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  Skid plates
  Posted by: rb56 on Oct-05-12 12:38 AM (EST)
   Category: Other Gear 

i bought a pelican 15.5 canoe in may and have enjoyed it more than i thought. i usually fish a lake and river that has concrete boat ramps and have suffered sufficient wear to warrant needing skids. i know the kevlar are suppose to be the best. i know the videos people make of doing it yourself on just about anything can be deceiving about how easy something is to do. my canoe is ramx like a coleman and is polyethylene. anyone had any experience please share and thanks.

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  skid plates and polyetthylene
  Posted by: pblanc on Oct-05-12 8:40 AM (EST)
-- Last Updated: Oct-05-12 8:45 AM EST --

First, Kevlar felt, which is used in most of the commercially available skid plates, is not the best, far from it. The Kevlar felt material is not very strong, results in a thick plate that creates lots of drag, and the material chips and abrades fairly easily. It is used because it is convenient and fairly cheap.

You are better off buying some cloth and cutting your own plates. I have used both Dynel and fiberglass for this purpose. S fiberglass is a bit stronger than E 'glass but the widely available E glass would be strong enough. Dynel soaks up more resin and results in a thicker plate (but not nearly as thick as Kevlar felt) so one layer is usually enough. With either E or S 'glass I would use 2 or 3 layers, of slightly different sizes cutting at least one layer 'on the bias' so that its fibers run at a 45 degree angle to those of the layer above or below it.

Either Dynel or fiberglass can be easily cut with a good pair of scissors. I would first cut out a template for your skid plate out of heavy packing paper. Fold your template down the long axis to make sure it is symmetrical. You can make the template any length and width you like. For most usages, a skid plate that starts about 6 inches below the top tip of the stem will be fine. Cut it in a tear drop shape (if that is what you want) and long enough to overlap the area of wear on the hull bottom by a couple of inches. You can use that paper template to mark out your fabric and draw a line on your hull to mask it.

The second consideration is getting a good bond to polyethylene. Polyethylene is a rather chemically inert polyolefin and adhesives have a very hard time getting a grip on it. Sometimes the old urethane adhesives (which stink to high heaven) sold with skid plate kits would yield an acceptable bond and sometimes not. I would use G Flex epoxy made by West Systems, however.

Even with G Flex, bonding to poly is a bit tricky. What I would do is temporarily tape your paper template to the hull and make sure it is centered, then mark along the edge with a Sharpie. Sand the poly inside your mark with something like 80 grit paper to rough up the surface a bit, then very extensively wash the hull with water and a degreasing agent (like Dawn dish soap), rinse well, then wipe down the area with isopropyl or denatured alcohol. After the alcohol has thoroughly evaporated you need to pretreat the surface of the hull by flaming it with an inexpensive propane torch. Don't omit this step. If you do, the epoxy will not bond.

Flame pretreatment is not intended to heat the plastic. What it does is temporarily 'etch' the polyolefin surface by oxidizing it. To effectively oxidize the poly you must contact the surface with the very tip of the inner blue cone of the flame and that little tip must contact every square centimeter that you want the adhesive to bond to, so it is best to do this in an area dimly lit enough that you can see the blue cone. You can pass the flame over the surface fairly quickly as you don't want to melt the plastic. Go over the surface in a very systematic fashion so you are sure you don't miss any.

Once you have pretreated the surface I would quickly mask off the perimeter of the area with painter's tape to contain the epoxy and provide an easy visual marker of where you want the edge of the cloth to wind up. Dynel and especially fiberglass cloth is woven and easily changes its shape after it is cut so as you wet it out with epoxy you want to make sure that it lays on the hull in its original cut shape. You want to start wetting out your cloth within 30 minutes of flaming the hull surface, if possible.

G Flex epoxy is easy to use. You mix it in any quantity you wish in a one-to-one ratio by eye. It is somewhat more viscous than traditional epoxy (not quite as thick as honey) so it takes a little more time to work it into the cloth, but it wets out fabric just fine and it has a little longer pot life than some other epoxies.

If you are using multiple layers of fabric it is not necessary to flame the surface of the wetted cloth before applying the next layer. I usually like to allow the first layer of cloth to cure to a 'green' state before applying the next, but some folks like to wet out multiple layers of cloth simultaneously. I wouldn't with the G Flex because of its viscosity. If you wait until the epoxy is completely cured before applying more, you should first wash the surface to remove any 'amine blush' which can interfere with getting a good bond. This is not necessary if you apply the next coat of epoxy while the first is still green.

After your last layer of fabric is on, you will need to apply another thin coat or two of epoxy to completely fill the weave of the cloth. After the epoxy is fully cured you can feather the edge of the patch (if you wish) with sandpaper. You can also paint the skid plate with spray paint. Krylon Fusion paints are popular for this purpose as they are allegedly formulated to achieve a better bond to plastics. The paint will scratch off, but it is very quick and easy to just mask off the plate and touch it up by spraying on a bit more. Before painting, again wash the surface of your patch to remove the amine blush.

You can buy 4 ounces of G Flex resin and 4 ounces of hardener in a kit for about 20 bucks:

http://www.jamestowndistributors.com/userportal/show_product.do?pid=8694&familyName=West+System+G%2FFlex+Liquid+Epoxy+Kits

I think that would be enough to apply a couple of skid plates.

Jamestown Distributors also sells fiberglass and Dynel cloth.

