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-   -   Davit rigging dilemma (http://www.trawlerforum.com/forums/s20/davit-rigging-dilemma-30167.html)

Pack Mule 02-02-2017 02:11 PM

Davit rigging dilemma
 
When I had my davits built I could not get the pick up points spaced far enough apart to meet up with the pickup up points on the dinghy. I had to work around a transom door on the starboard side. My davit points are about 6" in on each side from the dinghy pick up points. To get the dinghy up to the height I want my blocks have to get pretty close together and they are splayed out too much and the line starts to climb out of their pulleys.The closer the blocks get together the harder it is to pull the dinghy up . Anybody got any suggestions? I know I could redrill my padeys in the dinghy but that's adding more holes :eek:

psneeld 02-02-2017 03:45 PM

Spreader bar......ends of bar go to pick up points on dingy, davits lift straight to closer points on spreader bar.

The Other Gary 02-02-2017 03:52 PM

I added electric winches to each davit. The extra pull does not need the blocks I needed when I was muscling it up by hand.

Pack Mule 02-02-2017 06:21 PM

Quote:

Originally Posted by psneeld (Post 519392)
Spreader bar......ends of bar go to pick up points on dingy, davits lift straight to closer points on spreader bar.

That should work , might try it with a 2x4 or something first ,then have one made from stainless tubing .

healhustler 02-02-2017 06:33 PM

1 Attachment(s)
Marty: I forgot what the ends of your davits look like, but as you know, I put a couple of simple shackle pulleys on mine and used single Amsteel Grey 5400 lb. line so I can get maximum lift right to the end of the pulley. When at the top, the pulleys are at maybe 35 degrees or more to the outside.... preferable because it helps prevent lateral movement underway. A spreader bar, like Scott says, would do it, but if it is beneath your current davits, it will also take up more lifting space. You could probably shackle or clamp a home-made spreader bar on top of your current setup with just a hole or welded loop on each end, then use shackle blocks like in the photo to manage the angle. Total length from the tab on the davit where the shackle block goes through to the chain is 11 inches. Remove the unnecessary caribbeaner and its 8 inches. The chain is actually below the level of the tubes. A simple knot is tied in the Amsteel for my own convenience, but it could also be easily woven.

CPseudonym 02-02-2017 06:33 PM

Would be the cheapest, cleanest, best looking and easiest fix. Perfect it with four eye bolts and a 2 x 4 then pass that onto the welder who built your davits. :thumb::thumb:

Pack Mule 02-02-2017 07:18 PM

2 Attachment(s)
Here is my set up . I have added a swivel shackle at each end since I took this picture thinking that would help but as the blocks climb toward each other the line starts to climb out of the pulley and rub hard against the block sides . I got these old teak blocks from our own FF . This is kinda shade tree I know , but it's what I got .

healhustler 02-02-2017 11:20 PM

Ah, now I get it. The misalignment is more an issue of the two blocks than the angles to the connection points, no? Good looking setup, but you may have to sacrifice the blocks for something simple. My conversion from the 4-way block setup cost 120 bucks for two hand winches and another 50 or so for the line. Had the shackle pulleys already I think and I sold the 4-way line setup for another 60, so it ended up being about 100 bucks net to make the swap. Even the Admiral can handle the winches and it has become part of our MOB plan as well.

Pack Mule 02-03-2017 05:53 AM

Quote:

Originally Posted by healhustler (Post 519533)
Ah, now I get it. The misalignment is more an issue of the two blocks than the angles to the connection points, no? Good looking setup, but you may have to sacrifice the blocks for something simple. My conversion from the 4-way block setup cost 120 bucks for two hand winches and another 50 or so for the line. Had the shackle pulleys already I think and I sold the 4-way line setup for another 60, so it ended up being about 100 bucks net to make the swap. Even the Admiral can handle the winches and it has become part of our MOB plan as well.

Yes the block at the davit end wants to stay with the davit and the block at the dinghy pick up point wants to stay at the dinghy . The closer the blocks come together they start to fight each other .
The hand winch sounds like a good fix , then I would only need one block on each side . I can't begin to tell you how many times I've (I mean we've) raised and lowered the dinghy to try something different, but it's a whole lot more times than going for a dinghy ride:facepalm:. I think my first mate is starting to loose a little confidence in me on this situation. I get the :rolleyes: when I start to think of another way to fix this .
I just want to be that guy that grabs a bottle of wine, lowers the dinghy down with no foul language , and takes his first mate on a nice row around the marina . So far that ain't happened :flowers:

psneeld 02-03-2017 07:50 AM

cant tell...3 strand twisted line or braided?

braided may help as I have had many block and tackle setups that would twist like crazy with 3 strand....some do it with braided, some less, and some stopped twisting all together.

either way...I would go with winches if I could...I have seen setups where one power winch mounted overhead, coming to a "y" in the line and going through fair leads made a nice setup.

DHeckrotte 02-03-2017 10:29 AM

Our davit mfr (Ocean Marine Systems Ocean Marine Systems - Davits, Rails, Lifts, and Platforms. ) insisted that the davit arms not be parallel, that the falls not be vertical, and that the dink be hauled up tight against the davit arms. They say that the not-vertical falls ensure that the dink will not flop around underway. Basically, this ensures that the effort needed to raise the dink is ever more awful the higher it gets and the falls tend to twist. I added a winch to the motor end and can now get it up w/o help.

For your setup, experiment endlessly with the order in which the falls are rigged to find the least twist given the direction you're pulling. I rerove mine about five times each...then gave up and added the winch.

FOG 02-03-2017 10:45 AM

A wire rope between the two lifting rings made to the exact width of your davit attachments would keep your blocks vertical. This should work instead of a spreader bar if the bar takes up to much space.
Of course you would have to redo the wire rope from the lifting rings to the dink attachment points to make it all work, but if you added some turnbuckles it could all be adjustable. Good luck.

Pack Mule 02-06-2017 11:48 AM

Quote:

Originally Posted by Pack Mule (Post 519465)
Here is my set up . I have added a swivel shackle at each end since I took this picture thinking that would help but as the blocks climb toward each other the line starts to climb out of the pulley and rub hard against the block sides . I got these old teak blocks from our own FF . This is kinda shade tree I know , but it's what I got .

I talked with the folks at Trinka ( Johannsen Boat Works Inc. ) ,nice people by the way . It turns out that I have it rigged all wrong to start with . They have all the davit lines running through the bridle rings and attached to the pad eyes at the dinghy sole . I have been lifting from the ring with another line attached to the ring with a shackle attached to the pad eye in the dinghy sole .:facepalm:
This will not help with the fact that my davit pick up points are too close together but it will allow me to pick the dinghy up higher before my blocks get close to each other and start binding .

RT Firefly 02-06-2017 11:57 AM

Greetings,
Use the force Luke...
https://media.giphy.com/media/J4ivSa4mQ0D7O/giphy.gif

TJM 02-06-2017 01:38 PM

Being an Engineer I always look at the applied load vs how the designer intended the product to be used. The reason a spreader bar is used is to keep the load on the dinghy eye pads as designed, directly upward.
The chain usage in the post above applies a horizontal load (inward) on the dinghy. It may be fine but fiberglass does not give you any warning before failure, it cracks.

The spreader bar needs to have a thick vertical cross section, like a 2 x 4.
Typically SS or Aluminum tubing is used with a welded stiffener on top. 1/2" x 4" is usually strong enough. Tube diameter is a better characteristic than a thicker wall.


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