Skid Plate Questions

Hey, I've finally gotten back to my bottom replacement project (Tatman, 16').  The new bottom is on (actually took it for a spin, last week, one small leak) and I'm wondering what kind of skid plate to put on it.  A skid plate is a necessity on one river in particular in my neighborhood (E. Tn); otherwise I could probably do without it.

Originally, I used UHMW and I still have that, and had thought that I would go back with it until I noticed a couple of postings, recently, about using Formica as a skid plate.

Formica would solve several problems associated with UHMW: weight and a bunch of screw holes compromising the plywood bottom.  Plus, I like that it would be lower profile, and probably wouldn't need to cover the whole bottom, just the part that normally sits below the water line.

I'm assuming that you'd put the Formica on just like you would on a counter top using an adhesive.  5200 seems like an obvious choice, but does anyone know if the regular stuff that cabinet makers use would also work?  Surely, it would be cheaper.  Or maybe some other marine adhesive like 3M 4200?  Or Boatlife?

Or back to the UHMW, which is what I'll probably end up using because I've got it, it worked great, before, and it will take a beating. 

So what's the best way to attach it?  Before, I screwed through the UHMW and the plywood bottom into the chine log and the frames.  Is that still the way to do it?  If I'm careful, the old holes in the UHMW should line up with the same frames. 

But it seems like it'd be easier to screw it only into the hull (1/2" plywood), but I'm not sure that would be enough to hold it on as I could only penetrate about 3/8" w/o coming through the floor.

Either way, that brings up my concern about compromising the plywood by drilling a bunch of holes into it.  I'm assuming that I should pre-drill the new holes through the bottom if I'm going into the frames.  But is there a way to seal them?  A dab of 5200 or some other sealant in each hole, maybe?

Any feedback will be appreciated.

Thanks,


Jack

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Permalink Reply by Randy Dersham on February 9, 2012 at 11:58pm

Jack, most of the repairs we have done at our shop have been replacing bottoms because the UHMW has worked screws loose and rot is introduced.  Our shop boats now all have 19 or 20 oz tri-axel fiberglass cloth and epoxy.

Many in Western Oregon still prefer the UHMW because it is so slick and our climate is moderate and the UHMW doesn't expand and contract as much as other areas with wider temperature ranges in a single day.  The more your weather ranges in wide temperature from morning to evening the faster the screws will work lose. 

It is best to screw it into the frames because the short screws set into the 1/2 in plywood will be worked lose very quickly.

Permalink Reply by Jack Rose on February 10, 2012 at 8:59am

Randy, thanks for your reply.

I'm intrigued by your fiberglass idea, and still curious about Formica, but I'll probably just go back with the UHMW as it was pretty well attached when I took it off, and it is a bird in the hand.  But I might try a dab of sealant on each screw hole this time.

So can I still get a front bow eye and the UHMW oar block inserts from you?

Thanks again for sponsoring this forum.

Jack

Permalink Reply by Guy Fredrickson on February 12, 2012 at 8:25am

Thanks Randy.  Very useful information.  Guy

Permalink Reply by lhedrick on February 15, 2012 at 9:35am

Randy,

I have a friend with the same issue.  I told him I would help him glass the bottom.  

My question is do you round over the chine cap and glass to the edge, the top of it or just to the edge of the plywood?  He was thinking about laying down a fillet and glassing over the top edge of the chine cap.  It was my recomendation he not do this.  My suggestion was to us a 10 Oz axel fabric out to the edge.  Then one more layer of ten Oz plain weave glass which would go up to the top of the chine cap. or just a layer of tape.  My idea was that this would allow removal of the cap for replacement with out too much difficulty.  His chine seems to be epoxied on and is in good shape.  It would be rough to get it off to run glass under it.

I am a stitch and glue builder so I could use a little advise on this one.

Permalink Reply by Randy Dersham on February 15, 2012 at 11:22pm

Both methods require the chine batten to be removed before you put on the fiberglass.  The point is to protect the fiberglass edge.  If you glass out to the edge of the chine batten without protecting the edge of the fiberglass hitting rocks will eventually lift that edge and water will get between the wood and the fiberglass

If you try to glass over the chine batten you will eventually hit a rock hard enough to break through that glass and trap water.  That will cause rot on the chine batten quicker than other methods.

If he doesn't want to remove the chine batten and its in good shape then I recommend he screws down UHMW.  You will get less water damage from the screws than from trapped water with the fiberglass edges not being protected. 

If he really wants to glass the bottom but not remove the chine batten he could try to 'blend' or thin the edge with a sander as it nears the edge of the bottom.  The point would be to try to feather out the glass about a 1/2 in away from the chine batten. This moves the edge of the fiberglass away from the area that will take the most rock hits and damage. I don't really recommend this but I've seen it done.

The best would be to remove the chine batten.  For an epoxied on chine batten remove the screws then cut the chine batten off with a reciprocating saw using a fine toothed blade.  Leave about 1/6 of an inch of the chine batten.  Then sand with a belt sander the remaining batten.

Permalink Reply by Jack Rose on February 10, 2012 at 8:57am

Oops, replied to the wrong reply.

Permalink Reply by Terry E Walsh on February 10, 2012 at 5:02pm
Randy is right on! Considering were u live go with the fiberglass. It is a bit heavier but no problems like a lot of screws that can leak and rot the wood. Your climate is perfect for the glass and it will be good for 20 years I would guess. It is easy and fun to do.
Permalink Reply by Jack Rose on February 10, 2012 at 9:46pm

Terry, Randy, thanks for your advice.

