i550class.org

ALmost done with the uncooperative keel refit. Took the boat out for sea trials with the younger kid this past weekend....still have a tiny trickle of a leak, dammit! But it should be an easy fix. I do like the shallow draft and the huge cockpit does double as an excellent fishing platform. All-in-all, not a bad (dare I say it?) powerboat!

Has anyone considered a square top section to the blade where it is within the keel box and fairs into the hull surface/foil shape at its exit? It would entail careful measurement of the height cockpit sole to hull surface. I suspect that any tiny bit of water intrusion to a timber blade would lead to the problems of sticky blades. Most other boat have all plastic blades and avoid this issue. Even water intrusion in those blades would not cause material movement to as great an extent. Are the i550 blades being built the much tighter tolerances than other manufactured builders blades?

Hi Tim,

The PDX website is no more, but I recall the original PDX build log showing keel foils being built production boat style as left and right halves from female moulds, epoxied together over a core, with the 'embedded' portion of the keel section being rectangular. I have seen pictures on the Fast Composites (Phil's Foils) site of NC-milled foam keel plugs (not cores - the plug was used to make two moulds for keel skins) with rectangular top sections. Later PDX keels seem to rely on 'clamps.'

Production boats tend to be built with pretty loose tolerances and rely on wedges or other means for foil location. The J70 uses wedges and the Melges 20 uses a rectangular box and 'clamps' around the keel, like the Moran's PDX. I am more and more tending towards this approach. I think most people who have moulded their keel cassettes around their keels have used tolerances that are too tight. Putting two or three wraps of polyethylene vapour barrier around the keel before laying up the cassette doesn't give you a lot. Production dinghies with daggerboards (Laser, 29er, 49er) have carpet-like material at top and bottom of their cassettes implying clearances of 3mm or more ....

(Edit) Lee's Western Australia build laid up the keel cassette over 'carpet' to ensure smooth lifting of the keel

Warren,

I wish we had this post about 7 years earlier....It would have saved me (and others) from some headaches. I totally agree when you say " I think most people who have moulded their keel cassettes around their keels have used tolerances that are too tight"
Sleeves with 3mm carpet tolerance might work fine.
Keels built with rectangular top sections might be an even better solution

[...]

Jerome, you are SO right! Make it 9 years ago, for me

I'm pretty sure I've still got a mold styled from the Rocket22 keel trunk. It's a very snug fit until raised an inch, then lots of room for raising and lowering with ease.
The plastic blocks are attached at the top, such that the lower bolt 'might' sheer on impact, and there's lots of space for give, which gets filled with pour foam.