DN NA Class

How important is it to be close to 2and1/4" for your crown and does the deflection that you shoot for depend on the crown.
For example 2 and1/4" should deflect 1 and5/8" then a crown of 2" should only deflect 1and 1/2"?

Crown and deflection are linked.
I think a good basic rule of thumb is this.  When you are in the boat and coasting, you runners should be exactly perpendicular to the ice, and parallel to each other.    You can accomplish this with a low crown plank that is stiff, with a high crown plank that is soft, with a high crown plank that is stiff but has a slight gull wing, or angled pads under the chock.
In general a stiffer plank stays aligned better, but is harder to sail on rough ice and makes the mast act stiffer.   A softer plank is easier to sail, makes the mast feel softer and is much less jarring on rough ice then a stiff one. 
I am on the stiffer plank side of things.  My stiff planks are  1” crown 200 lbs/inch deflection, my newer planks are 2’-2 1/8” crown and are about 160 lbs/inch deflection.  These planks have an epoxy pad under the chocks so that the runners are perpendicular with my weight plus 30 lbs.

Note that my deflection numbers are quite a bit different from much of what the Midwest runs.   The east coast guys seem to run stiffer planks in general. 

Cheers
Eric Anderson US 5193

Thanks for that Eric.I seen on the Ron Sherry Videos he shoots for a deflection of 80% of the Crown.His Crown is 2and 1/4 " and it deflects 1 and 3/4" .Seems to work for him.