Saturday, January 17, 2015

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.

Skid strips installed

With the hull painted, my next step was to install the skid strips on the bottoms of the skegs.  I ordered UHMW (ultra-high molecular weight) plastic from US Plastic Corp.  I got two 1 1/2" wide10-foot lengths cut at the 7 foot mark for shipping.  I ripped them in the table saw to 1 1/4" wide, cut them to final length, rounded the ends, and routed a roundover on the edges.

I then drilled and countersunk screw holes in the plastic to match up with the prepared spacing on the skegs.  I drilled into the skegs in the places where I had previously overdrilled and filled with thickened epoxy.  I first put a tape flag on my drill bit so I would not go too deep and drilled pilot holes for the screws.

I then countersunk the skeg a bit, because I found when driving the screws in  I would auger up a little epoxy and then the skid strip wouldn't lie flat on the skeg.  On the second skeg I used a bit bigger drill and things went better.  You need to use a larger pilot drill than you would if driving the screw into wood.

The Weldon countersink shown here works great for any kind of counter sinking -- much superior to the other style that is star-shaped on the end and always tend to chatter.

 Here's the little countersink in the skeg.

Before screwing down the skid strip I prebent the most severe curve, holding it in place with a couple small clamps.

Screwing the strip on then went smoothly.

I continued to drive in all the screws. 

Here's a closer shot of the front end.

And an overall view.  I think it looks nice.