Have a Garmin 545s and am brand new to saltwater fishing. What's the advantage to dual-beam or single beam, wide beam or narrow beam, (how wide or narrow are we talkin'??) Any reccomended frequencies to use, whats the difference between them??? Been out to a few local wrecks and having trouble staying on them, what speed should the screen scroll be at, something tells me we're not over what the screen says we are sometimes. The Garmin book that came with the gps is garbage and any tips you guys could give would be greatly appreciated. Thanks guys.