Some help, please, with a balsa wood problem.

[onenomad]

I sure could use some input on a replacement material for saturated and rotten balsa planks. While doing a transom/cockpit deck repair, I noticed some seepage from what I thought was the hull laminate. It turned out that my boat has 1/2", vertical grain, balsa planks, laid fore and aft between the stringers and lifting strakes. They are/were covered with mat. I am in the process of cutting them out now. My question is; is it necessary to replace them with another material, or will foam be sufficient? The balsa is laid directly over the hull woven roving. I could put another layer of roving down, or just use foam. What do you think? The boat is a 21', outboard powered.
Thanks,
Gerry

 

[flounderman]

Re: Some help, please, with a balsa wood problem.

Gerry, I encountered 1/2" balsa core in my boat when doing my re-build. Get rid of the stuff. It runs from bow to stern. The balsa is used as a spacer to seperate a 2nd thin layer of mat/glass to form a structural member. It is there to give stiffness to the bottom, yeah sure, but when it gets wet it dissolves, kinda, and offers no support at all. You have other options for a replacement. Back to my tenure in the boat shop, you can add additional layers of mat & roving. Now this method adds weight but not that much. think about it and if you want to do more layers of mat/glass I will tell you wat to do and not do. Back when we were kids all fiberglass boats were a solid 3/4" thick or more, now they are 3/8" with balsa core. Jerry

 

[onenomad]

Re: Some help, please, with a balsa wood problem.

Jerry,
Your experience in the boat shop would be great. I would be happy to do a build-up w/o wood.
Thanks,
Gerry

 

[SgtMaj]

Re: Some help, please, with a balsa wood problem.

Or you can replace it with foam... balsa and foam are faily equal materials, except that balsa stands up better to chemicals and foam stands up better to water. But weight, stiffness, and support are all comparible.

 

[flounderman]

Re: Some help, please, with a balsa wood problem.

If you do not have a source for all your materials contact Fiberlay in Seattle, they may have a dist. in your area. Next thing is to map out the bottom of your boat, all dimensions, lengths - widths etc, where ever it breaks a flat plane. What you want to do is make a lay up schedule. You will cut your materials in manageable sizes. Better yet if you have a PO box I can make sketches and mail them to you. All this may seem like a lot of work but it is worth it. I have a engineering/construction background and I believe in making it strong. Jerry

 

[onenomad]

Re: Some help, please, with a balsa wood problem.

Jerry,
Sent you a PM with my mailing address. When my wife and I started our sailboat cruise, we layed over in Blaine from Oct, 01 to May,02. COLD winter. We were in Port Browning on N. Pender Is. when the 9/11 attack took place. We were heading to Mexico, and moving from one country to another got a little difficult for awhile. Looking forward to your input on the repair.
Thanks,
Gerry

 

[flounderman]

Re: Some help, please, with a balsa wood problem.

Gerry, give me a day or two and I will get something off to you. In the mean time can you up-load a few more pictures of the inside of your boat from the stern to the bow shooting down and thru the motor notch? Jerry

 

[onenomad]

Re: Some help, please, with a balsa wood problem.

OK, Jerry, I will upload some Saturday.

 

[flounderman]

Re: Some help, please, with a balsa wood problem.

It will be Saturday in 12 minutes. Englund Supply may have what you need. Is that where you shop? Jerry

 

[onenomad]

Re: Some help, please, with a balsa wood problem.

Yes, Englund Marine, I have done business with them for a number of years. Also, I was planning on using epoxy, rather than a polyester resin. I have had good luck with that in past projects.

 

[flounderman]

Re: Some help, please, with a balsa wood problem.

Gerry, There is a book you need to buy. It is "FIBERGLASS BOAT REPAIR & MAINTENANCE" by West Systems [not West Marine]. This book will guide you thru it all. It is available at West Marine or maybe Englund, $5 - $10. But, do not use their transom replacement method. Now if all the balsa core is not bad you can piece it back with slabs of 1/2" urethane foam insulation. Just skin the foil from it cut to size and apply thickened epoxy to bed ,weight it down with a piece of 2x4 let it set for a while and then do layers of glass. Mat will not work with epoxy. I learned with polyester and my boat is made of polyester so I stuck with it. No doubt epoxy is better , but. Jerry

 

[onenomad]

Re: Some help, please, with a balsa wood problem.

flounderman
Jerry,
OK, I ended up removing everything down to the hull roving. The hull was lined with end-grain balsa and matted over. Every piece was soaking wet/rotten. Even the lifting strake reinforcements were installed on top of the balsa, and they had deteriorated also. I guess in some ways, this might make it easier. At least everything is accessible now. You mentioned urethane foam. Do you think that is still an option?

