Must keep the mast from coming down (fiberglass)

[Project_Mayhem]

I was starting to see spider cracks around the mast step so I cut away the fiberglass skin and as expected I found wet and rotten wood underneath. I have it 95% cleaned up to re-glass it. It was 1/2" plywood under the skin with no filler that I could see. I'm familiar with different techniques but my question is which one to use?

I figured I'd pour some thickened epoxy into the cavity, then plywood, perhaps a layer of 1708 and then gelcoat? Or should I skip the 1708 and use all thickened epoxy and gelcoat?

I'm familar with the execution but I'm not sure which materials would be appropriate for this application

 

[dlochner]

So that we are clear on the situation a photo would be helpful.

After all the rotted and wet wood is removed, I would use a piece of well sealed plywood (marine or cabinet grade) or a piece of G10 as a core. set the core in a bed of epoxy thickened with an adhesive filler (can never remember the West System numbers) and then build up the top skin with something like 1708 to a thickness equal to the original top skin. Gelcoat or paint to protect the epoxy.

Thickened epoxy will be too brittle to use alone.

 

[Project_Mayhem]

Thanks Dave. What's the advantage of sealing the plywood beforehand when it's going to live in thickened epoxy? Absortion of unthickened epoxy?

 

[dlochner]

Thanks Dave. What's the advantage of sealing the plywood beforehand when it's going to live in thickened epoxy? Absortion of unthickened epoxy?

If you warm the plywood first, it will drive moisture and air out of the wood, coat it with neat epoxy and as it cools the epoxy will be sucked into the wood. This will provide a better bonding surface for the thickened epoxy that will be used to set it into the boat. If the epoxy completely cures, be sure to wash the amine blush off the wood and to roughen up the surface. If the epoxy is only partially cured, the thumbnail test, when it is set into the thickened epoxy it will form a chemical bond which is stronger than the mechanical bond that will form when if the epoxy has been allowed to cure.

 

[Project_Mayhem]

Dave, I know you've said otherwise but you could easily write a book on fiberglass repair. Your answers are logical, straightforward and very easy to understand. As always, thank you for your wonderful advice!

 

[jssailem]

An alternative to plywood (marine plywood - no voids) is Coosa Board. It is a composit. Strong. light weight. Less porous than plywood. Bonds well with epoxy. Andy at "Boatworks Today" used it to rebuild the transom on his Bertram speed boat. He used it in place of plywood.

 

[dlochner]

Dave, I know you've said otherwise but you could easily write a book on fiberglass repair. Your answers are logical, straightforward and very easy to understand. As always, thank you for your wonderful advice!

Thank you. The book to read is West Systems Manual. That's where I've learned most of what I know. I'm sure you can afford to buy it without breaking the bank.

Home | WEST SYSTEM Epoxy

The home of WEST SYSTEM marine-grade epoxy resins and hardeners for boat building, boat repair, home repair, and restoration.

www.westsystem.com

 

[Project_Mayhem]

When is it appropriate to use cabinet grade instead of marine grade?

 

[dlochner]

There are 2 big differences between regular ply and marine ply, the number of plies and the number of knots and voids. Marine ply has more plies, 5 to 7 and no knots or voids. Regular ply wood has 3 to 5 plies and may have knots, voids, or filled knots. Cabinet grade has 5 plies and may have a few small knots, but no voids.

More plies makes the plywood more stable and less likely to warp. Void free adds strength.

For things like bulkheads and cabin soles, items that are structural it is probably better to spring for marine grade. For non structural items, cabinet grade is fine. I've used it to make mounting blocks to mount things to the fiberglass hull or for cabinet faces, like at the Nav station when I replaced some electronics. It can also be used for shelving. And I would not hesitate to use it in your mast repair.

 

[Project_Mayhem]

I've read that marine grade is made with glue that has better moisture resistance than standard plywood. Is the same true for cabinet grade?

 

[dlochner]

I've read that marine grade is made with glue that is more moisture resistant. Is the same true for cabinet grade?

I've heard both, it is different and it isn't significantly different. If the plywood is epoxy coated, it shouldn't make any difference. I suppose I could test it by putting a piece in a bucket of water. There is some scrap in the basement, maybe I'll do that.

 

[Project_Mayhem]

I'll be using some leftover marine plywood I have on hand, but that's good to know. My local home depot has 68 sheets of cabinet grade in stock and it's only $55!

