Alternative to fiberglass for a Caledonia Yawl

[gonzo]

As for fiberglassing, why would it turn the boat ugly?

Because it it a lapstrake. The edges, instead of being crisp lines would an s-shaped curve. It makes no sense to fiberglass a lapstrake. However, beauty is in the eye of the beholder, so it is just my opinion.

 

[rnlock]

People used to seal boat decks with cotton, and build canoes that were sealed with cotton. I wonder if other fibers were used. If your friend doesn't want to use fiberglass, that might be an eco friendly alternative. Or not. One would have to compare the impact of industrial farming with that of fiberglass manufacturing. Cotton dust causes brown lung, though. In any case. One could look up how the fabric was used on decks and canoes.

In my experience, very light glass, maybe 30 gsm, with epoxy, followed by paint, can prevent plywood checking for many years. At least if you repair any dings before water can get in. The one exception was a plywood work bench I have, which was level, was outdoors in the weather, and had various objects sitting on it. Incidentally, 1/2" plywood vacuum bagged* either side of 2" XPS on makes a very sturdy, strong workbench surface that's still light enough to carry around.

Someone mentioned tar. We used to use pine tar, applied with a torch and a rag, as the base coat on the bottom of wood cross country skis. I wonder if it would bind plywood well enough to prevent checking and how well it would work as a primer or even a complete finish.


*Nothing high tech. Just Gorilla glue and a household vacuum.

 

[laukejas]

Because it it a lapstrake. The edges, instead of being crisp lines would an s-shaped curve. It makes no sense to fiberglass a lapstrake. However, beauty is in the eye of the beholder, so it is just my opinion.

Okay, I see. I thought that if one uses the method that Rumars suggested (trimming off each glass strip at the sharp edge of the lapstrakes), one could preserve these edges without rounding them over.

People used to seal boat decks with cotton, and build canoes that were sealed with cotton. I wonder if other fibers were used. If your friend doesn't want to use fiberglass, that might be an eco friendly alternative. Or not. One would have to compare the impact of industrial farming with that of fiberglass manufacturing. Cotton dust causes brown lung, though. In any case. One could look up how the fabric was used on decks and canoes.

In my experience, very light glass, maybe 30 gsm, with epoxy, followed by paint, can prevent plywood checking for many years. At least if you repair any dings before water can get in. The one exception was a plywood work bench I have, which was level, was outdoors in the weather, and had various objects sitting on it. Incidentally, 1/2" plywood vacuum bagged* either side of 2" XPS on makes a very sturdy, strong workbench surface that's still light enough to carry around.

Someone mentioned tar. We used to use pine tar, applied with a torch and a rag, as the base coat on the bottom of wood cross country skis. I wonder if it would bind plywood well enough to prevent checking and how well it would work as a primer or even a complete finish.


*Nothing high tech. Just Gorilla glue and a household vacuum.

Very interesting. In fact, that friend of mine used a cotton cloth with polyurethane paint (paint, put down cloth, paint over) on his old Finn's deck that I mentioned. Also did the same with varnish in a lot of places instead of paint. That boat is nearly 40 years old now, and is still in great shape. He said the cloth can be peeled off if necessary, it doesn't grip as well as epoxy+glass, but still, I was surprised this is at all possible. Probably not a good idea under the waterline though. As for tar, well, I've searched for any long-term experiences using it with plywood, but couldn't find much...

 

[baeckmo]

Hi, nice build, uplifting to see original craftmanship. I think it should not be paired with "modern chemistry"; here an alternative:

On the Swedish side of the Baltic (the "Roslagen" area) a mix of equal parts of light tar plus raw linseed oil and balsam terpentine, called "Roslagsmahogany", is used for anything outdoors, boats as well as furniture and buildings. It is said to work with birchplywood as long as the ply glue is waterresistant. You just oil the surfaces as long as they swallow; extra care with end wood. Redo when surface looks "dry" after use.

Tar is preventing bacterial- and fungiattacks, the terpentine is reducing the tar viscosity for better penetration, the raw linseed oil has low viscosity and is wetting deeply and it swells when oxidizing (closing open cell structures), which prevents moisture entrance. Allow to dry (linseed oil takes some time to oxidize) before launching. Good Luck!

 

[laukejas]

Hi, nice build, uplifting to see original craftmanship. I think it should not be paired with "modern chemistry"; here an alternative:

On the Swedish side of the Baltic (the "Roslagen" area) a mix of equal parts of light tar plus raw linseed oil and balsam terpentine, called "Roslagsmahogany", is used for anything outdoors, boats as well as furniture and buildings. It is said to work with birchplywood as long as the ply glue is waterresistant. You just oil the surfaces as long as they swallow; extra care with end wood. Redo when surface looks "dry" after use.

