there's 231 cubic inches per gallon of water and a gallon of water weighs
8.35 pounds
As someone else suggested, I would use two lengths of the lighter weight PVC
(used
for yard drainage and a similar product with holes is used for foundation
drainage).
They are only about $5 for 10' and the common pvc cements in the plumbing
department
make a reliable seal. Each 10' length would lift about 53 pounds.
If you want to get really high tech, rig up a valve system to flood the
tubes (to launch the
kayak) and a simple air pump to force the water out and lift the kayak out
of the water.
A commercial version of this is called a hydrahoist.
bill

"Norminn" wrote in message
...
I'm working on a project, using "something" plastic for a float on salt
water. Am contemplating using one of the low, rectangular plastic storage
containers if I can cement it closed to make it water-tight. Don't know
what kind of plastic they are typically made of - polystyrene,
polypropylene? Hubby and I like to engineer small, inconsequential
projects ) Trying to rig a small, floating platform to store kayak out
of the water. Any helpful suggestions appreciated. Since it's almost
Christmas, you're welcome to make fun, as well )