Big Food - UHMW keel shoe installation

[Yeadon]

This week, I began to install a UHMW shoe onto the keel of my peapod. As always, I've been documenting the process on my blog (http://superyeadon.wordpress.com/2007/12/31/big-food-the-shoe-project-ii/).

Often when pulling the boat up onto a beach, a bit of blue paint gets scraped off the hull. Skid shoes made of UHMW are pretty much impervious to gravel and rocks, and should minimize any paint that I leave in the lake.

In all, I worked about 10 hours on Sunday to prepare the bottom of
the boat, then template and fine tune the shape of the shoe.

Here are a few photos and a bit of description.

http://farm3.static.flickr.com/2057/2150718981_f4d66a86a4.jpg

(I'm using an open bay at Eric Hvalsoe's (http://www.hvalsoe-boats.com/), which means I need to hustle up and finish this project because he's got a bunch more work to do.)

Above, you can see where the paint has begun to scrape off the keel from numerous beach landings.

http://farm3.static.flickr.com/2357/2150720715_35205dd28c.jpg
Using a scissor-like scribe, I was able to transfer the shape of the keel onto to UHMW plastic.
http://farm3.static.flickr.com/2099/2150723143_29d98b6072.jpg
I rough cut the plastic with my Bosche jig saw, then lightly fastened it onto the keel for a finish cut with the router.
http://farm3.static.flickr.com/2085/2151512168_5f379b4623.jpg
(But first, Eric gave me a quick tutorial on proper router technique. )

Once I got the shoe fitted and centerboard slot cut, I used putty to fill any dings on the keel. After a bit of sanding, I applied Petit’s Old Salem wood sealer where the wood was bare. Finally, I brushed a coat of Micron CSC bottom paint onto the base of the keel. The UHMW shoe isn’t glued or epoxied to the keel, just fastened with #10 x 1" screws, so it’s my hope the bottom paint will keep any growth in that area to a minimum.

http://farm3.static.flickr.com/2172/2150723607_74804d16f3.jpg

More to come, I suppose, once I get back to work.

[Bill R]

Please forgive what may be a stupid question, but won't that have a tendancy to trap water between the UMHW and the wood, eventually resulting in rot?

If not, why not? What am I missing?

[AstoriaDave]

Pulled one of those UHMW PE shoes off the bottom of a drift boat a while back (fir ply construction), and there was a little rot, but not bad. Dry sailed, rot might not be an issue.

[Ian McColgin]

If you're done you're done, but I'd absolutely use a traditional underwater bedding compound there.

Also, the screws should be countersunk and bunged or puttied over to prevent them from catching on the ground and dragging the sacrifice pad off.

It'll be interesting to see if the UMHW outlasts dimensional lumber for a sacrifice pad.

G'luck

[Yeadon]

If you're done you're done, but I'd absolutely use a traditional underwater bedding compound there.

Also, the screws should be countersunk and bunged or puttied over to prevent them from catching on the ground and dragging the sacrifice pad off.

It'll be interesting to see if the UMHW outlasts dimensional lumber for a sacrifice pad.

G'luck

I've counterbored the fasteners so they're a touch under the surface of the shoe. I can't imagine what type of putty would stick to this thing. Maybe you could melt a bit of plastic back over the counterbored screws.


Please forgive what may be a stupid question, but won't that have a tendancy to trap water between the UMHW and the wood, eventually resulting in rot?

If not, why not? What am I missing?



Pulled one of those UHMW PE shoes off the bottom of a drift boat a while back (fir ply construction), and there was a little rot, but not bad. Dry sailed, rot might not be an issue.


These are fair questions.

I trailer and dry sail this boat, so it's my hope that the water will run back out between uses.

It's an interesting trade off. Without the shoe, rocks gouge the wood keel and create spots extremely susceptible to rot. With the shoe, you won't get gouges, but you have the potential of trapping a bit of moisture between the shoe and keel.

Bedding with dolphinite, or something along those lines is probably a smart thing to do. Agreed.

