Hey, Skip -
On Sun, Aug 29, 2010 at 04:09:23PM -0400, Flying Pig wrote:
>
> Extrapolating, assuming I get the risk factor successfully
> dealt for my particular setup, I'd attach those 4 points to the straps/large
> laid line?
Correct.
> I see nothing to prevent side-to-side movement in this setup
The large-diameter line, or straps, once snugged up, have essentially
zero stretch (you're looking at maybe a 2' run of, say, 3/4" laid
nylon.) Also, compressing the dinghy tubes against the stern on the
bottom and against the davit arms on top places a load on those lines
and creates a very large amount of stiction between the lower tube and
the stern (or the padding between the two), as well as some between the
top tube and the davit arms.
> Not having the impressive welding setup you do, let alone any skills if I
> did :{/), I'm unable to attach cleats permanently
Hey, you'd be mounting stainless to stainless - and I know that you can
drill and tap. :) Besides, if we run into each other, I'd be glad to
raft up with you and throw a bead or two on it.
> As long as I have your engineer's mind engaged, perhaps you could speculate
> on how to overcome the lifting challenges I have:
>
> When I designed our arch about 5 years or more ago, I used our current
> dinghy's hardpoint mounting setup to determine both spread and depth. As it
> was a fiberglass dinghy, with extended (moreso than our current) stern tubes
> and hard-point mounts at the bow locker, there were no safety issues nor fit
> difficulties.
>
> Our present dinghy has only a bow-eye back-end (a pad eye mounted to the bow
> eye bolts) and the transom eyes. That's way longer than the spread on our
> davit tubes. The inflatable tubes are also smaller diameter than our
> original, so that necessitated bringing in the hoist points from the
> original, in order to achieve the jam-fit in the corner between the arch and
> the support arm mentioned above. There's my graph-paper sketch of our arch,
> as well as lots of pictures, in our gallery, if you're interested...
Yeah, please give me the URL. My brain isn't engaging with your verbal
description too well; not your fault, I just feel like it's packed in
thick grease today. :\
> Walker Bay's factory solution to my dilemma, apparently common, as it's
> plastic, and not fiberglass, making it impossible for hard points inside the
> tubes area, is to put eye bolts in the removable-paneled floor system ("the
> bilge" feature on the Genesis models), make a lifting bridle, and haul away.
> They claim full safety in a dinghy filled with water; we have nothing other
> than the seats in ours when we hoist. However, there has been significant
> deformation of the floor system, and damage at the front where there's no
> forward latch for the locker section, due to the lifting stress on whatever
> type of plastic it is that it's made from.
Yikes. That doesn't bode well - I have a Genesis dinghy myself.
> Our dinghy hangs out notably from both sides of the arch, so there's no
> practical way to hoist using the davit arms, using their hard points,
> without a significant angle as it's raised (our lifting points are much
> closer together than theirs), or using a bar (making it impossible to lift
> high enough to prevent swing) to accommodate that difference (never mind
> what we're supposed to do with it when it's not slung!)...
>
> Does this presentation "parse" sufficiently?
This latter part is clear enough. Hmm... bear with me while I talk this
out. What if you cut the upright tubes of the davit a few inches below
the bend, then insert a short piece of heavy-wall stainless tube that
fits snugly inside it? You could then drill and pin the lower end of the
insert, which would allow you to pivot the arms. Set them in their
original position and drill through the upper end of the insert and the
bottom of the arm; then, rotate to (say) 30, 45, and 60 degrees and
drill through the holes in the outer tube. This would give you a set of
davits that can be nicely adjusted for width (although it'll change the
amount of setback on the arm ends). When you've set the position that
you want, just insert a ball-lock clevis pin and lock it in place.
Would something like that help you?
> PS What's a "pinxit"?
Latin for "(s)he painted it". It used to be quite common for a painter to
add it after his signature on the painting, as in "Rembrandt pinxit", so
it's the artistic equivalent of saying "John Hancock".
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