Float Depth & Kilkee Weed

Hi All,
New to fishing so would be great if I could get a few pointers and tips..
First off, when using a cigar float for example off rocks how do you ascertain the depth of the water?
I have the powergum for the stopknot etc but can't figure out how to get the depth at the bottom to then try differing depths.
I know how to plumb the depth when coarse fishing but this is a totally new ball game when fishing maybe 30ft plus.
Secondly, I tried fishing in Kilkee last week spinning frozen sandeel but each cast there was a huge amount of kelp and I literally couldn't fish.
Was I in the correct place - just off the raod where it takes a sharp left hand bend on the way up to the pollack holes?
Also, was I fishing using an incorrect method? I had a 3 way swivel with a 3oz lead with a 2 foot flowing hooklength being slowly retrieved.
Any help greatly appreciated!
PJ

Yer better off drilled bullet, bead, swivel- then a hook length 3 - 6ft flowing behind.... texas rig (google it) the hook to lessen snags too...

can't figure out how to get the depth at the bottom to then try differing depths.

I'm seriously thinking of getting one these! http://www.fishtec.co.uk/online.cfm/fis ... /yes/30614

A bit pricey but at least you know what you are fishing over

That fishfinder certainly looks good..
Guess that is the only way to get the depth

Yer better off drilled bullet, bead, swivel- then a hook length 3 - 6ft flowing behind.... texas rig (google it) the hook to lessen snags too...

Cheers - saw it on youtube. Good hook presentation