Strip planking / Cold molded ?

[fcfc]

I have only some limited experience with plywood boats. But that means hard chine. I would like to see somehing rounder.

I am looking at these two ways, since it is still more or less wood.

First, are there current books about these methods ?

Second, if I understood well, strip planking is more of a cored fiberglass boat, core being longitudinal red cedar beads ? This means that it is build over a male mold, not structural bulkheads. (as in typical plywood). You must be able to lay the inner skin. Am I right up to there ?

Cold molded wood is built on longitudinal cedar beads too. Does it need the inner composite fiber layer or the cedar is exposed to inside water. Must it be built on a mold, or can it be build directly on structural bulkheads ?

Thanks for answering.

[cyclops]

Yes, there are many books on ultra light weight strip planked canoes, kayaks,etc. Web search --strip planked canoes --and combos of similar words. There is a magazine just on them. Post back if no luck. I have picked up 17# strip canoes.

[PAR]

Strip planked construction can be a true wooden vessel, a composite, or a wood cored construction, depending on the designer's intent. There isn't a generic dust jacket that can be placed on the method. In short, no, I don't think you do understand well (your words).

A cold molded craft can be purely that, or a combination of other methods to bulk up to the required planking thickness. Both molded and strip plank methods can be built over bulkheads (and typically are) in addition to station molds (which may also become bulkheads)

Each design and designer will have a different take on the processes involved. Find one you're comfortable with and have at it.

[fcfc]

The building method I will be more comfortable with is the one with the best strength within 10-15 years and with maintenance costs I can afford. ( or adequate resale value in the worst case :( )

I hope to build only once, and to sail several years with ...

And you can find anything as contruction method for round chine hull, (Even limited to wood/epoxy), I am a bit lost at that point.

Thanks.

[bjl_sailor]

Look at Dudley Dix's radius chine sail boat designs. They are a combination of plywood on frame and cold molding. There is virtually no mold that isn't also a bulkhead hence you cut hull sections once and turn over a very solid unit.

www.dixdesign.com

[fcfc]

The only thing I do not understand with his design is that he uses plywood for his radius chine.

That means half of the fibers are working in the strip length direction, and the other half (the transverse ones) are short cut (the with of the strip). I fear the 2 * 6mm plywood have an equivalent strength of 2 * 3 mm veneer.

If you use 2 layer true diagonal veneer, no fibers are cut. You have half of the thickness fiber working in one way, the other half (ie the other layer) in the transerve way. No fiber cuts.

The other problem is that you have end grain wood (which can take water) on half the tickness, but all the girth of the strip. Classical veneer only have full thick endgrain at the 2 extremities.

Another point is that I am looking at displacement powerboats, not sail boats. But that has little to see with contruction method.

[Raggi_Thor]

You don't have to worry about end grain as everything is encapsulated in glass and epoxy.

The fiber orientation in Dudley's radiused chine is not bad at all. If you use classical veneer you have to lay them in different directions to stabialize the laminate, when you use plywood that is done allready so you can have only two layers and save a lot of time.

[chandler]

Gougeon Brothers have a good book on either method, though out of print it can be found on ebay. Cold molded hulls require far more temporary molds than strip planking. Cold molding pretty much requires a male mold as in fiberglass construction.
Strip planking can be done with far less molds. Either method can include permanent bulkheads.

[fcfc]

The fiber orientation in Dudley's radiused chine is not bad at all. If you use classical veneer you have to lay them in different directions to stabialize the laminate, when you use plywood that is done allready so you can have only two layers and save a lot of time.

I am note sure.

Imagine on 6 mm plywood layer vs 2 diagonal layers of 3 mm veneer.

In the direction of the plywood strips, both will have the same strength. same thickness of fibers, same length and direction (if wood of same quality).

But in the transverse direction of plywood strips, the plywood will offer nearly no strength. You will only have juxtapostion of small fibers of wood. = the length equal the width of the strip. To have the full transverse strength, you need to have the strips scarfed : impossible job.

On the opposite the veneer will have the same strength in both direction = the equivalent of *UNCUT* plywood sheet.

