Sheathed strip construction

[Garry]

Wow

[Peter HK]

Garry

There is one cosmetic issue with sheathed (wooden) strip construction. Due to the tendency of wood to swell and contract the strips show through the glass layer. This can happen quite quickly- within weeks.

I had a Farrier F31 tri (actually F9A as it was the home built strip planked version) and after a few years it was very noticeable.

Farrier now recommends vertical strip foam which he says is easier and obviously doesn't have the cosmetic issue. Epoxy is fine with foam too.

I agree wood is nice to work with and I never saw a piece of foam with a good grain ;D

Peter HK

[Joe Nelson CS#35]

What about Plascore?

http://www.plascore.com/pdf/Marine_Flyer.pdf

They are using it on another forum I visit to build driftboats.  Its a honeycomb product that has a covering over each side so that it can be covered with glass and epoxy.  Only problem I see is the engineering behind the keel attachment.  You cant put fasterners in it and expect them to hold.  I would assume that you can fillet and tape a bulkhead with no problem.  Would probably need to install a wood king plank to set keel bolts into.

[Designer]

While strip planked boats can have a print-through problem the Farrier trimarans are more susceptible than monohulls because they use so little glass over the planks to save weight. A similar sized monohull will use at least three times as much glass over the wood.

Print-through can be caused by post curing of the epoxy when the hull gets heated by the sun. It is a good idea to to paint the hull a light color to keep the hull cool. I like to leave the hull in the sun for a couple of days after glassing if possible to post cure before the final fairing.

The second problem is water vapor passing through the glass and allowing the wood to move. As with all vapor barriers, thicker is better and is not usually a problem with the typical monohull layup.

The greater stiffness of wood strip planking over foam helps to fair the boat fore and aft which is another small bonus.

I think that with normal care a modern strip/ glass built hull will turn out a very fine vessel.

[PAR]

What's not considered in sheathed strip and several other methods is the "goo factor" (my term for lots of epoxy use). I recently completed the scantlings for a Lord method stripped hull. The amount of goo, fillers and fabrics is staggering, especially compared to other more conventional approaches. If your not fond of goo and fabric work, some types of strip planking (there are several different types) can be very costly and messy.

This said, strip planking is about the easiest way to get a one off round bilge hull, for the amateur builder.

[Joe Nelson CS#35]

Gary,

Just curious...what are the specs on your strips and how much glass will be used over/under the stirps?  Or are we that far yet?  With enough glass, should be able to use thinner stirps.  I would personally rather use less wood and more glass and epoxy.  Glass is more predictable than wood.  A lot of boats in your size range will use biaxial cloth inside and out.  It is a little of a pain to fair, due to the stitching.  But you can run a scraper over it and remove most of the stitching after the initial glassing has cured.

[dale]

Gary,

Did you finish the Fisher book on strip planking?  If so, would you recommend it?  And is there enough info in it to actually do a boat?  I'm looking for the simplest way to do a round-bilged daysailer that would sit under cover 99 percent of the time.

[Charlie Jones]

actually thicker strips and less glass will contribute to a stiffer hull- wood has more inherent stiffness than glass, inch for inch, and doesn't fatigue nearly as badly, if at all in that type layup.

Many of the older strip hulls had no glass on them at all.

[Garry]

Here are a couple of links that Charlie posted elsewhere that support the thought that a wood and reinforced epoxy sandwich is more durable in the long run than a glass layup!

http://www.epoxyworks.com/21/long_term.html

http://www.epoxyworks.com/21/importance.html

[Dale Niemann]

Gary,

Based on my experience with building the John Marples 3 Meter tri "Bananas", cold molding is a real pain in the ass.  First you have to build a mold and then vacumn bag the hull.  I would estimate it took me about 3 times as long as strip would have.  The hull has held up very well though, for about 12 years now.

I built a 16 foot stripper canoe of redwood and it is still being used after about 35 years and that was before the Epoxy was fancy.

Another note.  My nephew has a Farrior 31 tri which was built using duracore strips with fiberglass.  I not sure of its age but at least 5 years old.  He has not experienced any print through or balsa problems as of now.  He watches it closely though.  His son sailed the Bahamas for 6 months with no problems and he trailers it all over the country.  He lives in California.  It is a great boat but way too much for me.

Dale

[Charlie Jones]

But you don't HAVE to vacumn bag when cold molding. My Cross 35 trimaran was cold molded 3 layers on the amas and 4 on the main hull. All set in epoxy and stapled on with bronze staples most of which got pulled back out.

It IS labor intensive, but vacumn bagging is just a different way of doing it . My two outer hulls took 1 week each to plank.

Shot taken on launch day- that's me that's circled- had hair then ;D This would have been in 1982 by the way and we had just lifted the boat over the two buildings in the back ground. The boat is still going strong, passing insurance surveys readily.

Let's face facts- unless you are satisfied with a crude or workboat finish, there IS no really simple way to build a boat- takes hard work no matter HOW you do it. It's just different degrees of work.

[Tom Lathrop]

[quote author=Charlie Jones

Let's face facts- unless you are satisfied with a crude or workboat finish, there IS no really simple way to build a boat- takes hard work no matter HOW you do it. It's just different degrees of work.

So true Charlie

[dale]

I don't think I'm under any delusions here.  They were all dispelled after building my 7 and 1/2 ft stitch & glue dinghy.  Took @140 hours.  I'm getting ready to do a canoe that Selway/Fisher says should take 18 hours.  Got my doubts on that amount of time.  We'll see.

[Garry]

Here is what Gougeon says about it in their book on boat construction:

"Strip composite construction has some very attractive features. It is one of the fastest ways to build one-off hulls. It produces a strong hull that can weigh less than a laminated veneer hull (due to fewer glass lines). The only disposables are the plywood or particle board panels left over from the temporary mold stations. Veneer spiling and fitting are unnecessary, and only mold frames are used, so the method is very quick. You can use lumber from your local dealer rather than veneers, which can be hard to find. The technique works well on compounded hulls and results in very strong and stiff craft with little or no interior framework. Glass fabric is used in strip composite construction to supply cross-grain strength to wood planking."

[Garry]

Dale asked:

Did you finish the Fisher book on strip planking?  If so, would you recommend it?  And is there enough info in it to actually do a boat?

Yes Dale, I would recommend the Selway book as a good basic book although their references to supplier are all British. For larger boats, I would also recommend "The Laminated Wood Boatbuilder" which has a lot of good techniques. The more I learn about strip plank construction, the more impressed I am with it.