[Canoez]

There are some materials that you can use to etch UHMWPE and Teflon so that you can bond to it with epoxies. I don't recall the name of the stuff - we've got some at work, I'll see if I can dig it up. It's nasty stuff to deal with, but works pretty well.

There are also flame and plasma treatments that you can use to make some of these slick plastics "bondable". Depends upon the specific plastic.

(They get the Teflon to stick to the pan, don't they?)

[Eric Hvalsoe]

I think the UHMW will outlast nearly anything else you will find on this earth. I tend not to tell somebody exactly how they should do something - a perfectly wise idea to use bedding compound between the UHMW and the keel, I do. On the other hand, Yeadon's apitong keel is pretty well protected with Old Salem and bottom paint. UHMW does not rot. I think it is silly to worry about plugging the shoe fastenings, in this case they could have even been run in a touch deeper. The fastening themselves were run in with bedding compound.
Eric

[Bill R]

Thanks. The reason I asked is I was contemplating doing the same for my little ply & goop skiff, but I couldnt figure out how to keep water from becoming trapped under the UHMW.

Please keep us posted with your results when it hits the water.

[DRB]

It is common knowledge among drift boat builders that UHMW is a nearly indistructable material when used for bottom protection. It has it's good points, but there are also some bad ones. There is nothing that will stick to this material, so trying to seal it in any way with epoxy or any other compound will prove fruitless. The bigest downfall of the UHMW is that it is very sensitive to temperature and will contract and expand at a rate 10 times of the wood that it is fastened to. If you could find something that would stick to it this would brake the seal. worse than that is the fact that the expansion and contraction will constantly work the screws back and forth wallowing out the holes and allowing water to enter the screw holes. The screw holes is where you will have problems with rot starting in on your wood. You may want to remove the shoe and inspect for this poblem from time to time. If it looks like It will be a problem you may want to try just useing a sacrificial wood skid shoe. Many drift boat builders have gone to fiberglassing there bottoms and then coating it with an epoxy graphite mixture. As it wares you can just give it another coat of the mixture. Never ever store your boat upside down anywhere that direct sunlight will hit the UHMW. the sun hitting the black UHMW will cause it to get hot quick and it will buckle very quickly.

[Eric Hvalsoe]

Thanks DRB, was not aware of the expansion/contraction properties. In my typical application I don't think this would be critical - fairly narrow shoes and running strips, I can see where movement might become a significant issue on a drift boat bottom panel. I've used the material on several boats over several years now.

[Thorne]

There was an earlier thread on abrasion protection where Todd B. discussed a Kevlar (?) felt-like material used by canoeists -- sounded like the bee's knees for pure abrasion protection, but of course doesn't supply much in the way of impact protection like UHMW.

[Yeadon]

Never ever store your boat upside down anywhere that direct sunlight will hit the UHMW. the sun hitting the black UHMW will cause it to get hot quick and it will buckle very quickly.

This is pretty interesting info and definitely worth avoiding. My UHMW is white, but I'll heed your warning just the same.

Earlier today, I unfastened the shoe and bedded it with Sikaflex 291. Got a pretty decent squeeze out along the edges. Tomorrow, I'll fasten several UHMW lap runners that I've fabricated. I'll be using BoatLife Life Seal (clear) to bed the runners.

Incidentally, it was in the 50s today, with a bit of rain in the late afternoon. Much warmer than last week which was in the 30s. Around here, this is sailing weather. Time to wrap this project up and get back outside.

[JOBBER]

1st post
I have been considering the same application for a small skiff myself. I never really was worried about the trapped moisture, because from previous post discussed slotting the UHMW strip for expansion/contraction. I live in IL, ambient temps craft may see -10 to 100. So growth may be significant. So the fit may have to be somewhat "loose". I have not been able to get past sealing where the screw meets the wood. To me this is where the rot will occur. Does anyone have ant ideas on sealing this connection point?

[Thorne]

The usual method to protect plywood from fastener rot is to drill an oversize hole, fill with thickened epoxy and let cure. Then drill an undersize hole and screw the fastener in place.

