Yes, they're only practical for the higher bands...at least if rigged as a vertical dipole. I can JUST fit an 8mHz dipole for the marine band on my boat.
I'm gonna try one for 40m, though, with the lower leg bent back above the deck aways. That might work OK...we'll see.
The license battle, er..., ordeal continues. I've passed the exams for OUPV and Master, and am still working on the remaining parts: First Aid/CPR, physical, hearing, eyesight, references, detailed sea time, etc., etc.
Decided to take the Marine Radio Operator's License exam...studied for it a bit...it's really easy. It was supposed to be administered twice in the past week, but the exams didn't arrive on time, so they're rescheduling. Jeez!
Then, as time permits, I'll go for the General Radio Operator's License which will allow me to operate any radio on any vessel, and to install and maintain them. Think I'll find a nice course somewhere near a sunny beach :-))