What Core Material would You Use?

[sgharford]

So I have the first section of the front deck of my 1976 43DC cut out. An area stretching about 10' x 12' will be replaced (from the very front of bow to about 6” behind forward V-berth hatch). Plan is to reuse the existing top skin. There is a 6' x 12' wide expanse of deck with no bulkhead support around the v-berth hatch. In front of hatch area are a bunch of holes for mounting bow pulpit, windless, cleats, and spare anchor chocks.

I'm between using Balsa or Coosa Bluewater 26 (leaning towards Coosa) as the replacement core. I like everything Coosa has to offer, although the compressibility of Balsa is about twice as good (1700 psi/sf verses about 1000 for Coosa Bluewater 26).. I just called Coosa and confirmed West Systems will adhere to it. 34Hat has used it as core material with very good results, although BoatsB seemed to have same reservations last time it was mentioned in another thread for similar application. Before I pull trigger, thought wise to ask my good friends at HOF their experience with Coosa and/or why Balsa (or another material) may be a better choice.

[Boatsb]

Is this the area where the windless and anchor chock are? If so you need to spread the stress over a larger area. a 1 x 2 foot area is too small for that type of stress.

I have filled voids in areas like that with laminated layers of 1/4 ply with mat and resin between making a virtually rot proof sandwich and of course having it as strong or stronger than the original. Balsa and coosa have their places but if there is a structural need neither is best.

[sgharford]

The replacement includes that area. Being an internet expurt, I googled compressive strength of 3/4" plywood and it's at 4500 psi verses 1000 for Coosa, 1700 for Balsa. So perhaps I'll use 1/4" layers as you suggested to get bend up front and Coosa for the rest. Thanks for that info Scott - very valuable info.

[Boatsb]

Do it in one piece. Not part ply and part coosa. That way the whole area is one solid piece and the stresses spread out over a larger area.

My guess is that the compression strength of the laminated ( slow cure resin) system with the resin penetrating the plywood and the glass layers in between would be closer to 7K lbs. Not that you need that much but its real solid when you do it that way.

[Jim saco]

Ive had good luck with divinycell. I used it on the underside of my cockpit when I replaced the foam core that had gotten wet. The po cut holes for pole holders and then calked them in. What a jackass. However I like scotts idea better where your going to mount your windlass. Id be afraid of compression then cracks on the divinycell. http://boatbuildercentral.com/products.php?cat=10

[sgharford]

Roger That. I was thinking about doing the whole thing in just ply right after last post. Lord knows the price is better for plywood anyway and not really worried about the extra weight.

I'm all ears for any other good advice regarding this project. I'm not going to lie, I kind of suck at this type of work and could use all the advice I can get.

[SKYCHENEY]

Roger That. I was thinking about doing the whole thing in just ply right after last post. Lord knows the price is better for plywood anyway and not really worried about the extra weight.

I'm all ears for any other good advice regarding this project. I'm not going to lie, I kind of suck at this type of work and could use all the advice I can get.

Don't forget to post some pictures so all of the experts that have never done this before can pick it apart and tell you how you did it wrong :D

[sgharford]

Don't forget to post some pictures so all of the experts that have never done this before can pick it apart and tell you how you did it wrong :D

Exactly! Figured I get project off on right foot and then screw it up from there for everyone's amusement. New twist on an old theme :)

[CDB101]

How about posting pictures since I am doing the same project and now with this new info I might follow suit. :cool: I was just planning on using balsa.

[Maynard Rupp]

I would not use plywood. Divinicell And Kledgecell come in various densities and will work much better. You can cut the material into many small pieces. The only purpose of the core is compression strength. One piece or many doesn't matter. You will find it much easier to work with the foam. The advantage of balsa is that it wicks the epoxy and won't delaminate. Of course, like the plywood, it will rot. Before I used plywood, (that would be an awful choice), i would go back with end grained balsa. The only concern with foam is if some 250lb. gorilla jumps from a dock 5' above the deck and lands on your deck with a giant thud. I have had that happen on my sailboat and the foam core did come loose. Those are the goods and bads. I would line the shaft hole of the windlass with a piece of PVC plumbing pipe, sanded and coated with filled West epoxy. I also used that same pipe type liner for the chain pipe. That seals the whole mess and prevents water intrusion.

