Tuesday, October 4, 2011

Chainplate Islands

For those that don't know what a chainplate island is (some call them housekeeping pads), they are nothing more than little raised areas where chainplates and other through deck hardware mount.  The idea is that since the pads raise the through deck opening up above the deck, there is less possibility of water intrusion.  Of course you still need to properly bed and seal the fittings but it seems reasonable to me and I think they look nice when made to look integral to the deck.

Originally I was going to do clay molds right on deck like what Don Casey did in Good Old Boat magazine (Issue 65 March/April 2009), but since Magic is not in the water and I know the boat is not level, I didn't want to cast pads that would be all out of level.  I also have a healthy respect/fear of my jackstands and feel no need to mess around with them unless it's absolutely necessary.  

I decided to build a mold for casting all the pads at once and came up with a design that would satisfy my requirements.   I decided on a 2"x2-3/4" pad with 15 degree bevels on 2 sides (the 2" fore and aft side). Using the miter saw I cut a bunch of beveled blocks 2-3/4" long out of 1/2" birch plywood and then cut 2 straight pieces to run the length of the mold from the same material.

Next I cut out a base plate that would serve as the bottom of the mold and be the interface where the chainplates slide through.  This whole mold building task was due in part to me wanting to put my new to me bandsaw to good use.  The bandsaw didn't disappoint.  I found it on Craigslist and paid $75 dollars for it.  The previous owner had bought a new one because he never had much luck getting this one to track straight without drift.  It was an old Reliant 14" that was just under 200 pounds and I knew I could get it working better than he did.  I replaced the top and bottom guide blocks, got a new Timberwolf blade and trued the wheels.  Now this thing is amazing.  I can cut a perfect line or curve in 5/4 rock maple without it even flinching.  Quite a bargain.  

Anyway, I used the bandsaw to cut out the slots for the chainplates in the bottom plate and a guide plate that would serve as part of the base of the mold.  I put clear packing tape on all the surfaces of the blocks and side rails and then laid down a piece of plastic sheet for the bottom and cut holes for the chainplate openings.  Then I cut out the base pieces with some old pine stock I had and assembled everything together.

I taped up all of the chainplates with masking tape and a layer of packing tape.  The combination gave me a little more than 1/16" on all sides of each chainplate so the fit would be too tight and I would be able to fit sealant into the pad when I rebedded the chainplates.  When I fitted the chainplates into the mold I pressed a little modeling clay around the edges where it goes through so no epoxy would drain out of the mold when I cast everything up.

Once I was satisfied with the setup I mixed up the epoxy, added enough Aerosil to thicken the mixture up to runny mayo consistency and then poured/slopped it in.  I filled each mold roughly 3/16" deep and called it a night.  When I came back the next morning everything appeared to have hardened up nicely so I took apart the mold, but when I tried to extract the first chainplate from the center of the pad, it cracked.  Damn it!

After instructing the kids that sailors have to talk funny and to not tell mom about my funny words,  I spent the next 30 minutes pulling out all but one of the chainplates with the same results.

Epic Fail....

2nd try = Much Better
After consulting the Plastic Classic Forum I came to the conclusion that I had probably mix up a hardener rich batch of epoxy that overheated and caused the brittleness.  I had eyeballed the mix because I did this in my shop and not in the boatshed where I have the proper volumetric measuring cups.  So I cleaned up the mold and coated everything with a paste wax to further aide in release (the chainplates were stubborn when pulling them out of the pads on the first round).  I also added some 'milled' fibers (1/8" fibers cut from 1708 fabric).  I'm going to leave the mold to set for at least 2 days to ensure a proper cure this time and hope I have better results.  I spent way too much time on this project and I hope I don't have to scrap the whole thing.

Update: I couldn't wait any longer.  I unscrewed the blocks from the mold just to get a feel for how things are setting up and I'm happy to report that all the pads popped out of the mold this time with no trouble.  I'll chalk it up to lesson learned: ALWAYS MEASURE YOUR EPOXY RATIOS....

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