Tom, are you *sure* that there is no pivot in the centreboard case of the glass fibre boat? Some boats had holes and a bolt, with washers either side of the centreboard case (which leak over time) and some have a fixed pivot inside the centreboard case – just a rod to act as a pivot in exactly the right place, fully encased so that there is no leak.

If your hull has the rod, your centreboard needs modifying by cutting a slot from the outside to the pivot point, and then a filler plate is fitted (the bit you cut out if the grain is right) with a plate to hold the board onto the pivot. This is much easier to see in a photo than describe in words… see http://www.milanesfoils.co.uk/products/gp14/egs-centreboard/index.html for an example of a centreboard with a slot to the pivot point.

If your hull has no pivot point at all – no bolt hole and no rod in the centreboard case… then you have a significant issue. I hope that you have a rod fitted.

Tom,

There is some confusion,  because I believe you may be using the term Mk 2 incorrectly;    the Mk 2 boat is an early GRP boat,  built from 1969,  and I am not clear whether any were built after the Mk 3 appeared in 1977.    To the best of my knowledge it uses the same centreboard as the Series 1 wooden boat,  and no modification is needed.

If however you mean that your replacement boat is a Holt Speed,  or later,  model,  with underfloor buoyancy,  the pivot is permanently bonded into the case,  and the board has a slot extending from the pivot hole to the leading edge;   and once the board has been fitted the open end of the slot is blocked off by an infill piece which (I think) is screwed in place.

Although the underwater profile of both centreboards is the same,  my understanding (from Tim Harper,  when he built A Capella for me,  and advised me that the Series 1 centreboard which I had acquired would not fit) is that the upper parts of the centreboards are not identical,  and that the earlier type of board will not fit the later boat.

Sorry to be the bearer of bad news!

Oliver

Steve also makes some very good points;   but the first thing is to identify whether your boat is or is not actually a Mk 2.

Can you upload some photos,  please,  showing the interior layout (including the buoyancy arrangements),   and the aft deck and the transom.

UPDATE,  0610 21 April:   I apologise that,  10 hours after asking for photos,  I will not now be able to respond for some time if they do now appear.   I go into hospital for planned surgery on my right hand in an hour’s time,  and I will then be unable to do any typing for perhaps the next three weeks.    Didn’t think of that when I requested the photos!

Oliver

• This reply was modified 2 years, 8 months ago by Oliver Shaw. Reason: Update

Tom,

Thank you for posting that image;   and I agree that it does appear that there was once a (stainless steel?) vertical carrier comprising two straps,  one each side,  with a pivot between them at the bottom of the straps.

I have the very vague impression that I have very occasionally seen that arrangement on some early GRP boats,  but only as a fully assembled system,  and I confess that I had forgotten it.   Could this be the Thames Marine version??

What follows is my strictly theoretical suggestions for how that could replicated now,  starting from scratch,  but I stress that I am not familiar with the detail of how this was fabricated originally.

It should be possible to make up a replacement,  out of stainless steel strip.   One supplier of strip is Just Stainless,   https://juststainless.co.uk/product-category/strips/   Alternatively,  if you are going to ask your friendly local stainless steel fabricator to do the metalwork,  they would probably have suitable strip in stock,  and all they would need would be a sketch,  with dimensions,  and a description.

I do not know how the pin was originally placed and secured;   but if starting from scratch now there would seem to be (at least) three options to consider,   all three for a semi-permanent pivot pin,   which would effectively be installed before the centreboard is fitted,  and then left in place.    The centreboard could then have a slot between the pivot hole and the leading edge,  as with the series 2 centreboard,   so the board could then be slotted into place,  and the slot then closed with a fillet,  again as per the series 2 board.    That may well not be original,  but I would confidently expect it to work.

The pin itself could in theory be fitted by machining a spigot at each end,  so that the holes drilled in the two strips are smaller diameter than the main body of the pin.    That would then give a guaranteed spacing between the two strips.   Then either the ends could be peened over,  or tack-welded (your local stainless steel fabricating firm would be happy to do this for you,  and also to machine the spigots),  or  –  somewhat questionably  –  bonded with Araldite.

A fourth option would seem to be to cut screw threads in both spigot and holes,  but because of the very small thickness of the strips this would need to be a very fine thread,  and I would think that each of the other alternatives is probably easier.    However the screw thread approach would enable the assembly to be disassembled later;   but I doubt whether that facility would ever be needed.

Whatever method is used for securing the pin,  it would seem to be a requirement of the construction that there should be no surplus weld or adhesive rounding off the inside corners,  i.e. the pin should have a constant diameter right up to the side carriers.  And there is probably little tolerance for excess material on the outside face of the carriers either.    Your fabricator may need to be briefed about those two constraints.

Hope this helps,

Oliver