Re: Floor Check
Hey Terry,
I'm having trouble getting myself oriented on those latest pictures you posted, I guess because they're such close ups. (all I can see is trees and roots, can't see the forest!)
Anyhow, let's see if I can explain my concern a little better. If I understand you correctly it looks like you're planning to secure that front panel that'll hold the pedestal just at the front and rear and maybe at the cleat on the hull side, but what about along the inside above the gas tank/stringer?
I know how small boats can rock and roll when you're offshore in the slop, and I'm sure that 21 will be more stable than my 20. However, my concern is dynamic loads and the twisting moment that pedestal will put into a relatively thin (1/2"?) flat panel that, by itself, is not very stiff in torsion. The loads can get real big really fast! (Connor's comment about his pedestal breaking off at the weld on his last Bahama trip started me thiking about this!) Let's say your pedestal is 3' tall and it's mounted in center of a floor panel that's 4' long and 2' wide, assume that you weigh 200 lbs, and that you get hit by a freak wave or wake while you're trolling along offshore that rocks the boat suddenly enough to impart a snap roll of about 2g's. (I've done a 2g barrel roll in a T-34 and it's not that violent; I'll bet 3 or 4 g's is not unrealistic, and as high as 8-10 g's in fore & aft pitching motions! For reference, USN carrier aircraft are designed for 10g vertical loads during landings, generally considered to be controlled crashes!) A 2g dynamic load means you'll temporarily weigh 400 lbs x 3' = 1,200 ft-lbs of torque going into that floor panel! Let's say the panel is only fastened at the sides, just to simplify things. To balance the 1,200 ft-lb twisting moment the pedestal is putting into the panel with an equal and opposite load along the sides, you'll have to have 600 lbs of load along each side of the panel, pushing up on one side and down on the other. The point is, I don't think it'll break, but it might feel surprisingly "wimbly"! I think it wants to fastened down along all 4 sides. The loads on the pedestal screws will be even higher for the same reasons, but I think you've added enough beef under the panel for that. You might even try mounting a pedestal seat on that panel and temporarily mounting in boat and rocking it around to see if it feels solid enough.
For comparison, I discovered when I installed my galley seat that the entire area under the box where the pedestal originally was (about 2'x2') is 3/4" plywood even though the rest of the deck is 1/2" balsa core, AND it has about 1 layer of glass on the bottom and 2 layers on the top AND it's laying on top of TWO stringers that are about 1' apart! Good Luck, Denny
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