As for protecting the surface of the ply, I'd think that an extra layer of fiberglass and epoxy would help, plus of course bedding the UHMW in Sikaflex, Vulkem116, etc.

Seems to me that slotting the UHMW might be asking for breakage or getting gravel caught in the slots -- perhaps small holes would give sufficient drainage?

[Canoez]

The usual method to protect plywood from fastener rot is to drill an oversize hole, fill with thickened epoxy and let cure. Then drill an undersize hole and screw the fastener in place.

As for protecting the surface of the ply, I'd think that an extra layer of fiberglass and epoxy would help, plus of course bedding the UHMW in Sikaflex, Vulkem116, etc.

Seems to me that slotting the UHMW might be asking for breakage or getting gravel caught in the slots -- perhaps small holes would give sufficient drainage?

The chemical for etching the Teflon is Sodium Napthalate. Nasty stuff. Doesn't appear to even touch the UHMWPE.

Thorne - you were thinking the same way that I was, - a slotted opening with a headed bolt and a washer to let the stuff expand the way cabinetmakers do with a wooden top that slides on dovetails for seasonal expansion and contraction. I got to the gunk filling the slots part in a hurry.

Perhaps just a sacrificial wooden (or metal) shoe? Plastic with better thermal expansion/contraction/water absorption properties? (i.e. closer to the wood itself.)

[Thorne]

Todd's recommendation of the Kevlar felt seemed spot on if no impact protection is required -- I think they hooked up a canoe on the tailgate of a truck and dragged the aft end around a parking lot -- no scrapes on the canoe.

And the felt wouldn't have the expansion/contraction issues of UHMW, but of course would hold moisture until dried.

[Canoez]

Todd's recommendation of the Kevlar felt seemed spot on if no impact protection is required -- I think they hooked up a canoe on the tailgate of a truck and dragged the aft end around a parking lot -- no scrapes on the canoe.

And the felt wouldn't have the expansion/contraction issues of UHMW, but of course would hold moisture until dried.

Well, the canoe doesn't weigh much and probably doesn't supply a whole lot of force to wear away the felt. A heavier boat might not do so well in terms of applying force to abrade the Kevlar.

Anyway - once the Kevlar fuzzes up from wear, it might be a bigger mess.

[JOBBER]

I reviewed Kevlar "felt" posts, they seem to address the abrasion issue nicely. Is the fiber composition such the fuzzies may not occur like woven cloth (longer fiber make-up)? The material comes in 40" sheet by the yard. Can this be cut to strips and joined then epoxied in place? Ideas on the joints - butt or scarfed? Thanks for great comments in this thread.

[DRB]

On my drift boats that take a constant beating over a variety of rocks and gravel both while launching and while scrapeing and skidding through the shallow parts of the river as well as banging off the occasional large rock while thrashing through white water, I use a bottom coating of 20 oz. triaxial epoxy fiberglass with 3 or 4 coats of 10% graphite powder and epoxy over the top of it. This treatment holds up very well. It usually takes two to three seasons before I need to recoat with another single coat of graphite and epoxy. The beating my boats take is probably much greater than that of the average skiff, dory or pea pod that is occasionally dragged up on the beach. Kevlar would be tremendous overkill for such a boat. There are some extreme drift boaters that will use kevlar lay ups on the bottom of their boats, but it is usually placed on the inside of the hull for puncture resistance while the outside is coated with fiberglass for abrasion resistance. Usually the kevlar will be topped with a layer of fiberglass, because the kevlar will not sand out well at all. Useing fiberglass on the bottom of a hull eliminates any fastener issues and if properly maintained will not allow in any moisture in the wood. It must be applied over clean bare wood to get succesful adhesion. Traditional boat builders often cringe over the thought of fiberglass, but if you are thinking of uhmw you have already gone by that point. I beleive that if the boat builders of years gone buy had access to some of the materials we have available today, many would have used them.
Keep it simple!

