Join Date: Apr 2006
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"I'm still torn between the choices... "
Try the 8db omni, and instead of lashing it to a whip, SUSPEND it from something. Suspend it with a foot or two or parachute cord (something like and flexible) so that the boat rocks under it, allowing the antenna to remain more vertical as the boat heels.
IIRC you should be able to suspend it rightside-up or upside-down, either way, without the signal being affected.