[lumina]

Ive had good luck with divinycell. I used it on the underside of my cockpit when I replaced the foam core that had gotten wet. The po cut holes for pole holders and then calked them in. What a jackass. However I like scotts idea better where your going to mount your windlass. Id be afraid of compression then cracks on the divinycell. http://boatbuildercentral.com/products.php?cat=10

Hi All,

I second the divinycell reccomendation. We used it when repairing the entire cockpit floor.

Can't speak to the windlass concern.....

[Boatsb]

Too bad I never actually did this kind of repair (insert sarcasm here) or I would be talking out my ....


FYI here is a C&P from the sites favorite son

Foam Cored Decks Foam might seem like a great replacement for balsa, since it doesn't rot. But that doesn't mean it won't deteriorate. It can and it does. By a variety of means and methods. The problem I have with foam is this: Balsa is balsa, and it doesn't come in 100 different formulations. With balsa, you know exactly how it's going to behave under all conditions. Not with foam. Try looking at a piece of foam and determining what it is. No way. All you can do press your fingernail into it and determine its density and compression strength. Or bend and break it.

You already know a lot about foams because you see lots of it used in packaging and insulation, so you know most of it is not very durable stuff. In fact, put it out in the sun for a couple of months and it will literally disappear. It evaporates. Literally. Then pour some solvents on it. Go into your paint locker and you'll find at least one that will dissolve it. Put it on the ground and step on it. Crushes pretty easy, no? Work your fingernails into it. Crumbles real nice, does it not? Now apply some heat to it. Doesn't have to be much, just bring a match near. Try to burn it with the match. Burns like crazy, right? Hot and fast. Now try the same things with a piece of balsa. In virtually every category, balsa out performs the foam. And when it comes to biodegrading (meaning rot), in many cases the balsa will still outperform the foam. Balsa, like teak, contains a toxin that fungi doesn't like. It doesn't rot until that toxin leaches away.

Another Problem: Most foams used in boat building have very low heat distortion values. Basic PVC foam Heat Distortion Temperature is around 150 degrees. That's about the temperature the white deck gets baking under the summer sun. Add some color to the surface and temperatures will begin to soar. I have measured black painted surfaces on boats as high s 237 degrees. That's why you see foam cored boats with painted dark trim, or dark gelcoat colors, that look like a checkerboard. Heat distortion is irreversible. These foams will also begin to stretch or creep when heated, resulting in the laminates loosing their design strength. Structures can actually change shape. The HDT of balsa is 360 degrees.

Shear Strength: The shear strength of most PVC foams is around 40-60 psi; some are much lower. Balsa is 400 psi. Not much else to say about this.

Why on earth would anyone want to use a material like this? But you know the answer already. Money. Do you really want a boat made with this stuff? Or do you want a boat made with a material that at least you know how it performs? The problem, you see, is that we do not know the properties of whatever foam is used in a boat. We may be able to determine that it is foam, but that's all. Which of the endless varieties of it may be, we have no idea, and so nothing can be said for how it will perform. After all, performance is proved by application experience, but if we have dozens of varieties of the material, who can keep score? Surveying foam cored boats gives me the willies if only because I don't know what's in there.


End of quote from you know who.




Reality is that most chocks and windlasses need backing blocks to protect the underside from compression stress especially when the windlass or chock has force applied to it like an anchor pulling as it is supposed to. Fighting chairs in cockpits have the same issues and I see problems from the deck being twisted from the load and causing the leaks. What does everyone do when they install a cleat or chock? The add a metal or plywood backing plate to spread the stress and prevent the compression of the core from the fasteners on the inside. There is also in many cases a mounting block used on the top for the same purpose. The foam is not the right material for the mounting areas especially since the balsa that was originally there had better compression properties and failed.

[bobk]

Here are some alternate ideas.

First, consider the deck to be a type of I beam. The top flange (deck skin) is loaded in compression in both planes. The bottom flange (skin) is primairly loaded in tension. The web or center core is loaded in compression vertically and tension and compression horizontally and therefore there is a shear component. For proper I beam function, the bottom should be roughly the same strength and modulus as the upper. So the first question I would raise (and did on my fore deck job) is, is the bottom skin thick enough. Answer, NO on most decks. It wasn't on Walt's either. So first suggestion is to beef it up with a couple of layers of glass. Woven roving or Fab mat would be my choice.

