Davits In SS rod
A set of davits is an important thing to have if you plan on having a dingy or tender. While our inflatable isn't really that heavy, add the motor and the bulk of it and things become quite unmanageable. With a davit setup and some blocks, hauling the dingy out of the water is easy.

Even just using it as a general purpose crane makes it invaluable. It's a long way up from the water to our poop deck!
 

Because we already have the radar arch there, I have decided to just mount them off each end, then poking back about 24" more. Based on weights of dinghy's and motors and averages, each davit should be able to support 160 lbs. That's not a huge amount of weight, but I'd like to use SS rod. Also the davits should be able to fold in towards the radar arch cutting down on windage and allowing it to act like a crane.

The pivoting joint will be a 1/2" bolt ( excuse the diagram it's no proportional at all!) snugly fit  inside some SS pipe. The reason behind the pipe is so there can be a stop tab  and so it can be removed if desired. The tab will snap into a slot in some 1/4" flatbar that is angled to accept the tab on swinging out, but needs a pull on the flatbar to release.

The whole thing is clamped on  under the "box" and clamped on with a "U" clamp at the forward end 18" away. A 2-d image is pretty hard to under stand so I'll be making a 3-d animation I suppose.

The loop on the crane end is just some rod curled around. I can't wait to start on this but right now it's -20º out and snowing so...

Update Feb 20 2008:
 
Here is the design I have come up with, all created in Maya 3d, and with a few explanations. Just wave the mouse over or download it here.

Of course it won't look as perfect after the weld blobs etc, but I'm going to try to get it as close as possible! I'll give it the old stress test using my body weight, from the ground, and Genas muscle on a 3:1 purchase, hopefully it is strong enough. If it passes, then they will be able to lift a dingy with the motor on, no problem.

Anyway, I have began to build it, and will continue today, weather permitting.( It *is* February after all! )
   
The lock mechanism relies on a piece of flat bar being twisted, then slotted to allow a pin to slide in, but not back out until the level below is pulled in. This will be easy to operate.

When pulled in, they can be secured with a low-tech length of rope, or perhaps the pulley rope, not sure.
Davits lock  in out position automatically
After 6 hours, I had both crane arms bent and tacked together.

It looks kinda ugly at the moment, but will look better after more welding, some grinding, and finally some polishing. Polishing round objects is relatively easier than flat things, like plate or flatbar.

Probably because there's always a more concentrated point on round things, but not enough of an area to overheat the buffing wheel. (There's a free tip!) I've even thought of how I could have made the "box" part less flat. Unfortunately it's unavoidable!

Well...off to build more!.

This update Feb 20, 2008

 
The bends went well! Just like the "blue-print" printed out

The "real thing" not so pretty!
The "box" that the arm attaches to needs to encase the release catch as shown in the video so the crane can fold inward to the radar arch. Because it is relatively large, it must be pretty-ish, which means careful welding. The arches shown in photo() are the access the nut for the catch once positioned and will be drilled at the end for the U-bolts to hold it onto the radar arch. They were bent and test fit on the actual arch; easier to do now than after its welded to the box.
The box is the load bearing area, but the frame to the other bar stops it from twisting down when under load. It is almost a 2:1 ratio there i.e. if the crane has 100 lbs on the end, the pull up on the support will be about 180lbs. The arch is very strong so it shouldn't be a problem with even the "motor end" of the dinghy.<100 lbs.
 		  
The smoothing of the welds and polishing took 3 days easy! I knew it would be a lot of work, but they are the perfect davits for our boat. My only concern was how much weight they will support. I overindulged at Christmas so I'm a pudgy 140 lbs. I though yes, that would be a good test for each davit. I tied a rope on then made a noose. No! Not for my neck, but for foot height. I watched the arch carefully as I hopped into it and it held my weight without any noticeable flexing. Much more rigid than I had expected!

The latches work as predicted, locking themselves on extending, and requiring release on retraction. If we are carrying the dinghy and motor for a choppy crossing, we will (or should) tie them together just in case. Of course the dinghy should be tied to the arch anyway to stop it from swinging back and forth possibly causing rub damage.

You must agree they're one of a kind!
 		  


 

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