Now, I may be wrong on that, but I need explanations.

[cyclops]

Have you a set of crush values that are of a "must resist psi" ? I have found the most intense crush values occur on a bad docking that overloads the hull skin and the supporting frames. The bulkheads usually are so strong as to cause instant hull skin or planking failures. I personally love 90 degree veneers in all plywood as it resists docking and pounding forces best. Very little actual " destructive tests" of any type of plywood are available to me.

[chandler]

Sorry, I didn't realize you were talking about plywood strips...

[cyclops]

Do not feel bad. 1/2 of the other times I am not on the right track.

[cyclops]

If memory still works. I believe a barrell outward curve in a sheet of plywood makes it almost industructable. Sooo if you put strips of ply on top of each other with a outward curve. Direction is not going to be too important unless it is designed as a record attempt boat.

[Raggi_Thor]

You will also have some stringers to take much of the longitudinal global stresses. 4mm plywood will have three layers, two of them running longitudinally and the one in the middle transversly (90 degrees to the keel).

[NUP]

as far as i understand the ceder strips are built over an inverted psudo bulkhead framework -ply or chipboard . which is later removed once the external hull has been glassed and the hull reverted keel down. the psudo frames are then removed and the inside of the hull can then be glassed.( it is much easier to glass downwards then upwards, so the outside hull is glassed keel up and the inside is glassed keel down

[Raggi_Thor]

fcfc,
If you want to read in french, look at:
http://www.icarai.net/
They have plans from Dudley Dix and others.

[nero]

Par had a correct reply.

This is half of one hull of my catamaran. I started putting the strips on the forms yesterday. The forms are female.

The boat is 18 mm cypress (quarter sawn) strips with the widest at 50 mm. The wood provides the structure fore and aft. Across the grain the uni and bi axel 10oz fiberglass cloth and epoxy hold it together. ... I hope.

I am trying a 'lock miter joint' to join my strips lengthwise. Some are epoxied together before I lay them on the boat. Others are joined on the boat. It seems to be working quite well. The joing lines up easier than a scarf joint. It also will be a bit better than a but joint.

I cut several ends at one time with the lock miter router bit and a Hitachi router. I need to make up a jig to make that process even faster.

Here are some of the build photos.

You can do a lot with strip planking as far as rounded shapes.

[jfblouin]

Very beautyful hull.

I use the joint named finger joint. For a 19 mm (3/4 ") plank, I have 62 mm (2 1/2 ") long of 1:20 (3 degres) surface plus 16.2 mm (5/8 ") of end-grain surface.

A 1:8 scarf for 19 mm (3/4 ") plank have 150 mm (6 ") of 7 degres surface.

My joint with epoxy is stronger than plain wood with small knots but less stronger than clear plain wood. I dont make compare with scarf.

[PAR]

In most applications, fancy joints on the strips aren't necessary, a butt joint will do and is the fast way through. Staggering the butts, like any joint should be, is the ticket. Most strip hulls get sheathed with something, veneers, glass, etc. so the need it's as big as it may seem. The strip just above and below the joined section of planking will lend a great deal of strength to the joint, if glued and fastened properly.

[yokebutt]

I kind of like the finger-joint, especially if you can do away with that step near the surface of the wood, since it effectively puts a butt-joint at the most highly stressed fibers. (in bending) We might as well start looking into it, because the long lengths of good lumber will not get any easier to find in the future. (nor any cheaper)

Yokebutt-joint. (No, contrary to popular belief, (although I can see why you suspect it) I don't smoke it)

[chandler]

The only problem with finger joints is they will create hard spots as opposed to a scarf. they will also break in any type of hard bend .

[Raggi_Thor]

When scarfing plywood, the scarf become stiffer than the plywwod around so you get a flat area. This is sometimes more work to fill and sand than two very small hard spots from a simple step joint.

[cyclops]

I have 1 option. NO long marine ply, over 10' ? Put down 3 staggered layers of 1/4" ply. It does work very well, as we Dinosours continue to do our best in a decreasing supply world of marine woods.