On to the core, I suggest you consider anything BUT wood. Coosa and divinycell are both good candidates if the top skin is reasonably think. But I would use something that is not compressible in the foredeck where cleats, chocks and windlass are to be attached. If you can work it out, fill this with thickened slow cure epoxy. You don't want Cabosil because it will get thick with just a little of the silica. Rather use fine glass beads or microballoons ($$). You can add a lot of these and dilute the epoxy and therfore the exotherm temperature rise of the mix. This solid core will prevent compression of the core when you tighten up the bolts.

Good luck.

Bobk

[Avenger]

Why not just bite the bullet and lay it up in solid glass. You can probably get away with 1/2 to 3/4 inch as long as you taper it into the cored sections. Plenty of compression strength, no rot. Put an aluminum backing plate under your windlass and cleats for load distribution and never worry about it again.

[bigbill]

scrod, solid glass is not as strong as cored. a buddy of mine works for seeman composites, and showed me with a test. 1/2 thick solid glass, and 1/8 glass-1/4 core-1/8 glass. the solid glass would bend easier than the cored stuff....... now for compression, you cant beat solid glass.

[Boatsb]

Why not just bite the bullet and lay it up in solid glass. You can probably get away with 1/2 to 3/4 inch as long as you taper it into the cored sections. Plenty of compression strength, no rot. Put an aluminum backing plate under your windlass and cleats for load distribution and never worry about it again.

Solid glass would be sweet but heavy and hard to work with such a thick area.

I have done a few dozen of the repairs with the glass and 1/4 ply sandwich and in 20 years not one has failed to my knowledge. I did hear one where the rest of the boat fell apart and it was the only sound area but that is another story.

Just remember that the method will saturate the plywood almost completely and therefore be almost rot proof. Also remember that the solid deck it creates will not be susceptible to the leaks caused by the bolts compressing the core and then releasing it. Straight thickened epoxy will not be as strong as the resin is brittle in comparison to the sandwich system and would have issues with cracking and expansion in the heat and cool cycles the deck goes through. Also epoxy creates some issues with bonding for polyester so be sure to keep that in mind.

[dsharp]

How much crown is in the deck?

[Avenger]

scrod, solid glass is not as strong as cored. a buddy of mine works for seeman composites, and showed me with a test. 1/2 thick solid glass, and 1/8 glass-1/4 core-1/8 glass. the solid glass would bend easier than the cored stuff....... now for compression, you cant beat solid glass.

I don't dispute that. Great for a deck or a hullside, but a highly stressed area with compression issues, I wouldn't see a little flexing as a bad thing.

Did your friend's demo include destructive testing? I'm curious which piece would have failed first and under what kind of loads?

I'm sure a cored repair would be acceptable as long as you can ensure that the compression and water intrusion issues are covered. Solid glass covers them too. I guess it depends on what you're comfortable with.

[captddis]

I wrote an article about doing about a 36x36 area under my windlass and rebuilding the pulpit sometime around 04. My post was promptly plagerized and should be easy to find.

[Boatsb]

someone here plagerized your article? That's just so wrong in so many ways. I hope they at least didn't screw it up.

[sgharford]

Captdis - I tried searching for your article and could not find it. I am very interested in reading it. I'm still leaning towards plywood. That 6x12 unsupported section I made mention of in first post is just as much concern as bow pulpit area for strength. I like the idea of layering the 1/4 plywood in staggered pieces to cover seams so that it is effectively one giant piece. Any seam in that 6x12 unsupported area is a weak point. Many times I’ll have 5 to 10 adults standing in this area. I could use 1/4 coosa in similar fashion, but I think I'm getting allot more bang for the buck with plywood. I have great respect for BoatsB advice and fact he has done it for 20 years with great success also helps mitigate any possible water intrusion worries. I'll treat install like balsa and over drill out all holes thru deck and fill with epoxy, just like balsa install.

As an aside, interesting article I read this morning about use of Balsa as core. The reason they make the roughly 4"x4" squares of cross grain glued together is so that any water intrusion that occurs will run along the grain of the balsa and stop when it hits the cross grain of adjoining piece.

[Pascal]

I would use Divinycel... This stuff is really good and that s what Hatteras has been using for a while now, isn't it? Light, very stiff, closed cell, easy to use and extremely strong

I m using it for the frames, deck, stringers of the 26' classic sloop I m building, great material

[bigbill]

As an aside, interesting article I read this morning about use of Balsa as core. The reason they make the roughly 4"x4" squares of cross grain glued together is so that any water intrusion that occurs will run along the grain of the balsa and stop when it hits the cross grain of adjoining piece.[/QUOTE]

how did that work for you. if this was true, you would only have a bad spot about 4x4..
i know it didn't work on my boat

[sgharford]

Mine completely delaminated from the skin so all the squares were sitting in a puddle. I threw in there as an interesting tib bit I thought I'd pass along. I thought all the squares where there because it was made from scraps of balsa and it was cheaper, like particle board.

