Davit Truss

[danielgoldberg]

As I posted elsewhere some time ago, we have a dilemna with our davits. Our B49 "got back," so to speak. With the transom so wide and so open, the davit arms need to be installed very far outboard, about 14' apart actually. This means that the dink we are going to hoist is going to be too short so that the falls won't drop in line, or anything close, to the lifting rings in the dink. I've been noodling for a while as to what to do. A spreader bar won't work because we want to hoist the engine on the dinghy, and the motor would interfere with the spreader bar. We've come up with a few other ideas that won't work either (I'm an expert at that). Finally, I inquired of Edson (makers of the davits) if there's a way to make the "connecting bar" (the bar that goes between the two davit arms) strong enough to withstand the load of lifting the bow of the dink. I would line up the stern of the dink, with motor, with one davit arm as you normally would do, but then hoist the bow of the dinghy from a tang welded to the connecting bar, rather than the other davit arm (because of the distance). See my pathetic drawing below. I've also included a picture of the stern with the davits (though no connecting bar), just so you can see the setup.

Edson came back that they can make the connecting bar as a truss, and thereby gain the necessary strength and rigidity to allow our proposed setup to work. I've asked them to shoot me a drawing of the proposed truss, just to make sure the thing is not a total eyesore, but it might be our solution.

Any thoughts from esteemed Sailnutter friends?

[PBzeer]

While any configuration seems like it will prove cumbersome, I would suggest a rectangular frame the length of the distance between the davits (so it fits on either side of the motor) to which the dink is secured, then raised.

[jorgenl]

Dan,

the solution is obvious - get a 16' RIB

[jason3317]

Dan,
Have you considered retaining the arches, adding the truss/crossmember as discussed....but, moving the block and tackles to the truss to accomodate a 93" center? I can't recall if the Edson design allows the tackle to be moved from the supports, but you could easily add a second tackle setup,

Jason

[xort]

Oh the horror of owning a big boat

I think what the previous post suggested is to have both lifting points be on the cross member. Sounds like a good idea, IF the boat can be secured that way and the weight can be supported well enough.

Enjoy

[JohnRPollard]

Originally Posted by PBzeer

While any configuration seems like it will prove cumbersome, I would suggest a rectangular frame the length of the distance between the davits (so it fits on either side of the motor) to which the dink is secured, then raised.

I was thinking along the same lines. Of course, you'd have to store it [the frame] on deck when the dinghy was not slung in the davits -- but maybe it [the frame] could lay across the davits themselves for storage.

Dan, if you're not following this, what John was suggesting was to contrive a way to spread the lift points on the dinghy, rather than narrow the lift points on the davits. The advantage to this approach is that the dinghy remains centered beneath the davits, and hopefully would not overhang to one side as in your drawing. It just seems there should be a way to avoid having a standard dinghy like this one from sticking out/overlapping such a wide-sterned boat.

[danielgoldberg]

Thanks guys. A few points.

1. My poor sketch is not to scale. The dink won't actually overhang outboard of the hull. It will get close to being flush, but it will be inboard by a few inches.

2. I thought of the idea of a spreader bar where there is a "square" or "rectangle" around the engine so that the spreader bar is not on the engine. Essentially the same concept John and John suggest, if I'm reading their idea correctly. The problem is that the "connecting bar," which is a bar that connects the davit arms and really is required on our setup because of the width, still would hit the top of the engine if the engine is inboard of the davit arms, which means I wouldn't be able to get enough lift. So, the motor needs to be outboard of the davit arms, which pretty much is the case on most davit installations.

3. Edson advises that we can't hoist the dink with motor entirely from the connecting bar, even with a truss. I have a thought along the lines PB suggested that I'm going back to them with, but from my discussions with them I'm highly doubtful they will do it. If the connecting bar were not one bar, but two, sufficiently apare so that the motor head fits in between, and then the two bars are trussed, query whether that would work. As I say, I doubt Edson will "approve" and build it, and I suspect the truss won't help because the load would be going the wrong way anyway. But we'll see.

This would be a lot easier of we were willing to hoist the dink without the motor, and then just install/remove the motor each time we launch/retrieve the dink. In that instance, we could use a standard spreader bar. But I really want to keep the motor on the dink. It's just so much easier to deploy/retrieve the dinghy.

Failing any other ideas, I'm going to give Edson's truss concept a try. If it doesn't work and/or we just don't like it, then I'll reconsider hoisting the motor separate from the dink, and hope my boys get strong enough soon so that instead of wrestling with it, I can just say, "Max, Hank, go drop the dink and put the motor on."

Thanks, if any of you have any further ideas, please let me have them.

[PBzeer]

Dan - by using a frame as I suggested, you can secure the dink to the frame in a position that the motor clears the davit arm. By positioning the motor end of the dink inboard of the davit arm, you not only clear the arm, but distribute the weight of the motor more evenly between the two davits.

[danielgoldberg]

Looks like we might have one. We're going to weld in attachment points for the connecting bar so that it is about 16" more forward. Then, have a spreader bar fabricated that goes around the outboard, as opposed to over the top (pretty much PB's idea), so that way we can hoist using a spreader bar and still get the dink up high enough to be pinned against the davits.

Now I just need to find a fabricator to make the spreader bar, but that should not be too hard.

Thanks all for your thoughts. Once I get it all done I'll post some pix.