Eastport Pram Build #9: Is That a Daggerboard I See Before Me?

August 24, 2014

So, this last couple of weeks have been all about major milestones.  These were the steps I’ve been dreading for months.  These are the steps that make or break the boat’s fit and finish – the difference between a professionally built boat and one slapped together by a wood butcher.  Okay, so enough melodrama, let’s get to it…

 

First, the daggerboard slot in the center thwart.  This had two very specific criteria, it had to be perfectly straight and it had to land perfectly on the slot in the daggerboard case, which wasn’t perfectly rectangular due to the plywood warping.

 

This is another advantage to building templates – I was able to mock up a slot and see how it looked and fit.  I set the template in place and traced the underside profile of the centerboard case.  I know that the sides are 1/4″ and I know how thick the ends are so I was able to find where the slot should land.  My first attempt on the template was done by plunging a circular saw into the masonite.  This cuts acceptably straight lines when doing rough carpentry, but not what is basically fine furniture for the boat thwart.  I was at least able to determine any offset issues on the finished seat.  Remember, the seat is laminated, so if I botched it, I’d have to cut out two more, glue them together, etc. so it would set me back a couple of days.

 

That’s just about the time the I remembered I had a spiral upcut bit for my router.  This is the exact application for this bit – cutting a plunged slot.  I marked the exact location of the slot on the real seat, setup a straight edge for the offset of the router base to bit, checked the bit location on the slot at least three times and did a shallow “test cut”.

 

 “Test cut” on seat…

 

A few more passes and I cut all the way through, but the daggerboard didn’t slide in.  No worries, I planned for that to tweak the width so that the slot falls right on the centerboard case.  I put the real seat in place on the boat and determined that 1/8″ wider on the starboard side should do the trick.  I moved the straight edge 1/8″ and made another pass.  Now for the test fit – it fit perfectly.  Whew!  It looks CNC machined!  A little 220 sandpaper and the slot is finished, and at least as importantly as the aesthetics, the daggerboard fits perfectly.  Remember, I don’t want the slot so wide that the daggerboard has a lot of slop, but I also plan on adding several coats of epoxy and possibly graphite and/or fiberglass.  Now to make the daggerboard go through the hull.  Yikes!

 

 Slot cut perfectly, does not follow curve of daggerboard slot… 

 

 

 Daggerboard fits perfectly with just the right amount of slop…

 

Epoxying the centerboard case to the hull is the next big step.  I buttered up the mating surfaces, including the 1/4″ edges and set the case in place.  I’d already drilled the screw holes and counter-sunk them for the silicon bronze screw heads.  Once in place, the leading edge of the case wasn’t touching the curvature of the hull, so I added some weight.  Perfect!

 

 Centerboard case curing in place…

 

The next day, I mixed up another batch of peanut butter and did the fancy fillet.  Remember, the centerboard case is the most structurally important part of the hull.  Imagine running aground at a few knots and hitting a rock – all of that force is instantly shock load transferred to the case, so the fillet increases the bonded surface area, making the case pretty much bulletproof in case of a catastrophic grounding.  Hopefully, I’ll never have to test it…

 

 Centerboard case fillet…

 

The centerboard case fillet should also be aesthetically pleasing since it’s smack dab in the middle of the boat and is displayed quite prominently  on the finished product, so I smeared some peanut butter, waited for it to semi-cure, and sculpted it into the fancy fillet shown below…

 

 Forward fillet fancied up…

 

 

 Aft end fillet…

 

Now for the moment we’ve all been waiting for…  Cutting the hole in the hull for the daggerboard.  This is by far the most important make or break moment in the boat build.  I could’ve made another seat if I’d botched the slot, but I can’t make another boat at this point.