[Boatsb]

As an aside, interesting article I read this morning about use of Balsa as core. The reason they make the roughly 4"x4" squares of cross grain glued together is so that any water intrusion that occurs will run along the grain of the balsa and stop when it hits the cross grain of adjoining piece.

how did that work for you. if this was true, you would only have a bad spot about 4x4..
i know it didn't work on my boat[/QUOTE]

Balsa is great stuff for certain uses. the strength to weight ratio is incredible. I built a model bridge span using balsa and held hundreds of pounds with this 4.5 oz structure.

The issue is the end grain is a wick for moisture. even if it does not carry to the next cube through its side contact the water will break the bond at the bottom and travel at the skin to the next piece.

Closed cell foam is better in the fact that it will not absorb moisture but it will also lose the bond if left in water long enough.

Now think about the strength of plywood as compared to a similar dimensioned piece of solid wood.Plywood is stronger and more flexible. laminate the curved crown of the deck with multiple layers of the plywood and you have a strong deck. laminate them with a resin ( poly or epoxy) and you have an almost waterproof strong deck especially if you add in the mat between layers.


Its the same idea as the Glu Lam beams used in construction of houses and buildings.

[sgharford]

Balsa is great stuff for certain uses. the strength to weight ratio is incredible. I built a model bridge span using balsa and held hundreds of pounds with this 4.5 oz structure.


I did that project too when I was working on my BS in Mechanical Engineering! We scarfed the joints, should have used glue - ours only held about 80 lbs.

[Avenger]

And here I always thought they were cut into squares so the core could conform to the shape of the deck or hull. Whoda thunk?

BTW, my earlier suggestion on the solid glass was only meant for the pulpit/windlass area since that's what everybody was focusing on. Doing the entire repair that way would be a bit too much even for my style of overdoing things. It was clear in my head, but not in my post. Sorry.

[Boatsb]

I did that project too when I was working on my BS in Mechanical Engineering! We scarfed the joints, should have used glue - ours only held about 80 lbs.

I did it in 11th Grade AP physics class. had a great teacher that really motivated us to learn more about anything that interested us. The let him go before he had tenure because they had a bunch of olf fat stupid women who were not very interested in teaching afraid he would become their boss and make them work.

[captddis]

Captdis - I tried searching for your article and could not find it. I am very interested in reading it. I'm still leaning towards plywood. That 6x12 unsupported section I made mention of in first post is just as much concern as bow pulpit area for strength. I like the idea of layering the 1/4 plywood in staggered pieces to cover seams so that it is effectively one giant piece. Any seam in that 6x12 unsupported area is a weak point. Many times I’ll have 5 to 10 adults standing in this area. I could use 1/4 coosa in similar fashion, but I think I'm getting allot more bang for the buck with plywood. I have great respect for BoatsB advice and fact he has done it for 20 years with great success also helps mitigate any possible water intrusion worries. I'll treat install like balsa and over drill out all holes thru deck and fill with epoxy, just like balsa install.

As an aside, interesting article I read this morning about use of Balsa as core. The reason they make the roughly 4"x4" squares of cross grain glued together is so that any water intrusion that occurs will run along the grain of the balsa and stop when it hits the cross grain of adjoining piece.

I will try to find it or I will redo it. I did use epoxy saturated plywood under the windlass and pulpit.
Used all epoxy on the repairs. It was amazing how much stronger the epoxy is.

[Ernie Piotrowski]

I would give Nidacore a try. Replaced the cockpit on the 32 flybridge when the circular hatches leaked and left the core a pile of mush. The product is a honeycomb design made in thinknesses of 1/2 to 6+. Mine is a SCUBA charter boat with the cockpit holding 24 tanks, weight belts, gear bags and 8 persons. My son tried to dent the circular hatch cutout with a 16oz claw hamme(claw end) and couldn't even dent it. There are a couple of offshore CC mfg using the material. I wouldn't use anything else if future repairs in other areas become necessary. Total weight on the cockpit it approx 2500-3500 lbs. No flex and no water intrusion/migration worries. Google the item and they will be happy to send you info and a sample. Good luck with your repair.

