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Refurbishing and improving Centerboard


Wommasehn
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Mucklas Centerboard pivot - or rather the bushing in the trunks wall - has an issue: it leaked until I fixed it last summer from inside the cabin/the bilge. Since then it seems watertight but I fear, there might still be water ingressing into the plywood from inside the trunk. To take care of that, I had to take out the CB which is a nasty job. Only getting it back in is worse.

 

Now that the board is out anyway, I want to take the opportunity and put a little more lead in it. You might call the thing "swing keel" anyway if you like. 

It is made of 4 layers of 12 mm plywood , with the lower parts of the two middle layers being replaced by lead-plates. So the ballast is in the lower third/forth and in between two plywood parts (yes, meanwhile I know that solid wood would be stronger but this is how the designer specified it and it has held up for about 25 years now. Can't be totally wrong).

A few years ago, I sawed out  a chunk in the middle, made a mould from it and cast it in lead. Now, I decided to take out pieces of the outer plywood layers close to the lower end and cast them in lead too to create two more leaden pieces low down. They will weigh something like 4 kgs each. This will give a total of around 65-70 kgs of lead in the CB/swing keel.

 

 

 

The hole on the lower side of the picture is the pivot-hole.

432699460_2022-12-1714_41_05.thumb.jpg.bb9db928fdb5d9890885f8c752e77477.jpg

 

 

 

This is the starboard side with the piece of ply already taken out.

1150633063_2022-12-1714_40_19.thumb.jpg.0886b4badd87873cb55b4cc3322d01c5.jpg

 

Of course, I will glass the whole thing over which should add a good deal of strength  -but then again, I am not quite shure if this is enough. The critical region is where the CB exits the CB-trunk. There is the fulcrum which takes the load and there is the transition from the rectangular part inside the trunk to the NACA-profile. 

The board fits snugly into the trunk so there is hardly any room to make it thicker and hence stronger.

 

Now, finally here's my question: should I rely on the fibreglass for reinforcement (I could take off some of the wood to get in another layer of glass) or should I rather rely on metal ? 

 

For the latter, I have an idea: I might router a groove of maybe 20 cm lenghthwise on both sides through this loaded zone around the CB-slot and epoxy in  a threaded rod. This might give a lot of additional strengh.

What do you think??

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