As far as a chartplotter inside an Alcan would you require an external receiver or would a unit with built in antenna work within the boat ? Just wondering if the metal would affect reception.
Older gps receivers will have trouble with the aluminum. Some of the newer chart pletters have "high sensitvity" gps receivers built in. These seem to do fine without direct exposure to the sky. Howe've received, if you want rock solid signal an external antenna/receiver will always be better.