Replacing the core from the inside.

[Mike2444]

I'm about to start a major core-replacement project on my boat; a 1970 Cheoy Lee Offshore 40. Since I plan to basically strip the interior, I envision replacing the core from inside the cabin.

This was done with "Owl" -- a Rhodes Reliant (the sistership of the O40). Photos of this restoration can be found HERE (http://www.rhodesowl.com/). In particular, the "underdeck" section shows photos of the core replacement and laying up a new inner skin.

http://www.rhodesowl.com/group09/images/Image-07.jpg

[gonzo]

It can be done. You'll get a shower of resin and glass. but that's the fun of working on your own boat:)

[Mike2444]

I've been bathing in resin and glass for two years, so I'm used to it. Last winter I took the teak off the deck and refinished the glass beneath.

Back to the new project; here's another photo of "Owl" showing the vacuum-bagged roving over the new core in the cabin roof. I'm not planning on doing the cabin roof, and I'd like to get away without vacuum bagging, but haven't an alternative yet.

http://www.rhodesowl.com/group09/images/Image-04.jpg

[Mike2444]

I've been reading "Fiberglass Boar Repair Manual" by Vaitses.

He suggests that when replacing core from the inside (working "upside down") one should clean up the inside of the outer skin, wet it out, and apply the core material along with a layer of mat (wetted out, of course) and brace as best you can. The trick, though, is that you let the resin get tacky before applying the core material to the deck skin.

This seems reasonable, as I would think that when tacky the core/mat will adhere better to the deck skin, making for a better bond. Nowhere in this book does he insist that vacuum bagging be used, as I've seen suggested in other places.

Any thoughts on this?

[gonzo]

They make bonding compound for the application. It is sticky

[Mike2444]

Thank you.

[Steve W]

Mike,im curious why you did not do your recoring from the top after you had removed the teak? The usual reason for doing it from the bottom is to save having to deal with the cosmetics and particually the non skid on the top,but you had the perfect opportunity to do it from the top with gravity on your side. Anyway what is done is done so since you are doing it from underneath you are best to use vacuum bagging as, planned out properly you can mitigate much of the messiness caused by fighting gravity plus you will get a 1st class bond.While it is certainly possible to just tom the core into place remember that the top skin is not rigid so when you prop the core up you are also pushing up the top skin so you will need to be aware and check the top for fair with a batten and actually use weights from the top to hold the top skin down against the props from the bottom,its more dicking around than a well thought out vacuum bag and you wont get as good a job.With the vac bag you are drawing the two sides together which is a much more satisfactory way of doing it.There is no reason to fear vacuum bagging and you dont need to spend a lot on a pump,you dont need a large cfm but you do want high vacuum and careful settup so you dont have leaks.Harbor freight or your local body shop supply store will have a pump for just a couple of hundred bucks.
Good luck,Steve.

[rwatson]

As well as vacuum bagging, could you build a bit of a shelf below the underside and Inflate a bag? The pressure would keep the materials pressed hard to the 'ceiling'

If you were clever, you might be able to apply the pre-impregnated cloth to the top of the partially inflatable bag, so that when you applied full pressure, it raised the cloth hard against the partially cured CSM.

Just an idea.

[Steve W]

rwatson,the problem with recoring from either side is that the remaining skin is often flimsy which is why vacuum is a natural,what i usually do is make up a platten with sawkerf channels to evacuate the air which allows me to layup everything downhand on something semi rigid and just lift it up into place,stick the bag and suck.once the core is in place you have something solid,i never layup the glass overhead,too messy.
Steve.

[Frosty]

This looks like a horrendous job for the DIY, is it economically viable.

I think I would be throwing any boat away that needed that.

Now I remember why I hate core boats, yet I have one,--- only above the water line.

[Scrumble]

Make it easy on yourself, turn the boat upside down.

[Scrumble]

Sorry just joking before.

Seriously haven't you heard of placement aids for reinforcing fabrics like Airtac-2 and infusion of the layup. Works any which way.

[gonzo]

I found that it is easier to recore with plywood because it doesn't make the deck all lumpy. There is no good way to keep it flat if you use foam.

[gonzo]

With plywood, you hold it tight with screws set through the seams in the teak deck.

[rwatson]

I found that it is easier to recore with plywood because it doesn't make the deck all lumpy. There is no good way to keep it flat if you use foam.

Good point Gonz. I presume you are talking about the lack of 'self fairing' that foam hasnt got.

I have been toying with the idea of doing a layup on smooth melamime tables with a light FG mat, and pressing core down onto it with weights or vacuum.

If the FG skin is the right thickness, it would act like plywood and be 'self fairing ' and totally smooth on the 'outside'.

Anyone ever tried it ?

[alan white]

With plywood, you hold it tight with screws set through the seams in the teak deck.

I completely agree that plywood is potentially faster and stronger and flatter, if heavier.
You don't always have teak on the deck, but screws and washers would still work. The non-skid probably needs to be renewed anyway. A 6" x 6" screw pattern would be about right for 1/2" plywood, 8" x 8" for 3/4".
Prop it first and use pieces narrow enough to work with slightly compound curvatures. Much easier and neater. Easier to hold the shape by propping too, and you'd reduce potential lumpiness in flat areas.

[alan white]

Plywood can be tortured easily if it's thin enough by propping the middle. Unlike cold-molding, which requires pinning down the edges, doing it inside the boat only requires a stick of the right length every so often along the length of a wide plywood "plank".