I owe the yard guy at Shotley a bottle of decent single malt!

[pvb]

Same in this scenario as the weight of the boat causes the water pressure inside to pipe to increase against a heads acting as a nozzle.

Not at all the same; the pressure in the pipe has nothing to do with the weight of the boat, simply the depth below the waterline. And the pressure is actually incredibly low (think how easily you can stop the inflow of water with your hand when you take out the log impeller).

It's well worth checking the condition of all pipes frequently - especially the cockpit drains, as almost everyone leaves those seacocks open....

The Shotley guys are some of the most sensible I've found in any marina, and they also check around all the berths every day.