Tar is preventing bacterial- and fungiattacks, the terpentine is reducing the tar viscosity for better penetration, the raw linseed oil has low viscosity and is wetting deeply and it swells when oxidizing (closing open cell structures), which prevents moisture entrance. Allow to dry (linseed oil takes some time to oxidize) before launching. Good Luck!

Thank you very much for the suggestion! Perhaps you know, what is the life expectancy of plywood treated like this, assuming typical boat use (most of the time in the water, lifted out in winter)?

 

[gonzo]

Okay, I see. I thought that if one uses the method that Rumars suggested (trimming off each glass strip at the sharp edge of the lapstrakes), one could preserve these edges without rounding them over.

The edges is were plywood fails first.

 

[baeckmo]

The edges is were plywood fails first.

...yes, and the end-wood for homogeneus wood, if not treated correctly. I can't give a life expectation for ply, but last year I wrote off a cheap (as in galvanized nails) pine lapstrake double-ender aged about fifty. Ribs had been smashed beyond repair when grounding on an underwater stone fence, but the planking was still mostly intact.

I think what kills the ply is bad end preparation and in our climate zone if the boat is pulled out too late, not having time to dry out properly before freezing time. Once splitting is initiated, new layers are open to air and water, which is jummy-jum for bacteria and fungi. I have an old "koster" (a traditional double-ender) in oak held together with juniper plugs. She is now 113 years old, hull treated similar to the "Roslagen soup". Twenty years ago, she was hauled too late, and some oak had to be swapped. It is actually "delaminating" along the annual growth-rings when the remaining internal water is freezing. I associate that (peraps wrongly...!) with the decay of plywood.

 

[laukejas]

...yes, and the end-wood for homogeneus wood, if not treated correctly. I can't give a life expectation for ply, but last year I wrote off a cheap (as in galvanized nails) pine lapstrake double-ender aged about fifty. Ribs had been smashed beyond repair when grounding on an underwater stone fence, but the planking was still mostly intact.

I think what kills the ply is bad end preparation and in our climate zone if the boat is pulled out too late, not having time to dry out properly before freezing time. Once splitting is initiated, new layers are open to air and water, which is jummy-jum for bacteria and fungi. I have an old "koster" (a traditional double-ender) in oak held together with juniper plugs. She is now 113 years old, hull treated similar to the "Roslagen soup". Twenty years ago, she was hauled too late, and some oak had to be swapped. It is actually "delaminating" along the annual growth-rings when the remaining internal water is freezing. I associate that (peraps wrongly...!) with the decay of plywood.

Okay, thank you - but as I understand, this method is probably not compatible with painting the hull? My friend does intend to paint it; perhaps I should have emphasized on this before..

 

[rnlock]

Okay, thank you - but as I understand, this method is probably not compatible with painting the hull? My friend does intend to paint it; perhaps I should have emphasized on this before..

You can paint over linseed oil, though you might want to wait a while. You've probably seen that around the edges of many old windows. I think glazier's putty is made with linseed oil. "Boiled" linseed oil is supposed to harden faster than raw linseed oil. It's not really boiled these days. There's a chemical added that hastens the cure. Raw linseed oil can get moldy. I think it can even turn black, though that may not actually be a bad thing. Unless a couple of boats I've seen were actually treated with something like baeckmo's Roslagsmahogany. I made a kayak paddle that surprised me by turning grey. Maybe a few more coats would make it black. Incidentlly, I think flax seed oil is food-grade linseed oil. I stopped taking the stuff, but an occasional burst capsule does nice things for our cutting boards.

I don't know if you can paint over tar. Tar is a vague term which can cover many things. Come to think of it, I think I have a can of roofing tar that says you can paint over it after a couple of months. Maybe the chemical in "boiled" linseed oil would make it set up sooner, or maybe some "japan drier" would. I imagine those chemicals may be nasty, but probably no nastier than oil paint. I expect pine tar would set up on it's own, judging by what happens to pine sap that leaks out of a tree. Can you still buy pine tar, though? The last time I got some was many years ago.

If linseed oil can prevent checking and damage to the edges of plywood, that would be handy. There's some plywood on the outside of my garage, and linseed oil could be more convenient than light glass if I make another plywood boat.

