View Full Version : HardiePlank for wormshoe

06-27-2014, 06:35 PM
Thinking about it.
Cut it into strips and glue them together with construction adhesive to get a thicker board.
Then drill holes and screw into keel.

What is the compressive strength of hardiplank?

06-27-2014, 09:06 PM
Skid bar perhaps, but the usual worm shoe is designed to be eaten by worms instead of the boat.

"So the point of the sacrificial shoe is to have an easily replaceable piece which will take the damage and keep the ‘worms’ occupied and out of the main structural timbers."


David G
06-27-2014, 09:09 PM
Nope... too brittle. Esp. in smaller pieces.

06-27-2014, 09:29 PM
What David said. It's surprisingly fragile to handle. It makes great siding, but I think it would disintigrate if it was submerged as a conglomerate of strips. Best stick to a hard wood, metal, or UHMW.

06-27-2014, 09:34 PM
If you want something almost indestructible try HDPE although there may be a difference in expansion rates ?

Eric Hvalsoe
06-27-2014, 09:43 PM
I plan to try TREX composite decking for my next small craft keel shoe. Different animal than hardy board. Expensive, but not as outrageous as UHMW.

06-27-2014, 09:50 PM
Another possibility is H3 or H4 ply , that's what it's called here . A CCA impregnated ply that is definitely unpalatable .

David G
06-28-2014, 12:16 AM
Eric, I have a client who used Trex for the massive rub rail on his big workboat. Tough enough for the duty, but it really expands and contracts with variations in temperature. His long strips buckled between fasteners, then shrunk in the cold. A couple cycles of that, and all the fasteners were loose. We later replaced it with Ipe.

06-28-2014, 01:14 AM
Hardieplank would turn to mush submerged, I should think. Why don't you just make up the shoe from strips of fibreglass, chpped strand or double bias for thickness?


06-28-2014, 01:22 AM
Hardi won't do. Brittle, for one thing. Heavy, for another. And, not designed for nautical stresses.

06-28-2014, 05:42 AM
Hardie plank likely wont work as people say it is too fragile for the environment and you dont want something coming loose. Perhaps that would work on a real small boat.
For a larger heavy boat what is needed is strong dimensionally stable something.
Thick HDPE Plastic will work or thick fiberglass plank.

Wormshoe does not have to be wood, whole point is that bottom paint scrapes off a wooden keel exposing wood so something needs to lay under the keel so that bottom paint scraping off the keel is still covered. A wormshoe does not need to be sacrificial, it could be solid bronze.

I also wonder about the plastic deck boards. I dont mean the boards with hollow undersections, I recall seeing solid plastic deck boards. I wonder how much compressive weight force they can take.

A thick strip of polyethylene plastic is stable and wont crack.

IPE being so dense would work good. How much longer would IPE last as a wormshoe?

06-28-2014, 06:03 AM
IPE is here locally at Yukon lumber.
For reference price, here is an online link for 1x4 boards which is not too bad.
I dont need to replace all the worm shoe.

06-28-2014, 08:48 AM
Ok, I called Yukon lumber.
'5/4', five quarter, which really measures an inch thick , 5.5 " wide for $7.40 per foot long length.
'4/4' four quarter, which really measure 3/4 inch thick, 5.5 " wide for $5.70 per foot long length.

So if I needed 8 feet that will be 8 times 6 or ~$48 with tax.
It might be that I can use the cutoff to glue side by side another section of worm shoe, dependent on keel width.

06-28-2014, 09:03 AM
How about Azek deck boards?
I can get locally for $2.90 per linear foot.

AZEKŪ Brand Cellular PVC is a synthetic wood that will never crack, warp, or rot. It's impervious to moisture, salt, and insects but feels and sounds like real wood!

I wont use it IF it is not dense enough to support the weight of the boat.
What goes on the keel must be strong enough so that if your jacking the keel, it dos not crush under the force.
Common pine will crush, I tried that before.
Oak does not nor will IPE.

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Eric Hvalsoe
06-28-2014, 09:33 AM
Eric, I have a client who used Trex for the massive rub rail on his big workboat. Tough enough for the duty, but it really expands and contracts with variations in temperature. His long strips buckled between fasteners, then shrunk in the cold. A couple cycles of that, and all the fasteners were loose. We later replaced it with Ipe.

Wonder if it moves as much as UHMW. MY UHMW keel shoe moved quite a bit over the years - still not a bad choice, but topsides might be a different story. The stuff is known to be a bit unstable.

There was some reason that I thought TREX was a better choice than AZEK but I can't remember why. I know people who have submerged TREX rubs and grounding strips, they are sold on it. Apparently it also will glue up with epoxy, in a couple of cases it was bonded successfully to a glass epoxy substrate.

There may be some movement with all these synthetics, even if they do not 'cup' or 'warp' like real wood. Hasten to add, I don't know the context of OP - size, type of vessel.

Eric Hvalsoe
06-28-2014, 09:36 AM
Oak or Ipe are certainly dense enough for the job as well. White oak would be a traditional solution.

