UHMW for keel strips

Brad Taylor (NC)

Brad Taylor (NC)

Well-known member
Hey guys, I'm working on new boat design that will be specifically set up for a mudmotor. I would really like to use UHMW for keel strips but am concerned about a couple of things. Is there anyone that knows if there is a bedding compound that will actually seal underneath the keel strip? Is it really a concern if it is fastened with screws? Is the shrinking/expanding of the product a concern if it is 3/4" thick? Does anyone know of a better product with similar properties that can be bonded to the hull?

Thanks,
Brad
 
From wikipedia, easier than me explaining....

Ultra high molecular weight polyethylene (UHMWPE), also known as high modulus polyethylene (HMPE) or high performance polyethylene (HPPE), is a thermoplastic. It has extremely long chains, with molecular weight numbering in the millions, usually between 2 and 6 million. The longer chain serves to transfer load more effectively to the polymer backbone by strengthening intermolecular interactions. This results in a very tough material, with the highest impact strength of any thermoplastic presently made. It is highly resistant to corrosive chemicals, with exception of oxidizing acids. It has extremely low moisture absorption, very low coefficient of friction, is self lubricating and is highly resistant to abrasion (15 times more resistant to abrasion than carbon steel). Its coefficient of friction is significantly lower than that of nylon and acetal, and is comparable to teflon, but UHMWPE has better abrasion resistance than teflon. It is odorless, tasteless, and nontoxic.
 
The drift boat guys usually fasten it to the bottom with screws. Apparently there is not way to bond it or glue it on....so the water that gets between the UHMW sheet and the actual hull drains out when the boat is pulled. I think it's sketchy myself but I'm in the process of getting a new drift boat and I think I'm going to go with a UHMW sheet screwed to the bottom. I'd say your best choice for a contact on this would be Don Hill, Greg Tatman or Ray's River Dories and see what they think. I know Don Hill has some info on that website. The drifter will go through a helluva lot more than a duckboat so anything they do should work well for you.
 
Brad
There is a new UHMW product avaialbe that can be glued with an adhesive. Go over to the RIVERJET.com forum, they will be able to steer you towards the stuff.
 
Brad and Jay,
The stuff is the material that Ren Tolman uses on the bottom of his Tolman skiff boats in the cobble bottom of the Alaskan rivers.
He came on it from the commercial fisherman who use it for any area that will see heavy abrasion. IE rub rails and pot hauling areas. The only thing better is plate steel. Think alaskan crab boat or new england offshore lobster boat.
Hamilton Marine out of Maine has a variety of shaped extrusions and will sell sheet as well. The fastener is what needs to be sealed not the UHMW. It does not get glued. Use big washers and 5200. I would thru bolt where you can and screw where you have too. Screws should be into solid backing blocks not just plywood.
If you need abrasion resistant material on the bottom of a small boat it is the only material I would consider using if the hull is not metal to start with.
 
Bob (and everyone else),

I appreciate your response. I've found 2 different companies that actually have several products that will bond to it. One carries a 3M doublesided adhesive tape that will work if adhered with mechanical fasteners as well. They also have a epoxy system that is vacuum bagged as well that said is extremely strong. The other (interstate plastics) sells the UHMW as well and offer a product with these specs, not sure the manufacturer:

B-45TH

Adhesive
Sealant
Conformal coating


Flexible two-part thixotropic epoxy,
2:1 mix ratio


Excellent
adhesion to
low surface energy plastics without primer.
Bonding dissimilar materials.
Chemical and shock resistance.
Ease of use.


Bonds difficult-to-bond substrates and dissimilar materials such as UHMW,
polyethylene and acetal (Delrin) to steel, wood, plastics, rubber, urethane
and concrete. Survives harsh environments, particularly moisture, marine and
sub sea. Exceptional performance as a universal adhesive for industrial
applications. Will cure underwater. Can be applied to oily surfaces.
Ambient 24 hour or accelerated thermal cure.

If I can find something that will work I am extremely excited about the possiblity of using it as keel strips. I'll keep you guys posted and if anyone else has experience with UHMW I'd love to hear it.

Brad
 
Brad,

It looks like you may have found a better way using newer high tech products but here are my thoughts.

I agree with what has been said regarding the sealing being needed at the fastener only however a good bedding compound greatly adds to the strength of the installation.


keelstrip.jpg


In my drawing the red portion would be the bedding compound. By filling any gaps between the hull and the keelson strip, any shocks encountered from hitting rocks and other debris will be transfered directly to the hull. With out sufficient bedding compound the shock load must transfer thru the fasteners. As shown in the drawing the bedding should form a shallow keyway. Even tho it may only adhere to the hull and not the UHMW, it still needs to be there to carry the load. The fasteners in effect just hold the keelson strip in the keyway.

