Better stripping technique

[Timbard]

Technique maybe of Interest - fast/solid

We have a 15 meter cedar strip tradtional gentlemens launch under design/construction and in discussing the options of strip forms with our designer of 60 years experience I queried what form the strips would take. Looking through the literature it seems the cove and half round and some form of modified tongue and groove were options, although I have built a canoe years ago out of butted rectangualar redwood strips. He said for a boat this size we will use 25X50 mm retangular strips. "that cove they cut and the bull nose that matches, all that wood you paid for they made into sawdust". So the tecnique is to use 3-inch long hot melt glue coated staples (about paperclip size wire). Starting at the bow fasten the first strip to the stem with a pneumatic gun and continue around to the bow on the other side fastening the the strips with grain parrallel staples to the bulkheads (the staples will pretty much bury themsleves in the wood and be almost invisible under even the clear cloth/resin. Then using a simple spacer (about 1 mm thick) start back around the hull stapling every foot (completely through the new board and into the one below) or so and into each bulkhead. Slide the spacer along to control the space between boards. When you get to the stem reverse hands and start back around. From experience of others it turns out that alternating hands and a bit of thinking will prevent stapling on top of staple. The hot melt glue melts on insertion due to friction, and the staples cannot be removed, but it also fixes the spacing since the glue is in both boards. When it come to fiberglasseing the resin will go into each slot and totally encapulate each strip. From experience one man can strip about one foot of hull per day on the 35 foot sail boat.

[jfblouin]

Very interresting.

I search a good method to encapsulate easily wood strip into Epoxy and I find it today.

Does the resin well go into each slot (and fill all the slot) on 3/4" (19 mm) planking?

Does I have to thicken the resin?

[jfblouin]

Anybody have more comments on this technics?

I want to be sure before use it in my project. Please give comments!!!!

[JEM]

If you strip using bead and cove, you'll spend more time getting a proper fit from strip to strip. It may be easier to use strips with beveled edges.

I have not build a strip-built boat so this is just info I've read from Nick Shades' book.

[jfblouin]

This technic allow to use Epoxy only at the end of the procedure. I can't do that with bead and cove. Put Epoxy during stripping is a messy job.

[cyclops]

I would have loved to pick my Woodie in 1920 to 1930, when carpenters were so talented on boats. Now, I am forced to learn all the trades to a acceptable level so I can pick a good professional to help me in each phase.

[cyclops]

JF. You bring up a sore point about wood planks and epoxy. Hacker Boat Company had a few lawsuits because they decided to epoxy encase the first few finished hulls. A slight bump or crack in the coat started Black Rot and it spread till the wood was removed. They learned and converted to the completely coated board assembly procedure. Perfect since then.

[jfblouin]

I want to build my hull with this schedule:
1- layup of strip plank over mald mold with Epoxy only on strip plank's end at keel and stem junction
2- One external coat of unthicken Epoxy resin
3- Fill gaps between planks by external with thicken resin (silica fumed and a fibre filler)
4- layup of fiberglass in Epoxy matrix on external side
5- reverse the hull up side down
6- light coat of Epoxy without fillers inside the hull
7- Filling gaps with thicken Epoxy
8- Layup of fiberglass in Epoxy inside the hull
9- installation of bulkheads and stringer with fillet joint and fiberglass tape renforcement

With this schedule, I hope that mess will be reduce to minimum

[Timbard]

I talked with him today about the system. He told me that they don't do anything special (fillers or thinning) with resin. The manufactures have put a lot of thought and testing into the resin formuations so "don't fool with it". The spacer he uses is an old flat table knife, like grandma had ~1 mm thick. When the resin is on and the cloth rolled out the resin will fill the space between the strips without much dripping on the inside.

I hope you get the concept!

Regards

[John ilett]

Just to consider another technique even though I have not used this stuff myself.

There is a single component polyurethane adhesive that can be used to glue the strips as each is placed on the mould in the usual way.

This glue "Purbond" http://www.purbond.com/products.asp?base_id=6&lng=en comes in a ready to apply sqeeze type bottle so no mixing as with epoxy. Then it also expands/foams a small amount so you can be reasonably sure it will fill any gaps.

As it resembles a foam once expanded it may also sand off quite easy compared to epoxy glues.

[jfblouin]

About Polyurethane glue

Someone said that Epoxy dont make a good and durable bond with Polyurethane. I dont know.

About stripping technics

I try a sample area with this technic. I use unfilled resin and that not work propely. When I cut the sample, I find air inside the joint. See graphic below.

[cyclops]

I can be slow on picking up stuff. BUUUT. Why do I try to get all the bubbles out of every glue and epoxy and then even consider using a glue that causes bubbles? It has to be the worst structural glue invented!

[John ilett]

The sheet poyurethane foam people often come across has a very low density and hence not so good for anything to bond well with. Your only talking about the bond to the small gaps inbetween the planks to the laminate so it not as though the whole structure is reliant on this bonding. I think this purbond ends up with a far higher density than the average sheet type polyerethane foam.

Do you really think the bond between the planks has be 100% structural if the hull is sheathed with a laminate. Isn't the foamed polyurethane glue not any different to a foam core in a sandwich hull?

I do not know the exact density of the Purbond but it may well be 200-300kg per cubic metre which would be more than 3 times the density of a common PVC foam boat.

[cyclops]

Yes, it needs to be as strong, to prevent the planks / strips from flexing and the foamy glue from deforming. The flexing of the foamy glue will cause the thin layer of glass cloth to crack all over causing water to be sucked in and out where the glue is. Long live Black Rot.

[chandler]

polyurethene glue does expand like a foam. it also does not sand well. it also stains your skin black until you actually grow a new layer. DON"T get it on your skin.