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Not sure how many still view this site, but here it is.

https://www.iceboat.org/2021/11/28/dn-western-challenge-called-on-3-5-dec-christina/

I am probably too late to stop you, but 1 3/4 inches deflection under your weight is the recommended standard deflection for a plank.  Why do you want to make it stiffer?  I may make your DN harder to sail, although some do like a twitchy boat.

Thanks a lot Bob!

It will probably stiffen it 3 or 4 pounds per inch.

Hi group,
I apologize if the topic was already covered. (I know Warren was looking for the info a while back)

I would like to know how much stiffness is going to be added by wrapping fiberglass on the plank.

For now, I plan to wrap the entire plank, plus an additional 4 feet center section, with a 4" overlap in the bottom section.

Current deflection of the plank is 45 mm (1"3/4) with skippers weight

Thanks a lot,
Nic

Great Western Challenge called ON !!!  Dec. 3-5 Best Ice in MN.  The Fun starts on Friday, always the best day.  It's time to get the whole gang back together.  Everyone is welcome.  We will keep posting updates here as they are available.
THINK ICE !!!!!!!1

Forecast for Thanksgiving in Ashby has 5 nights in a row of 8F. Could be a foot of ice on Christina and many other options!

Hi Warren,
It is exactly what I was looking for, thanks a lot!!!!

I am almost done with the spare hull, so this is going to be next!
Cheers,
Nic

the subject needs corrected its the main block 75mm not a 57mm 

Hi Nic,

Spring back of a curved lamination after removal from the mould is proportional to the thickness of the individual laminations and inversely proportional to the square of the number of laminations, if all the laminations have the same young's modulus.  The proviso isn't true if you are using different woods for the skins and the core (but Young's Molulus doesn't vary all that much between species), and the 'rule' also assumes equal thickness laminations, but it's probably close enough to say springback is something like 1/n squared.

So a two layer plank will spring back about a quarter (1/2 squared) of the crown of the mould and a three lamination plank will spring back about a ninth (1/3 squared) of the crown of the mould.  My experience is that the 1/9th estimate is pretty good.

Warren Nethercote
KC 3786

Thanks Bob,
I think I will go with the epoxy and make things simple!
If you have any information on how much crown to put in the gluing process so I get the right one post cure, I am interested

Take care!!
Nic