[Boatsb]

I love Nidacore but it is not for structural use. The forces on the windlass and chocks would tear it up.

[Kiwipushrod]

Plywood, and treated besides.

When the Balsa a.k.a. Sponge starts pulling water, You can't stop it, ask the SeaRay guys.

Kiwi

[Boatsb]

You cant use treated plywood. It wont bond with the resin

[sgharford]

Hi Scott - I should Not using any woven or matt in any this, correct? Planning on using West System to do it all - from laminating 3 sheets of 1/4" plywood together to reapplying the cut out top skin to last layer of plywood. Would you recommend a filler like West System 404 to thicken it up some, or just go with straight epoxy using slow hardener?

[34Hatt]

No Matt with epoxy use 1208 bi axial and cloth.
And yes thickener you want it to stay and not run out the seams plus it won't be a perfect matching surface's if there is air its N.G and weak!
You never get the skin down without air using straight West.

[Boatsb]

West is a great system but expensive. I use it quite often but I also use polyester when practical. If it is a large section you can use poly and save considerably but remember to allow the resin to cure slowly. As to using matt with west there are a few available mats that are ok with epoxy. Regular mat may contain binders that are not epoxy friendly.

[34Hatt]

West is a great system but expensive. I use it quite often but I also use polyester when practical. If it is a large section you can use poly and save considerably but remember to allow the resin to cure slowly. As to using matt with west there are a few available mats that are ok with epoxy. Regular mat may contain binders that are not epoxy friendly.

He wants to re use his skin so I don't suggest going with poly. If it was me core would go in with epoxy then switch to poly.
Using 1208 it already has a mat on one side so no need for the special stuff and 1208 is much stronger. Mat is used to bond things together and he is using epoxy so no real need for extra mat.

[sgharford]

Thanks Guys! I’m thinking matt between existing lower fiberglass skin and first layer of plywood as well as top layer of plywood and existing skin only. Since I am reusing existing skin, I think buildup will be too high between plywood layers if use mat there as well. If you guys think using cloth between plywood layers better maybe I should go with one layer of 1/4" plywood and one layer of 3/8" plywood which leaves 1/8" for glass buildup between layers?

As for plywood, is Pine (sanded finish) ok or should I go with a harder wood like Birch or maybe even Oak? The price difference is nominal between them. Pine seems like way to go as I do need slight crown, but I’m not afraid to ask anyway.

For those interested in core material cost, I figure I need 4 sheets of ¾” 4x8 for this job, or 12 sheets of ¼” plywood. Cost for 12 sheets of ¼” Pine ply is about $250 (Lowes, pick up), 4 sheets ¾” balsa is about $900 (Jamestown w/ shipping) and 4 sheets Coosa Bluewater 26 is $1350 (Hamilton Marine w/shipping). I’ll probably stick with West System as it’s the only thing I have ever used, and am pretty comfortable using it.

[Boatsb]

But a 6 x 12 area can be laminated with the core wood easily with poly and the skin attached with epoxy. Its not a good idea to go from epoxy to poly. Just poly to epoxy. The poly will not bond well to the epoxy.

[34Hatt]

But a 6 x 12 area can be laminated with the core wood easily with poly and the skin attached with epoxy. Its not a good idea to go from epoxy to poly. Just poly to epoxy. The poly will not bond well to the epoxy.

But he is doing all Epoxy and when I go epoxy to poly is after coring so its only a small seem line.

Scott I know even west does not bond well to OAK so that's a NO.
Birch maybe but just a good exterior pine well do. Coat it all first then wipe down with water after full cure to get rid of the blush.
I would shrink the thickness of the wood to put more glass in-between stronger and less chance of air.

12 sheets how about some pictures of this Hole?
I mean Crater!

[Pascal]

I don't know where the anonymous quote / rant is from but it is not accurate. Divinycel is NOT cheaper than balsa and while affected by UV, it does t "disappear" after a couple months in the sun...

I have some scrap pieces sitting that have been sitting in the sun for a year and while discolored they re still hard to break.

Speaking of which, the higher density Divinycel doesn't compress easily and while it should be backed up for cleats and other high stress items it will not compress

There is a reason Hatteras is now using it instead of balsa...

And considering the amount of work involved, i really wouldnt try to save a few bucks and stick with West epoxy for the entire project

[sgharford]

But he is doing all Epoxy and when I go epoxy to poly is after coring so its only a small seem line.

