epoxy laminate schedules

If it is traditional strip planked the traditional epoxy composite overlay does not much for structure.

The idea is abrasion resistance and as a permeability barrier.

So depending on boat size and use the thickness is varies. On a small boat of 6m / 20ft. it could be a single layer of 5 oz stain weave polyester... or E fiberglass and 0.5mm / 0.02" thick total for occasional sport use. On an 25m / 80ft. it could be just that as the small boat or a made or several layers and perhaps 3 mm / .125" thick for a work boat. It could be simply a epoxy coating without reinforcement. Usually a tight weave is used for best finish... but is harder to properly wet out. The barrier thickness needs to be at least 0.25 mm / .01" total coating thickness minimum.

I would say a nice thick coat or two of epoxy and then a layup of the reinforcement and then another thick coat. Do your primary fairing first on the wood and secondary to smooth the surface after done... before the final barrier coat. Now for technique... well that depends on how you have the hull laying... and situation of skill and facility available.

I will be happy to answer your questions Wireless if you can give me some specifics on what you have and are trying to accomplish, I build cold-moulded wood and composite boats now but started out lapstrake and strip planking and have sheathed numerous boats over the years giving them new life.

VERY interesting project Pascal! I can't say I've ever heard of Divinycell used for framing and wondered how it was fastening planking to during the build. Did you "sister" the foam with something more solid to hold the fasteners or fasten angle brackets like we do on all of our Divinycell bulkheads? Also, the use of S-glass instead of E-glass is intriguing. I've always thought about building a replica runabout using foam core/epoxy/aramid and adding a layer of wood veneer in strips for the look but never thought about combining the technologies lie you did.

Ok, the broken frames can be sistered with plywood on both sides to regain their strength, it's very commonly done and works well. Use a good quality marine grade plywood, 1/2 or 3/4" both sides and offset the joints.

If sounds like the hull is fine as it is and you aren't looking to add a tremendous amount of strength, correct? If so, then a single layer of biax weave should be sufficient overlapping at the chines/keel, 1208 and 1708 are very commonly available and often used in this situation but not the best choice in my opinion.

You will still have a certain amount of movement in the structure and the glass will move differently which often causes cracking at the glass seams. With a single layer of glass there's really no way around the problem, butt joints or overlaps which get sanded fair and made into butt joints anyway are stress concentration areas, the fibers carying the load ending at the butt joint cannot transfer the stress to the next course of cloth..

Since you are using epoxy I would suggest using two layers of a 1200 or 1700 instead and offsetting the strips of glass. The difference is in the chopped strand mat (the 08 part of the number) or lack of. Chopped mat was added to fiberglass weave mainly for polyester resins but isn't required or often desirable for epoxy. You can apply two layers of 1700 and have the same wet out thickness and weight as a single layer of 1708 but double the strength of the laminate and stresses will travel interlayer across seams much better. Using a weave with different axis orientation (0/90* vs. +/-45*) for one of the layers is another good idea and would further distribute stress. It is an additional step but can be done at the same time to save some effort once you get used to it, having a thinner viscosity resin also helps but not so thin as drainout becomes a problem.

You really shouldn't "replace" framing with an additional inside skin, sistering them will be sufficient. A problem many sheathed boats have is water being trapped on the inside causing rot. Since you have access now, I would at the minimum thoroughly epoxy coat everything, at least two coats and fill any and all voids/cracks in grain to seal it up completely. Glassing the inside of a framed boat is a ROYAL pain and a lot of work. You have to round over all the framing, pull fillets in all the inside corners first and keel/chine/floor frame bolts can be a nightmare. If you don't (and most don't) glass inside at least seal it as best you can and install a dripless shaft seal if it has one. Keeping the bilge dry is essential to long life once it's sheathed unlike when it wasn't.

Wireless:
I would not recommend laminating on a layer of glass or other material on the "INSIDE" of the hull. But you can coat inside with an epoxy or epoxy paint for barrier protection... with proper preparation.

Why is on a traditionally built hull you cannot ever layup over the frames and planking junctions without a huge effort to not have voids between the wood and laminate. See the voids become problems for trapping moisture and air against the wood and causing deterioration.

As to covering the exterior. The correct technique is BUTT seams and multiple layers with offset staggering of seams... but the seams must be perfect. This is not usually possible with wet layup and boat construction... or lets us say amateur technique. Usually it is used with pre-pregs... which are not in the realm of possibility of your situation. You can do it in wet layups which I will explain later. In your case you may find using a thinner weave lighter fabric and three layers better.. maybe something around 1.8 - 2.2 oz per yard of material. Weave and orientation matters practically as to draping.

