Some more nice plywood

A little good news, some seriously scary shit, and a very impressive trip...

I miss the French canals.

Listening to Soldat Louis

So it goes...

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Quality Plywood Epoxy Encapsulation

I am a believer in epoxy encapsulation of wood; I wasnt always. Encapsulation entails coating the wood with multiple coats of epoxy, saturating the wood surface and building up a moisture-barrier. The moisture barrier is key for bilges and underbodies as it keeps water out of a laminate and maintains a more constant wood moisture content in timbers. Wood movement and ingress of water is what often gives wooden boats a bad name: high maintenance. Encapsulating forms a stable base for varnish and paint. We tell customers to expect a 10 year life for their paint. After 10 years of normal use they may need to do a fresh coat. That is as good as any fiberglass boat maintenance.

What convinced us of the merits of epoxy encapsulation was a visit to my friend Stevens house. He has a faering he built with his son that shows the effects of different plywoods and of epoxy coating wood.

You can see three panels in this Faering. The darker plank is Joubert Sapele faced Okoume (varnished), the middle strake is Okoume by Joubert, and the lower plank in the photo is Shelman Okoume. All planks are finished with a Behr spar varnish.

This is the same boat closer up to one of the tanktops. It is Joubert Okoume. The neighboring plank is Shelman Okoume. Both were varnished the same. The tank top is more degraded and molded than the plank. The tank top along the edge of the plank is perfectly clear. This strip was inadvertently epoxy coated when the squeeze out from the glue joint was spread during the clean up process. The same thing happened in the next photo: can you see where the epoxy is?

The results? It is clear that the epoxy coated areas of plywood are making the plywood much more durable and holding up much, much better. The sheer strake is probably holding up better because it is higher in the boat and receives less foot traffic and a lower angle of sunlight upon it. The middle strake and tank tops get more direct sunlight. But the different brands of plywood may have to do with the difference between planks made of Joubert vs Shelman. It is too bad Shelman went out of business. Clearly, Sapele holds up great and Steven made a good decision putting it in as the garboard. With that said, I have also seen Sapele planked boats flake and shed paint after many years and these were boats that were not epoxy coats.

The moral of the story: epoxy encapsulation is a good thing.

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New Plywood Garvey Design

I have been working intermittently on a new 16ft design for awhile, the start of a range of small powerboats for protected water use. The design is still a way off being complete but the prototype is already being built by Kevin Agee in Hampton, Virginia and is progressing well.

I am using a garvey-type hull that can be easily built from either plywood or aluminium. It has Veed sections forward to soften the ride in a bit of a chop, with twisted bottom panels that run out to a shallow V at the transom for easy planing.

The version that Kevin is building has a self-draining wet deck with swivel seats on bases bolted to the deck. It has integral floodable tanks under the deck to hold bait and catch.There will also be a "sit-inside" version with bench seats, with the tanks under the seats.

Kevin is building from okoume plywood, cut from full-size paper patterns that we have supplied. When the design is complete then we will also offer plywood kits, cut by CNC machine. The photos below show the basics of construction as far as it has gone to date.

Bottom panels with slots for bulkhead tabs

Glass-taping joints in panels.

Bottom panels stitched together & bulkheads set up

Sides added and stitched to bottom

Foredeck added and stitched in.

Turned over and laid flat, ready to epoxy seams.

Now Kevin is doing the epoxy bonding of the chines and centreline joint with filled epoxy, prior to removing the copper wire ties, then glass-taping.

This design will be added to our design list in a few months when the plans are complete. See our current design list at http://dixdesign.com/priceabr.htm.

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Water Rat in 4mm Plywood Sailing Version

Water Rat is a 3 foot wide plywood kayak which can be built with a length of either 9 or 1010". This boat has an unusual, but attractive shape, and has proved to be quite popular. She was initially drawn by my friend Doug Laver back in the days when we were working at my workshop in Brisbane, and we had started experimenting with Gregg Carlsons Hull Designer program.The plans that Doug and I used originally were very difficult to interpret when it came to the shape of the developed panel sections, and I subsequently redrew them in a CAD program, incorporating a few variations and conventional dimensioning. You can read about the boat in a previous post here:-    http://rosslillistonewoodenboat.blogspot.com.au/2011/11/water-rat-developments.html

Dougs original Water Rat with my son, Steven, showing off the boats stability. Steve was about 12 then, and I havent seen this activity performed by an adult - but for a canoe she is a very stable boat.

