Cabin-top core repair questions

[Kenneth K]

I'm repairing a small section of cabin-top coring damage that occurred under my center/forward dorade guard base. I removed the wet balsa and have a piece of plywood ready to go into its place. I'm pretty familiar handling thickened epoxy, and will smear thickened epoxy around the plywood when I install it.



My questions is, should I also cover the plywood & thickened epoxy with a layer of cloth/mat? If so:

- should I use cloth or mat?
- what weight?
- does the cloth or mat need to be added before the thickened epoxy has set?
- do I need to prep the existing adjacent fiberglass to ensure good adhesion? What's the best way to prep it?

Thanks.

Note to other 32-3 owners: It's worthwhile inspecting the forward "stanchion" base under the center leg of the dorade guard. While the left and right legs sit squarely atop the uniform non-skid surface, the center base bridges two non-skid areas with a recessed, smooth-deck area in between.



The center bolt of my forward stanchion base had almost no sealant under it, and this was the cause of the leak.

 

[Loren Beach]

- should I use cloth or mat?
- what weight?
- does the cloth or mat need to be added before the thickened epoxy has set?
- do I need to prep the existing adjacent fiberglass to ensure good adhesion? What's the best way to prep it?

The West System booklets and 'net info can help with this. I would over lay the new coring with a layer of "bi-ax" and extend it an inch or so beyond the edge of the area, onto the old frp skin. Thickened epoxy, somewhat, is good for filling in if the surface is not quite level.
Rough up the surface you want to bond to with some 60 or 80 grit,

 

[jtsai]

Note to other 32-3 owners: It's worthwhile inspecting the forward "stanchion" base under the center leg of the dorade guard. While the left and right legs sit squarely atop the uniform non-skid surface, the center base bridges two non-skid areas with a recessed, smooth-deck area in between.

View attachment 43608 View attachment 43607

The center bolt of my forward stanchion base had almost no sealant under it, and this was the cause of the leak.

Thanks Kenneth, I will certainly check mine. I am also salivating over your SS dorado vent, where did you get it?

 

[bigd14]

should I use cloth or mat?
- what weight?
- does the cloth or mat need to be added before the thickened epoxy has set?
- do I need to prep the existing adjacent fiberglass to ensure good adhesion? What's the best way to prep it?

Hey Ken- I agree you should add a layer of fiberglass over this repair (btw for ordering purposes the bi-ax Loren refers to is technically called 1708 Biaxial Cloth). For a repair area this small either the 1708 or the regular fiberglass cloth will probably be fine, whatever you have on hand or can find without buying a huge roll of it. I don't think the weight matters too much. If using the lighter cloth I would probably add a 2-4 concentrically bigger layers to tie it all together or a single layer of biax as Loren suggested above. I find it's easier to set the cloth over the thickened epoxy after it has started to harden but before it's fully cured, otherwise you have to rinse it off with water to remove amine blush and then sand it. For prep of adjacent fiberglass you'll need to get the headliner glue off, and its generally best to sand down old fiberglass anyway. So sand with 100 grit and then wash with acetone before fiberglassing over. Good luck with the project!

Edit- if you have plans to travel south to PDX before completing this project I have plenty of scraps of biax and regular cloth lying around you are welcome to have!

 

[Christian Williams]

your SS dorado vent, where did you get it?

Vetus cowls will work. Shiny, and they match my stainless Dorade vents.

...

The Vetus bases are too small for the factory hole. I had a plastics shop make adapter rings, which screw to the deck. The Vetus base is fastened to that. The stainless cowls are held by a collar that matches the base radius well, and look pretty standard.

 

[Jerry VB]

The vents from Buchan Marine are exact replacements - the screw holes even line up.
https://www.buchanmarine.com/product-page/stainless-low-profile
https://www.buchanmarine.com/product-page/stainless-oval-vents

 

[Nick J]

When I did this on my 25+ I used 2 layers of 1708 to replace the bottom laminate. I used a grinder to feather out the existing laminate to a 12:1 ratio. The areas I addressed were much larger, so I applied the core with thickened epoxy and let it cure before adding the 1708. You could probably do it all in one shot. If you have G10 laying around, it would be a good idea to use it around where the post mounts and balsa or plywood for the surrounding areas. That way you don't have to worry about drilling out the new plywood, filling with epoxy, and drilling the final hole.

 

[Nick J]

The vents from Buchan Marine are exact replacements - the screw holes even line up.
https://www.buchanmarine.com/product-page/stainless-low-profile
https://www.buchanmarine.com/product-page/stainless-oval-vents

I went with Buchan as well and I'm happy with them. They aren't as nice as Vetus because they rely on a set screw that tightens against the threads to stop the vent from backing out, but at half the cost it's a good trade off. Here's a pic from last weekend at Blake Island.

 

[Kenneth K]

Thanks for all the info everyone. I have some cloth and mat FG scraps laying around so maybe I'll piece together a double layer wetted-out piece to lay over the wood & filler. I'll likely try to do it all at once since it's only about a 3" x 5" area.

Yeah, I wish I'd thought of using G10 core before cutting & shaping the plywood. Now I'll have to go back and drill & fill the mounting hole afterwards.

 

[Kenneth K]

....your SS dorade vent, where did you get it?

It's a Vetus "Jerry" model vent I bought several years ago. I remember thinking it was pricey then, but I know it wasn't crazy ($400+) like they are now. Various mfg's seem to make round, teardrop, and oval variations of the vent. It' just personal preference, but I thought this one looked most like the original Ericson (plastic) one in shape.

Like Christian's, mine wasn't a direct fit. After removing the four mounting screws from the original base, I couldn't get the base to budge. I think it was glued in with sealant. The four holes in the Vetus base didn't line up with the four original holes so I just drilled & tapped new threads into the old base (it's just chromed brass/bronze, so it's easy to drill & tap) and screwed the new base to the top of the old one.

Original base

Vetus base on top of original base (before tapping and drilling)

 

[Jerry VB]

Very interesting... my vents (and the Buchans) have a six hole pattern but yours and Christian's are four holes.

 

[Kenneth K]

Very interesting... my vents (and the Buchans) have a six hole pattern but yours and Christian's are four holes.

My dorade vent (in front of the mast) has the 4-hole pattern shown above. The cowl vents at the stern are the 6-hole pattern. That Buchan stuff looks to be good quality.

 

[Prairie Schooner]

The center bolt of my forward stanchion base had almost no sealant under it, and this was the cause of the leak.

Yeah, on the 35, and apparently the 38, all three bases straddle non-skid areas. It might be over-kill, but I built up pads for ours with epoxy/glass fiber. In addition to drilling and potting, and splashing on some gelcoat. Not proud of the artistry, but it'll be functional.



I also reamed out the dorade box drain a little so it would drain better. As well as sealing the inside of the box.

 

[Jerry VB]

For the Buchan Marine vents: the screw that prevents the vent from turning does not work very well. It is metal-on-threads which doesn't hold very well and, if you overtighten the screw so it holds well, you likely will damage the threads of the vent socket.

I bought a packet of 3/8" felt bumper "dots" from the hardware store and crammed one in the screw hole before screwing the vent into the socket. This gives the locking screw something compliant to press into the socket threads. I'm pleased with how it works.