Hull & Keel

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The Improbable hull is cold-molded (glued) of three layers of kauri, a rare New Zealand wood prized for its properties of light weight, stiffness, strength, rot resistance, and consistency.  It is virtually unavailable now, yet another detail adding to the importance of preserving Improbable. The basic structure, starting from the inside, is of longitudinal (fore-aft oriented) stringers, then two layers of ¼” kauri @45deg (90deg to each other), then an outside longitudinal layer of ½” kauri.  With the emphasis on longitudinal stiffness, the interior bulkheads and laminated kauri beams provide the athwartships stiffness. The mast is keel-stepped on a very significant welded steel structure that also ties to most of the keel bolts, along with having the engine mounted on it!  This whole structure sits over the many laminated kauri beams, so the mast compression loads and keel loads are all nicely tied together. 


Although not a modern high-aspect ratio foil with a bulb, the Improbable keel is a very effective design and structure that was ahead of its time.  The overall case is welded steel, with 7500 lbs of lead poured in. However, one very cool feature is that the lead is not poured to the top…the top of the keel is actually a fuel tank.  A very practical use of space and placement of weight!

Overview Keel

Overview Hull

Philosophy

The existing hull and keel are in nearly perfect condition, and represent one of biggest reasons for doing the whole Project Improbable refit.

Plan

Not much happening to most of the hull (the rudder change is significant, but that’s another subject!). However, there will some fairing done, which will mostly be fairing the keel. Also, ideally, I’ll put on a fairing over the prop shaft and strut. There will be fewer thru-hulls, etc. And possibly I’ll add a bit of added foam on centerline at the bow as a crash pad for the logs and debris that might we might run into. This would hardly be noticeable after painting, adding just a few inches to the bow at the waterline. What might be more noticeable is a short extension on the transom that will serve as step for getting into the dinghy, etc.

Challenges

Probably the most intimidating hurdle on the hull is simply getting all the old bottom paint off. My dad did a full strip of the hull back in the 80’s(?) and sealed the entire hull with a layer of epoxy & light fiberglass cloth. The epoxy/glass layer seems fine, however there is a LOT of old bottom paint on top of the epoxy, that has accumulated over the decades since. I’ve removed some in a test area using a heat gun, which was very slow just to do a small spot. Hopefully won’t have to use paint stripper over the entire bottom. Or worse, have to aggressively grind all the old paint off. Not looking forward at all to this particular task.

Progress

As of March 2022, the focus is mostly on the rudder project. Saving the bottom paint removal, keel fairing, prop shaft housing, transom step/scoop, etc. for later….