Wood, Plastic, Fiberglass

Came across a YouTube series of an interesting build. The build has been underway for awhile, but the vids started recently.
This 43ft Alden Schooner is being built using UHMW for frames and fiberglass for floor timbers.
A laminated backbone, with strip planking inner layer using running bevels for the strips.
A later vid will deal with the frames.
Perhaps the UHMW was placed in an oven to make it "plastic", to allow it to be formed within the rib-bands, similar to a steam bent oak frame?
Anyway, found the vids to be quite interesting, and I'll be following along with them.
Building Evelyn: A New Alden Schooner, EP1 - YouTube

 

Using UHMW for the frames is a very very good idea.
Like he said, it wont rot, crack, break, and the screws can not pull out from the UHMW plastic.
I like everyway he is building this wood boat, tight glued seams and all.
Composite construction using the best materials for their various properties for the intended purposes.

Question is where can you buy UHMW plastic framing?

If your going to use wood, locust is a good choice for frames, it is a rot free, strong, common wood. the strength of a wood boat is in its many interconnected parts joined together. A well built wood boat in good shape is naturally stronger than a fiberglass boat especially the smaller LOA ones, as it has to be to hold itself all together.

 

My question is how is uhmw bonded?

 

Ultra High Molecular Weight what???
It's polyethylene or high density polyethylene (HDPE) and can be bought from any plastic stockholder. You can't really glue polyethylene; it's what all your epoxy, PU glue and gunnable sealants are packaged in. Tips from a shipright (youtube channel) also uses HDPE/UHMWPE for frames.

 

No glues, simply screws. for the plastic frames. Wish my boat had been built like the video.
My boat, the wood frames are oak, and oak cracks and rots.
They are not glued in anywhere from OEM construction, just nails and screws.
Same thing will be true HDPE plastic frames. Your basically using gallon milk bottle plastic but in lumber form.

 

The frames on Evelyn look to be two layers of HDPE.
Might he have bent them in "cold" over ribbands?
Or, perhaps by putting them in some kind of oven, (or steambox,) the plastic would become "plastic" and allow for tight radius bending with little effort?
I do like the idea of massive Fiberglass floors, wood floors have always been a problem,, many are the wood boats that have had little problem(s) with planking or keel, but wood floors, with lots of exposed end-grain and having the floor/frame fasteners close to all that end-grain are not ideal.
Caveat; bronze floors, now I can get behind those,, give you something to polish when you're bored.

 

It can be welded using specialised equipment that use hot air, or better still, hot nitrogen gas.

 

The weakness of polyethylene is that it creeps. It will deform and elongate with time.

 

One thing it must do is be allowed to bend, which I think some of these plastic lumbers will not do as they are a composite mixture.
I dont know if they are heating it or simply forcing it to bend when used as a frame, likely that depends on the amount of the bend What they are using looks like pure white HDPE like would be formed from recycled HDPE milk bottles.

I repaired my portable 8000 watt generator HDPE gas tank using a solder gun and milk bottles. There is a small beetle insect that eats holes in plastic gas cans. They smell the ethanol and drill holes into the plastic. they can pepper a tank with hundreds of 1/8 "holes. And also had a gouge in the tank edge. All very successfully repaired.

those ethanol loving beetles will also eat small holes into rubber fuel lines and all plastic gas cans.

Camphor Shoot Borer (Cnestus mutilatus) (psu.edu)

 

The all UHMWPE framed boat is a perfect example of what happens when you don't actually understand the difference between strenght and stiffness.
The plastic frames are simply bent in place by hand, and that immediately tells us what the problem is, stiffness. This is like using rubber for the frames, massively strong but lacking stiffness.

For the boat in the OP they are simply a big waste of money and labour. It will probably still work out, but not by any merit of the re-engineering, just by accident, owning to some quirks of the original carvel design.

 

The builder of that boat, if you watch his other videos, has used these plastic frames before in wood boat repair. This is not a one off boat.
And the planking aids in aiding stiffness.
Since he has the experience, I dont view this as an experiment.

The price is probably too high to buy for plastic lumber.
My own boat frame repairs, I used PT pine as much as possible, and it worked out fine and still holds the screws. Since 2005, no rot, no cracks, while some of the remaining oak frames I left as ok back then are showing rot and even breaking. But since my planks are all glued and I have a rubber seal coat on the outside of the hull, nothing bad happens. Last year, one of the oak 'floors' (joists), the end rotted off including about a foot of oak framing. I simply crawled back in there, with boat in the water, used a chisel and saw and cut out the bad pieces, had to also cut off 4 bronze screws, had no leaks. I scarfed on a section of PT pine wood. Been fine since then, but still prefer a floor to be one solid piece. On top of the floors runs these very long 3 by 5 Douglas Fir stringers, which has an inset edge where it touches the floors, so I had to get creative in fitting in new wood. I ended up splitting the new floor section longwise into 3 pieces, fit each piece, then glued and screwed it in place.

My boat is many oak floors about 7 inch on center under the motors, and maybe 8 to 9 inch center elsewhere, and under them are the bent frames which follow the cut of the floors, hull is round chine.

It was an interesting view seeing some bronze screws sticking up out of the planking with no frame in that spot. That floor repair was where the hull is starting to curve up at the chine.

 

HDPE vs UHMW | Compare Polyethylene Materials & Properties | Curbell Plastics https://www.curbellplastics.com/Research-Solutions/Plastic-Properties/HDPE-vs-UHMW

HDPE and UHMW are two different materials as seen on the table in the attached article. While the tensile strength appears to be significant it comes at a cost of elongation of either 350% or 600% before the max tensile strength occurs. So by
that time the mechanical attached wood will have failed. The different heat expansion constants may be an issue and put additional load/stress at the mechanical fasteners.
Obviously, the UHMW frames work but some questions I would ask is this: Does this material combination of wood and plastic (a) offer a longer service life ie if the service life is dictated by the wood, why would you need longer lasting frames (b)produce issues of creep, (c)permit both materials, mechanical fastened, allow the plastic to utilize it higher tensile strength (d) introduce mechanical stress concentration issues at the fasteners due to the different linear expansion rates (e) introduce higher costs than the rest of the boat done in wood.
I would expect there are other questions.

Tideman Boats Tideman Boats BV | Indestructible HDPE Workboats https://tidemanboats.com/ does build out of HDPE but all components are the same so the expansion rates are the same.

 

HDPE is very useful for harsh marine conditions
Marine Piling & Timber - Tangent (tangentmaterials.com)

 

rubber seal coat????????? what type etc, sounds interesting

 

I used a common polyurethane caulk made by Loctite similar to but cheaper cost than 5200.
I mixed in 30% milled FG fibers 1/32". Then I smeared it on the hull in an even layer of about 1/8" thick using a plastic 6" putty knife..
I used about 100 cartridge tubes. And it is sandable and paintable. I did that in 2014, and now in 2021, coating is still ok.
It actually goes on very easy, much easier than you may think, it takes little skill.
I suppose 5200 is also doable like this.

You end up with a sealed bottom coated in rubber. The rubber is like a tire on the bottom of the boat.

The yellow coating is Santired Permaflex, but that is harder to use. I ground off 10 feet from bow back to wood and put on the Black PL. Then did the same on the Stern part of the boat.