Classic Boat — March 2018

TIMBER FOR NEW BUILDS

TIMBER FOR STRIP PLANKING

Above: Douglas

fir planking in the

early stages of

build for the new

Spirit 111

superyacht

Boatbuilders may choose to source timber for strip

planking in the form of sawn boards and machine it

themselves, but they can also buy it machined and

ready to use. Whereas with traditional hull construction

planks are tapered at their ends to reflect the smaller

girth of a boat at bow and stern, with strip planking the

planks are nearly always parallel so that they simply

‘run out’ at the sheer and/or at the centreline.

Robbins Timber is one company that provides strip

planking ready machined in two different formats:

‘rapid strip’, and ‘bead and cove’, both of which are

designed to increase the gluing surfaces between

planks. The rapid strip is essentially a loose-fitting

tongue and groove. Each plank is fitted with the

groove in the upper edge so that it can be easily filled

with the adhesive. When the next plank up is then

fitted, it forces the glue out and spreads it. The

disadvantage of rapid strip is that it leaves a slight gap

that needs filling between the planks on the outside of

the hull (or at least where the outside has any sort of

convex curve) whereas the bead and butt – each plank

of which has one concave edge to match the convex

edge of the adjacent plank – tends to need more

cleaning up on the inside of the hull.

minimum panel weight, so that the weight per square

metre was the same as the traditional boats including

their frames. This led to the choice of^5 / 8 in-thick Sitka

spruce, simply because that would give a panel weight

closest to the minimum allowed.

While some strip-planked hulls have layers of

epoxy/glass on the outside, for extra strength and

impact resistance, others are veneered and may

sometimes be varnished. Khaya and sipo are the most

popular choices for this as it is readily available and

glues well, although Cockwells was lucky enough to

obtain, from Stones Marine Timber, some rarely

available Brazilian mahogany for the tender it built for

the 1937 motor yacht Malahne in 2015. For internal

framework on strip-planked boats, laminated sapele

or khaya are the favoured choices.

Khaya also tends to be used for the veneers on cold-

moulded boats, although for reasons of economy,

plywood is sometimes used for unexposed layers, or

external layers when they are painted.

Plywood is very much the favoured material for glued

clinker construction, as it gives greater strength than

solid timber in this application. If it is going to have a

varnished finish, then there are plywoods available with

visually pleasing outer veneers, and the unsightly end

grain on the plank edges can be hidden by strength-

giving epoxy fillets.

Next month: Decks, brightwork and interiors

Above: Plywood is

very much the

favoured material

for glued clinker

construction