Pre-glassing for glued ply lapstrake?

[Jamaica Mike]

One concern I have in building a glued ply rowing boat (or power boat, for that matter) is durability and the potential for damage of the strakes and water / rot incursion.

I am thinking that scarfed, rough shaped ply strakes could be pre-glassed, then fitted and cut to final dimensions for application to the hull.

Is this practical? Will it make the boat more water and rot proof? How much will it effect the flexibility of the plywood strakes?

I was planning on CPES and paint for the interior and exterior if I don't / can't make the pre-glassing idea work.

Thanks.

JM

[imported_Steven Bauer]

Have you studied Dale's techniques at www.alistego.com (http://www.alistego.com) ? Look in the planking section. He puts the strake on, then glasses it, then cuts the bevel for the next strake to land on. I think he only does this below the waterline. He posts here sometimes, maybe he'll wander along and chime in.

Steven

[dmede]

My understanding is that most glued ply lap boats are not glassed. They may be epoxy sealed but glass is not typically used (except occasionally over the keel and garboard strakes for some extra bottom protection). If it is used it is very hard to apply after building of course, due to the shape of the planks.

In building a 15' glued ply lap canoe I have found common house paint and cheap Man-O-War varnish to be fine sealants. If the boat doesn't live in the water and is properly cared for, you don't really need to epoxy seal the whole thing, and would be wasting good money in doing so, IMO.

dave

[ 01-18-2005, 01:32 PM: Message edited by: dmede ]

[JimD]

I pre-glass plywood panels every chance I get. About the only sound reason I've ever heard for not doing it is that if the plank has to make a really tight bend at the bow there's a chance you could get minor cracks in it but my experience has shown that with light cloth ie 4 oz the fg is at least as flexable as the plywood its going on. On the other hand I recall Iain Oughtred saying in his book on ply lap boatbuilding that he has never glassed any of his plylap boats, which doesn't mean you can't if you want to for the extra protection the glass provides.

[Dale H]

Not that I'm any kind of expert or anything, but I have learnd a couple of things.

1. Lapstrake ply boats do not need glass unless the surface is prone to checking.
2. Not glassing gives you a much lighter boat. Our canoes have a couple of coats of epoxy and lots of varnish. These take abuse pretty well.
3. Glassing will help with abrasion resistance some, but adds only a little actual strength. I do this for trailer rash resistance.

The above is confirmed by some Doug. Fir samples with various finishes that I have had out in all our Canadian weather for about 5 years continuously. Maybe I shoud take a picture and share the results here?

Hope this helps.

Dale

[NormMessinger]

Pre glassing will not protect the edges of the plywood which is the most vulnerable to water penetration.

[paul oman]

different epoxies have different amounts of flex. Some brands might handle a hull curve, other might not. You can add flex to epoxies in several ways - most simple is thinning he epoxy with solvent....

paul oman
progressive epoxy polymers
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

[bheys]

I added fiberglass to the garboard and broadstrakes for some extra abrasion resistance when pulling the boat up on beaches. With a somewhat red face, I'll admit to smacking into some submerged rocks while sailing along at a pretty good clip. The glass appeared to prevent any damage.
http://www.imagestation.com/picture/sraid61/p3b1fa306971cea2e32054996de0015a9/fc3741d4.jpg

You can see how the tape keeps the glass off the plank lands on the garboards. However I did plane through some of the glass when establishing the land for the keel. I couldn't tell you if adding the glass is worth it. After all, it's pretty easy to repair any hull trauma that the fiberglass would otherwise prevent. I just happened to have the cloth on hand.

[Jamaica Mike]

Thank you for all the thoughtful responses. This boat will be used hard in saltwater around coral heads, rocks etc. It will be dragged up the beach and stored upside down in the open. I am looking for the few extra years that the glass would give me, if the glassing can be made to work. In Jamaica we have ants and termites that will eat an unprotected hull into a pile of dust and hardware in very little time.

Weight is less important than durability.

Thanks again.

JM

[JimD]

JM, as to protecting against coral or dragging onto rocky beaches you may be expecting too much from fiberglass. Also, you might wish to look at using other cloths such as dynel of kevlar which are said to provide better abrasion resistance at least for the bottom of the boat.

[imported_Steven Bauer]

Jamaica, WI as in Jamaica, mon! I thought you lived in WIsconsin! There might be a town named Jamaica in Wisconsin. redface.gif

Steven

[Dale H]

Absolutely right Norm, that's why I always add a pretty sustantial epoxy fillet along the exposed edge of the plywood.

Dale

[JimConlin]

I recollect that Robb White's boats are lapstrake, with the planks sheathed with glass before hanging.
Sounds like a lot of work, but it seems to me that glass would be of value in a lapstrake planked boat at the outer bottom edges of planks (to resist knocks), extending into the laps (to spread loads), and on plank faces that were prone to checking (only a problem with fir ply).

What say you?

[Jamaica Mike]

Originally posted by JimConlin:
I recollect that Robb White's boats are lapstrake, with the planks sheathed with glass before hanging.
Sounds like a lot of work, but it seems to me that glass would be of value in a lapstrake planked boat at the outer bottom edges of planks (to resist knocks), extending into the laps (to spread loads), and on plank faces that were prone to checking (only a problem with fir ply).

What say you?I think that, providing the details are worked out for fitting the laps, the glassing before hanging would be the easiest method. Not fast, but plank faces could be glassed, filled, sanded and primed before hanging. I am going to epoxy the planks together along the laps, and to the frames, so that no fasteners penetrate the planks.

Norm - you're right, the plank edges would need proper filling and sealing. I will be storing the boat upside down between daily useage, and rain, dirt, sand, etc. would accumulate on the exposed edge surfaces.

