Centreboard opening measurements Plan Build

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Centreboard opening measurements Plan Build

Post by ChristineD »

I'm confused about size of the centreboard opening. Maybe a senior's moment?

The centreboard is shown in the plans as having a thickness of 32 mm
The side of the case is 9mm
The side of the seat with the little tab is 9mm
There are 2 spaces of 4.5 mm each on either side of the board which is 9mm

All this adds up to 59 mm

The plans show an opening width of 68.5 mm

What am I missing? Help.

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Re: Centreboard opening measurements Plan Build

Post by simeoniii »

Christine -

Your confusion probably has nothing to do with anything "senior"!

The slot, of course, depends on how thick the head of your glassed and finished CB ended up.
Mine was 35mm. It was a kit CB foil which started as two halves, each of 18mm. Vacuumed-bagged boards will be less, maybe down to 32 -34mm.

The centerboard shoulders should end up being around 32 - 35mm after glassing.
Add a 4.5mm gap space on either side plus 9 mm case sides on each side and that will result in a sized to fit centerboard slot on the hull of 59 - 62mm.

The trunk assembly should fit through the hull CB slot so that the bottom of the trunk is flush with the hull bottom. Leave the logs long at the bottom to be trimmed later. You'll want the log tops cut flush so the seat-top can be dry-fit laid down during assembly of the Bulkheads 4 - 7 to ensure they remain nicely vertical during glue-up

The CB trunk logs should be 38mm fore/aft and a width of 41 - 44mm (sized to fit)

You say "The plans show an opening width of 68.5mm". I don't find that on my plans (rev Jan 1, 2012).

My Plans Sheet 5 shows the slot and says "Approx 56mm sized to fit constructed centerboard plus 4.5mm gap on either side". Maybe the plans need to be changed to read "Approx 62 - 67mm (sized to fit constructed centerboard plus 4.5 - 6mm gap on either side plus the 18mm for CB trunk sides)"

FYI, the CNC kits are now being shipped with CB slots cut to 67mm
I feel the 4.5mm on each side of the CB is too tight and probably should be at least 6mm. This would make the slot 62 - 65mm. See slot and gasket comments on the below thread on the subject at http://smallcraftadvisor.com/message-bo ... f=3&t=1581

Hope this answer is more help than confusion to you.
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Re: Centreboard opening measurements Plan Build

Post by ram »

This is probably a bit late, but I left the hull assembly as a winter project and am just getting to it. Like Christine, my plans (March 1, 2012) suggest an opening of 68.5 mm. My constructed board is only 30 mm thick (solid mahogany), so my conclusion is that I need a gap of 30 + 9 + 18 = 57 mm.

I was also very confused trying to figure out the difference between 39 and 68.5. Got it now that the well extends down and uses an additional 18 mm. It would be nice if the plans were corrected, i.e., "approximately 60 mm, calculated as the maximum thickness of the constructed centerboard plus 27 mm (being a 4.5 mm space on each side of the centerboard plus 18 mm for the two 9 mm walls of the extruding well)". Or something to that effect.
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