The ACE 250 does TOO work in wet sand
I have one and have used it with some success in the wet sands here in NW Florida. That being said, it is a bit "chatty" and you have to be using headphones (I feel) to get the most out of it. I have found enough items to know that it will find targets in the wet sand AND under water.
You can check out this thread with pic's...
http://metaldetectingforum.com/showthread.php?t=69996
Or this one...
http://metaldetectingforum.com/showthread.php?t=70584
I set my ACE to Custom Mode so it saves the settings, then disc out 5 cent and all to the LEFT of 5 cent. I leave my sensitivity at 6 of 8 and am VERY careful to NOT touch the sand while swinging as this will cause a false every time. You are going to still get chirps and see a pointer in the disc'ed out area from time to time. When you find a real target, you'll get a repeatable solid signal. The only caveat in this is that the soil in your beaches may be different enough to not allow these settings to work.
What you are trying to do was not something that the designers planned for the ACE I'm sure. It's like brushing your teeth with a scrub brush instead of a toothbrush, it'll work with the right technique most of the time but it won't be pretty and it may not be fun either. Hope this helps and I'm curious how your soil conditions affect yours.
Oh, and remember, your coil may be waterproof, but the control unit IS NOT!
Good Luck and HH!