Airmar M260

[JohnB]

I have one, they work great.
As for mounting, take a level, across the top, side to side.
Hold it to where it's level, measure the gap. On the other side of it, where your going to cut, draw a line equal to the gap measurement you just did, then draw a line on the sides from that line, to the edge. I cut mine with a jig saw with a med blade. You might want to take a grinder and rough up the surface on the boat, then wipe down with acetone.
I would suggest using GE 2, marine silicone to mount it. Supposedly, they have found that mineral oil softens 5200. If you have to move it, you will be able to unattach it.
Mine has been in 3 years, and has held up find. I put a bead on the bottom, and set it in place, then after it dried, put a bead on the inside and outside. You might want to put some corrosion X on the top "stainless" plate. Every one of those I have seen, rust in about 3 months. For what you pay for it, it sure is a cheap piece of stainless. I used mineral oil in mine, some are using antifreeze. If you have any questions, send me a PM, or you can give me a call. They are great ducers.