Daggerboard box

I have removed the daggerboard box in my renovation project. Shall I let the glassfibre on the outside go into the daggerboard box? I build a new box, due to rot, so the wood will be new. The glassfibre was only on the bottom of the boat around the slot. Any recommendations on how to the job? The slot in the bottom has a slightly different shape at the ends.

When I repaired (not rebuilt) my center board box, I remove the metal strips on the bottom of the Mirror on each side of the slot and cleaned out the area. Then I epoxied in new fiber glass strips. After having done this I did have to sand down the bottom of the slot so that the dagger board would slip through freely. Of course the metal strips were replaced. I hope this helps. Others may have better suggestions.

The best solution might be to make the slot in the bottom rectangular and make room for fiber glass. Sand down the plywood inside the centre board box as well to make room for the fibre glass. Each strip is said to need 0.2 mm. The fibre glass and epoxy must make this area stronger and more water tight than with only resin and paint.

If I then use 4 strips I can get fiber glass all way around inside the box. Two long ones cover the long sides and two short ones for the short sides. A little to much material in the corners will not cause any problems with the dagger board. The long ones will have full width where it goes into the box and approximately half width at the ends. If I then want to have the slot dagger board shaped that can be done with micro ballons.

The original solution on our boat was that the fibre glass was only on the bottom of the boat itself as an reinforcement. Perhaps an additional strip outside the ones going into the centre board box would be good?

A good number of screws was used through the bottom and into the pieces of wood at the bottom of the centre board. Will I need those screws? For strength? To get pressure on the resin? Or is enough/better to make some way to clamp when I put the centre board box in place?

Is the best way to assembly all pieces on the centre board box and then mount the whole assembly to the boat?


62816inBerlin's picture

I went through a similar (long overdue) set of repairs last year.

After removing the fibreglass tape with a hot-air pistol and scraper, I pried the case from the hull. The plywood had developed rot in places, which explains why I had trouble with the slight but irreparable leakage in the past few years:
rotted edges

The centreboard case had not been fitted very well anyway:
centreboard case

So I decided to make a reinforcement plywood "keelson":

To glue this in, I needed clamps. To my distress, I found that my C-clamps would not fit in the slot adequately. After taking the angles of the hull with a feeler, I made three massive "clamps" out of scrap wood and carriage bolts with wing nuts (actually I only found two fitting wing nuts in my junk collection, as can be seen):
keelson and clamps

Before starting with any gluing, I fitted everything together temporarily to ensure that it fitted;
 centreboard case

Next, I glued in the "keelson", clamping it in place with the three bolts. After this had set, I glued the snug-fitting centreboard case into the assembly (no screws or nails needed) and glued fibreglass tapes into the case, wrapping them over the sides of the hull (some filler was used to make up for the ragged plywood edges.
I jammed wads of paper solidly into the slot to push the box against the keelson. To press the fibreglass tape to the hull bottom, I put a wooden batten on each side of the slot and pulled these down with two of the "clamps" and rope "Spanish windlasses". The polyethylene bag material was put over the epoxy resin to prevent the paper, the battens and the clamps sticking:

When the epoxy had set and the clamps and polyethylene had been removed, the result was like this:

The wrinkles had to be sanded down, then I screwed the brasss strips back on primed the whole area:
sanded and primed

After varnishing, the inside of the finished job looked like this:

To my dismay, the centreboard jammed when I inserted it. I used a rasp, coarse file and lots of sandpaper to widen the slot by removing epoxy from inside the case. The "wads of paper" solution was definitely not good enough. I should have used a solid wooden wedge or something similar to make sure there is enough width.
In the end, I also shaved a few microns off the centreboard as well so that it slides down easily without jamming .
The whole repair job has held admirably and the boat is totally watertight again. On our messabout I capsized when gybing on a downwind run in a rain squall because my boom downhaul caught on the board which I'd raised. This must have put quite a strain on the joints and of course my hanging on to the board in order to right the boat also will have put a load on it. However there have been no signs of any cracking or other damage.

I hope this helps you to find a solution;


A1 description. Will be very helpful to those who need to make similar repairs. You are a true craftsman.

Three things caused the troubles:
- The fibre glass didn't go into the centre board box from the bottom side. It shall go into the centre board box according to the current building instruction.
- The old resin used to glue the parts together has broken down with time letting the water in and the parts to separate from each other.
- The previous owner who tighten the boat on the inside made the water to stay in the wood longer.

In fact all glued parts had separated, only screws, "silicon" and nails kept things together. The glassfibre on the inside had separated from the centre board box. Rot in the plywood at the bottom supports because of the "silicon" on the inside. The box were flexing 4 cm in the front top end.

If things had been in an earlier stage, I think fiber glass in the box from the outside and epoxy resin (without taking all things appart) could have been enough.


62816inBerlin's picture

Leif, my sympathy to you: you're probably going to have to rebuild the entire centreboard case by the sound of it.
Gernot H.