Re: [bolger] glacial erratics > Options for ply thickness for similar sharpie construction on simila

One variable that hasn't been mentioned yet is whether the boat will be used in a glaciated area or not.
 
Here is a good picture of a beach with larger glacial erratics mixed in with the cobles:
 http://en.wikipedia.org/wiki/Coble
Erratics can be house sized too, however these are easier to spot on beaches than the smaller ones.
 http://en.wikipedia.org/wiki/Glacial_erratic
 
In my area there are many beaches with 1-3 foot diameter erratics with at least half their diameter exposed above the cobbles. Having an extra thick bottom on a boat makes it much less of an issue if a wave trough dumps your boat down on top of one of these protruding rocks. Since the water is often a bit murky in this region, it isn't easy to see the rocks from a distance. In addition, from a distance the wave peaks can obscure the swirls in a trough indicating a rock close to the surface.
 
While careful observant navigation can avoid the erratics most of the time, it seems a poor bet to say you will avoid them 100% of the time. Also, if you are landing in choppy surf, by the time you see the signs of a submerged erratic, it could easily be too late to steer around it because turning sharply would risk being hit broadside by a breaking wave.
 
Having a thick fiberglassed bottom greatly simplifies dealing with the combination of erratics and surf on beaches.
 
I'm just assuming that exposed glacial erratics on beaches are a problem in all glaciated areas, not just around the Salish Sea.
 
Are glacial erratics on beaches a problem on the east coast of North America and it Europe too?
 
May your day be filled with clarity, grace, strength, insight, balance, cooperation, and warm laughter,
Roger