Red I'm not so sure about that... the depth finder on my jetboat only reads up to about 35mph and then it's display stops reading numbers (displays "--" as it can't read the bottom anymore). I've read that air bubbles sliding under the hull as the boat picks up speed interfere with the depth sounder's signal (it can't penetrate air) and they lose the ability to read the bottom after that. I've read that in-hull depth sounders are even more sensitive to the watercraft's speed.
What I think depth finders are great for is when you're pulling up to a sand bar or beach to drop anchor, here you're already going slow and the depth finder let's you know when you should shut off the engine and drop anchor (about 4 feet deep water... as opposed to pulling into 1 foot of water and sucking up sand and debris into your jetpump!). With my RXT I've stopped too soon and hopped-off into 12 feet of water and had to swim the thing into water where I could stand up several times, and stopped too late once and hopped-off into shin-deep water.... Ooops! :-O
At anything above a fast idle depth finder's don't help much as there's little you can do if you're coming up on a real shallow spot (in most cases if you're going fast you should just keep going, you'll skim right over the shallow spot it would be worse to try to stop in fact!). It is also nice to slow down to verify the water depth you're boating in, just so you know the area you're in is 14 feet deep for instance or 30 feet deep or whatever... then back on your way or back to making big S turns or circles when pulling a tuber or skier or kneeboarder or whatever). That's how I use the depth finder on my jetboat... would love to add an OEM depth finder to my RXT but dang they are mighty pricey from what I've seen on Ebay! Eeeek!
Regards!
- Michael
