floating boat lift

This one doesn't float, but it lifts my 3.5 metric tonnes boat high and dry.
Two threaded spindles, bronze nuts with ball bearings under them for easy turning under load and some stainless steel tube to form a vise.
Under the bow, not visible, is small carrier with rubber rolls.

I've used this system for many years, five years ago added another 4" to the bow carrier when the sea-level rose and recently discarded it all because the flood extremes are catching up with me again.

 

CDK,
Your boat and location match my own situation fairly closely. Do you have any photos you could post showing more details? Thanks.

 

I'll put the boat in the water tomorrow and will take some new pictures...

 

All pictures were taken from the next pier, so they show no details, but I made you a crude drawing, showing half of the lift and the bow rollers.