"A" rib pops out from keelson

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"A" rib pops out from keelson

Post by RangerTim »

Even before the introduction of aluminum crossribs, the Folbot Aleut, Yukon, and Edisto (those new enough to use T-bar rudder control rather than sliding pegs, which would include the 2000 -2002 model years) had a problem with the "A" rib moving forward under pressure from the rudder foot control.  When the user's feet pushed against the T bar, the T bar pushed against the rudder control mast. The rudder control mast, held to the plastic "A" rib by a delrin ring, pushed against the bottom of the rib. The rib's bottom "ears" would then pop out of the keelson plate. A tab on the keelson plate that popped up when the rib was attached was meant to prevent this from happening. The tab did not always do its job. Folbot solved the problem for plastic-ribbed boats with a delrin T mounted to the plate.  The short vertical leg of the T fit into a notch in the delrin ring, absorbing the forward pressure. 

In 2003 Folbot introduced tubular aluminum crossribs. Rather than a delrin ring to hold the rudder control mast to the "A" rib, the aluminum-ribbed boats have an aluminum bracket attached to the rib with star knobs, The rib mounting ears are smaller than those on the plastic ribs. That first year Folbot still used the large-keyhole plate style developed for the plastic crossribs. Once again, the keelson tab did not always do its job. The "A" rib's bottom ears frequently popped out. In subsequent years the keyhole size was reduced. 

I have a 2003 Yukon.  The aluminum "A" rib was popping out with every use. At first I thought the rib was pushing forward. While that may have been, it was also pulling up and out of the slot, even without being pushed forward. Downward pressure on the keelson from a Balogh sail rig mast did not help.

I have come up with a fix, I think. A screw and star knob hold the keelson plate to the rudder mast bracket. I made my own rudder mast bracket from plate aluminum, as a second Yukon purchased in California (but not yet picked up) lacks the stock ring. I'm not sure if the fix will work with the stock ring. Pictures are attached. I have not had a chance to field test it yet. While it adds weight and another assembly step, for me the benefit justifies the cost. 

Parts (available at most hardware stores):

2" 1/4x20 stainless machine screw (same thread as washboard carriage bolts)

1/4" stainless fender washer

Nylon spacer

Star knob (a two-lobed version because that was what Lowe's had)

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Re: "A" rib pops out from keelson

Post by flatwater »

Looks good.

I was the one who first alerted Phil to the problem with the new aluminum crossframes back in 2004 and discussed possible solutions with him. The problem was two-fold. The aluminum tabs would actually bend and the poly keel plate would flex, allowing the tab to pull straight up out of the slot.

He ended up using a tougher aluminum alloy for the tabs and reduced the keyhole to a half-keyhole.
As you've noted, that was adequate for normal paddling but sailing puts more stress on those aluminum tabs and they pull right out of the keyhole slot.
Your solution looks to be rock solid.
Nice work.
Five Folbots - Super TSF, two GIIs, Kodiak, Gremlin

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