Towed generators are practical for working sailboats. It is free
energy and they have usable output.

BUT.

1. Most sail boats spend over 95% of their time at a dock or at
anchor. The towed generator is useless then.
2. If you are motoring it is an extremely expensive and inefficient
way of generating power. Put an extra alternator on your engine and
gain a 500% increase in efficiency and a fraction of the installation
and maintenance cost.