Monday, August 24, 2009

Dinghy Davits

Some time ago, Michele and I bought a Chesapeake Light Craft sailing pram, intending to carry it as our dinghy. Well, it took quite a bit of time, but we finally got the sail kit, had the kit finished, and had the pram modified to accomodate it (thanks, David!). With the pram ready, it was time to get davits installed on the boat.

I spent lots of time investigating options: Kato, Ocean Marine, Hurley, Forespar, St. Croix, and some others. I even went so far as to purchase and return Hurley davits; I liked the swim platform mount (no transom modifications), but in the end, decided the dinghy needed to be up higher to avoid swamping in rough seas. I finally settled on St. Croix removable davits, for a couple reasons:
  1. they're removable, leaving only the shoe on the transom, which is great when we don't want to take the dinghy with us,
  2. the swim platform is relatively unobstructed when the dinghy is launched, vs. rotating styles that have cross-supports,
  3. they're less expensive than most rotating styles.
Installation, however, is a bit of a concern. The transom top is not big enough to accomodate the shoes -- they'll hang off the back by about an inch. Plus, it is unsupported, so the weight of the dinghy will have a tendency to twist the transom top upward. St. Croix offers a "Sportfish" mount, which installs under the transom top, and connects down to the cockpit sole. However, because our transom top isn't big enough, it would not fit underneath. We'll need to find another way to reinforce it.

Mark Cline has the same davits on his Cape Dory, Brandywine. I studied his installation, and then with his help, did a similar install on Mariner II. Here's a series of pictures, along with my comments.

This is "before":

Holes drilled for the mounting shoes:

We fabricated a base for each of the shoes out of 1/4" starboard. This was both to give the shoe extra support where it will hang off the back of the transom, and to dress up the appearance. We cut the starboard plates on a table saw, with a 30° angle on the edges, and sanded them smooth:

Backing plate made out of 1/2" thick starboard. This is a temporary plate -- I made templates for much bigger backing plates that will extend from the hawse to the first stanchion on each side. The inside bolt from the hawse and all three stanchion bolts will also go through the backing plate. (Update: the permanent bigger plates are now installed.)


Here are the mounted shoes. It took some time to get the angle just right before we started drilling. We put the davit arms in the shoes, and tied a string to end of the arms to keep them at the right distance. It took three of us to manage this -- one person holding each davit arm and shoe, and one keeping the end of the arms spaced apart and marking the positions.

This is "after":

Mark's feeling, based on his experience, is that this is sufficient in the short term, but that I'll want to either glass in some reinforcement under the transom top, or find some other reinforcement. I'm considering running a shroud cable from the underside of the transom cap down to the deck. That would be an easy installation: I could attach an eye directly to the center bolt of the plate, attach the turnbuckle & cable, and run it to a pad eye (through-bolted and backed) on the deck by the scuppers.

Now we just need to get the davit rigged, and hang the dinghy.

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