Unless you have movement in the wooden substrate (boat structure) which transfers to the skin covering. Then you have to be very careful:

Generally...
Be sure to evenly rotate the orientation of the weave between layers (in a high stress area you can orient for best strength and you can add layers there), and they do make unidirectional tape which has a backing to hold it together during layup. However, in areas across joints in the wood that may move you will be best served by laying on the bias across the joint or having the most fibers involved in taking the tensile load (stretching load) or compressive load... consider carefully these areas and imagine how the movement is. If the movement creates shear (a sliding movement between members across the joint) you must orient to eliminate the sliding by having the fibers take the load in tensile means... along the longitudinal axis of the fiber. Think of the fibers as little ropes and if it stretches one way you will have to have the orientation in the direction of movement and orient the little ropes in a line parallel with the movement.

If you have movement between members across a joint... which is common on some joints in wooden boats.... you are in deep merde. I do not use the term stress concentration as it may not not be able to tell where the stress is highest and can only look for signs of movement, and the substrate members are individually taking the stress and strain... which results in differential movement between the members. This is usually either usually at joints. The movement is the real problem for you in your situation.


If you glass across the joint that sees movement then you are now creating a stress concentration in the composite material bridging the gap... and it will have to be designed to be strong enough to take the load ... which can be immense.

Read and think of the following article... which references failure mode of glass and carbon fibers.
Stress?strain curve - Wikipedia, the free encyclopedia

Movement between members can be a shear situation where the sliding action between the wooden substrate members OR can be bending between members... sometimes is can be a tensile situation but usually this is localized. Note the sliding or shear can be in several directions. You CANNOT take expect glass fibers in matrix like epoxy to take localized bending load (act like a hinge) or shear oriented across the fibers, at right angle to the fiber orientation. So if a joint works by sliding you cannot bridge the joint by orienting fibers 90 degrees across it you must orient in the at a very shallow angle across it in line with the movement... to take the load... otherwise they will fail. And, you much gradually spread the load into the structural members on either side of the joint. On a strip planked boat usually the substrate is stable as to these problems. But there are three potential areas of concern:

In strip planking he areas to be concerned are at the deck joint; keel or ballast if a sail boat joint, which includes where the sides come together at the bow, and: the joint at the transom. Usually the joint with the ballast is not glassed over unless the joint is very stable. The problem areas to really look at before you start are the transom and secondly the deck joint. As it is an old boat look for cracking in the paint to indicate possible trouble spots as most paint is not real flexible and will show any problem areas indicating movement. Remember in a wooden boat the joint works and the stress is taken by the members on either side. Cold molding and strip planking are similar and basically make large areas of the boat a laminate single structure... but at the transitions of the keel, transom, deck and stem that is where the load transfers from on to the other structure and they are all joints!

Handling the joints

As I said in the previous writing. If you bridge joints that see any movement across structural members... the loads can be immense.

So I would have the glass end at these joints... and allow them to work as they always have for the boat. Think of the two sides of the hull; the transom; the keel, and; the stem are single components being joined together in the original construction. So cover them to the joint and leave the joint work as it always has. In a thin lamination for barrier and abrasion resistance... you can go ahead and layup over the potential problem joints which see movement and then use a knife to cut through the lamination at the joint so the components work as before. Unless you want to get into a situation were you re-engineer the boat. That is how it has worked for a long time... why create problems you don't need... if there is any movement the glass epoxy thin covering will crack anyway in use... and possibly delaminate locally from the substrate. Remember you are protecting the substrate not re-engineer how the boat functions structurally.

Excellent descriptions of the mechanics involved in laminate engineering karo!

The slipping in joints on strip planked (on frame) hulls usually is longitudinal hence the use of +/-45* cloth to bridge across those joints has proven more successful than 0/90*. I am also suprised at the very light weaves you mentioned, 1.8-2.2 oz. I know it's available and used in some military and aircraft applications but I've never seen anything lighter than 6oz used in recreational marine. The more layers the better and with that light cloth I would indeed recommend 3 or more.

For a long time hulls that were in good shape and not working much would be glassed with a single layer of 1808, but seam trouble on the cloth strips prompted a swith to 1708 which was better on the strips of wood but not the seams. For the last 8 years or so I've switched to two layers of 1700 in most jobs with very good results. Hulls that worked so much you could see daylight through the planking like venetian blinds are often done with C-FLex and 3M5200 as the bedding agent to allow planking movement beneath the fibers but the OP's boat doesn't sound that far gone.

One other item worthy of mention to the OP is to make sure the hull is allowed to dry out to less than 15% moisture content not just in the surface of the wood but all the way through. If it isn't dry when it's glassed it will continue to dry and the wood will shrink causing at best a bad case of print through or at worst seam cracking when the fibers shrink so much they can cause delamination.

A short answer to your question is no or at least it's not advised unless you have a big budget and are madly in love with the boat.

Turning a plank on frame into a cold molded boat could be done but not without completely re-engineering the entire structure. Certainly scantlings could be derrived to make use of the existing core but the inside skin has to be uninterrupted which would mean complete removal of all framing and a female jig would have to be built to hold her shape while that was done. Extra laminations would have to be done on both sides of the core to accomodate high load locations like chainplates, keel and possibly mast step, things that the framing is taking care of now. Of course anything CAN be done, but the expenditure will be tremendous!