 

[jssailem]

Good price on plywood. Likely to work fine for a few years. How long do you think you will own the boat? Marine Plywood will extend that life time.

 

[Project_Mayhem]

Hopefully only a couple more years. We went to the yard a couple of weeks ago, took one look at the amount of work needed, we both felt overwhelmed, walked around looking at other boats and went home

 

[Timm R Oday25]

I've been there myself in feeling overwhelmed . Our boats are supposed to be a stress reliever ..not a stress inducer . There have been times ,I've second guessed mysefl as to whether or not I should have bought a boat or a motorcycle . After the task is completed it makes it harder for me to step away from it .
Early in my ownership ,I installed the rudder before launching . As I was backing the boat down the ramp , the rudder caught the concrete ramp and broke the transom in half . I was just sick with dread ,when the first boatyard quoted me $6000.00 to fix it . THat was $500.00 more than I paid for the boat . For a week I worked under the cockpit rebuilding the transom from the inside . It was dark ,cramped ,cold and the expoxy fumes made for a week I'll not soon forget .

 

[dlochner]

Hopefully only a couple more years. We went to the yard a couple of weeks ago, took one look at the amount of work needed, we both felt overwhelmed, walked around looking at other boats and went home

We all get that way sometimes. This spring I have several major projects on my own boat that must be done before we head off on a long cruise while prepping a volunteer crew to work on a 65' schooner that I'm overseeing a major refit of. Stress and big projects are staring me in the face.

The approach I take is to find some part of the job that I can complete quickly and easily. Once I get started the motivation returns.

How do you tackle a big boat project? Just like you eat and elephant, one bit at a time.

 

[Project_Mayhem]

I've been there myself in feeling overwhelmed . Our boats are supposed to be a stress reliever ..not a stress inducer . There have been times ,I've second guessed mysefl as to whether or not I should have bought a boat or a motorcycle . After the task is completed it makes it harder for me to step away from it .
Early in my ownership ,I installed the rudder before launching . As I was backing the boat down the ramp , the rudder caught the concrete ramp and broke the transom in half . I was just sick with dread ,when the first boatyard quoted me $6000.00 to fix it . THat was $500.00 more than I paid for the boat . For a week I worked under the cockpit rebuilding the transom from the inside . It was dark ,cramped ,cold and the expoxy fumes made for a week I'll not soon forget .

I did a partial transom rebuild last spring after water had dripped out the gudgeon bolt hole as I tightened it down (we tore one apart in a storm). Being cramped in that space with a grinder was bad. I also rebuilt the the deck upto the anchor locker "partition". Now that was a grueling experience I will never forget. I learned a valuable lesson - full face masks are leaps and bounds better than half face, even if it is Chinese made

The approach I take is to find some part of the job that I can complete quickly and easily. Once I get started the motivation returns.

Amen to that! There's nothing more motivating than a purring engine that was once dead or a glossy hull! Ok well maybe a stinky head but that's not positive motivation.

As you can all see by the number of threads I've started this week, the motivation has returned. I'm currently working on the mast step and its wiring, a flooring project and some engine work. I switch between them as I wait for parts or advise/research.

 

[Barnacle Bill]

I would get rid of the plywood. That is old school. It would be better to have solid fiberglass under the mast built up with resin and woven roving for strength and then finish the top layers with matt and cloth for smoothness and of course the finish before gel coat would be a fiberglass putty for fairing, but not strength. I wouldn't even use epoxy. I'd use polyester fiberglass (that is what the boat is made out of). There is some incompatibility with gelcoat over epoxy. Not so with polyester and it is plenty strong. Everyone thinks epoxy is the means to all boat repair. I sell West System and I have done fiberglass repair for decades. That is my 2 cents.

 

[Project_Mayhem]

Plywood will probably outlast the boat and is faster to install than building up than mat or cloth

 

[dLj]

When is it appropriate to use cabinet grade instead of marine grade?

Cabinet grade is not recommended. If using non-marine grade, then you should use a grade rated for exterior use. Exterior grade plywoods that get epoxy encapsulated will perform on a par with marine grade plywood.

Plywood aimed at interior applications do not have glue that withstands moisture well at all. Get a small inhomogeneity in your epoxy and you are loosing your glue layers.

dj