Upper crust effort with awesome results, ArkEH. What a super project...mega-congrats. Great to have ya here; hope you don't mind the rest of us hitchhikers.
8 telephone type poles to support 8' x 30' of dock makes my overkill engineering look like tinker toys. I can't argue; it's a nearly unbeatable trump card for that size project. The only heavier engineering that I recall on this forum (or anywhere, for that matter) was someone's pic of a poured concrete pier.
How deep will normal pool be at the end of the 30' pier length?
Forgive me if you have already visited the
Building a Pier thread, or the
Using footers or sinking posts thread. These are a couple that may provide some brain food.
I think that ultimately your options are somewhat limited, but then there really aren't alot even when the water line is lower than the support zone. Bob Lusk promotes use of drill rod or tubing in your post-water zone. As I recall, his engineering is pretty much the same as you have noted. The only other practical option that I foresee is a hybrid. Poles for the first half, and floating for the second. Actually, this hybrid may turn out to be a hidden blessing if you should go through weather conditions where the water level would drop. That would turn out to be a certifiable brainstorm if the last section was on hinges and would follow the water level. A pond your size and depth can lose 2 or 3 feet of water depth and still be totally usable for the motorized water toys. It would suck if the pier access was 5 or 6 feet above the water level. If you could provide enough bouancy near the end of the pier so that it would support the last section if the water level dropped, a set of very stout galv or SS strap type hinges might complete the structure. If you provided some buoyancy at the hinge end of this cantilever section AND if the pins could be removed from the hinges, the entire pier section could be floated off the end and back to shore or elsewhere for maint or mitigation of extreme low water level.
