body and fender guy either, that is some serious hard work to do, but it can be done by most DIY folks.

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dg
NACRA 5.2 #400
This End Up
Original owner since 1975
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No cracking or chipping anywhere on my boat, just dings and scratches already from who knows what (nothing serious)

Mine was painted in 2011 -
the fabricator has perma-crew (wife and daughter who sail all the time) to help handle this large beast (6.0 w/wings, spin and net front tramp) and told me "this boat was designed to never touch sand" - even with foam chocks and care ... this is hard to do sailing solo