BTW. The UHMW doesn't have to be tapered but I like the looks of it that way. Also, gap shown is exaggerated for illustration only.
 
Dave that was kind of my thought too. Basically a gasket underneath, so I was originally thinking about one 3M products, something along the lines of 5200, can't remember the name right now. My fear of having the little strip on the outer edge like in your drawing (which by the way I appreciate you taking the time to do) is that it would eventually tear out if not bonded to the UHMW. Potentially leading to a section water could enter. Again this all goes back to, we're talking about a duckboat that will rarely be in water for over 5-6 hours at a time, not moored somewhere. I'm hoping the product I posted the specs to doesn't cost an arm in a leg as the UMHW is relatively inexpensive if you consider the time spent laying several layers of glass and a layer of zynol over the top. Which brings me to an aside, I came across zynol when looking at kevlar for a final coat on the bottom. The company that carries it claims it is stronger and more abrasion resistant that kevlar at about the same price.

My thoughts on the bottom of this boat (which is 17'x48" by the way) is to lay 3 layers of 6 oz glass, one layer of zynol and final two coats of epoxy being thickened with graphite and then sanded with 220. Not having to spend the time glassing two 18' strips and 2 15' strips several times with sanding is worth the cost of UHMW in itself.

Thanks again and I appreciate all of the input so far.

Brad
 
That's really interesting. Everybody I've spoken with about this ie boat builders claims that it just doesn't hold up well when you try to bed it or bond it. Hyde drift boats uses a concave washer that actually fits into the UHMW so it's flush and no fastener sticks out. These are the same washers that are used to line dump trucks that have a UHMW liner. I assume that's what the other guys use.

I can tell you this, as a fishing guide if there is any doubt at all about the longevity and durability I'd be very cautious. I just sold my glass drifter because I got sick of doing bottom jobs on it. Even with 5 layers of West/graphite, the river I usually fish was too hard on that bottom. At this point I have a couple options, a plastic boat or a aluminum with the UHMW shoe. If I could find a plastic boat that had the layout I'm looking for I'd go that direction but at this point I'll probably go with low-side aluminum with a shoe.

I don't mean to ramble but it's an interesting topic. I'll be really curious to see if you have good luck with trying to bond it. I think flexibility will be the big issue. A drift boat bottom flexes while a harder bottom boat usually won't so much, so that may mitigate any delamination. Please, keep us posted on this.
 
Jay appreciate your input. Thats why I really like this site, lots of different backgrounds. Do you by chance have a link to the concave washers you're talking about? I like the idea of bolting as opposed to screwing. However, there is no false floor in this boat so I would like to use the bolt head on the interior of the boat with a nut and washer on the exterior. I suppose I could countersink and over bore the UHMW so that the nut would be recessed, but I would be concerned about interferences with waterflow and how it might affect performance. Although I think it would be minimal.

As a side note, the boat will be designed for the rigors of a mudmotor and takes styling cues from both the Duckhunter and the Hellcat. The purpose of this boat won't be jumping dikes or anything along those lines, but simply getting to where the birds are but still having a boat that is very concealable and with good lines. I've been running a 21 hp hyperdrive on my original duckhunter which is made entirely from exterior ply (I've sinced switched to all okoume) and only sheathed with 6oz of glass have only had minor issues with the hull. I've flipped it over once 2.5 years and done a few small repairs but that is it.

Brad
 
you're right...rambling can be good sometimes and this site is certainly full of us ramblers. I don't have a link but you can call Steve Hyde at Hyde Drift boats or email him...you should be able to find his email addy at hydeboats.com. A few years ago when Steve was living in Newaygo, MI he showed the washers to me because I basically called him a bald-faced liar when he said they screw the UHMW on the bottom and it doesn't impact the handling of the boat. Those washers were very unique.

Keep us posted.
 
Brad,

If you are wanting to fasten from the inside of the hull, (assuming you have complete access) you could tap threads directly in the UHMW. If your strip is thick enough to allow you to recess a nut, you should have enough thread depth in a blind hole that would not break out the exposed face of your strip. Standard tapping methods will work just fine. Keep drill speeds slow enough to not heat up and melt the UHMW.
 
Dave thats kind of what I was thinking. Do you suppose the opening on the exterior side where the nut will be would create any performance issues or possible catch spots? To bad there isn't a way to insert a UHMW plug once I bolted it in place, but that leads me back to the original question of how to adhere it...lol I can access the entire strip if I do this early enough in the stages of the boat.

