The size of the anchor depends very much on the size of the boat.
The type of bottom—mud, sand, grass, coral or rock—will dictate a different choice of anchor, as will the size and windage of the boat, the wind and water conditions. Some situations also call for more than one anchor to be used.
A Guide to Safe Anchoring
You should have a minimum of 3x the length of rope for the depth of water that you’re anchoring in (the Coast Guard recommendation is 5–7 times). As an example, if you are anchoring in 20 feet of water, drop anchor 70 feet upwind, allowing 10 feet for the anchor to catch, then pay out 60 feet of line before tying off.
Using a chain attached to an anchor is designed to cause the anchor to tip over and it also acts as a shock absorber. The anchor is weighted on its side and stops it lifting up and pulling loose with the gentle wave action on the boat.
By dropping the first anchor from the middle of the bow of the pontoon there’ll be less resistance to both the water and wind. This will cause less pull on the anchor. Using a second, if necessary, to keep the boat from swinging.
Sourcing the right anchor or anchors, some chain and lots of rope is a necessity for safe boating.
A guide to anchoring in all conditions is available for free download from this link.