[Don Kurylko]

Thanks DRB. Very succinct and to the point. Might I recommend that sometime in the future you try pure copper powder mixed with Epoxy resin instead of graphite powder on the bottom of your hull. I have found that this combination has a much, much greater resistance to abrasion than graphite, particularly if it is left un-sanded after it has cured. Sanding reduces its abrasion qualities a bit, but it increases its anti-fouling properties, if that’s an issue. Mixing ratio is generally 2 parts copper powder to 3 parts Epoxy resin by volume. I initially apply about 4 or 5 coats "hot on hot" for best results. This yields about 20 to 30 mils of thickness. Copper powder is available through WEST Systems.

[Todd Bradshaw]

There are epoxy resins that stick quite well to UHMW polyethylene. What do you thing ski bottoms are made of and attached with? The polyethylene is prepared by sanding (no etching needed) and then flame treated. You run it quickly through the blue part of a torch flame. This polarizes the surface of the plastic and helps the resin stick better (at least that's what they told us in ski mechanic school). The resin itself is thick and cloudy with a slightly milky gold color - very different from normal boat resins. It's a slow cure, that's best done with the aid of a hot box. With proper prep, it worked just fine for replacing portions of ski bottoms. It's pretty expensive resin and looks to be the same stuff that plastic canoe manufacturers send out for repair of polyethylene and Royalex canoes or for adding Kevlar skid plates to them. You could likely use it to bond a strip of UHMW to a boat's keel, but if the plastic does expand and contract that much, a decently thick plastic plate would likely shear away.

Kevlar felt has little in common with Kevlar layup fabric. It looks and feels like the fabric of a very heavy chamois shirt, rather than a woven laminating fabric. It's only purpose is abrasion resistance and it does it extremely well. It will fuzz, but that's part of the plan.

History lesson: Climber's rucksacks and haulsacks used to be made of cotton canvas. Then somebody invented nylon pack cloth and claimed that it was lighter, stronger, more waterproof, rot-proof and a great backpack fabric. A whole bunch of pack manufacturers started using it and among the items made with it were their climbing packs. Climbers who bought them soon found that dragging them on rocks tended to abrade right through the fabric - much. much faster than it ever had on their old canvas packs. Somebody did some testing and figured out that when abraded, the spun canvas fibers would get fuzzy and the fuzz tended to form a pretty decent abrasion barrier, like little shock absorbers on the surface. The cloth made from extruded nylon fibers indeed had higher tear strength, but was so thin that by the time it got fuzzy, it was prety well shot. So the answer to making more abrasion resistant nylon was to make it fuzzy on the outside. The result has become most popular abrasion-resistant luggage fabric in the world - cordura nylon.

Kevlar felt is the cordura of Kevlars. A combination of it's ability to fuzz and it's bulky thickness (four or five times that of most Kevlar layup weaves) are what make it wear so well. It will, however, eat up a lot of resin, so it's best for smallish selective reinforcements. Covering the entire bottom of a plywood skiff, for example, would be both a heavy addition and an expensive one. For something like a keel strip or stem plates though, it might be ideal.

You can also mix carborundum grit with epoxy and use it as a coating. They were doing that on Colorado River dory runners for a while. The boats would actually leave grooves in the rocks! Graphite or other mixtures might be easier to deal with, but plain graphite, while slick, is pretty soft (softer than plain resin). Some colodial silica or metal powder mixed in will make it wear better.

[Canoez]

Todd,

Can you tell me more about this epoxy for the ski bottoms? Do you have a particular brand name in mind? We've got some projects here where we'd like to bond to UHMWPE and we have not been successful. Ultimatley, we're using prepared UHMW tapes with some sort of silicone adhesive that's been applied by the manufacturer - and it's not standing up.

We've tried a variety of recommended adhesives and have used flame and plasma treatment without success. I do know that there is a limit to the "open time" after treating the plastic before you bond, so that prep happens immediately before bonding.

[DRB]

This is some good info we are exchanging here. Although we may be getting away from Yeadon's acctual application a bit I have already learned of a couple things that might be worth experimenting with. The copper powder sounds like it would be worth a try, but I am also very interested in this carborundrum grit that Todd talks about. Todd, do you know were this material could be obtained?

