CLASSIC SIX METRE NEWSLETTER

The first thing to bear in mind is that a reasonably sound hull is the only place to start. If the
hull is old and tired, no amount of secondary reinforcement is likely to work. A well built
wooden hull, with sound plank and hull fastenings and exhibiting no abnormal tendency to
work or flex, is the only worthwhile starting point. The clearest indication of a wooden hull
“working” is usually plank seams showing. On a well found hull it may be possible to stiffen
the hull generally by the traditional method of splining the seams (inserting timber fillets,
glued along both edges to the neighbouring planks). This helps prevent the differential
movement along the plank edges. If that doesn’t work or isn’t an option, we need to go into
more detail about the causes and potential solutions.
Let’s start with the global loads. Almost all sailing boats are resisting loads which try to fold
them up in the middle. The forestay and backstay / runners are all pulling upwards, whilst the
mast pushes down. So we have to try and ensure the hull can resist that. All first-year naval
architects are introduced to the concept of the “ship girder”; they are taught to treat the hull as
a box; the deeper the box, and the stronger the bottom, the better it will be at resisting the
long bending loads. Fortunately a 6M is usually quite a good shape box, being relatively
deep; this is especially fortunate because adding material to resist these longitudinal loads is
difficult once the boat has been built. In a wooden boat, it is usually impossible to effectively
or efficiently add material low down where it is most helpful (near or under the wood keel or
ballast keel), so we are normally looking for ways to support and brace the ends; pillars and
braces for the overhangs, and reinforcing the stem to wood keel or counter to sternpost
connections.
We also need to make sure the forestay load is transmitted into the only substantial structural
item around; the stem. That can mean taking the end of the forestay down through the deck
and actually attaching it directly to the stem face, or more commonly having a tie or wire
brace from the top of the inside of the stem to the underside of the head-stay fitting.
Above: bottom of the diagonal assembly – mast step with
turnbuckles connected to the bottom of the connecting plates
(Photo of Bihannic, taken with the permission of Laurent Lafaille)
Left: top of the diagonal assembly – metal plate on the beam
shelf tied into the shrouds and then connected to turnbuckles
and connecting plates (Photo of Bob Kat II, taken with the permission
of Doug Petersen)
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