Tag Archives: centreboard

Caledonia yawl project: fitting the centerboard well & breasthooks

I finally glued the last gunwale and with the magic of a belt sander I borrowed from my neighbour. I have been able to make it look nice and smooth. This is a tool I thought I’d only need occasionally but now that I’ve started to use it, it appears indispensable and I suppose that looking back shaping the keelson might have been easier if I had it.

20180414_165434

Next I tackled assembling all the pieces for the centerboard case.

20180415_151246

It is not super complex but you do need to pay attention to the dimensions in the plans and since they are unique it takes some planning to figure out what size stock you need to match the need. I spent a fair bit of time looking at the rows of clear douglas fir at the lumber yard figuring out what I wanted.

20180415_181735

what felt good is that everything roughed in really nicely.

20180424_221412

The last challenge is to get the centerboard pivot location placed at the right spot. The plans are good but my centerboard ended up slightly oversized and I have to figure out if I will need to modify the board .

20180421_162631

I still need to put graphite epoxy on the inside faces of the centerboard case and shape the forward brace.

then I tackled the breasthooks.  In the plans for the gunter yawl and gunter sloop version the breasthooks are much smaller than for the lug yawl version. The sides are only 6″ long vs. 10″ long.

20180414_213333

I made templates and played around with different ways to scribe the inside curve. I tried a compass but in the end fount that a very thin and flexible batten was the easiest.

20180414_213342

the wood came from offcuts from my neighbours hose renovation. He had found reclaimed fir from a warehouse demolition that was milled into 3×14 lumber for his rafters. Needless to say this douglas fir was dry and seasoned. When I glued it I put in threaded bronze rod to help tie the pieces together so that the glued surface is not the only part taking the load.

20180428_151532

this is patient work with multiple angles to keep track of. I felt like the breasthooks are one of the most sculptural parts I’ve had to work on so far.

20180428_151538

I worked at it with the block plane, the belt sander the random orbital sander and the very useful rasp.

20180428_191453_001

I alternated working on the bow and stern breasthooks to try and keep each learning from one process fresh for the other.  The only concern that came up is that there was a very slight offset in height of the gunwhales at the bow. The bow breasthook had to be shaped in such a way to to blend the difference and hide it.

20180428_163351

bit by bit I got it to take form

20180428_205602

and I’m quite happy with the results.

20180505_191150

 

 

 

Caledonia yawl project: Back in the boat shed

This fall has been overwhelmed with other projects, namely completing my bike shed and going to the THNK  school of creative leadership. Both eminently worthwhile pursuits, but they have displaced what little time I’ve set aside to move forward on this boat building project. It’s winter again and although Vancouver is not particularly cold the temperature has been hovering around three degrees Celsius in the morning and not much warmer in the afternoon which makes epoxy work more difficult.

Thankfully I have my makeshift oven.

Laminating my last knee
Where I can keep the latest knee I laminated warm enough to cure.

Next up the final fairing of the centreboard.

Continue reading Caledonia yawl project: Back in the boat shed

Caledonia Yawl project: Carbon, Graphite and laminations

This evening was productive. 

I managed to add the Uni-directional carbon fibre to the port side of the centreboard.

  

I also laminated another knee.

  
And also covered the port side of the rudder with epoxy mixed with graphite powder (west system 423) and a little colloidal silica (west system 406). This was a big step because now I can’t see the wood grain or the Kevlar weave pattern. All that remains is the shape of the blade, which is looking good.

  

Caledonia yawl project: laminating the knees and carbon on centreboard

Today I helped my friend get a new fridge in a house where the widest door was 28″ wide. We had to take apart the sliding door.

 

everything is back together but you can see the areas where i dug out the nails
 
This evening I managed to get a couple hours and I put the unidirectional carbon fibre on one side of the centreboard. I wet the surface with epoxy and the layed it down and squeegeed more epoxy onto the surface.