Brad
 
Brad,

[font=Verdana,Arial,Helvetica]
Do you suppose the opening on the exterior side where the nut will be would create any performance issues or possible catch spots?
Click to expand...
[/font]Yes and no, hows that for an answer?

Everything is a trade off.

If I let my anchor on my kayak drag the surface of the water I can feel the effect on my performance. If I had a motor pushing me, it probably would be unnoticeable. I suspect the same with the performance aspect of the opening in the keelsons.

On the other hand what you don't want, is to have your fastener too close to the surface. Imagine if you were to run over a sharp chunk of iron, rock, or whathaveyou. It is slicing it's way along your UHMW when all of a sudden it hits your fastener. Bamm, it tears out your fastener.

In my opinion the fastener should be recessed slightly below the exposed surface, enough to allow for some gouging of the parent material. These recesses will slightly affect performance, but like I said, everything is a trade off.

Just my thoughts.
 
When they line those dump trucks with UHMW they have all of those issues. The way I understand it, the rocks they haul beat the crap out of the beds and when they unload they need them to slide out quickly. Imagine one of those giant "mountain" dump trucks unloading rocks the size of refrigerators. Those "well washers" that I was referring to earlier are designed the withstand that kind of impact.
 
Jay I found the Hyde website and sent Steve an email so hopefully he'll respond with a source for the washers, you've definitely got my interest peaked.

Dave, thats kind of what I was assuming on fastening from the outside as well. The strips will be 3/4" so I would think a 3/8" recess would work if I had to go that route. I'm waiting to hear back from the two companies with the epoxy products that will bond it to the boat.

I'll keep you guys posted when I hear something and really appreciate your input.

Thanks,
Brad
 
The strips are intended to help keep the bottom off the hard but will not be used to cover the whole thing as in a dump body. The fasteners are counter sunk so they don't get the brunt of the wear until quite a bit of the strip is worn away. As for drift boats or mud motor boats, just like dump trucks they get hammered. Thats why they use aluminum. For a guide the boat is a wear item that is depreciated on your taxes just like a dump body and scrapped out after the thing is worn out and should have been paid for long ago. UHMW in trucks does work on rocks but is really intended to help with sticky loads that would require the driver to hand shovel the part that does not load out at the dump site. For rock haulers steel is the material of choice just like for heavy service offshore draggers. Better properties in the smack down department when a bit of overzelous operation occurs on the part of the guy with the excavator.
Bottom keelsons are only a replaceable wear item, not a subistute for a stronger hull material like aluminum or steel. I still recomend the 5200 as bedding and get new ones if you blow out the original, epoxy or methacralate would be much harder to remove. UHMW is way more slippery than brass or Al. and I think easier to repair than wood under either of the two other choices.
Good luck.
 
Brad,

One thing to think about is wear of the strip. If you plan to have this wear out in say the next 5 years or so and need to replace it, you are having 2 issues.
1. If you screw from the inside (my prefered way) you will have a bugger later removing all the screws.
2. If you use 5200, well, good luck getting that goop off....most wooden boat builders (from other sites) only use the 4200 or other products like Sikaflex or things along that nature. 5200 is truly a wonder, but as a bedding compound for somthing that may need to be replaced, it is a nightmare. Now, if replacement is not your concern (lack of abuse so it should last...or "hell, I sold it to some other guy so who cares" ) than this maybe more of an option.

All the sail guys DON'T use 5200 on any bedding projects (well, not at least the guys who know about the repair issues.....
 
you can FORGET "wearing" them out.....you might rip one off and you might have one fall off if you don't attach it properly but the talk on this thread of "wearing it out and having to replace it" is a fallacy.....

The trailer mfg. industry uses UHMW pads as glide strips for sliding suspensions.....these strips are often as long as 12' in length and about 1/4" thick. The pad sits between the slide rail of the suspension and the slide box of the actual suspension....the "fit" of those two componants is "sloppy" so that the suspension can be slid even when the trailer is not sitting level.

Semi-Trailer suspensions are expected to last 1MILLION miles in regular service, (minus wheels seals, brake pads and drums). Doesn't matter what the "interval" is, 5 years or 20, to get to that million miles the componants, including the slide pads, are expected to last that long.

Now imagine a trailer that grosses 80K or more, whose suspension can be slid multiple times a day, whose slide box is riding "loose" against the pads, and the pads which are in contact with the steel and subjected to "movement" constantly......and this happens 300 plus days a year....

Now compare that to the 30 or so days a year that a duck boat is going to be on the water.....

The "fear" that a UHMW pad on a boat is going to "wear out" is simply unreasonable.....like I said you might rip one off and you might have one fall off, (BTW the trailer industry uses the SCM glue pads between the strip and the steel), but you won't "wear it off".....

Steve
 
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