Harley,

GI Joes has one that is 28 lbs that will be fine. I have a 19 ft North River windshield boat, and it holds me fine. You'll need to get 4 ft of chain and connection hardware. Connect the chain to the bottom of the anchor, and then use zip ties to connect the chain to the top end of the anchor. Tie the rope to the end of the chain.

With the rocking chair anchors, weight isn't the issue - width and length of the tines is. With the 28 lb'r, I've anchored all the way up into Bonneville, and held just fine.

If you want more information, PM me, and I could shoot a digital pic of mine and send it to you.
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