I have an older wood Eggharbor 37 want to use HDPE for worm shoe

Had to look up a worm shoe. We have a similar sacrificial keel iron for our boats. Few years back my friend had one from 304 that had been worm holed so bad it would catch his net. We blocked it and made a thicker one out of uhmw. Think it was 1.5 or 2 inches thick and about 4 inches wide. Worked great for a few weeks up until a particular hit caused a crack, it eventually disappeared enough he had to haul as the exposed cap screws caught on everything.

Don't remember it being hard to block but our keels are near level so hauled are easy to stabilize.

It seals readily with 5200, we always counter bore with a 1/16th up for expansion. Probably be fine under water, ours is mostly used for gear chaffe areas.

 

I have avoided glassing underwater wood, simply cause I think it will eventually fail. The white oak keel will get wet and expand and crack loose from the glass, on this boat you cannot encapsulate the keel on the inside and the inside does get wet with various things, sometimes some rain. All that water will go down into the keel. And there is way too much interior framing and structures. I figure I have to allow the wood to move.
The visible keel is what you would call a bronze bolted on wooden skeg, 4" wide and very tall in back of the boat. It is made of multiple pieces of large white oak timbers.

What it bolts to is the inner keel, white oak about 3 or 4 " thick and 7" wide, socketed for frames (ribs) and also cut with a large angled ledge for the first outside mahogany planks to screw onto. Laid across the top are white oak floors, long big tall timbers stretch from chine to chine every foot or every 2 feet depending what parts need floor support. All of that can never be encapsulated. And if you did how could you trust it to stay sealed with glass fiber

 

The keel on my boat is also flat and runs 3/4 the length of the boat. Last 6 feet of underwater hull has props, rudders, and no keel. Twin engines.

Today you can get Duplex Stainless steel sheet. It is designed to be very crevice corrosion resistant in sea water, and is used in off shore rig construction. It is more corrosion resistant than bronze.

 

Yeah my current boat has a derivative of 316 that appears to be good stuff.

I'd think on a flat keel the worry of a boat sliding of blocking is a long shot. I'd probably step up to the uhmw on the keel, I've cracked hdpe before (rare but on a cold day on single point pressure it's happened) but the only time we broke uhmw was when we also mangled everything under it as well...

Cost isn't a lot different per sheet, although its not as aesthetic as it's surface isn't usually as homogeneous. Would be tough below the waterline.

 

Why not just use the same thompsonized wood or foundation grade CCA treated SYP?

 

Back in 2005, when I was hauled out and jacking the keel up, I used some PT pine, and I recall it was getting crushed. There was too much boat weight on the pine. But oak did not crush, could handle the boat weight spread over a small area like a block. The boat weighs about 20,000 pounds. Keel width is 4 inches and keel bottom is flat.
I was jacking up to move keel blocks to install a new worm shoe.

That white oak keel back then was strong enough that I was able to lift in the center like where engines sit, the boat and much of the entire boat was also lifting up versus just compressing in that area. The keel is like a skeg, so it is pretty deep in the mid-section and back aft up to 24" tall. It is 1/2" bronze bolted together to the true keel inside the boat. The inner keel wood is white oak 7 " wide and about 3" deep and also large skeg oak timbers are bronze bolted together with hidden bolts to hold skeg together, before it was bolted onto inner keel by OEM back in 1970

 

Here you can see a freshly coated with Sanitred permaflex hull and keel which shows keel timbers at the time had nicely dried out displaying their size Since the planks are 4/4 mahogany they had dried out before I sealed seams with PL and the Sanitred. And for 20 years, they never opened up or cracked on the seams

The keel wood is not actually fully split open along seams the edges are more dried than the centers. I did later on after letting it dry more, tightened up the keel bolts and put Loctite PL filling the gaps




Forward view shows how the keel get less tall, and honestly their is less weight up front than in the back
Sanitred was the perfect coating for 20 years, but has some long term adhesion issues, which I why I was thinking use 5200. Now Santired had no adhesion issue on other polyurethane like the Loctite PL. Sanitred did not fall off the hull, but it was on in some places more like a tight fit glove on your hand. See other that that is it the perfect coating. I think the wood slight movements over time tore itself free of the coating as the Sanitred is pretty tough and not as easy to stretch, the 5200 having a shore hardness of 68 versus 80, I think will yield more and stay on the wood better. Perhaps a perfect coating could be 5200 direct to wood with a single top layer of Sanitred. The Sanitred, like when you use a barnacle scraper holds up to that well. And you can not damage it with a pressure washer.

Do not use Sanitred in the plank seams, use the PL only, the PL by iself is like a form fitting resilient closed cell hard foam gasket. PL is a foaming glue, and sticks well to wood, so when wood swells or shrinks, being like a strong closed cell foam, it moves with wood. I think if all you wanted is sealing then even Great Stuff closed cell foam in plank seams would work fine, then an overcoat of something like polyurethane to seal the wood hull. That poly coating on the wood also holds all the planks locked together very strong. And the planks will not be sliding past each other. You do know, carvel planked boats, the plank edges work on each other wearing down the plank edges by rubbing and compression.

 

Very important point about using the PL foaming glue in the seems and NOT a solid elastomer. If the caulk can't compress without bulging, it will generate tremendous pressure. If the layer of caulk is a lot wider than thick, there is no place for the stuff in the middle to go, so it acts like it is extremely hard.

