Window blinds are called Venetian blinds on this side of the pond, too, Snuffy. but I thought perhaps there was some special quirk to Anglo-venetian blinds that I didn't know about.
And the pun is, of course, on the idea that a blind is also a hiding place. Hence, the gondola for trysting is a venetian blind.

And the line should read "so, tied to a jetty.."
Damn the typos, full speed ahead.
Blessings,
Barbara