I know that I exagerated when I said that "nothing will stick to uhmw". I should have said that nothing will stick to it easily and in my case feasably either. I also know that somebody somewere makes sheets of uhmw that are somehow bonded to a material on one side that can be glued, but you would still have the expansion problem when used with wood. I beleive this material is sometimes used for the inside of dump trucks. I use uhmw on my trailer bunks. I wish I had some pictures of it on a hot day so I could show you. I can tell you that it buckles severly because in the heat it will expand way further than the wood.

I have never worked with the kevlar felt. When it balls up and gets fuzzy after abrasion I would think that it would get pretty sticky as far as being able to slide around on rocks, but it would be something to experiment with. I am currently building a Simmons Sea Skiff and I am interested in finding the ideal protection for the skid shoe on this boat. For now it has a heavy build up of fiberglass with the graphite coating. If I am not happy with how that works out I might want to experiment with something else.
Thanks for the info

[JimConlin]

What are the sources for graphite powder?

[Todd Bradshaw]

Graphite powder is sold by companies like Gougeon brothers (WEST filler #423). They suggest using up to 10% by volume, which is enough to form a built-in UV barrier on the surface that will protect the epoxy, though a lot of the canoe people are adding considerably more. Whenever you use the stuff, have some small straight-sided plastic containers handy. Apply what you need and then toss a couple more spoonfulls of the powder into the leftover mixture and pour it into the small containers. Let it harden into blocks and you can later machine them into very tough plastic gizmos. The winch pad and the angled base under the cheek block next to it were made this way. The winch base was just a matter of finding a round plastic tub the right size (like a yogurt container) pouring the goo in, later sanding the top flat and flipping it over.

http://webpages.charter.net/tbradshaw/%2372%20furler%20line%20copy.jpg

I called Penn fishing reels once to ask what the frames for their graphite spinning reels, spools etc. were actually made of? The answer was graphite powder mixed with a polymer (resin of some sort). I also made the halyard sheaves for my Starboat this way from a block of excess epoxy/graphite mix.

[Canoez]

Jim - West System 423 Graphite powder - through their regular vendors.

[Todd Bradshaw]

Canoez, It's been more than 15 years since I worked on skis and I'm trying to remember the name of the suppliers that we got our resin from. Reliable Racing Supply? maybe? Old Town canoe has small cans of it for repairs and Kevlar felt skid plate applications to their plastic boats, but I hate to think of what they probably want for the stuff as retail repair supplies tend to get marked up a lot. I'll keep digging.

You can also buy UHMW sintered polyethylene that has been treated for adhesion with more normal resins and glues. Usually this is some sort of abrasion process and it's also often bonded to a light layer of cloth which you saturate with resin during the glueing process. We used to occasionally use sheets of this cloth-backed stuff for replacing good-sized chunks of ski bases. Unlike the plain UHMW sheets, you don't need to do the sanding and flame prep with this stuff. You gust apply the epoxy and clamp it. Here is one source, though I don't know how thick your plastic needs to be. Ski stuff is pretty thin.

http://www.durasurf.com/products.htm

Keep in mind that there are also different types of polyethylene used for this type of thing. The most common are extruded and sintered. To make extruded PE, you melt polyethylene powder and squirt or roll it out into sheets, rods, etc. For rotomolded kayaks and similar products, they dump it into a heated mold and tumble the mold to coat the inside - like the Pepto-Bismol test. Sintered PE is harder and more durable. The powder is heated, but not melted and then it is pressed under tons and tons of pressure until the particles stick together and form a sheet. It's harder because it's been compacted under so much pressure and the process actually leaves teeny-tiny spaces or pores between the particles. I don't remember whether all UHMW grade polyethylene is sintered or not, but to get that kind of density and toughness, it well may be. The pores are also why it makes the best ski bases as the sintered base will actually absorb ski wax down into the pores. An extruded base on a cheap ski won't do that. The wax just sits on top of the extruded plastic and wears off pretty quickly. Do these same pores also absorb epoxy or glue when you try to bond sintered polyethylene to something else? I don't know, but it's a possibility.