 

[BillP]

Re: Some help, please, with a balsa wood problem.

I rebuilt a vintage glass boat bottom with a ply core...with epoxy. This was a total rebuild of rotten stringers, floors and transom. First of all I'd use ply instead of foam...it's easier and stronger and my boat showed it's a good method. Weight probably won't be an issue if you don't mind a couple extra lbs. The boat had a 1/2" ply core glassed down with only mat and the stringers sat on top. The core wasn't rotten but I had to take it out anyway just to make sure. Thinner ply could be used but I copied what was original.

After prepping the hull, I set a new piece of ply core in with thickened epoxy and let it kick before doing stringer work. Old car batteries work especially well for holding boat parts like this down. I scored the ply so it would flex enough to conform to the hull...scores were installed down against the hull. Then I tacked stringers on the ply core and glassed everything in.

Also, be aware that there IS mat made to use with epoxy. Polyester resin uses a different mat. BTW...this is glassing 101 and if a "boat shop" doesn't know this I'd be careful about relying on their glassing experience. Basically, polyester mat has a binder that holds the fabric strands together and the styrene in polyester resin dissolves the binder. Epoxy doesn't have styrene in it and won't dissolve poly mat binder. Epoxy mat has no binders that need dissolving.

Here's pics of the core with score lines...and a pic of the ply glued down with stringers tacked to it. It's a pt ply core with pt ply side stringers and pt dimensional lumber for the center stringer.

 

[onenomad]

Re: Some help, please, with a balsa wood problem.

That is what I wanted to hear and see. Your job was more complicated than mine will be. I have only 2 fore & aft "planks", one about 6" wide and one about 10" wide, one each side. I also can bed a small plank horizontally, about 2" wide in the strake pocket, with the strake vertical support on top of that. Seems like this method will surely simplify my project, and be a permanent fix. Thanks again for your input.
Gerry

 

[flounderman]

Re: Some help, please, with a balsa wood problem.

Gerry, what BillP did is good. You can use ply or urethane, the ply is stiffer but the urethane won't rot. Next question is, how long does this need to last? I am 61 so a "lifetime" warranty does not mean a lot. The strake pockets can be layered with stichbond[1708] or glass/roving. 3 layers is good. Run your stringers on top of the glass not the stiffiner. The expanding foam [floation] as some call it is as much a structural componet in the "hull to floor" void as the stiffener. It sounds like I don't need to do a layup schedule. Jerry

 

[onenomad]

Re: Some help, please, with a balsa wood problem.

Hi Jerry,
With everyones help, I think I am getting a grip on the process now. A "lifetime warranty" has an even shorter term for me, than for you. I think if I use plywood as a stiffener, I will seal it with penetrating epoxy. I've done this before, and it makes the wood "almost like a composite". I'll bed it in thickened epoxy and cover with fg cloth. I'm sure that it will last longer than I will. I believe that I will be OK on the lay up schedule. Thanks again for your help.
Gerry

 

[jbustamante1]

Re: Some help, please, with a balsa wood problem.

"Also, be aware that there IS mat made to use with epoxy. Polyester resin uses a different mat. BTW...this is glassing 101 and if a "boat shop" doesn't know this I'd be careful about relying on their glassing experience. Basically, polyester mat has a binder that holds the fabric strands together and the styrene in polyester resin dissolves the binder. Epoxy doesn't have styrene in it and won't dissolve poly mat binder. Epoxy mat has no binders that need dissolving."

Thanks very much to all of you for this thread. It helps me very much. i am new in this art and I would like some clarification on the above paragraph.
What kind of epoxy was used to glued the ply to the fiberglass?

What do you think about adding one layer of fiberglass to the existing and then the ply using the resin as a binder?

Thanks one more time!

 

[erikgreen]

Re: Some help, please, with a balsa wood problem.

Yep, plywood as a stiffener is a good call. You can use some that's somewhat thinner than the original balsa. Basically you're changing from using a composite cored strip for stiffness to using a plywood plank, which is a perfectly valid thing to do. It'll only be marginally heavier, certainly lighter than the wet balsa was.

Glue it in with thickened epoxy, cover with a layer of cloth to protect it, done.

Erik