  
It’s not perfectly smooth, but I’m happy with the result. I’ll be covering it with graphite epoxy soon and that will be sanded smooth.

I also started laminating the knees that will connect the thwart to the gunnels.

  

I used 2 1/4 thick fir lamimations left over from making the stems. With some luck ill be able to cut them down the centreline and get two knees out of each one.

Caledonia yawl project: final shaping of rudder and centreboard 

Experience in working on gyprock and mudding all the joints and corners and having to then sand them down to a fair blend to the straight board stock, is that it is worth spending a little more time sanding even if to the eye and to the fingers it appears to be smooth. 
  
Once I add the unidirectional carbon fibre and epoxy I will certainly discover new spots that are not quite right for the centreboard and rudder NACA profiles. Sanding down epoxy is much harder than bare cedar.

I’m feeling fairly confident about the shape now and I’m looking forward to adding the epoxy and carbon fibre.

   
 

  
This beautiful cedar will soon disappear behind layers of carbon, Kevlar and graphite. The only part of the boat I felt would benefit from additional strength beyond just wood fivers.

Caledonia yawl project: final shaping the centreboard

Last night I got back out to the boatyard and spent a couple hours planing down the shape of the board to the depths I’d marked with the kerfs I made with the pull-saw. This technique is really helpful to keep tabs on the progress as I was using a power planer then a block plane and finally a random orbital sander with 60 grit paper.


 Once I got the taper cut for the leading and trailing edge I worked on rounding out the leading edge with the sander as well as the two ridges on each side.

The next step is to get ready to put some uni-directional carbon fiber on the sides and some kevlar fiber on the edges.

Caledonia yawl project: kerfs, planing and sanding

With a bit of further reading and some confidence building after my first set of kerfs on the starboard side of the centreboard I’m back to work on the port side.

 

It is slower progress but hand planing really makes you feel the wood and control the shape.
  
 

After removing the bulk of the material with the power planer, I switched to the small block plane which seemed to work better than the larger plane with the cedar and the curves. It also is pleasant to work making almost no noise and creating nice wood shavings and no dust.

For the transition to the part of the centreboard that pivots I need to use my random orbit sander with 60 grit. Ideally I’d like to use a disk sander or a belt sander.

Caledonia yawl project: shaping the centreboard foil profile

This part of the project was quite simply described by Ian Oughtred in his book “glued lapstrake boat building” as just rounding over the leading edge and shaping a taper for the trailing edge.

Knowing the density of water and the impact of good foil profiles for sailing performance I needed just a little more of a systematic approach. Something between CNC machining a NACA 0080 profile and sculpting it by eye.

I found two approaches that appealed to me. One was to map out the NACA profile in Excel and print out a template with a 40mm offset for a router bit and cut out the profile with the router using a plywood Guide.

Full instructions and a link to download the excel file here.

The problem was that in printing you need to calibrate for both the x & y axis. In my case when I got back to the boat shed I found that the y axis was off by 10% in the printouts. So I could not use it without reprinting. Additionally my centreboard tapers from the top to the bottom so I would need to cut several templates for the changing chord length.

Instead of going back and calibrating the print area, I resorted to a good system described in a paper by German epoxy company Gurit on building strongest & stiffest centreboards.

Gurit Guide to Wooden Foil Construction Figure 5
Gurit Guide to Wooden Foil Construction Figure 5
Testing the kerf method on an offcut from the centreboard.
Cutting the trailing edge kerfs on the centreboard
cutting the first leading edge kerfs on the centreboard

The method describes dividing the  chord of the centreboard into seven equal sections. Since the Caledonia Yawl centreboard tapers from 400mm to 230mm I did this at both ends for each chord length and then drew the lines to join them.  This allowed me to cut the kerfs to match the changing slope of the leading edge and the trailing edge to keep the same profile along the length of the board.

The other challenge is to kerf the taper of the maximum width of the centreboard as the chord gets shorter at the bottom.