DRB, the felt won't "ball-up". It just gets fuzzy from lots of abrasion and very slowly wears away. It can look a little ratty when it gets fuzzy (though the fuzz is usually only about 1/16" long) but it can be overcoated and faired into the shape with other fillers. You can't sand it smooth, so if a spot gets fuzzy and you want to clean it up, the best way would be to coat it with something like a graphite mix until the fuzz is burried and then sand that smooth. The graphite top coat will then abrade and occasionally need touch-up, but under it you will know that you have a layer of something that won't abrade through.

[Todd Bradshaw]

http://tds.loctite.com/tds5/docs/HYSA9462-EN.PDF

This seems to be the one that pops up most often for epoxy bonding UHNW polyethylene and it's working characteristics sound a lot like the stuff we used. Might be worth a call to Loctite/Hysol to see what they suggest.

[Eric D]

Todd,
Not starting an arguement, but the comment on UV protection on the graphite is not completely correct. When I spoke to the West reps 2 weeks ago on that very topic, they said it will SLOW the UV issue but not stop it. They said that your milage will vary and in maybe 5 years or so IF you notice it getting chauky, you will need to recoat. Now if this is on the bottom, stored in a shed/garage etc. it is even less likely, but I was previously under the impression that it was the bees knees and all I needed for 100% UV protection and I am just pointing out that the WEST guys say no....Also, Larry at RAKA says the same thing...

As far as the discussion above, great info, keep it going, I am loving it. I have also heard several guys on other forums will defend a plain unpainted, unepoxied white oak runner will outlast any of the above since it will be able to dry out better. With the assumption that it is gonna be sacrificial anyhow. What do you guys think of that? (obviously bedded with screws and some gouge done well)

[michigangeorge]

Good God Guys! If ever I'm happy going back to low tech this is a prime example of why (poor english I know). Get a piece of oak (red or white makes no difference for this purpose) bed it with good old roofing tar and screw the som bitch down! Replace as needed :-)

[Keith Wilson]

A couple of thoughts - UHMW does indeed change size quite a lot (we use a lot of it for chainguides and the like), so I'd probably make countersunk slots for all the screws except the center ones. That will allow it to slide under the faster heads - and it will slide; it's very good at that. I'd use roofing tar between the UHMW and the keel. It won't stick to the plastic much if at all (nothing I know of does), but it will stick to the wood and be trapped in the gap. Can't hurt, doesn't cost much, will keep some if not all of the water out, and is a good combination of low-tech and high-tech.

[Todd Bradshaw]

George, That's certainly another possible approach to the situation, though given the choice, I'd take the white over the red (goes better with fish). Personally, I've always enjoyed dabbling in goo technology (goo-nology?) and there is plenty of it to experiment with. I also come from a canoe/kayak/whitewater background, where plenty of rocky water is involved and you need the most protection possible without changing the shape of the hull or adding much weight. Screwing a big thick hunk of oak onto the bottom of one of those boats is generally somewhat less than ideal.

Eric, you are correct. For obvious reasons, no powder held together with epoxy resin (especially at only 10%)can form a 100% UV barrier for that resin and the surface will chalk over time and wear away - exposing more so that the process can begin again. It will, however, drastically slow the deterioration and tends to prevent deep damage pretty well, so the piece will usually maintain it's structural strength. A thick layer of plain, unprotected WEST epoxy, for example will turn yellow over a season or two and get rubbery to the point that you can rub it off, all the way down. Mixed with graphite, pigment , metal powders or a number of other fillers it will chalk on the surface, but remain decently stable below for quite some time.

[JimConlin]

Jim - West System 423 Graphite powder - through their regular vendors.

I was hoping for something more reasonably priced. It's only graphite.

[Canoez]

Todd,

Hadn't tried the sintered stuff. Most of what we get it mill extruded. If the adhesive's viscosity is low enough, I'm sure it would penetrate. Particularly when heated for cure, or drawn in under vacuum.