Scott I know even west does not bond well to OAK so that's a NO.
Birch maybe but just a good exterior pine well do. Coat it all first then wipe down with water after full cure to get rid of the blush.
I would shrink the thickness of the wood to put more glass in-between stronger and less chance of air.

12 sheets how about some pictures of this Hole?
I mean Crater!

Thanks for heads up on Oak - seemed to stiff anyway. I'll go with Pine I guess. I need 12 sheets instead of 4 because I need to build up to 3/4" thickness. My idea is this - put the first layer of ply down with epoxy, then cover the first layer seams with second layer by cutting them different lengths. I'll cover 2nd layer seams in same manner with 3rd layer. This way the whole 10'x12' is like one giant piece. That's what I like most about this method (and the compressive strength of Plywood of course) - One giant piece instead of seams if I were to use single pieces of 3/4" core material. Working with 1/4" layers at a time should allow me to mold to existing crown allot easier too. Additionally, I can do sections at a time since there is no way just the lower skin will support my weight - it's notch up from paper in thickness. I can do first two layers of ply up front, then cut out another swath of upper skin while standing on first two layers of plywood, and overlap joints as I go. It seems feasible.


And considering the amount of work involved, i really wouldnt try to save a few bucks and stick with West epoxy for the entire project

You never hear anything bad spoken about West System (edit - except the price!).

[Pascal]

My concern with this method would be the amount of resin ($ and weight) all those layers of ply are going to absorb. You re also going to have to clamp / weight each layer down every time to get a good bond and avoid voids.

I just don't see the compressibility issue with the Divinycel as long as you use the grey higher density. I pulled a piece, put it on the floor and stood on it balancing on one heel... That s well over 200lbs of weight applied over a square inch of surface. I can't even see an indent/compression mark. Again this is a lot stronger than most people think...

It would be easy to make a working platform using some 2x4 and ply so you don t put any weight on the lower layer.

How do you plan on putting pressure on the core to bond it to the lower layer? You can't put weight on it... I d drill holes thru the core and lower glass layer, the use some steel wire and clamps to pull it together. This way you don't risk deforming the lower layer with weight

Once it has cured, remove the wire clamps, epoxy the holes and you re good to go with your upper layer

[sgharford]

Hey - that's clever drilling holes and pouring glass in to fill void. Think I'll use that one. Like the idea of wire ties to clamp together too. I had inkling somewhere along line that headliner may have to come down underneath for access. I was picturing cinderblocks in my head, but perhaps short screws will do it too. There is about 1" of space between the headliner and bottom skin, so as long as screws not to long, maybe not a problem. Bigger problem is bottom skin really is like paper, not sure it will take any stress of this type. So if I take head liner down, put a wood backing plate behind it, well hek - could just use screws instead of wire I guess in that instance too. Once I get first plywood sheet down with appropriate crown and the resin dries, I could use short wood screws on second sheet to 'clamp' it down (with epoxy in between) to first sheet.

Reality is crown is very minor. I may be able to cut first layer to fit, mimic neccessary crown by placing middle of that piece on top of broom handle, place cinderblocks on edges of wood, wet it down, and let it dry with curve in it - then slap in place with expoxy. Don't want to ovethink this too much, yet.

I could use some extra weight up front, although not up so high. I have all rope anchor rode (it does me fine, except I swing wider then most in crowded anchorage) and currently on full trim at cruise until I get down to 2/3's a tank of fuel.

[Pascal]

I didn't mean wire ties... I meant cheap galvanized cable, cut in foot long sections. Put thru hole tie a nut underneath duct tape to prevent it from falling thru while you clamp the top side. Then from the top you pull on the wire and clamp it tight. Use those rectangular cable clamps with 2 screws, $1 a piece at HD

Or if you don't have access under the deck, instead of taking down the headliner, get some long thin bolts, bent about an inch at a 90 angle. Insert into the hole so the shorter end of the L catches the bottom skin. Then screw the nut at the top... I ve been playing with this to repair a delaminated hobie hull. I ve also used a varaiyion of the cable clamp method to clamp planks without leaving screw holes...

[Boatsb]

Reinventing the wheel is just so much fun.

I have done it before and will say the poly is easier to do multiple layers because there is no need to sand and wash between layers. Use a mahagony ply and it bonds well and is inexpensive in marine ply.

[Canuck Dennis]

Did someone say "Pine" ???

