Installing the centerboard slot gasket

With the skid strips installed I had one more job on the bottom of the hull to complete, and that was installation of the centerboard gasket.

The purpose of this gasket is to reduce turbulence at the centerboard/hull interface and the open part of the centerboard slot.  It also helps to keep sand and pebbles out of the slot when sitting on the beach.  Pebbles in the slot can jam the board in the up position.

There are a number of ways to attach a gasket, and I chose to use adhesive tape.  I also chose to install the gasket on the hull bottom without routing any kind of recess.  Here's the tape that I ordered.

I ordered 3" wide gasket material from Anapolis Performance Sailing.  This gasket material is a plastic somewhat thinner than a credit card, smooth on one side and with a thin dacron material bonded to the other side.

I believe the dacron material is so that you can epoxy on the gasket, but I thought it would be potentially difficult to get epoxy only where I wanted it, so I decided to go with the tape.  I assumed I would need to scuff up the shiny side and apply that side to the tape, leaving the cloth covered side down.  

Ideally I would want the shiny side out, so I did a test, taping two test sections to the rear of the skeg.  To my surprise, the cloth side seemed to adhere very well to the tape, so I decided to tape to that side and leave the shiny side out.

I first masked off the area where I would apply the tape so that I could scuff up the paint just in that area.  I planned to keep the tape away from the edge of the slot so that the gasket has room to flex.

I then cleaned up the dust, wiped the area down with acetone, and after that evaporated I put the tape on the hull, pressing firmly.  Here on the forward end I cut the corner a bit to keep away from the corner of the hull.

Next I cut the gasket material to size.  I had to trim the width a bit.  I lined up one side of the gasket with the centerline of the slot, and overlapped the other by about 1/4".  My idea in having this a bit asymetrical is that it reduces the likelihood of the material 'tenting' and failing to lie flat with the board retracted.

Since there is tape on the front of the slot I marked and cut the gasket to allow the edges to flex open.

At the rear of the slot I marked and cut a V-shaped opening to allow water to drain out.

Then I removed the protective plastic from the tape and pressed the gasket into place. 

So things then looked like this. 

Lifting up the hull and turning it on its side, I installed the centerboard to see how things looked. 

I could see that I would need to do something at the front of the slot.  It seemed clear that this was a recipe to scoop up a bunch of water. 

First I viewed the gasket from above and sketched out a curve.

Which looked like this on the flat.

I cut the marked area away, and then after roughing up the gasket I adhered another bit of gasket with another piece of tape.  I then extended the board again and trimmed the edges so it looked like this.

And with the board retracted things close up very nicely.

I'm hoping this installation method holds up long term, but if it doesn't I can always try something else the next time.

Pivot bushings installed

After the oversized, epoxy-filled pivot holes in the rudder and centerboard cured, I drilled them out with a forstner bit to the right size for the bronze bushings, and proceeded to prepare the bushings.  My local hardware store didn't sell bushings long enough for the full width of the parts, so I bought them in pairs.  I used one full length (1 1/8 inches) and shortened the second one to make up the length required.

I first cut the bushing to rough length with a hacksaw, then chucked it up in the metal lathe and faced of the end.  I was having fun, so decided to spend the time turning a shoulder on one part and boring a recess in the other for a nicer job.  I then turned some coarse threads on the outside to give the epoxy something to grip.

Can hardly see the joint when these go together.  Nice to have a lathe... 

Here's a shot showing the threading in progress on one of the bushings that goes in the centerboard case.

However, to save time on the rudder pivot I just used a butt joint.  

I put a piece of tape across the bottom of the holes, coated the outsides with unthickened epoxy, and inserted them in the holes.

When I installed the centerboard case bushings, I combined two steps.  Instead of drilling the holes oversized, filling them with epoxy, and then drilling them out again, I instead drilled oversize and then cast the bushings in place.

To hold them in perfect alignment, I used a spacer block that fit exactly inside the case.  I taped both sides, and drilled a 1/2" hole on the drill press.  Here's the spacer block installed in the centerboard case.

I then could put a greased 1/2" rod through the bushing and block to ensure the bushing was perpendicular.

I coated the inside of the hole with unthickened epoxy, then coated both the inside of the hole and the outside of the bushing with thickened epoxy and inserted the bushing.  Then poked around with a toothpick to try to make sure there were no air bubbles in there.  If I were doing this again, I would drill the oversized hole larger to make it easier to get the epoxy in there.  The bushing is 3/4" outside diameter, and the hole is 7/8", so just 1/16" gap.

I filled the top hole, then the next morning turned the part over and did the other side.  After the epoxy cured I removed the rod and was able to drop the pivot bolt in with no binding, so I was pleased with my success in getting these bushings aligned with each other, and perpendicular to the surface.

I liked doing this work on the flat vs. trying to install these after the centerboard case was in the boat.  Other than dealing with large parts it was fairly easy to keep holes perpendicular on the drill press, checking alignment with a small square.

First dry fitting, and centerboard case work

With the jig done, it was time to fasten on the bottom of the hull. Lined up perfectly centered, the hull panel is held on with four screws through plywood pads and into two cross members on the jig.

I then squared up all the routed aligning indentations with a small chisel, and squared up the corresponding tabs on the bulkheads with a file, and then did a dry-fit of the parts.  That was pretty neat - I can really get a sense of the size and shape of the hull now!

Before gluing any of that in, I need to finalize the centerboard case.  I decided to epoxy the doublers on to the panels before installation.

The next pieces I need will be the solid stock for the ends of the case, and that's still getting epoxy coats, so is delaying the process.  But that gives me time to think about where I want hatches.  

And opportunity to keep applying fairing mix and smoothing that off the rudder and centerboard. With each iteration they get closer to done...