 

Ironically, this is the only time where I actually had to go buy tools to accomplish a build step.  I bought a 12″ drill bit extension to drill down through the installed centerboard case.  One on each end and a couple down the middle to destabilize the hull so it doesn’t fight the router bit.  The 1/2″ flush-cutting trim bit is absolutely necessary to insert through the pilot hole and follow the inside edge of the daggerboard slot, cutting a perfectly matching slot.  The reason why the slot in the hole has to be perfect is because I don’t want a lip for the daggerboard to hit as I’m dropping in the slot, possibly delaminating the hull from the case.  Also, the machining process can’t mar the waterproofing on the interior of the slot, so the following router bearing is the perfect solution.  If I’d just blindly cut the slot with a jigsaw, It might not have followed the inside of the slot perfectly, either creating a lip or cutting into the walls of the slot and it probably would’ve damaged the waterproofing layer.  Keep in mind the finished hull/case assembly has to be totally waterproof since it’s below the waterline and will be very difficult to repair if it sustains any water damage.  I did cut a slot between all of the pilot holes to further undermine the strength of the part of the hull being removed.

 

 

 Flush cut trim bit.  Router rests on the bottom of the upside down hull.
Bearing follows inside contour of imperfect centerboard case shape. 

 

 

 Pilot holes and connecting jigsaw slots.  Ready to route…

 

After a deep breath, I dove right in because procrastination would only increase my anxiety.  Inserting the router bit into an enlarged pilot hole (Confession:  I rocked the drill bit side to side stupidly while enlarging the pilot hole to fit the router bit, thereby nicking the interior of the case.  Sigh…  I’ll fix that later.), I very gingerly routed out the slot.  Remember, the wood is fiberglass reinforced on both sides.  I didn’t know if it would cut smoothly or just gouge giant chunks out of my boat.  The good news is that the newly sharp bit cut through the hull like butter…  Perfectly matched slot with the interior of the case, so no lips and no further interior damage to the waterproofing.

 

 This slot does follow the slight curve of the case…

 

 

 Right on the centerline…

 

Now for the moment of truth, dropping in the daggerboard.  SUCCESS!  It slid perfectly right down through the seat, case and out the bottom of the hull!

 

 Houston, we have a sailboat…

 

 

 Like a proud papa, I can’t get enough of this shot…

 

So now it was time to affix the center thwart.  Peanut butter on the edges of the daggerboard case and beam support, then drop the seat in place with weights to hold it in place.  Little did I know that the port side got caught on the edge of one of the side panels so it didn’t drop totally in place.  Of course, I discovered this the next day after the epoxy had cured.  It’s one of those “only I can see it” things that’s prevalent in my larger woodworking projects.

 

 Weights holding center thwart in place… 

 

 

 Center thwart affixed and daggerboard installed…

 

 

 Everything on the centerline as expected…

 

So now came the step that I hadn’t been looking forward to, but not necessarily dreading – epoxying all of the undersides to make the flotation tanks watertight.  I set the boat on the floor since I couldn’t reach bending over with the boat on the sawhorses.  I then spent a few hours on my hands and knees buttering up the undersides.  Note:  I didn’t try the pastry bag trick because I would be squeezing the peanut butter upwards, but the trade-off was that I needed a bunch more peanut butter to apply the initial bead, then reclaimed most of it when I scraped it with the filleting tool.  The end result was a lot of wasted peanut butter at the end.  I’ll need to figure something out for the aft thwart. I also didn’t bother smoothing the underneath fillets.

 

 Fillet under the forward thwart to make flotation tank watertight…

 

 

 Finished fillet around edge of forward thwart…

 

 

 Added rough fillet to center bulkead/thwart assembly…

 

Okay, now to seriously think about adding the skeg and skids…  I cut my skids a lot thicker than the plans for two reasons, first more protection while dragging on the beach, second I the skids couldn’t be any thinner than my tablesaw push stick for safety reasons.  This meant that they were going to be very difficult to bend to the bottom contour of the hull without stressing the attachment points while the epoxy was curing.  To put as much prebend as possible in the skids, I bent them over a “form” and continuously wetted them out with water.  After a day of wetting and drying overnight on the “form”, they sprang back to almost straight – just about an inch of bend.  Sigh…  Oh well, at least I tried.  I was able to pretty easily flex the skid over the hull without putting severe stress on the bottom.  I guess I’ll give it a go tomorrow…

 

 

New totals:

  • Installing daggerboard case = 1 hour

  • Daggerboard slots in seat and hull = 1 hour

  • Filleting undersides of thwarts = 3 hours

Total:  60 hours

 

  • Drill bit extension = $8

  • Flush cut trim router bit = $20

Total:  $983

 

 

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