06-28-2014, 09:43 AM
Interesting! We have two completely different definitions of "worm shoe" here --
1. a rubbing / grounding strip made from a hard and worm-proof material.
2. A piece of wood exposed on the bottom of the boat, often the lowest part so it touches bottom first, made of sacrificial worm-edible wood that attracts worms away from the wood hull.

We've had other discussions of this here, and I admit that I'm not totally convinced that attracting worms to one part of the boat is better than not attracting them at all. But if you look up "worm shoe" I think you'll find that most sources define it as a worm-edible material.

06-28-2014, 10:10 AM
Appication is wormshoe on my 37 EggHarbor.

37 feet
17,000 lbs
with 3/4 length keel.
maybe 3.5 to 4 inches width.
The area that has gone wormy is the deepest part of the wormshoe, maybe 8 feet.
Towards the bow area is fine, that curves upwards and never touches the bottom.

I plan to reuse the screw holes, so will need to make a pattern using paper board and the old wormshoe.

06-29-2014, 08:42 PM
As some have said, the idea of a worm shoe is not to be "tasty", the idea is to be reasonably rugged and disposable, so that IF the bottom paint gets worn off, and If worms get in, they grow in wood that is expendable.
Wood of choice used to be red oak. And normal practice is to put a layer of roofing felt between the shoe and the keel ( often bedded in simply roofing tar).

06-29-2014, 10:11 PM
Right, but some of the posts above are recommending materials that are not edible at all, much less "tasty". Bronze, HDPE, TREX, Polyethelene plastic, etc.

"What we have here is a failure to communicate..." As I said earlier, you can have skid-bars / plates / material to protect the hull, or you can have a chunk of edible wood to do the same AND attract worms away from the hull. Not necessarily the same thing.

George Ray
06-29-2014, 10:28 PM
attract worms away from the hull
I think this is 'red herring'.

Where terado navalis exists there are more than enough to attach and munch on any and all available delectable consumables.

More likely the point of a worm shoe is to insure that those places that are likely to loose the covering of repellent antifouling paint then expose something that the worms/gribbles are at least slower to eat up. In the south east USA greenheart was/is a favorite, teak is better than mahogany or oak, ipe is soooo hard it may be good.

06-30-2014, 12:01 AM
Makes sense... so edible, but tough to chew.

06-30-2014, 12:08 AM
If you think of the bottom paint as armor against worms, a grounding event would skuff a chink in the armor. The worms would start working in from that weakness. The idea is to replace the shoe before they get to through the layer of tar and into the backbone timbers.

Something synthetic would work well because they couldn't eat through it at all, so the armor is that much thicker.

From a worm perspective it would be great. From a stability perspective I'm not so sure.

06-30-2014, 02:06 AM
I thought teredo is only a tropical sea phenomena?

06-30-2014, 02:24 AM
Wish it was! We have plenty of them here in the temperate waters of the Tasman.


07-01-2014, 12:27 PM
I bought a 14 foot plank of Cumaru for 3.63 a foot.
It is a true wood deck plank size. Very heavy very dense and straight. Nice looking wood.
It is almost same as IPE, essentially the same wood.

So $53 total, got this from Portsmouth Lumber in Virginia.

07-01-2014, 02:54 PM
picture of my Cumaru board.

07-01-2014, 04:59 PM
Sorry, I lost track here. Is there a consensus? It seems folly to presume to attract worms away from the hull as the larva are mindless legions that stick to whatever they can and start eating. So the goal seems to be something inedible that has the expansion and contraction properties of the rest of the hull, yes? Can some wise man post the expansion coefficients of HDPE, UHMW, and whatever else that is as tough and slippery as moose tendon? Cheaper than solid Teflon would be good, added points if the stuff will bond to epoxy! :-)

08-08-2014, 07:33 AM
Got a Cumaru section installed finally.
This wood is really heavy. In a few years I will report back on how it performed.
Screwed on with bronze screws and sealed holes with PL + sawdust mix. where sides meet keel, sealed with black PL.
I painted the top and sides with some Behr 100% acylic green paint. Just another barrier. For the bottom of the true keel, I coated with black PL .
So it is oak keel, black PL, green paint, cumaru wood, PL premium , then will get red bottom paint.

a beautiful wood. I like that it is so hard, I think the worms may not be interested.

Jim Ledger
08-08-2014, 07:45 AM
After having completed a 1500SF Ipe deck (house) I think I can say that the Cumaru is Ipe. As I understand it, Ipe is a marketing name which comprises many species, Angelique, and probably Cumaru included. As a worm shoe Ipe would be hard to beat, however it is difficult to bend in the full inch thickness. It's a most unpleasant wood to machine.

08-08-2014, 07:53 AM
It sands well. It cuts well with a saw. Any screws or nails you must pre drill.
It is a stiff board. This part of the shoe does have a slight curve, I used a jack to press it up to the keel when screwed it on.
I think it would make a great keel wood. It is very very heavy.

One piece I glued with PL and it glued fine. So you can glue it. I took a steel brush and ran it over the surface to be glued. I read somewhere it might be difficult to glue? But maybe only with certain kinds of wood glue.

Jim Ledger
08-08-2014, 08:11 AM
I just glued a lot of 5/4x4 decking planks together, face-to-face, with epoxy, in order to make railings. I'm betting they hold.