Propeller Clearance Indicator

This would be a modified fish finder/depth finder that would be clipped onto the engine shaft. When the engine was lowered a button sticking out from the device between the stern and engine would turn it on when lowering the engine pushed the button against the stern. Further on down the engine cowling there would be a forward-looking sensor that measured the ground clearance between the propeller and the lake bottom. An alarm would go off if you were closing in on a spot that you couldn't clear. This would have saved me a couple of hundred bucks one time turning around in a small channel. Not seeing how close I was to the bottom the engine sucked up a full load of mud and conked out. It would also have saved the bottom of another boat that hit an unmarked rock not far from the shoreline. As an added bonus the alarm would remind people that they hadn't raised their engine when they were pulling it back up onto a trailer. I don't know how many times I've seen people forget to raise the engine and have it scrape the ground when they started pulling the boat out of the water. The device would probably cost around 150/200 dollars - a fair cost to prevent damaging engines that are easily worth more than 5000 dollars.

I did a search on this site and didn't find anything like it. Google may have something similar though.

A clearance indicator on trucks might be helpful too. It's not exactly a rare sight to see one stuck under an overpass it couldn't clear.