My boat came with a Navman 4380 color fishfinder.. I have had really
poor results with this fishfinder working when I'm on plane. I was
hoping it would work at least for a low planing speed like 20-25 mph,
but the screen just goes white. I have tried tilting the transducer
forward a little, but it still exhibits this performance. The transom
mount transducer was installed by the dealer, and looks to be properly
located.

I'm scratching my head wondering if this behavior is related to the
mounting position.. or if Navman's are just sucky fish finders?

It's nice to see the SmartCraft gauges linked to my Merc Optimax... but
I'm getting frustrated with this thing.

Does anyone have any experience with Navman fishfinders?

Pics of mounting:
http://aycu34.webshots.com/image/279...6884250_rs.jpg
http://aycu17.webshots.com/image/113...8036262_rs.jpg