Ross Trinder, from Toowoomba in Queensland, Australia, has built a number of boats recently including a Green Island 15, one of my First Mates, and a Water Rat. My good friend Al Burke also built a Water Rat, but used 4mm plywood instead of the 6mm plywood specified. Al applied some strategic stiffening materials and as you can see in the comments, his boat weighed in at 17 kg.

Ross Trinder is now building a second Water Rat, and this time he also is using 4 mm ply. Another variation on the theme being experimented with by Geoff Leedham in his boatbuilding program at a school in Alice Springs, Outback Australia, is to use 4 mm plywood for the entire boat with the exception of the bottom panel, which is made from 6 mm plywood.

This boat is a very simple project which involves very little time and very little money. However, it represents a great way to gain experience in the use of  epoxy and plywood, and the resulting boat is great fun to use, is very stable, and is surprisingly seaworthy in protected waters.

Ross Trinder has asked me whether it would be practical to fit Water Rat with a sailing rig. Given that she is 3 feet wide and carries her breadth out into the bow and the stern, I think that she would be able to carry sail reasonably well, and the only real challenge is to decide how best to give her some lateral plane. My first reaction is to make use of the leeboard, but Im beginning to think that an off centre dagger board would suit the boat very well. I will be doing some preliminary drawings shortly, and will post them here.

In the meantime, here are some photographs of the early stages of construction of Ross Trinders 4 mm Water Rat. You can also see Al Burkes finished 4 mm version via the link at the end of the first paragraph.

In this photograph the panels and bulkheads have been cut out accurately, have had holes drilled along the edges of the panels, and the boat assembled using plastic cable ties. After having ensured that there is no twist in the boat, Ross has placed a series of short tabs of thickened epoxy between the cable ties in the forward and middle sections of the boat.

Here you can see how the "tack-welds"of thickened epoxy remain clear of the cable ties, and are very small in cross-section. After the epoxy has cured, the cable ties will be removed and a larger fillets of thickened epoxy will be applied in a continuous run over the top of the "tack-welds" and have glass tapes laid over them while still wet.

Note how the bow and stern transoms, and the bulkheads, have centrelines marked. These are lined up with the centreline on the bottom panel, and as long as there is no twist allowed, the boat must come out the correct shape - even though there is no strong-back or mold.

Here you can get a good idea of the shape of the boat, and as long as the panels are cut out accurately, the shape of the boat is smooth and fair. This particular boat goes together very easily, and it may be possible to get away with as few as half of the cable ties you see in the photo.

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Distributing point load stresses in plywood boats

A very common fault seen in plywood boat construction and design is that of having structural components terminate in the middle of a plywood panel. The most common case is that of thwarts attaching to topside panels, but there are many others. Sometimes the designer or builder will have allowed for this by incorporating other stiffening structures on the outside of the boat, such as spray rails, but often the structure is inadequately supported.

What frequently happens in such cases is that a crack eventually appears where the hardpoint in the structure terminates against the flexible panel.

Here is an example of what Im talking about. The two vertical strips of bare plywood on the white topside panel are where Ive been stripping paint in preparation for gluing some reinforcing frames on either side of the thwart.

In the photo above, the boat had very flimsy plywood hull panels, and the the main thwart (painted grey) terminated against the topside panel without any framing to distribute the stresses. Eventually, cracks will appear around the edges and corners of the thwart, because the plywood can move and flex, but the thwart is relatively immovable. This is a very bad example of design. What I was doing as part of this repair job was to strip paint on either side of the thwart so that I could glue and screw in a pair of frames on each side of the boat to distribute the point loads out into the gunwale and the chine joint.

Here is the result with the new frames in position. I do not like this boat, but the panel cracking problem has hopefully been solved.

In my own designs, I try to avoid any point loads from structural components which terminate in the middle of panels - here are a couple of examples: -

This is the thwart structure on First Mate. One side of the thwart is supported by the midships ring-frame and the other side is supported by half-frames which run from the inside of the gunwale down to the very strong glass-taped joint between the topside panel and the chine panel.

The stresses are gently distributed out into the structure, and both ends of the half-frame coincide with a very strong part of the boats hull.

This is the internal structure of Periwinkle. Note how once again, the thwart is supported by either a ring-frame or a half-frame with terminates against the gunwale and a strong plank lap joint. Note also how the side deck knees run down to finish on a strong plank-lap joint.

Side deck knees in First Mate, tapered and running down to finish on the very stiff joint between the topside panels and the chine panels. The two cross-braces are just temporary, and help to hold the line of the topside panels fair until the side decks are attached. 

Modern plywood hulls can be wonderfully strong and yet still be light, but the flexibility of the material must be understood if the boat is going to last a long time.

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