You've asked some big questions - mostly the answers are site-specific, hard
to address with email. But I'll try!
--
Sal's Dad


I have just got a deal on 1200 BF of 1 X 6 X 5'2 rough cedar. $.12 / bf.

I have 10 plastic oil barrels, with as many more as I can load in my old
cargo van, at 10 per trip, 15 bucks each, used for poly b, a wetting agent
used by a local concrete plant.

These should work fine; they need to be securely framed into your floats -
top, bottom, sides, ends. Put them at the far corners of the dock, for
stability. You can probably adjust your deck "joists" to securely hold the
barrels, an inch or so shy of the deck boards. Then the whole assembly can
be only 3 or 4 inches taller than the barrel diameter.

Not sure if this 'pic' will work for you, but:

____________________________ (cedar deck)
| _--_ | | | | _--_ | (treated joists)
/ \ / \
\ _ _ / \ _ _ / (barrel)
| -- | | -- | (lower skids)



I have a bunch of plastic coated ss clothesline,
Sometimes stainless doesn't do as well as you'd think in marine
environments!

A couple of moorings and an old 50 foot dock in ruins in my front yard. 20
feet beyond the rubble, the water drops off to 60 feet deep.
Perfect!


I have built one 5' x 5' dock skeleton for 3 barrels, all in cedar, just
for eyeballing. Cedar splits very easily.
5x5 is way too small - unstable. Pre-drill holes in the cedar. If using
nails, blunt the ends so you punch, rather than split, holes as you drive
them.


My riverfront is tidal, with a 2 foot range, and it freezes as hard and
deep as only a canadian could love.

I need suggestions as to how to engineer the most dock for the least
additional money.

I was thinking, since the cedar is lightweigh and a little fragile, that I
might need to buy some heavier structural lumber and use the cedar for
topping only, but I need to yank the docks for the winter, and I want to
be able to do it with only one helper.
Yes- use treated lumber for the frame. 2x6 should be plenty, from what
you've described. Just figure maximum spans of 10' or so. You might do
well to build a "skid" ramp over the rubble - a couple timbers, sloping up
from the water to dry land, at high tide. You can roll the docks easily
with 2" steel pipe as rollers. Just match up your land-side skids pretty
close with the framing under the barrels.



I was thinking to run a cable between the moorings and dock the boat to
the cable, leaving the lightweight, more or less free floating dock to be
a gangway to the stone rubble dock ruin, which could be used to support a
deck over the really rough part of the dock ruin out towards the end,
which is a couple of feet underwater at high tide.
This sounds complicated. Why not a multi-part dock - a fixed section to
near the end of the rubble, then a short ramp to a floating section?


I am thinking patio block footings amongst the rubble, and seek advice as
to the most efficient (read cheap) engineering approach and, er, free
designs (ahem!)


Good luck!