Are you sure it the gauge and not just the float in the "suction tube" in the tank?
There are a few threads about this problem....have you searched for them yet?
Also some on how to repair the fuse (I think) in the tube.
I'm rewiring the dash, sort of. The person who had the boat before me put a fuel gauge in (by using wire taps) that didn't belong. it was not registering below full. both wires from the sender on the same peg. I checked the resistance on both sender wires. One is about 25 ohs the other is about 235/240 ohms. I think the sender is ok. I'll take any help.
Just rechecked using a much better vom, only have 4.8 ohms at full tank. I believe there might be a problem with the sender. I will look up the threads you suggested. Any other help would be appreciated.