[jim rosenthal]

If you're going to use marine plywood, use 6mm marine ply, all hardwoods, and build it up as you said. Use epoxy or vinylester, don't use polyester. It isn't a very good glue, and the cost difference isn't much- your big investment is in your labor.

Coosa panel is very tough, and comes in more robust grades. It has one advantage over ply or balsa- it will not rot, no matter WHAT. I have used the multiple-this-layer idea with Coosa board and it worked very well, made a very strong repair of a rotted area in my boats rear cabin bulkhead.

The reason a lot of folks use West Epoxy is that they are familiar with it and it works consistently- no surprises. A job like this is difficult enough without your materials surprising you.

[Pascal]

If you apply the glass layers sequentially before the epoxy has cured, blush is a non issue and you don't have to wash/sand

[Boatsb]

6 x 12 is a large area for a single person to do. Its a bit easier with 2the and a helper. As for the west being a known you are correct. But doing that large of a section as a monolithic lamination it would be quite a feat

[sgharford]

Great Feedback - Thanks everyone. Currently, I am working on getting all the goo of existing aluminum window frames that I have in garage for powder coating. They have been bubba-fied, with everything from Butyl tape, 5200, Sika, and good ole’ clear silicone stuck to interior and exterior frames. For that, A Fein type multi-tool with round saw blade (I have harbor freight single speed $20 version that works great) to cut off chunky stuff and a heat gun and scraper for residue are only things working. Everything else just smears it.

I did visit boat and determined the headliner will have to come out. The whole deck is sagging and I believe I will have to prop up from below. The lower skin is so bad (floppy) that I may even cut it out as it will possibly take more effort to re-adhere to new core then simply replacing. I hope to take day off this week, take headliner down, and pray for proper inspiration.

[BOATER BOB]

Chech out Nidda core

[Mario Tranquilein]

hi to all: I have a friend that do the repair in his Hatt 38 same big area he do this: Cut deck layer with a router, removed all the rotten balsa core and leave it spot less, with poly resin and cabosil he seal all the edges so water can penetrate anymore, he use marine plywood in cut in two parts he do long cuts under so the panel can take the curve of the deck, before installed them he resin the panel under and put big amounts of resin with cabosil, then leave cements blocks lot of them for two days so no bubbles could form, with only that you could jump and feels like a rock!, then resin the plywood panel and again put a lot of resin with cabosil and glue the deck skin, leave it with the cements blocks for a couple of days, the edges of the skin he use resin with mat so no litle craks appear later. The result a super strong and cheap repair and the water line don't low an 1' the boat doesn't know the repai was done.

Hope this be helpfull.

Mario

ps: I need to do it too because my hatt is for sale :(

[sgharford]

Thanks Mario, I believe I am going to take similar approach. Honestly, this was going to be the 2nd job I outsourced to yard since I bought boat 4 years ago (the first was taking the bottom down). They have dragged their feet for months and when the fella doing work finally made cut in first section, he cut right within 1" of edge of deck, so now you can't properly grind out groove at seam to fill with epoxy when we reuse upper skin. He used a Fein tool with carbide bit to make cut, which tells me he has never done this before as that is excruciatingly slow and prone to cutting lower skin. These 2 things tell me he’s never done this before and not doing proper research to make sure he’s doing it correctly. I took 2 of 3 sections up over weekend. A circular saw set to 3/4" works perfect for making initial cut into deck. I used a cordless DeWalt with smaller circular blade that made the wide sweeping arch cut no problem. My 2 cents - don't go too far past where the deck starts sounding solid with your cut, the bond is extraordinarily good where balsa is dry and you will not get up an area that goes further in then about 9 inches of good balsa core. I also bit the bullet and took headliner down from below as there was allot of mildew showing thru. I forgot how cheap 2x4's and plywood sheathing is - $50 for 2 sheets of plywood and 8 2x4'x and all the soon-to-be exposed deck areas are now supported from underneath. To get old balsa core wood off from existing skins, I recommend 2 cheapy $20 harbor freight multi-tools (the Fein copy's) - one with scraper blade and one with plunge saw blade. These things are wicked powerful, I have Craftsman one at home and the harbor freight model blows it away. Anyway, where the old balsa will not scrape off from upper or lower skin, use the plunge saw bit to remove. This plunge bit is especially handy where good balsa is around outer perimeter of your cut - like I said before, it really sticks where balsa is dry. You'll need a dust pan and a good shop vac when all said and done. Oh yeah, don’t ware old sneakers – they will mare the deck. Ware old deck shoes. Yeah, you going to have to repaint with non skid anyway, but it’s a buzz kill none the less. I'm going to leave for at least 1 week to let it dry out up there. I'm still leaning toward 1/4" mahogany plywood for new core.

