On 23/03/2023 22:26, sully wrote:
For any boat experts lurking here:
I ran across a strange phenomenon last summer which was puzzling me, but I ran into it again this week now I'm really flummoxed,
I have an 80s era Stampfli double I rescued from a norcal barn. The hull looked to be in impeccable shape when I first saw it some years ago, when I recovered it, I learned the hull had numerous long checks along the grains of the shell, some as
long as a 18 inches.
I've had lots of old wood boat checks before, no problem. However, these checks were collapsing the hull, turning inward rather than splitting out.
I think I took photos before I wrapped the boat for storage this summer.
what would cause this?
I thought this was a one off. Perhaps the barn storage caused some unique damage, maybe some weight compressed the hull some way. No idea.
But this year I brought in a gorgeous 2x of same make and era that had been stored in a garage in SoCal since mid 80s. It was unblemished, but didn't do really close inspection. A couple weeks ago, the ceiling rack failed and caused some minor
damage to hull near the stern seat at keel.
Tragic.
Rest of boat looked ok. Later, I did close inspection of hull and found same sort of implosion checking about a foot from the bow. The check was about a foot long, not visible, just you could compress the boat at that spot.
The check ran on both sides of the boat.
the people who this boat knew what they were doing, I doubt they picked up boat roughly from the bow and stern and squeezed. But that's how this sort of damage could be done, by squeezing the end of the boat to hold up the weight of it.
My question is have you ever seen this sort of damage on wood shells? I never have in any other wood boat and I've seen hundreds, and a lot of damaged boats that I rescued.
Xeno will be sharing contact info with someone that could help me with an expert in Switzerland, but in meantime...
Anyone?
Sully -
These weren't "mahogany" - blond or otherwise. They're in a single
veneer of a low-density wood called Obeche, but similar in construction
to traditional single-skin Cedar shells.
All wood is fibrous, those fibres generally (but not always) bonded as
strictly parallel bundles with natural wood resins, e.g. lignin. As a
result, timber has significantly different physical properties along,
across & into its grain. Strength (& stiffness) across the grain is
thus be more dependent on that resin's properties than on those of the
fibres, & may be <10% of that along the grain, which is why we can split
logs along their grain but not across. In that respect they're no
different from unidirectional carbon, glass or other laminates.
One tailors the physical properties of both wood and synthetic fibre
laminates by arranging for fibres to be aligned in those directions
which optimise the resulting product for the expected loads. Before
there were reliable bonding resins to make laminates, single veneer
shells maximised longitudinal strength & stiffness in the hope that
transverse service & impact loads would be light. As a consequence,
such shells had a nasty tendency to develop longitudinal splits, & older
shells ended up with multiple internal wooden patches, copper-riveted
through the skin & sealed there with shellac or similar - called
"tingles" here in the UK. Even 50 years ago you'd see many boats with
these tingles here in the UK, even though long before then the
availability of easily-formed thin marine ply meant that all new wood
boats were being built with this more-robust material.
Some shell builders, notably Staempfli, built beautiful cedar
single-veneer shells & enhanced the cross-grain resilience of their
skins by applying at first a layer of silk, later of Dacron, held in
place by the lacquer finish which made the cloth effectively invisible. However, being on the outside, this cloth did not prevent the skins from spitting under inward impacts - which I think is your problem?
Once the silk or other cloth layer starts to separate from the veneer at
a split it can be tricky to stop it from peeling & to secure the exposed
cloth edges when making a repair. The availability of good epoxy resins
did make it possible, even 50 years ago, to repair splits in
single-veneer skins - but there was a knack to restoring the undeformed
shape of the skin, which could otherwise tend to cockle into a tighter transverse curvature, causing a groove in the repaired area.
HTH?
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
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Email:
carl@carldouglasrowing.com Tel: +44(0)1932-570946 Fax: -563682
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