Dynel, Cleats, and Building Jig

Since last update I applied dynel fabric to the leading edge and bottom of the rudder and centerboard.  Dynel is reputed to have very good abrasion resistance, and I put several layers on the parts that will drag first when the water gets thin.  Shown here is the front corner of the centerboard.

I also cut, planed, and routed some stock for cleats to reinforce the joints where plywood pieces meet in the boat.  These are just plain pine boards from Menards.  I've got 80' prepared.  There are some knots in this #2 lumber, but I will just cut around those and work with the clear wood.  Yellow cedar is recommended, but not to be found around here.  I will precoat these pieces with three coats of epoxy on the sides that will not be glued to other pieces.

Then I got started assembling the building jig.  I set up the legs and started gathering pieces, 

And held them in place with some clamps, 

And spent quite a bit of time shimming and checking for level both lengthwise and crosswise.

Then I screwed the bottom to the legs, and screwed in cleats to hold the sides to the bottom.  It stiffened up very nicely and now feels sturdy.

And ended the night by placing the first boat part on the jig - the hull bottom.  I think the shop is going to start feeling pretty small soon...

Rudder/centerboard work and more puzzle joints

Since last update I have been epoxy coating and sanding more parts, and am running out of those.  I've been finishing up the rudder and centerboard by adding  fiberglass cloth to the trailing edges and the top edges.

Then I got a little carried away and started applying epoxy mixed for fairing, but just realized while writing this I haven't put on the dynel cloth on the front edges, so will need to backtrack a bit on that.

I also glued up the puzzle joints in the deck side pieces tonight.  One more puzzle joint glue up to go, where these side pieces are joined to the front piece.  I plan to do that before assembling the jig for the boat, which will take up a lot of my workspace.

Cleanup

Spent a little time today trimming off the excess fiberglass and feathering in the overlap, photos below.  I need to check with the SCAMP community regarding a couple things.

First, I wonder if there is any reason to keep areas like this square?

I'm thinking of putting about 1/4" round over on there and then fiberglassing the edge.

Secondly, I thought I was done applying glass on these parts (other than doubling up the edges), but then I saw a couple references today to other builders putting on two layers of fiberglass.  I reviewed the build manual and didn't see reference to that there, so not sure where that came from.

Rudder and centerboard fiberglassing

The rudder and centerboard glue-up turned out great.  I spent some time cleaning up glue squeeze-out and making sure all the surfaces were rounded off to the extent I thought right, and then decided to go ahead and put the fiberglass on.

Since the entire sides of the parts get fiberglass, and the cloth is to wrap around the leading edges, I wondered how to hold the parts while I applied the cloth and epoxy.  I decided to put a couple dowels in a stick of wood that would match up with the holes in the parts.  Then I could put the stick in the vise and have unobstructed access to one side at a time.

Here's the rudder ready to go.  Since this part was light I was not too worried about the strength of my fixture.

The centerboard was a different story.  There's about 22 lbs of lead in the board, and it's all hanging out at the far end.  Kinda scary - I wondered if I'd be able to cantilever that out.  I used a 5/8 wooden dowel in the big hole, and a steel pin in the small hole.  And I had to triangulate the stick with a brace against the bench so the whole works would not twist in the vise.  Seemed to hold OK for this job.

Holding the parts like this worked out well.  I had access to the entire side, and could work the far side where the fiberglass wrapped around.  

Here's the rudder with the fiberglass wet out.  The white patch is some fairing compound (epoxy and glass microballoons) showing through the cloth.

Today, after the first sides were cured, I trimmed the excess fiberglass off, and feathered in the edge of the cloth that would be covered when applying glass to the second side.  Here I'm using a utility knife blade as a scraper, and that worked very well.  This is a tip from Howard Rice on the SCAMP forum.  

After getting the parts cleaned up, I reversed the holding jigs and applied cloth to the other sides.

Rudder and centerboard lamination

I decided it was time to get the rudder and centerboard pieces assembled, so I spread glue on the mating faces, using a notched spreader to distribute the epoxy across the surface.

 Then applied clamps until I had squeeze out all along the seam.

Here's a shot of the centerboard clamping.  It takes a lot of clamps!  At the far end of the table you can catch a glimpse of my 23 gauge pin nailer.  After I slid the halves around until they were in alignment I shot a few 1" stainless pins in to keep the parts from sliding around while clamping pressure was applied.  That worked well.

I've also glued up the puzzle joint in the cockpit sole, and have been busy epoxy coating all the major parts of the boat that would need it sooner or later.  Sole, sole doubler, deck parts, transom cap.  I'm running out of parts, so that's good.  It will be nice to have them all ready to go at assembly time.

More centerboard weight

Before I glued in the centerboard weights I put them on the scale to see how far off my target of 22 lbs I ended up.  I found they weighed 20 1/4 lbs, which was not too far off.  However, I decided that at this stage I could easily get closer than that, and by doing so I wouldn't always have a nagging feeling that I was a little light in the centerboard!

I had gathered up a bunch of the lead shavings from the initial machining (see one of the first posts in this blog), and I melted those down with a propane torch and a little cast iron ladle I picked up at an antique store once.

I drilled two test holes with Forstner bits, 3/4" and 1", and filled them with lead.  I then weighed the slugs and calculated how many I would need to make up the 1 3/4 lb deficit.  I ended up needing about 20 of the larger size, so I drilled 10 holes in each of  the two halves of the centerboard to a depth of about 5/16".

And poured them full of lead.  I had shavings enough for only about half the job, so I melted the remainder off of one of my leftover ingots by putting it in the flame and catching the drips in the ladle.  That worked out smoother than I expected.

One job for tomorrow is to scrape these down to level, and then these halves will be ready for assembly.