[Boatsb]

Thanks Mario, I believe I am going to take similar approach. Honestly, this was going to be the 2nd job I outsourced to yard since I bought boat 4 years ago (the first was taking the bottom down). They have dragged their feet for months and when the fella doing work finally made cut in first section, he cut right within 1" of edge of deck, so now you can't properly grind out groove at seam to fill with epoxy when we reuse upper skin. He used a Fein tool with carbide bit to make cut, which tells me he has never done this before as that is excruciatingly slow and prone to cutting lower skin. These 2 things tell me he’s never done this before and not doing proper research to make sure he’s doing it correctly. I took 2 of 3 sections up over weekend. A circular saw set to 3/4" works perfect for making initial cut into deck. I used a cordless DeWalt with smaller circular blade that made the wide sweeping arch cut no problem. My 2 cents - don't go too far past where the deck starts sounding solid with your cut, the bond is extraordinarily good where balsa is dry and you will not get up an area that goes further in then about 9 inches of good balsa core. I also bit the bullet and took headliner down from below as there was allot of mildew showing thru. I forgot how cheap 2x4's and plywood sheathing is - $50 for 2 sheets of plywood and 8 2x4'x and all the soon-to-be exposed deck areas are now supported from underneath. To get old balsa core wood off from existing skins, I recommend 2 cheapy $20 harbor freight multi-tools (the Fein copy's) - one with scraper blade and one with plunge saw blade. These things are wicked powerful, I have Craftsman one at home and the harbor freight model blows it away. Anyway, where the old balsa will not scrape off from upper or lower skin, use the plunge saw bit to remove. This plunge bit is especially handy where good balsa is around outer perimeter of your cut - like I said before, it really sticks where balsa is dry. You'll need a dust pan and a good shop vac when all said and done. Oh yeah, don’t ware old sneakers – they will mare the deck. Ware old deck shoes. Yeah, you going to have to repaint with non skid anyway, but it’s a buzz kill none the less. I'm going to leave for at least 1 week to let it dry out up there. I'm still leaning toward 1/4" mahogany plywood for new core.


Grasshopper you are doing well. When you can snatch this nickel from my hand you will be a sailboater.

[sgharford]

Grasshopper you are doing well. When you can snatch this nickel from my hand you will be a sailboater.

Ha! I WAS a sailboater for 25 years. Sometimes I can't even look at myself in the mirror. I'm doing some more 'due dillegence' aka internet research before I call you. Kind of funny how one can make a big deal of something in your head, then you get down there with tools in hand and a couple of hours later it's done and you're like what the hek was I worried about? I guess a natural reaction, one probably shouldn’t feel good about cutting open a 10’x12’ section of deck on something as fine as a Hatteras Motor Yacht having never done anything like it before. Anyway, I feel I'm over the hump on this one – with some special thanks to you guys at HOF. I have many projects (car and house ones too) this winter and really wanted to sub this one out - so much for that. The boat is torn apart, as usual, - all the window frames are out for powder coating and new glass and I cut the teak main salon door entry open to get old fridge out/get same size one back in. Golden rule this winter project season is if it doesn't come out fairly easily, there is still something holding it down so don't pry it out, just cut some more - too much fine teak and soft aluminum in the mix for my taste, use to cast iron and copper cable from prior seasons. Wish I had more time to spend in yard, but you know with this economy and all everybody's got to do more with less. I’ll keep posting and asking questions as I make progress and will throw up some pictures at some point. My photobucket account keeps crapping out when I try to upload, so I need to find a different site.

[Triskele]

You cant use treated plywood. It wont bond with the resin

Scott...

Do you recommend Marine A/B fur? If not, which marine plywood?

[jim rosenthal]

I think you would want real marine plywood, which is made of hardwood veneers and waterproof adhesive- the stuff they build hulls out of. This would come from a specialty wood supply place, not HD or Lowe's. A half-inch thick chunk of that might have eleven or twelve veneers in it, laminated under pressure, and yes it will bond with epoxy.

[Boatsb]

3 layers of 1/4 luan will yield abut one inch with a layer of Mat in between. The marine version will saturate through with a slow epoxy and be completely sealed if you do it right.