Norway Spruce for strip planking?

Hmmm. Catamaran? There will be the matter of engineering the cross structure as well as scantlings for hull & deck, etc. The Gerr book is not intended for multihulls, but we might still be able to use it as a rough guide. What's the beam of a single hull?

Anyone have a better reference for multihull scantlings? When you say load method, PAR, are you suggesting we start with a pressure head, then look at panel sizes?

You're looking at longitudinal strips on transverse frames, so I figure you have those two directions covered OK. You'll have to build on temporary station molds, of course, if you're going to sheath the inside before attaching the hull to the transverse frames. Let's imagine you're going to use all unidirectional glass (though in the end you probably won't). You don't need longitudinal. You might want some transverse for hoop strength, but my feeling is you mainly want +/-45. While tensile and compression strength is greatest in the direction of fiber orientation, +/-45 gives you the greatest shear strength.

 

Stephen Diltmore you're confounding:

- The old strip plank square battens glued or not (in this case read lead has been used) always NAILED with transversal structure. In fact it's a classic wood with very narrow planks: thus suppressing the problems of wood quality, cutting of the planks, and seams.

- The composite strip plank. The battens are GLUED, the longitudinal strength is given by the wood and the transversal strength is given by layers of fiberglass, better with unidirectional +45/-45 on bigger yachts. You obtain a MONOCOQUE structure with a smooth inside not being cluttered by ribs or other elements. The global resistance is given the thickness of the hull, and the marriage wood-fiberglass.
Any light wood that glues well will give good results, except balsa whose structural properties, wen used in longitudinal planks, are too low. Fir is too dense; to keep the weight in the limits the fir planks has to be reduced in thickness with a loss of general and local strength (unless designed by the NA as heavy dsplacement or with special requisites). It's a monocoque rigid structure where the skins are bearing all the loads, so it's better to get the better ratio resistance/density and optimize the thickness of the skin.

The strip foam is simply a sandwich where, for convenience, the foam is cut in strips to follow the shape of the mold. The foam has not any longitudinal nor transversal strength, it's simply a core. It's a simple variation of the classic sandwich method and it uses generally polyester resins.

The beauty of the composite strip wood plank is that results are very good and durable with simple tools and skills.

On all methods using a core (wood, plywood, foam, honeycomb) you have to make plugs for the screws. In monolithic fiberglass is highly advisable to seal as the exposed fibers of the hole will suck water. Even in aluminium is better to use plugs and to seal; the contact with another metal as the screw will lead to electrolytic corrosion that occurs also in classic wood yes!

A rule of thumb is NEVER mix different resins and glues nor use light hollow thermoplastics fillers as glue. Other rule is never dilute an epoxy with a solvent.

The experience talks by the advice of PAR. I'll add that resorcinol is more expensive than epoxy, and stains horribly, and out of reach for the common home builder. It's a thing of the past, except for non protected ( ie epoxy coated) laminates.

The beauty of epoxy is to use ONE thin resin, with different hardeners (fast and slow) and a few fillers to make the product adapted to your needs. The results has been known to be excellent since 40 years.

Last advice read the the Gougeon Brothers on boat construction boat. You'll have a complete exposition on wood epoxy boatbuilding. It's worth the reading; informative, well written with excellent illustrations. http://www.google.fr/url?sa=t&rct=j...zoGoBg&usg=AFQjCNFAHsGMeNCMNsdI2vJdqvGPIWF5aA

 

The typo of the "Load" method has been corrected Steven. We need to talk apples and apples here as again there are several different permutations of strip planking, each with issues that must be addressed.

Without a design or build method and of course the related volumetric and dimensional data, speculation to strip and other scantlings is silly.

Traditional strip planking is basically narrow carvel planking, without caulked seams, but this is only one of (again) at least a dozen methods, which fall into three general categories: traditional, reinforced strip and composite (cored). All produce a monocoque hull shell, though some are stiffer and/or lighter, while others not so much.

 

The Lord method is useful only on high speed MONOHULL motor boats, where a high resistance to impacts on the waves is primordial on large flat panels. Useless for multihulls which have not large flats panels impacting the water and need a good global rigidity for the rig. Sailing multis are not fast enough to have the problems of a 60 knots planing hull.
The method asks for special dispositions in berthing the engines and for the propeller shafts. The engineering is pretty delicate as no hard points are allowed; ageing, fatigue, natural frequencies, local deflections, resilience of the materials have to be taken in count with good precision. The structure works by stress dissipation, so it has to work by local deformation (like the legs of a skier) but keeping a good general rigidity.
Beautiful method but very delicate, that explains why it has not been widely used as it's out of reach of most NA and shipyards...And for the non educated yachtman, the view of the waving bottom panels is frightening. The noise made by the hull on a 100 feet patrol boat at 55 knots is also, lets say daunting.

 

Ilan Voyager.
Could you expand on this please,

"nor use light hollow thermoplastics fillers as glue"

Cheers, RR.

