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 15, 2012 at 9:04am

I haven't weighed the difference between a UHMW bottom and a fiberglass bottom.  I believe that the difference is going to be very small.  The UHMW is heavy for its size and so is the fiberglass.

Cost is the other issue.  If you already have UHMW and it works for you then it's a lot less expensive to simply screw it back on.  If you pull the screws and re-bed them at the beginning of each season then it could work well for years.  Where people rot out bottoms with UHMW is when the screws are worked lose.  That happens faster in environments that have a wide temperature change in a single day. Use 3M 5200.  It is permanent; however, you can use a drill to back out a screw embedded with 5200  because the threads cut the 5200.  Also the 5200 will not adhere to the UHMW.  So I believe the best way to install UHMW is to use as few of screws as possible, screw through the bottom into a frame, embed them with 5200 and then take the couple of hours on your first trip out of the year to pull and re-embed those screws once a year.

For the gap created by the rounded over bottom I use EZ Fillet from Systems Three.  It is formulated for boat fillets and is somewhat flexible.There is a thread on this site and a follow up on Brad Dimock's personal blog about a flexible epoxy that he likes a lot.  The key is to use good filler for strength and an epoxy with some flex so it is not brittle.

Permalink Reply by Jack Rose on February 13, 2012 at 10:27am

Hey Guys, thanks for all the advice.  I had been planning to just go back with my UHMW bottom, though with the reservations stated above.  But now you've got me thinking about fiberglass.

So I've read elsewhere on this forum that you can't bend fiberglass around a tight radius, and that attempting to do so from the bottom to the sides leads to a real possibility of compromising the barrier and letting water in.  And it also makes future bottom replacement that much more difficult.

Then, others say otherwise, that they wrap it up a few inches.

I believe that Randy said, somewhere, that he just applies the fiberglass to the bottom and doesn't wrap it.

I'm thinking I'll follow that advice, then put a bead of 5200 over the bottom/side seam and screw an oak chine cap over that.

Anyone got any strong feelings against or in addition to that?

Thanks.

Permalink Reply by Jonathan Clarke on February 13, 2012 at 11:55am

As with almost any subject, there are multiple schools of thought on this.  Some folks wrap the fiberglass up onto the hull sides after rounding the edge of the bottom.  Jason Knight, who contributes great stuff on this board, did an outstanding photo essay on this approach here:

http://www.woodenboatpeople.com/profiles/blogs/fiberglass-bottom-in...

and here:

http://www.woodenboatpeople.com/profiles/blogs/progress-report-32909

There are some folks who I respect a great deal who maintain one ought not wrap the glass around the bottom.  For a number of reasons, I took their approach when I refinished the existing bottom on my boat, which originally had no glass cloth, just an epoxy coating.  With the chine caps already on, I used a belt sander to put a gradual taper in the bottom as it approached the chine caps.  The taper was was just deep enough at the outside edge to accomodate the thickness of the fiberglass, plus a bit of "insurance" room.  One must trim the glass cloth just a bit inside the caps so that smacking a rock doesn't snag glass fibers.  It's not classic or even orthodox boat building by a long shot, but I've been happy with the results thus far.

Permalink Reply by Rick Newman on February 13, 2012 at 9:11pm

5200 is a great product for sticking wood together and sealing holes. It is so great that just about any wood you stick will stay stuck even when you want to separate it for later repairs. One suggestion might be to only apply the 5200 to the holes and or screws to prevent water intrusion yet still allow long term repairs.

Good luck!

Rick Newman

Permalink Reply by Jack Rose on February 13, 2012 at 9:35pm

Rick, I can second that (and thanks for all your posts and photos).  You can read my post, elsewhere, on removing the old bottom that I had attached with 5200, 16 years ago.  I used everything in the toolbox, from the heat gun to the blow torch to the Sawzall before finally settling on a draw-knife, which worked beautifully.

Maybe I should consider something less tenacious, like 3M 4200 or Boatlife, since the purpose is really only to seal that seam and not to actually adhere the chine cap.  Actually, I had great luck sealing around the fly line deck with regular old silicone caulk.  It held up nicely, but of course, it wasn't below the waterline.

And Jonathon, thanks for reminding me of Jason's photo blog.  I followed it while he was doing it, but at 55+ I had forgotten about it.

You guys have convinced me to go the fiberglass route.  So now I'm wondering about the graphite part.  Any info on that?  Where to get it, what ratio to mix it at, how many coats?

(edit - just found a couple of good threads on that: http://www.woodenboatpeople.com/forum/topics/boat-bottom?commentId=... and http://www.woodenboatpeople.com/forum/topics/graphite-powder?commen...)

Elsewhere, here, folks have recommended Raka for fiberglass cloth.  Epoxy, too?  And somewhere, I saw a reference to a Silver Tip (I think it was called) epoxy that doesn't blush.  Any thoughts?

And flow coats, are they just additional coats of the same epoxy that was used to wet out the cloth, or are they coats of a different type of epoxy?

Thanks again,

Jack

Permalink Reply by Rick Newman on February 13, 2012 at 11:16pm

Jack, Fiberglass Supply www.fiberglasssupply.com has Silvertip made by System III, graphite, E-glass, S-glass, bi-axial fiberglass cloth and much more. They have been easy to deal with, fair priced and ship in a timely manner. There are others out there, but with both FS and me being in Washington State they are the best for me. Silvertip is formulated to be used for both laminating and for flow coats.

They also have the Resin Research epoxy that Brad Dimock is now using because of its flexible characteristics. They list graphite powder, but I couldn't find it when I just looked. Add the powder to the last coat(s). Check out this link ; http://forum.woodenboat.com/showthread.php?88110-Epoxy-graphite-mix

Rick Newman

Permalink Reply by Jack Rose on February 14, 2012 at 9:05pm

Rick, thanks for the info.  I'll try to call them, tomorrow.

I've enjoyed Brad Dimock's blog on restoring the Betty Boop.  Matter of fact, his and most of the blog projects make mine seem rather simple, so I think it's time to quit over-thinking and jump in.  Besides, I proved last week that it's a boat again, we're just talking about a skid-plate, here.

And again, thanks for all your photos.  I've been poring through the photo archives looking for ideas on re-doing the seats and compartments in my boat, and your photos from the McKenzie River drift boat gatherings are a great resource.

Anyway, I'm heading out of town for a week, so if I can get the glass cloth and epoxy and graphite ordered, tomorrow, it should be waiting for me when I get back.

Launch date is March 1st, the 16 year anniversary of the first launching.

Thanks again,

Jack

P.S. By the way, I'm a photographer in real life.  That's what pays my bills.  You have a good eye for a nice picture.  I'm glad you're not in E. Tennessee.

Permalink Reply by Rick Newman on February 14, 2012 at 10:16pm

Jack, thanks for the nice thoughts. I just took a few shots out at LaPush, Washington at just about the farthest North town on the Pacific Coast. I would love to share some with you. Stand by for a friend request and message.

Again, good luck on your boat.

Rick Newman

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