Fiber Cloth on new Wooden Hull

[teoman]

Fiber on wood is ggetting quite common..

I am currently building a 36' lobster boat. The hull is made from 2 layer of strip plank chestnut wood (each 0.5 inch width), nailed and epoxied together.

People over here recommended that I should epoxy the inside without cloth.(not required for structural reasons, just to protect the wood they say.)
And they recommend a fiber glass sheating of the hull on the outside with cloth.

I am worried a little doing it on both sides. Can anyone give an idea ??
The boat is being built brand new.
Also the fiber coathing on the outside is not reuqired for structural reasons.

thanks for your help..

[lewisboats]

What does the designer spec for coatings?

[gonzo]

A cloth of 10oz or so will make the surface more abrasion resistant. If you epoxy one side you should do the other too.

[teoman]

Actually the designer, neither the planss reflect any need for fiber coating inside or outside. It would be purely for protecting thee wood, if does really protect ??

I understand that an old boat may need it, but is it still the case for a new hull ??

[alan white]

Can you better describe the construction? Is this a typical double-planked carvel hull?

[Ilan Voyager]

In fact as the planks have been glued with with epoxy (excellent glue, but it does not stand wood swelling) epoxy "encapsulation" inside and outside to keep the wood dry is mandatory.

Inside 3 coats are sufficient, outside it's better to add resistance abrasion with glass 6 or 10 oz. The glass has another advantage; it permits to control the thickness of the epoxy coat.

[alan white]

How wide are the strips? and do the strips simply stagger seams (both fore and aft, but offset), or does one layer go at some different angle? And what kind of framing lies against the hull? How closely spaced, what fasteners, and so forth. In other words, if you are going to get some advice that makes sense, you'll have to carefully describe the construction method.

[teoman]

Thanks for your feedbacks. Here are some pics of the boat, and the construction type. The thickness of each layer is 0.5 inch. Epoxied togetheer.

[alan white]

This is a kind of updated double-plank method combined with a variation of cold molding, with the frames as the tensile element. The right wood (I know nothing of your planking material except to say chestnut must be like oak (?), and I'd not use a hardwood in such a construction, but rather pine or cedar or some similar softwood. the softwood could be made into wider planks than hardwood---- if using hardwood planks, how wide are you going?
Maybe it's my ignorence, but is this an accepted method in Turkey? Again, I can't comment on Turkish wood varieties.
obviously, glassing the inside is not feasable, but the exterior could be done for abrasion resisance and some tensile contribution in addition to the frames. This is based on the total encapsulation of the planking in epoxy, with epoxy between the layers as well.
Not a bad method with the right wood.

[teoman]

Thanks. Yes chestnu is like Oak, it is quite hard compared to pine. It has a much longer life.
It is quite expensive, and used mostly on large wooden yacht. It gives very low humidity.
It is mainly used here in Turkey.

May I ask one more thing. If I glass the outside, with time, isn't it going to crack and maybe alow water to go through and create problem ??

[alan white]

Well this is what I'm talking about. I've asked what the planking width is, but you haven't said. I would not be comfortable using chestnut as a planking material on that construction. As I said, I would prefer a wood like cedar.
I don't think chestnut is a good choice for an encapsulated planking material of any width but especially for normal plank widths of over 100mm.
I can well imagine using chestnut where the planks are allowed to swell and shrink. Hardwoods have successfully been used for hundreds of years for planking material.
However, it sounds like you've been thinking about taking a tried and true construction method and attempting to modernize it by encapsulating it with epoxy.
While some hardwoods might work in this situation, an oak-like wood is probably too hard to carry over into an encapsulated hull design. Spanish cedar or luan or various other cedars would be more ideal, and the hardness of the hull could be achieved by a couple of layers of heavy glass cloth.

[alan white]

Originally Posted by teoman

Thanks. Yes chestnu is like Oak, it is quite hard compared to pine. It has a much longer life.
It is quite expensive, and used mostly on large wooden yacht. It gives very low humidity.
It is mainly used here in Turkey.

May I ask one more thing. If I glass the outside, with time, isn't it going to crack and maybe alow water to go through and create problem ??

Regarding cracking, this is what I mean when I suggest a soft wood, as softwood are far less apt to crack the glass skin. I'm sure the chestnut lasts well when caulked in the traditional way, but you are talking about using epoxy, so it's possible that the epoxy/glassed hull would last a very long time with very little maintainance. that is, if you use the right core wood.

