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Old 06-11-2013, 08:29   #16
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Re: Cracked Davit :banghead:

I vote for fixing the davit (maybe add a gusset). Lighten the dink by removing the console and switch to smaller engine.

Leave the engine on the dink. The convenience of an instantly deploy-able dinghy is priceless.

Steve
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Old 06-11-2013, 08:50   #17
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Re: Cracked Davit :banghead:

I'd say call the manufacturer and ask if they've encountered this before and if they have a fix. If they do great problem solved, follow their instructions and make inspecting the davits part of your normal maintenance. If they are of no help find a trustworthy welder/mechanic/engineer and ask them to not only fix this but to go over both davits and inspect/repair/reinforce as necessary.

No matter what you do you will never not worry about your davits again. You will have it in the back of your mind to check regularly. Don't stress about it too much just find someone capable of making a quality repair and inspection. i.e. a seasoned aircraft mechanic may be a good place to start, they should have access to metallurgical testing equipment and have a good idea on the stresses put on the metal
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Old 06-11-2013, 09:12   #18
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Re: Cracked Davit :banghead:

Quote:
Originally Posted by ontherocks83 View Post
I'd say call the manufacturer and ask if they've encountered this before and if they have a fix. If they do great problem solved, follow their instructions and make inspecting the davits part of your normal maintenance. If they are of no help find a trustworthy welder/mechanic/engineer and ask them to not only fix this but to go over both davits and inspect/repair/reinforce as necessary.

No matter what you do you will never not worry about your davits again. You will have it in the back of your mind to check regularly. Don't stress about it too much just find someone capable of making a quality repair and inspection. i.e. a seasoned aircraft mechanic may be a good place to start, they should have access to metallurgical testing equipment and have a good idea on the stresses put on the metal
^^ Dockhead, I think this is good advice. To me, the big question is whether one or both davits will need replacing, if you are committed to having the dinghy in davits under way, rather than lashed down on the foredeck. Questions I'd have are why did the crack develop there? Is there a microscopic mate to it on the other side? Is it at a stress riser from a weld?

If, as you suggest, you downsize somewhat with the dinghy, then the foredeck storage option becomes more doable. [On our smaller boat than yours, we actually dinsinflate the tubes, to make it fit better, and use an electric inflater to inflate.]

If you go to a 15 horse OB, which is what we have, it will be a simple matter to use a harness and a halyard to put it on the dinghy. We find we prefer to do this amidships, with the dink in the water. Takes only moments. However, I do wonder if you'd be happy with the 15 horse and the large crews (6 or 7, I believe you've reported), 'cause the 25 shall have had an easier time with their weight, not a problem, of course, if you're in the habit of moving them in 2 groups.

My 2 cents.

Ann
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Old 06-11-2013, 09:29   #19
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Re: Cracked Davit :banghead:

Just a quick question - if the left davit is failing from fatigue, what about the starboard davit? They are the same age so surely it should be equally fatigued?

It might be worth checking it just in case and having them both fixed at the same time.
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Old 06-11-2013, 09:53   #20
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Re: Cracked Davit :banghead:

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Originally Posted by beverley View Post
Just a quick question - if the left davit is failing from fatigue, what about the starboard davit? They are the same age so surely it should be equally fatigued?

It might be worth checking it just in case and having them both fixed at the same time.
Not knowing his set up I'm assuming this may be due to the extra weight of the outboard on that side of the dinghy. that's a lot of extra weight compared to the bow.

Obviously this is only true if the stern of the dinghy is hung off that davit. If that is not the case there may be a much bigger problem
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Old 06-11-2013, 10:24   #21
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Re: Cracked Davit :banghead:

Quote:
Originally Posted by Panope View Post
I vote for fixing the davit (maybe add a gusset). Lighten the dink by removing the console and switch to smaller engine.

Leave the engine on the dink. The convenience of an instantly deploy-able dinghy is priceless.

