I read the posts and have done both floating methods.
Utility poles will last forever as a float base, however I used 4 wide bridged with 4 X 4 stock using 12" spikes and then planking with boards.
Be sure to use rot resistand 4 X 4"s as the poles will never rot.
4 wide is needed as with time the poles will almost submerge leaving less and less floatation.
The upside is that this will make a rock steady dock.
Foam floatation is what I currently use
We get 8 or 10" X 20" X 96" foam 'floats'.
I usually make a 'pallet' type of deck using 2 x 6 for framing when the dock is about 6" wide and 2" X 8" when 10 or 12" wide.
The frame is just like what you'd make for a patio deck and decked in the same way.
Differance is that under side needs 'under decking' to support the foam. (like a pallet that has some boards under as well).
This also ties the whole dock into a nice rigid frame.
To keep the foam floats from sliding away I generallt drive wooden (sharpened) 'stakes into the foam between the underdecking planks. Kinda like anchoring sod on a hills.
Works just great and I have probably over a dozen floating around our lake with most about 10 yrs old.
I finally had to rebuild the first which was 22 yrs old just last summer.
Downside of foam floatation is a kinda 'bobbing' effect with high floatation, ie you step down into the boat.
On the other hand, floating high means that the wood structure is all out of the water and hence resists rot.
The log dock floats low and you step up into the boat.
Never use drums or worst yet steel barrels, they just beg for trouble.
Up here we let them winter in the water. The foam simply compress a little when the ice sets in and promptly springs back in the spring.
Our ice was 12" thick and the docks had 4' of snow on them.
Not all foam is good for floatation as some will absorb up to 75% water. A 'monocelular' foam is needed. (not the cheap white styrene).
For light duty I have even made an 8' X 8' using 3" 2'X8' slabs of pink urathame insulation foam boards and a 2 x 4 frame.
(An adult gets wet feet stepping on a corner, but 2 folks in the center stay dry.)
Good luck!
