The prior owner always kept the dinghy on the deck, since they found no simple way to tie between pilings with it still on the davits; on many catamarans if you connect dock lines to the stock cleats in standard criss-cross practice, they pass right through the dinghy.
The conflict in space is resolved using a short lanyard to deflect the line down and away from the dingy. All of the parts come from the local rock climbing store. As a mountaineer from way-back, they all came from my too-worn-to-climb pile.
The carabiners should be the wire gate type. The conventional biners in the first photograph soon locked up with corrosion and was replaced with a wire gate biners. Wire gate biners are handling the marine environment without corrosion or ill effect. I do feel it is important to use climbing biners because the are MUCH lighter than stainless marine biners, which prevents banging on the hull and gel coat damage. They carry the same 4500-pound strength rating.
Replace the washer under the one of the nuts securing the transom hand rail with a stainless bolt hanger. The nice thing about bolt hangers is that they require only a single (often pre-existing) bolt, are 5600-pound test with a 3/8-inch bolt, and are available in 316 stainless for just a few dollars. Very handy on boats, I have 10 installed, assorted places. Add a 1/4-inch quick link, a 6-inch webbing sling, a carabiner, and wrap the rough parts in 2" hollow nylon webbing to prevent chafe and guard against UV. Neat, durable, and mightily strong.Also a handy tow point for kayaks and dinghies.
How much force? I took a bunch of load cell measurements at the dock in moderate and storm conditions a few years ago. I also did this on bulkheads.
PDQ Altair 32/34