 

The classic hollow thermoplastics filler is the phenolic microbaloon (the dark red one). Another is the microlight (copolymer microbaloon) of Gougeon, there are many others in the industry made with plastics. Very lightweight, smooth with good feathering qualities and very soft so it's easy to sand.
As glue fillers the drawbacks are price and the worst; simply not strong enough mostly in tension. Another drawback is sensitivity to temperature and water absorption.
As PAR explained you need in gluing a joint strong enough with good adhesion and that's achieved with the fillers he gave like the cotton flour. Introducing fibers improves highly the tension resistance.
There are also mineral light fillers like the glass and quartz microspheres.
Most of the glass microspheres have poor adhesion to the resin and are unsuitable for gluing if tension stresses are applied like on a bulkhead.

 

Okay I agree up to a point, certainly with highly stressed bonds like bulkheads and laminations.
However with strip composites using lightweight timbers such as cedar, balsa and Paulonia, whats the point of using an adhesive that is 10 times or more the shear strength of the core ?
You are making the planing and sanding process prior to glassing very very difficult, a heavy hard glue line every 50mm is going to end in tears !
For strip composite the "adhesive" only needs to be marginally stronger than the planking or core.

 

I'm not sure where you think we disagree, Ilan Voyager; but I did undertand Ranger1973's comment above to suggest some form of edge glued strip, sheathed. I took that to imply minimizing metal fasteners. Am I wrong, Ranger?

My answer to Ranger's question is: if you can really be sure all internal gaps will be entirely filled with epoxy post-assembly, it's true that sealing the end-grain of planks pre-assembly is superfluous. But if you can't be sure, doing something to seal end-grain pre-assembly is good practice. With respect to elements other than the planks, my answer is yes - sealing the end grain is good practice in my view. I don't think the seal at the end-grain needs to be 100%. Red lead is not 100%. I'm suggesting something is a lot better than nothing. While skepticism about some of the vender's claims may be justified, the concept of substituting CPES for red lead seems like a good one to me. I.V.'s point that you want to make sure your products are compatible is a good one. I don't see that as an issue with CPES, an epoxy in solvents, since that's exactly what most epoxy primers are. But any 2 part product will be less convenient / more time consuming to use repeatedly than a single part product. I don't have a perfect answer.

So Ilan Voyager - what's your take on the sanding question? If you get a line of hard epoxy at each seam, how do you sand that down, both outside and (more difficult) inside, without sanding down the wood faster than the epoxy? [I see RedReuben has just asked a similar question.] Is using one of the sandable epoxy fillers I mentioned in my post #22 a possible solution? Would your criticism of thermoplastic spheres apply to any of these pre-mixed products?

 

Better sander perhaps IMHO...

 

We built a lot of successful sportfishing boats in the 52 to 70 foot range with balsa Duracore. The strips were glued with West thickened with 407 low density. The strips had screws every few feet to keep them aligned until they got hung to the molds. Our approach was to make panels about twelve strips at a time with the finger joint ends staggered in a ladder. These boats are all 40 knots plus and get worked hard in rough seas.

 

To everyone, but Ilan Voyager in particular:

What do you make of Paul Oman's claims for Aluthane's ability to seal wood and compatability with other products? [from http://www.epoxyproducts.com/0402moist.pdf]:

It makes an ideal primer under other coatings, or metallic silvery gray topcoat over epoxies etc. (it has been used on metal bridges and both its performance and its appearance). Urethanes are by nature never recommended for immersion service, but I thought perhaps this product might be an exception (despite the chemists' warnings). I coated a hard commercial Armstrong 12 X 12 floor tile and a similar sized piece of plywood with aluthane and submerged them both for five months in a New Hampshire pond. Upon subsequent examination there was no blistering, peeling or any sort of damage to the coating on either of the two test panels. Darn impressive!

LINKS
Aluthane (www.epoxyproducts.com/aluthane.html)
Primers (www.epoxyproducts.com/primer.html)
Wood sealing tests (www.epoxyproducts.com/woodseal.html) <--------------------------
Data/MSDS (www.epoxyproducts.com/datamsds.html)​

Note:
My result with polyurethane between strips was bad, especially when done in wet/cold conditions, confirming Ilan Voyager's observation that he has seen disastrous results from using polyurethanes. So I have no basis for recommending the use of polyurethane between strips. If I were to try it again it would be with dried wood in dry conditions not below 15 degrees C.

 

Where the West thickened with 407 low density wound up hardening proud of the surface, were you able to sand it down without substantially reducing the thickness of the wood laminate surface? Was this done on the inside of a curved hull?

 

With endgrain wood it's never a problem to sand epoxy leftovers..

 

Not sure what you're saying.
The inside and outside surfaces of a strip plank hull are not endgrain;
nor is the surface of Duracore face laminates.
Cured epoxy (without filler) is definitely harder than wood.
It may be that done properly this is not a problem; but if you could please say more about how to go about doing it properly it'd be helpful.

Thanks

 

Here's what you get using gorilla glue (foaming polyurethane)
[from http://gotransat.com/build.html]