JM

[Cuyahoga Chuck]

I may misunderstand the method under discussion but it seems to me that planing the bed for the adjacent plank would be much more difficult if the plank was already covered with 'glass.
My planes lose their edge very fast when asked to cut thru' the glue in plywood. Hacking thru' 6 OZ 'glass would certainly make the edge go bye-bye quickly.
Since the integrety of the lap joint is derived from the closness of the fit it seem to me to be foolish to inject some hard to cut membrane into the mix when you're trying to deftly cut no more than necessary from the edge of a long thin board.
I notice that Tom Hill only covered the garboard planks on the boat in his book.
Charlie

[htom]

I thought that they were cutting and shaping the plank, planing the lap, and then fiberglassing the plank face and the lap, so that the overhanging plank would be epoxied to fiberglass, not wood.

I can't see a good way to wrap the fiberglass around the bottom of the plank to protect the edge. :(

[JimD]

I almost never take a plane to plywood. Easier to fair with a belt sander and the FG has no ill effect on it.

[almeyer]

Do a search thingy for threads on the Navigators built by Barrett Faneuf (sorry if I've butchered the name). The Navigators were built glued ply lapstrake, and used dynel on the bottom and garboard. Barrett did an excellent of building the boats (2 at once!), and she's got a very detailed ImageStation album.

[Urk]

A good way to protect the keel of a dinghy which is going to repeatedly be pulled up on sandy beaches, is to mix some carborundum powder with epoxy and paint/screed it on after the timber underneath has been well wetted out with epoxy. A neat job can be got by masking and removing this whilst the epoxy is still wet. The ONLY way to remove this mixture is with heat and a scraper. The people who run commercial kayaking businesses here do this.
Eric

[dcobbett]

I buy MAS epoxy from William Clements because he is somewhat local to where I live. He builds "Small" plus a variety of lap strake canoes. During one of my trips to his shop, he told me one of the first things he usually does is coat both sides of the sheets of ply with epoxy, and one reason for doing this is to facilitate cleanup during the building process.

[Jamaica Mike]

Originally posted by Urk:
A good way to protect the keel of a dinghy which is going to repeatedly be pulled up on sandy beaches, is to mix some carborundum powder with epoxy and paint/screed it on after the timber underneath has been well wetted out with epoxy. A neat job can be got by masking and removing this whilst the epoxy is still wet. The ONLY way to remove this mixture is with heat and a scraper. The people who run commercial kayaking businesses here do this.
EricCARBORUNDUM POWDER? I have never heard of this before. Is the carborundum / epoxy mix extremely hard when cured? Can you provide more detail on this - mixes, granularity of the carborundum, thockness of application, and who is actually using this method?

Thanks.

JM

[Steve Lansdowne]

Canoe builders sometimes mix a black powder additive with the epoxy that goes on the bottom of the boat to make that area more slippery and scratch resistant. A West System "barrier coating" product ("graphite?" -- it is black) is what they use. Is this the same thing as "carborundum?"

[JimConlin]

West System sells a graphite powder as an epoxy additive. I've used it for dinghy bottoms where abrasive use is expected and for the inside of daggerboard trunks for low friction and reduced fouling. It's also useful as a general pigment for epoxy composite parts. I've used it to color glass channels for companionway drop boards. I think it's popular for bottoms of drift boats.
For larger quantities, graphite is sold as a lubricant for planting corn. Search for graphite seed lubricant or thereabouts.

[Cuyahoga Chuck]

Carborundum is a man made grit that was invented around 1900 as an abrasive and is still used today to make grinding wheels.
Graphite is a form of the element carbon which is noted for its lubricating properties.
It is the current rage as a bottom coating mixed with epoxy. The downside is that most paints and varnishes will not stick to a graphite/epoxy composite so it must be protected by other means from the harmful effects of sunlight.
Charlie

[Urk]

The Graphite additive as sold by WEST is just that. It is black and is used to make things slippery combined with epoxy. I used it on the bottom of my driftboat and it is reasonably effective. The Carborundum is, I believe, the stuff that grinding wheels are made of. The powder that I use is blue/grey in colour and sparkles. It is the consistency of very fine sand and I generally mix it up to a viscosity that can just be applied with a paintbrush and then I use a plastic squeegee to level it. It is extremely hard and abrasion-resistant. I have attacked it with a 36 grit sanding disc and it takes a few seconds for the disc to be blunt with a barely visible whorl on the surface of the mixture. I think that this is merely the surface epoxy being removed. When I leaned on the machine it did take some mixture off but I think that the heat generated by friction softened it. As I said, many of the kayaking companies in the top of the South Island of NZ use it. A friend and I built some 43ft Wakas (Mauri war canoes) stripped and sheathed and used this below the waterlines and despite very hard usage the hulls show no sign of wear. He is on vacation so I cannot contact him for more info on where he sourced this stuff from. I get small amounts from him when I need it. I have done the keel of my kayak with this method and am very happy with it. The colour ends up a pleasant silvery grey and in the unlikely event of it ever needing to be overcoated, I guess that the suface could be softened chemically (because sandpaper won't key it very well) and recoated. The thickness of the coating ends up at about 2mm as it needs to be reasonably thick to get a high Carborundum to epoxy ratio. I thoroughly recommend this stuff but the user has to bear in mind that it cannot be sanded or shaped after it has set and it will add some weight to a boat. It also requires some vigilance as it is setting to get it smooth. Hope this is of some help.

[Jamaica Mike]

Urk:

Thanks for the additional detail on the carborundum/epoxy mix. This sounds like an excellent solution to an old problem.

When I get to this point on my little boat, I'd do some experimenting with this solution.

JM