Stop you might be in need of a Naval Architect and Engineer

Bill106 sounds like you have much practical experience and skill in these repair improvements! Thinking maybe Wirless should hire you... after hearing his plan@?!
Thanks for the comment.
Why use the three layers of thinner material is that for the type of situation supposed here... covering a boat for barrier and abrasion resistance is that it is much easier to handle thin layers during layup as once can paint on the resin and then drape the cloth and smooth out while getting pretty much full wetting and then paint another coat of epoxy over... and so on... and it will be easier simpler and quicker for an amateur... you can even go away let set up between layer too. Even 5 oz material takes more skill and the results will be more critical to achieve for an amateur. Whatever will result in high resin to fiber ratios and will not be optimal for structure but the thinner plies will come closer.

Yes, my experience is aircraft and automotive racing as to composites.
Sorry for the typos in my I sometimes cannot see them the first time or two through... and I get in a rush and get sloppy.

Anyway, Wireless... OMG.
You are talking a major reengineering of the boat. Really using it as a rough form for something structurally totally different. Your project is more challenging than Pascal's new build... and more risky.

Boats... are or were primarily engineered by rules of thumb... or scantlings, and still are to some extent. Why, is with practical experience it become known what worked and what did not. Lloyds, ABS etc still have this aspect to their rules. But now-a-days the computer and modeling rule. Why, is until the computer calculating the true situation was not possible... so it was done by experience... which by collective experience became rules or thumb or scantlings. The intuitive process was more important than the quantitative understanding because you could not calculate the true stresses and stains. Now-a-days its still the same but the tools are available to quantitatively check your guesses. What you are accomplishing is much on the level of Pascal's new build using the original boat as a starting place or form. Practically you have very much less control of the situation than he does.
But likely you will (or have to) over engineer the thing, and if your practical technique is good as to accomplishing the work you will succeed. But I wonder if you will save or spend more money than Pascal... ? But the result will be heavier than the original boat if you are not careful.

So you will have to consider the Naval Architecture aspects of ballast ratios, buoyancy... etc. You may end up with an unhappy performing result if you are not careful.

As to sandwich construction with a wood core... it is NOT SANDWICH construction... structurally. Unless you make the skins impossibly heavy the core material you suppose is actually structurally just a thick ply of a less dense and strong material with different properties than the skins. I don't think your planking is "end grain Mahogany". So for any practical application of what you suggest, the mahogany planking, will take the bending, hogging loads and the skins will take the shear loads... at very best, and very heavy, maybe the skins and "core planking" will share the loads. This is opposite the concept of sandwich construction so there are no guides to give you any quantitative guide as to how much, how thick or anything. Usually in sandwich construction the core takes the shear loads and the skin all others. I am quite sure this will not happen in your case. So don't think it works anything like sandwich structures... it don't in this case. It will be more like a very thick single skin structure so plan accordingly or perhaps like a laminated fiberglass bow arm (bows and arrows ref). It will be a single skin material with hard surfaces and a bond lines between. The idea of removing frames needs to be thought about... and someone with engineering and naval architecture background consulted.

I think your critical aspect in this will be the bond line between your wood planking and the skins and what is feasible there... as the shear forces from bending and hogging will transfer shapely across that bond line which is not very thick... and quite brittle... and you are likely to experience de-laminations between the fiberglass skins and planking if you aren't careful. It is not be a "bond" failure really, I am not talking about failure of the bond line itself, but that the wood is much weaker (about 7-10 times) than the epoxy bond line so the wood fibers at the juncture will shear... if you do microscopic examination you will see its the wood that failed not the bond to it. By using an epoxy adhesive with more elongation and a thicker bond line will help prevent this or prestressing the skins. Pascal having the thick core to spread the shear stress though more gradually will have much less likelihood of de-lamination at the bond line... FYI.

I would just fix the boat as it was designed and add a layer of the epoxy glass for barrier and abrasion resistance as you first indicated.

ACtually Wireless plank on frame and strip planked are the same animal. Breaking or cracking frames is also fairly common be it due to grounding, pounding or overpowering and abuse. Many times the hull skin doesn't appear to be damaged and may in fact not be, the stiffer frames won't bend and give and if the impacts great enough they will break. It's very common in the sportfish world to doube and even triple frame thickness in engine rooms and bottoms to add stiffness but even then they still break or crack. Many started sistering frames with plywood for added strength and it works very well especially on knuckles (chines) where they usually are two seperate frames bolted together.

Back to your project, removing a frame or two here and there usually won't change her shape noticably, removing a series of them will more than likely though. You will end up glassing the inside in sections which will bring another dimension to overlaps and glass seams which will further add weight to correct. It can be done but unless you are willing to invest much more than it will ever be worth restoring her I'd advise against doing it. Fix the broken frames, epoxy coat inside and glass the outside and enjoy.

Agree big time

agree big time!