No argument about oak blocks for supporting a hull. If it's good enough for a Trident sub, it should support an Egg. SYP is not as hard, but nearly as strong as white oak. Since you are considering HDPE, I can't see any problem substituting SYP.

The variation in strength for relatively good SYP is very wide. Density is a very good indication of most mechanical properties, and the junk used for pressure treated SYP varies more than the stuff covered by the Southern Forest Products Association table .

Careful selection of SYP pressure treated wood is the key to making good use of the stuff. I have seen 1/16" of summer wood with 1/2" of early wood in some pieces, which were very light and weak. I have also seen pieces with more late wood than early wood that were far heavier and stiffer. I just replaced the gunnels on a small Bolger sailboat with select AC2 decking. Selected visually by me, not the grade. Very hard stiff wood, about 50/50 early and late wood. (It's an instant boat, 15 years old and no place to waste premium wood. Patch it or burn it was the question.)

Mechanical properties are closely tied to density. It was interesting to note that the Wood handbook says:

 

The PL premium polyurethane glue when put into a plank seam can be compressed and when pressure goes away it moves back. It really does a good job of gluing plank edges and allowing for plank expansion and drying out. I have had no troubles using it. The other thing. plank seams are beveled. You have a squared edge but moving towards the outside, a caulking bevel is cut in the wood, Traditionally, cotton is driven into the caulking bevel to tighten up by friction plank to plank edges, then some kind of paying compound smeared on top. So tightly caulked planks do develop pressures as they swell anyway regardless. When you view my inner plank seams, they look tight fit, on the outside you can see a wide caulking band which is filled up the pure Loctite PL premium polyurethane construction adhesive.

A huge pressure from tight planks gets relieved in 2 ways, plank edge compression or the screws pull and the planks push away from the frames. Years ago on a haul, I had couple bottom planks doing that about 3 foot length 3 planks away from the keel. To fix, I ran a circular saw down the plank seam, re-screwed the area with longer bronze screws, and then refilled the seam with PL. It was not the PL that did that, it just was something to do with the screws pulling from frames in that spot. It did not recur.

On my boat, the frames have large oak floors sitting against them, right on top of them, so the longer screws ran into stronger wood.

There was never any leak, The Sanitred Permaflex stretched and accommodated the plank movement. I noticed it when sighting down the hull on a haul out

 

Couldn’t you soak wood in something toxic to teredo worms? Just asking.. pressure treat or dip treat in a toxin; they get in 1/8” and die? Or is the first worm sacrificed for more?

 

Marine treated wood is made that way, they pressure treat to a high level.
It does help, I dont think it is perfect.
And when I tell the wooden boat forum those things, I get downvoted and people hate it.
They say it is harmful to the environment and people using that wood are killing the little buggers, poisoning the water. There are these extremists and religious environmental zealots who worship the earth and the waters. It just never stops, go down that road, and you get more lunacy, progressively everything becomes environmentally poisonous, and man is a parasite on the planet.


A guy in NY state says the state outlawed use of treated wood for docks?
Blue run states are like that... all our docks in Va are using treated wood, it looks very green tinged. Docks in some states and EU, they have to use untreated wood, exotic tropical hard woods, and they have a lot of dock work replacement they must do. I think the wood exporters in Brazil are happy.

 

I made a decision. will buy a CCA 2.5 treated piece of SYP, 2 x 12 x 16 foot board and cut that up for a worm shoe.
Price locally here is only $67 in Portsmouth VA at Treated Lumber Outlet.
I still plan to use the Nylon cloth to partially wrap over keel bottom before the wood shoe goes on. Plan to use 316 SS 3" deck screws to attack to skeg keel bottom.
What flipped me this way, I need some of that wood to finish part of my keel repair, and I don't want to buy more white oak.
And since I can get wood treated to a level that prevent sea borers, why not do it. Just feels right I suppose.
Now this wood is a genuine 2" thick and current worm shoe is 1" thick.

Debating whether to slice the wood in half to get 1" thickness or just go with 2" thick shoe. Boat is 37 feet but keel bottom to cover is less than that. More like less than 30 feet. You just can not stop the paint on a keel bottom from being tore up by a lift sling.

Some of the people at the wood boat forum will hate it, but I don't tell them stuff unless I am trying to set off certain people, which is very easy to blow them up. So after its done, which will take a while will show some pics. The things some of them say...

Hey it is a long term experiment, will find out if it really does prevent borers. I was told it is fine for submerged seawater use.

 

Longevity depends on the exact species of borer present in your area and the level of treatment (how much arsen is in the wood). Use the full 2 inches, today's SYP is plantation wood and much softer then old growth stuff. The slings are more likely to crush the edge, you want more wood there.
OTOH 67$ might also get you enough roofing copper or lead to cover the area and that's a guaranteed solution.

 

The wood is rough cut . Actual dimensions of 2" by 7.75" by 16 feet. I got 2 boards. They did not have rough cut in the larger sizes, would have to be special ordered.

It looks real good, flat and dry. Knot free, one board has a tiny knot. The wood looks mothing like in a big box store. Will post pics. I can split one board in half and do the entire shoe as a 2 inch thick shoe. Skeg keel is actually 3.5" width

IT is treated at 2.5 CCA, the max allowed.

 

pics, one board has tight growth rings, will use that for some keel repairs. Other can be the worm shoe.
I just lucked out on that, forgot to even look, they are physically perfect looking.