I was hoping for something more reasonably priced. It's only graphite.

Jim,

You can also purchase powdered graphite from McMaster-Carr in 5 lb bags of powder for about $35. However as it is intended as a lubricant, I don't know if it's been adulterated with anything else. You could give them a call and I'm sure they'd tell you or supply you with an MSDS sheet that would let you know. The stuff from Gougeon Bros. is intended for use with epoxy, so at least it's a known quantity.

I always figure that if you're going to take the time to do good work, the right materials are relatively cheap in the whole scheme of things.

[JimConlin]

...
I always figure that if you're going to take the time to do good work, the right materials are relatively cheap in the whole scheme of things.
On that issue, you're preaching to the converted. While I'll often defended the Gougeons' epoxies as offering a very good product at a reasonable price, I've not felt that their additives were reasonably priced and have found satisfactory substitutes for most of 'em.

[DRB]

RAKA has graphite powder for $7.00 per qt./ 16 oz. this stuff goes a long way when mixed at 10% per volume. I have found that all RAKA products are very good quality and very cost competitive and they will also give good practical advice on the use of their products. I always ask for Larry.
I am still trying to find some of that "Carborundum grit". Does anyone know where to get it?.

[Canoez]

I am still trying to find some of that "Carborundum grit". Does anyone know where to get it?.

One possible source:

http://www.kramerindustriesonline.com/blasting-media/silicon-carbide.htm

Silicon Carbide = Carborundum, IIRC.

[Todd Bradshaw]

Sorry, forgot to answer that one. You can buy abrasive grit in various sizes from the lapidary supply places. They use it in rock polishing tumblers. You throw the rocks in the tumbler with some grit and water, turn it on and let it run for a few days. Then you clean it out, put the rocks back in with the next, finer grit and tumble it some more, etc. etc. etc. until you're up to polishing compounds. If you really want to, you could also buy some glue and make your own sandpaper :)

http://www.lapidarysupplies.net/tumblersgrits.html

[Don Kurylko]

Sand would probably work just as well as carborundum in this application and would be “dirt” cheap, so to speak. The trick would be to find the very finest powdered form available so that it will stay in suspension with the Epoxy resin and not precipitate out too quickly, as large grains would tend to do. This can be a problem - leaving all the sand on the bottom of the roller tray if you are applying with a roller. Frequent stirring will be required to keep things well mixed.

On horizontal surfaces, I would recommend first spreading the mixture over the working area with a Nylon squeegee to get a nice consistent layout and then rolling out with a short knap paint roller for a smoother finish.

Granite flour comes to mind as a possible additive. Probably free for the taking at your local tombstone factory! :D

[Yeadon]

So, I've installed the UHMW shoe, plus a pair of sacrificial lap protectors on each side of the boat. I ended up bedding the shoe, but didn't plug/bung the UHMW.

Overall, I found the UHMW pretty easy to work with ... it can be planed with a good sharp bench plane and is easily shaved with a router. You really can't run it through a thickness planer, it's a bit brittle for that. (We were curious, so we'd run it through the planer. The result was pretty uneven.)

If anybody out there would just as soon use oak, dimensioned lumber, etc, in lieu of the UHMW, well, I'd figure that'd do the job, too. Might even smell good when you cut it.

[Enelson]

I bought UHMW bars and boards from Garland Manufacturing in Maine http://www.garlandmfg.com They actually extrude the material there, and their warehouse looks like a plastic lumberyard with all different shapes and sizes right there on the floor.

When I asked them how to apply it, I was told to use a product from 3M called VHB. It's a structural mounting tape that seems to hold almost any kind of plastic to anything else. It was clamped to the VHB and the aluminum keel/strake for about 2 days, and since then I haven't been able to get it to budge at all.

I don't think it would work on a painted wood keel, but you never know until you try.

[Enelson]

There is a company in Maine that actually manufactures this stuff.

http://www.garlandmfg.com/plastics/products.html

:D

[TimH]

my question is how long will the paint stick to the plastic?