Liberty, the F24 that sailed this year (2020) after 4 years of restoration, was deemed by marine insurance surveyors to be beyond economic repair following damage to her starboard frames and planking. The injuries were caused through a bilge keel when bow waves from a passing vessel caused the keel to strike the ground.
The Finesse was manufactured with a choice of a drop keel or bilge keels. In reality, the drop keel was a default choice. Some had steel bilge keels as well, and these substantial items were designed to allow the boat to
stand upright when drying out. Each is attached to the hull by 5 pairs of bolts which pass through a wooden shoe (to adapt to the curvature of the hull). Inside, the bolts pass through the 4” x 1 1/4” bilge stringer which runs the length of the boat inside the frames. The space between the hull planks and the stringer is taken up by filling pieces. The bilge stringer construction is designed to withstand a force equivalent to a portion of the weight of the boat, since a boat without bilge keels will lie over on this part of the hull when drying out. The whole bilge keel structure is, therefore, extremely strong in compression.
The bilge keel option has advantages and disadvantages. They make drying out much more comfortable and they help upwind sailing without deploying the drop keel. On the other hand, a grounded boat cannot be freed by tilting over to reduce the draught; the keels can become foul with floating weed; they present a small increase in hull drag; and they add to the maintenance of the boat, requiring anodes for corrosion protection and periodic bolt renewals.
No-one was present when Liberty was damaged. The marine surveyor suggested that the planks and frames failed as a result of the starboard bilge keel being crushed inwards as the boat dropped off the bow wave. However, it seems more plausible to me that the keel dug into the ground and acted as a lever, temporarily twisting the bilge stringer in the centre of its length. In this scenario, the frames and planks were torn apart; there is evidence of copper fastenings being ripped out of their planks.
Whatever happened, it was obviously an extremely traumatic event for the boat. What lessons can be learned? A boat fitted with bilge keels needs sheltered conditions for drying out, that much is clear. Possibly the bilge keels are too robust- they could have acted as the weakest link and deformed sacrificially. There is food for though there for those who have these keels or for anyone considering retro-fitting them. As for Liberty- she has been sold to a Falmouth boatyard. The only repair scenario that made any sense was that the labour and boat-building skills would be supplied by her next owner.
My thanks to Hugh Brading, the previous owner, and to Martin Patten at Marine Techniques for sight of his damage survey. -DM