My biggest concern about fiberglass is that I use this boat mostly on the Hiwassee river. The river is considered a Class II whitewater river with one Class III.  The rapids are fairly technical, not lots of big water, wave trains, but lots of rocks.  

And I'm no geologist, but it's not a free stone stream.  All the rocks are still part of the earth, and they appear to have been laid down in layers (sedimentary, I guess) and then upturned into vertical ledges that tend to run perpendicular to the current.  It's hard enough to wade, but it's even rougher on a boat's bottom.

So my fear is that all those edges would wreak havoc on fiberglass, allowing all sorts of leakage between the glass and the plywood which would never dry out.

Or maybe I'm wrong.  Maybe fiberglass is tougher than I expect.  All the guides use Hydes and Clackacrafts, but then, they don't have to worry about rotting wood, either.

The original UHMW skid plate worked, but it also required a hundred or so holes into the plywood, so maybe it's not really any better.  And then, too, I am having to replace the bottom, but that's mostly due to the idiot who tried to store his boat outside for several years without an adequate cover (my wife keeps reminding me that I'm going to all this effort for want of a $200 boat cover).

Anyway, any advice given the geology of the Hiwassee?

From what I've read the process would be to glass the bottom, but not wrap it up the sides.  Two 10 oz. layers or one 20 oz?  Then I seal the seam between the bottom and sides and replace the oak chine caps.  Do you protect the edges of the fiberglass at all, or just rely on the chine caps?  And how about graphite?  Is that worth the extra effort/expense?

Sorry for all the questions.  Thanks for all the answers.


Jack

Permalink Reply by Terry E Walsh on February 11, 2012 at 11:54am
Jack, I live on the Colorado, Wyo border, fish the north platte, big horn mostly, both chocked full of sharp rocks. I actually put 2 sheets of 20 oz on the bottom, and 2 strips of 4 inch to cover bottom and 2 inches up the sides. Over kill but I have hit plenty of sharp rocks in the past four years and absolutely no damage or leaks and my boat is a 1964 model.Works great and u don't have to worry about the cold weather shrinking and stretching the umhw! Good luck......I did not use the graphite. Terry
Permalink Reply by Jonathan Clarke on February 11, 2012 at 4:15pm

It's the combination of epoxy and fiberglass that creates a durable surface.  The drill is to saturate the bare plywood with low viscosity marine epoxy, which both seals the plywood against moisture and provides a surface to which the bond the glass cloth with more marine epoxy.  Fill the weave with epoxy and add graphite powder in the last couple of flow coats and the bottom will be as tough as that on any commercially made fiberglass boat.  The upper St. Croix River in my area has stretches of bedrock bottom like you mention.  In low water, my boat makes some protesting noises as I go over the stuff, but I've never roughed up the bottom.

Permalink Reply by Randy Dersham on February 14, 2012 at 11:42pm

CLICK HERE to go to the thread that covers fiberglassing a boat bottom.  A.J. DeRosa and I discuss two ways to protect the edge of the fiberglass.  A.J.'s way is tried and true and has been used by Ray Heater and Cyrus Happy of Ray's River Dories for many years.  My way is a little newer to river boats but is common to lake boats.

I've attached an image of the two methods to show how similar they are and point out the differences.  This is an image of a cross section of the center of an upside down boat. I did not show a bottom frame for simplicity.  The dark black line is the fiberglass cloth and epoxy.

 

You will either protect the edge of the fiberglass with the chine batten by removing the batten, applying the bottom glass and epoxy and then re-attaching the chine batten with the bottom of the batten level with the outside surface of the glass. 


On the left is the method that A.J. describes. On the right is the method that we use for glass bottoms in our shop. The dark black line is the fiberglass cloth. Notice that in both methods the chine batten is bedded last and the edges of the fiberglass cloth are protected.


Rather than get into a lengthy discussion about pro's and cons I will make a list of methods to always or never do.

Always soak the end grain of the plywood with epoxy before either method.
Always protect the edges of the fiberglass cloth at the chine. Notice that on the left the fiberglass edge is covered by the cine batten, on the right it is tucked under the chine batten.
Never run the fiberglass over the bottom of the chine to the outside edge of the chine batten
Never wrap the fiberglass over the chine batten
If you are fiberglassing the sides of the boat with a light weight cloth then protect that edge under the chine batten.
Never attempt to wrap fiberglass over a sharp corner, especially on a boat's chine.

Today most west coast boats protect their chine batten with either a strip of UHMW or a stainless steel half round. Either of those two protectors prevent rocks from chewing away at the chine batten, so the battens are replaced less often. It is my opinion that replacing a chine batten today is usually because of rot or leaks caused by failed bedding.

Permalink Reply by Jack Rose on February 15, 2012 at 7:49am

Randy, thanks, that's exactly what I needed. Sorry I had missed that thread, it would have saved you guys a bunch of time.

But OK, one more question.  Using your method, what do you use for filling between the chine cap and the rounded over edge of the bottom?  It seems that Jason Knight addressed that in his blog, but I can't find it.

Is it thickened epoxy or is that too brittle?  Got another recommendation?

And one more last question, do you have any idea about the weight of a fiberglass bottom vs. UHMW?  You guys have sold me on fiberglass (anyone need a slightly used UHMW bottom?), but I am curious about the weight difference.

Also, I'm still looking for a front bow eye and UHMW oar inserts (not the block).  Are you still selling those (truly my last question)?

Again, thanks for this site.  It's an incredible resource.


Jack

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