In the future, learn to approach concrete boat ramps abeam (sideways). Don't ground the stem of your boat on a concrete ramp. Contrary to the notion that a lot of folks have that Royalex and polyethylene are 'industructable' materials, neither are all that abrasion resistant and can wear through within a season of this type of repeated abuse. with practice you can carefully ground the boat sideways on the slanting ramp and step out of it amidships, sometimes without getting your feet wet.

 
 
  thanks
  Posted by: rb56 on Oct-09-12 6:23 AM (EST)
thanks on that info. i was under the impression i couldn't use glass on the poly. i have begun a different approach and usually have been reversing my trolling motor to not ride up on it so far. also usually alone and loading onto my pickup needed some sliding around to position it. again thanks for the info.
 
 
  keel Easy
  Posted by: mikehenebry on Oct-09-12 9:02 AM (EST)
I would take the easy way out and use Keel Easy keel strips. They are self-adhering and many times (seven I believe) more abrasion resistant that fiberglass. I installed these on my kayak in about 15 minutes.
 
 
  Keel Easy
  Posted by: pblanc on Oct-09-12 2:29 PM (EST)
I have not used Keel Easy strips. I am not inclined to do so in the future because they are too thick for my tastes.

I have heard quite a few favorable reviews of Keel Easy but to my recollection they all came from folks shortly after the installation.

Keel Easy strips are basically PVC bonded with heat activated contact cement. I would be concerned about the long-term durability of the contact cement bond based on my experience with other contact cements.

As for abrasion resistance, this link is to a thread on another forum. The eighth post in the thread suggests that the Keel Easy strips might not be so wonderfully abrasion resistant as claimed:

http://cboats.net/cforum/viewtopic.php?f=2&t=7965363&hilit=Keel+Easy

A nice thing about skid plates constructed from fabric like Dynel or fiberglass is that they are easily repaired if needed. Small dings into the fabric can just be filled in with epoxy. If the plate wears through, a small fabric patch can be applied over the point of wear.
 
 
  Keeleazy
  Posted by: booztalkin on Oct-09-12 8:06 PM (EST)
I think it is wonderful stuff and was definitely glad to have some on my fiberglass kayak when I was beaching it frequently on rocky shorelines.

However, I got hung up on rocks at one point and peeled off about six inches of the keeleazy, and I can't imagine that happening with a FG and epoxy treatment.

~~Chip
 
 
  shear stress
  Posted by: pblanc on Oct-10-12 7:47 AM (EST)
Most adhesive bonds resist tensional stress better than they do shear stress.

Skid plates on boats are subjected to considerable shear stress when the abrasion plate catches on an immovable object when the boat is in motion. This is particularly true for a plate on the stern (when the boat is moving forward). The lip at the more central edge of the stern plate tends to catch on rocks and shelves or gravelly stream bottoms as the boat moves over them. The thicker the abrasion plate and less well the edge is feathered the more likely the plate is to catch and the greater the shear stress testing the adhesive bond.
 
 
  A thought
  Posted by: jimyaker on Oct-09-12 5:31 PM (EST)
can you potentially reduce the wear and tear on the boat by avoiding contact with the concrete and asphault ramps? PE is pretty durable on natural surfaces like grass, dirt, small rocks.

I don't baby my plastic boats, but I'm confident it would take many years for the abuse to cause the hull to fail.

If you are ramming it up on shore to keep your feet dry, a nice pair of waterproof boots may be an inexpensive solution.
 
 
  tougher than keel-eazy
  Posted by: sapien on Oct-09-12 8:46 PM (EST)
Rec-Repair patches (www.recrepair.com) can be used as skid plates, either in the 3x10" or 4x12" size. you would want the "permanent bond" version; the temp bond will come loose with exposure to water. they are trimmable with strong scissors or a utility knife, and the edges can be filed before installing to taper them down to the hull surface.

they also make purpose-made canoe skid plates but they're too expensive.
 
 
  Question for P Blanc re royalex
  Posted by: gingernc on Oct-10-12 8:43 PM (EST)
P Blanc, that was a good explanation of applying epoxy and fiberglass to polyethylene. How about to Royalex? Probably omit the flame? Anything else different.
Thanks.
G in NC
 
 
  According to West Systems
  Posted by: pblanc on Oct-10-12 9:26 PM (EST)
pretreatment by flame oxidation of ABS (Royalex) is "optional". The adhesion data provided by West shows little advantage for flame treatment of ABS however.

The first time I bonded skid plates to a Royalex boat with G Flex I used a propane torch to pretreat the hull. Since then I have applied more than a dozen without the flame pretreatment and the bond has been just fine.

It is possible to use more conventional epoxies (like West 105/206) to bond to Royalex, but at least in theory the cured G Flex has a lower modulus of elasticity (is more flexible) than the conventional epoxy, therefore resulting in a better compliance match with ABS.
 
 
  Agree with PBlanc
  Posted by: dougd on Oct-11-12 7:39 AM (EST)
After a lot of reading and discussion I ended up using Dynel and a mixture of WS resin and G-Flex mixed in on the skid plates I put on my Courier. They are rock solid and have taken some hard hits on these rocky NE rivers. All that's happened so far is the paint has scrapped off.

The Courier is RX and I did nothing more than run some sandpaper over it first to rough it up a tad. It has held just fine without the heat treatment. In fact I patched one bad crack and 120 small holes in that boat and have not had one problem to date! A link to some of how I did work on that hull:

http://scooter-bangortoportland.blogspot.com/2011/01/rebuild-of-mad-river-courier.html

dougd
 
 
  Thanks, guys!
  Posted by: gingernc on Oct-11-12 8:32 AM (EST)
 

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