[Ilan Voyager]

The boat is made, so a discussion about the wood to use is pointless now. I do repeat, the epoxy as glue on wood has a major drawback: the glue lines do not withstand the stresses made by wood changes of dimensions by the effect of humidity.
It's why epoxy glue cannot be used on laminated beams left unprotected (or just painted) in exterior conditions.
Resorcinol has not this problem, and it has been used successfully on simply painted boats.
So the boat must now be completely coated with epoxy, one of best known water barriers, for stabilizing the wood.

You'll find very useful information in the Forest Products Laboratory internet site
http://www.fpl.fs.fed.us/search/index.php
and make a search with the word epoxy.

To get the task done you have 2 directions:

1-Use a a true naval epoxy resin for wood with 2 main characteristics;
-About 1000 centipoises of viscosity with only reactive diluent. Thus you won't never use solvents that degrades the impermeability of the epoxy. And the resin is fluid enough to penetrate the wood without need of dilution. Heating is the best solution to lower the viscosity of a resin. Such fluid resins are a pleasure to use.

- A minimum of 5 % of max elongation so the resin won't crack or to be prone to micro-fissuration.
A lot of epoxy resins have only 2% elongation; that's not enough, the resin will crack.
As the resin is used as "sealer" the ultimate resistance is of little importance, but no-brittleness is of great importance. The no-blushing quality and the easiness of sanding are primordial. They do save a lot of hard work. Greasy surface and clogged sanding paper are a pain.

The inside of the boat will be too difficult to cover with fiberglass. 3 "thin" coats on all surfaces are a good measure. An extra coat in the bilges is not a luxury. It's better to leave the epoxy resin without finishing paint in the bilges, so any infiltration of water in the wood will be immediately visible as the wood darkens when wet.

Outside you can use fiberglass (but it's not mandatory) 6 or 10 oz, in satin weave so it's highly deformable to follow the contours of the boat without wrinkles and the weave is very small, easy to fill. It's pretty expensive but 2 coats of a 6 oz satin is very effective and long lasting.

The glass has 3 main advantages; better resistance to small knocks and abrasion, impedes the cracking and checking, and more important it permits to control the thickness of the epoxy coat. It's primordial to have an even epoxy coat on the outside. It's highly counseled to use at least 4 to 6 coats of epoxy under the waterline.

2- To be sure and eventually to improve the adhesion of the epoxy on the wood as your planks seem to be rather large.
I have no idea of the behavior of the wood you have used with epoxy as I have no experience with it.
I would check the adhesion of the epoxy by using 2 simple and cheap tests: one of peeling with fiberglass, one similar to the test used for the adhesion of paints on a substrate.

It's very probable that the results will be satisfactory.

If not, you may have four causes (separate or combined)
- too nice and fine sanding. The pores of the wood are clogged with a very fine dust and the resin won't penetrate. Easy solution; rougher sanding, open pores and a good vacuum cleaning. Epoxy needs some teeth to grasp on the wood.
- wood too dense. That seems unlikely, but it happens with some very dense tropical woods.
- wood oil or resin. For example Teak is a wood known to be difficult to glue. A good cleaning with a suitable solvent will probably solve the problem.
- very acidic wood like some oaks. Epoxy resin is very basic, I mean the PH is pretty high and sometimes on a very few woods the chemistry between a very acid wood and the basic resin is not good. That's more difficult to solve.
A cleaning with monoethylene glycol diluted at 50% with water gives often good results.

In short words the advice given by your fellow countrymen was good: resin inside, glass and resin outside.

[alan white]

I didn't get that the boat was already planked,Ilan, but if so I apologize to the builder for misunderstanding the situation.

[Ilan Voyager]

Alan, I made almost the same mistake... when I saw the pic of the planking I understood that the planking was already done. I doubt that in Turkey (very beautiful country, excellent food and the Izmir wines are marvels) Teoman would find the soft woods at a affordable price. So he used a local and affordable wood.

After seeing the Model (1).pdf I would suggest to use the fiberglass cloth with a angle of around 45°. That improves the strength of the glass-epoxy coat, as two stands of fiber will cross on each glue joint.

The delicate point is the chine where glass fiber is mandatory with great care. Epoxy resin alone won't last. Such angles around 90° are delicate to finish.

If using a 5 to 6% elongation resin the finish will last without problems, the resin being enough flexible. Most good European naval epoxy resins are of this quality.

The lines, and structure shown in the PDF look very similar to Italian runaboats made in the 60's in plywood.

A "brutal" but strong way to cover the angle is to use stainless steel sheet 0.45 to 0.6 mm thick glued with polyurethane and screwed. It asks for some good craftsmanship to get a nice result.