 

[laukejas]

You can paint over linseed oil, though you might want to wait a while. You've probably seen that around the edges of many old windows. I think glazier's putty is made with linseed oil. "Boiled" linseed oil is supposed to harden faster than raw linseed oil. It's not really boiled these days. There's a chemical added that hastens the cure. Raw linseed oil can get moldy. I think it can even turn black, though that may not actually be a bad thing. Unless a couple of boats I've seen were actually treated with something like baeckmo's Roslagsmahogany. I made a kayak paddle that surprised me by turning grey. Maybe a few more coats would make it black. Incidentlly, I think flax seed oil is food-grade linseed oil. I stopped taking the stuff, but an occasional burst capsule does nice things for our cutting boards.

I don't know if you can paint over tar. Tar is a vague term which can cover many things. Come to think of it, I think I have a can of roofing tar that says you can paint over it after a couple of months. Maybe the chemical in "boiled" linseed oil would make it set up sooner, or maybe some "japan drier" would. I imagine those chemicals may be nasty, but probably no nastier than oil paint. I expect pine tar would set up on it's own, judging by what happens to pine sap that leaks out of a tree. Can you still buy pine tar, though? The last time I got some was many years ago.

If linseed oil can prevent checking and damage to the edges of plywood, that would be handy. There's some plywood on the outside of my garage, and linseed oil could be more convenient than light glass if I make another plywood boat.

Okay, we can get some boiled linseed oil here. Is any paint compatible with it, or just specific kinds? Typically you want to remove any oils from surface before painting, so this is confusing me... Can any paint really stick to linseed oiled plywood? What kind of surface prep is required? Same goes for tar.

If this indeed offers better protection than epoxy or epoxy+glass, it would be a great option. But I hope someone can confirm this - like I said, my friend is open to making samples to test out various coatings, but we don't know of any way to make an accelerated longevity test to know how well would that method protect this plywood boat over several decades. If we mess up and go the wrong route, and the boat starts to mold or rot in a few years, it might be extremely laborious or even impossible to switch to another coating...

 

[wet feet]

Boiled linseed oil would add some durability but I would have more faith in the Deks-Olje D1 and a subsequent coating of D2,which I suggested a while ago.I have little doubt that oil will penetrate better than a polymer with a cure time of a few hours and it will have more flexibility.
Perhaps the boat should have been converted to traditional plank on frame at the planning stage as most places have some kind of trees and the repair process has been understood for centuries.I have repaired a glued clinker hull but won't mind if I never do so again,undoing screws and removing roves isn't so bad.

 

[baeckmo]

Okay, we can get some boiled linseed oil here.

That's not what I said; it should be the raw (=unboiled) linseed oil! Raw and boiled oil behave differently when curing/hardening. Painting is done with traditional paints, based on linseed oil, that goes together with the mix stuff.

 

[laukejas]

Boiled linseed oil would add some durability but I would have more faith in the Deks-Olje D1 and a subsequent coating of D2,which I suggested a while ago.I have little doubt that oil will penetrate better than a polymer with a cure time of a few hours and it will have more flexibility.
Perhaps the boat should have been converted to traditional plank on frame at the planning stage as most places have some kind of trees and the repair process has been understood for centuries.I have repaired a glued clinker hull but won't mind if I never do so again,undoing screws and removing roves isn't so bad.

Thank you, we do have D1 and D2 available (pricy but doable). Thing is, they specifically say it is meant to be used above the waterline. What do you think of that? As for planking instead of plywood, yeah, but that would make the boat several times heavier, and to make a plank boat last decades, you need to put a lot of work on it every season...

That's not what I said; it should be the raw (=unboiled) linseed oil! Raw and boiled oil behave differently when curing/hardening. Painting is done with traditional paints, based on linseed oil, that goes together with the mix stuff.

Sorry, I misread it! Okay, we'll try this as well. Many great suggestions on this thread. I only wish there was some way to compare all these methods, using epoxy+fiberglass as a baseline, to put it all in perspective on how much longevity each provides in comparison. Like I said, we will test everything we can, but testing for longevity when we're talking about decades might be impossible to do in short term. Not sure how to do an accelerated test...

 

[gonzo]

As for planking instead of plywood, yeah, but that would make the boat several times heavier

Solid wood of the same species is lighter that plywood. That is because glue is denser than wood.

 

[laukejas]

Solid wood of the same species is lighter that plywood. That is because glue is denser than wood.

True, but isn't thin wood more susceptible to splitting and damage per same weight or thickness? For example, I've built all my boats with 4mm plywood; I can't imagine solid planks of 4mm holding up without glassing at least. Even 6mm would probably be too thin if we go for the same density rather than same thickness. The thinnest I've seen was 10mm I think, in strip builds, but they again rely on fiberglass. Feel free to correct me, I might be completely wrong here as I've ever only used plywood for hulls (really wish we could get some low-density Cedar here in Lithuania for a strip plank build... Zero chance though).