Steve
+1

This set up with a similar dinghy, survived a storm with wind gusts to 70 knots and 30 foot sea's for 17 hours with no damage at all. Maybe that is not a long time if you are on a passage but it was hit with lots of water for a long time and is no worse for the wear.
Bigger boats are about convenience and having the ability to have less compromise. If you can make it safe AND convenient do it!
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Old 06-11-2013, 10:45   #22
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Re: Cracked Davit :banghead:

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Originally Posted by Dockhead View Post
Don't get me wrong -- I think 15,000 miles in the English Channel and Bay of Biscay is very good service out of a setup like this. That's easily equivalent to a couple of circumnavigations, given the strong conditions here. I'm not blaming the davits -- just thinking whether there's an even better way to do it.
Cracked at the weld after 15,000 nm swinging 150 kilos. Repair the weld, maybe beef up the weld on the other davit, and go sail another 15,000 mn.
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Old 06-11-2013, 10:50   #23
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Could it not just be that you've been lucky so far in tthat the davits are rated for 175k and the end with the outboard has been getting overloaded all this time?
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Old 06-11-2013, 10:58   #24
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Re: Cracked Davit :banghead:

We have just fitted davits to our new to us 36 footer, rated for 600lbs but we are only lifting the dink (100lbs RIB) because I chickened out and added a motor lift crane come davit to lift off the 85lb weight Mercury 9.9 and sit it on a transom bracket. Our davits have a S/S stabilizing strut ( a standard option) fitted between the two arms and also have a pair of extra support struts down to the transom, also a standard available extra. I have also rigged couple of tie down tensioners on 1" webbing, one to go from transom eye to oppositeside pushpit upright and the other from a bow quarter ring acting in opposition, in effect acting like a pair of tight spring lines to try and keep the dink from oscillating from side to side in a seaway.

AS you know we are very familiar with the areas and conditions you sail in and understand well the how it happens if not knowing the simple answer solution. I think I would find some way of routinely getting the motor off the rig, even if going back to it being tiller steered unless maybe at anchor long enough to justify a more lengthy remote reconnect time.

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Old 06-11-2013, 11:15   #25
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Re: Cracked Davit :banghead:

Did the Davit crack through the weld or immediately adjacent to it?. If it cracked adjacent to the weld then it failed in the heat affected zone and may be sign of improper weld technique causing excess hardening of the parent metal. A proper re weld should solve the problem.
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Old 06-11-2013, 11:36   #26
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Re: Cracked Davit :banghead:

I'm dealing with less weight and on a smaller vessel, but I have similar concerns with my davits offshore. My davits are 2&1/2" diameter SS pipe. For increased support I tied my davits into the frame of my rigging with added shrouds from the distal ends of each davit to my mizzen masthead. My ketch rig includes a triatic that carries this "frame" across to my main and returns to the hull at the stem. I understand those that might suggest that any failure would now compromise more of my rig; however, I'm pleased with the "unibody frame".
.....
Here, you can see the two metal tangs leading down from the aft of my mizzen,- each cabled to a separate davit.


You may be able to view the cable attached to the aft end of each davit in this last photo. I have turnbuckles on each davit connection to adjust tension. This has been serving me well
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Old 06-11-2013, 12:02   #27
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Re: Cracked Davit :banghead:

Quote:
Originally Posted by Tantalus View Post
Could it not just be that you've been lucky so far in tthat the davits are rated for 175k and the end with the outboard has been getting overloaded all this time?
Granted you are not over the limit, but certainly you are close on the motor end. What with the sea, the WL may have had less in mind.

I'm not going to suggest going lighter or hauling the thing on deck; you have enough boat and all of that is a lot o work. I might go with simpler dingy (I don't care for remote steering even on large dinghies; it eats up too much space--I prefer good seats and a tiller extension). But assuming you want to stay with what you have, which is valid...
* Was the dingy struck heavily by any waves? if so, something needs to change because the forces are too great. a lighter dingy won't help much. You may need to go higher and perhaps further in.
* Why not go one size larger? Yeah, I know... $$$.
* Tricing-up the dinghy will help quite a bit. Not just strapping it against sway, but straps going around and up.


I'm not sure I would try to weld it up. You'll just worry about it. I don't think I would try a cable lift; the stiffness (stretch) in the cable vs. the structure of the davit means the davit will still see shock loads before the cable can help, and think of the complexity if the masthead is pumping even a few inches? Bad idea in my engineer's opinion.

Why don't they build asymmetrical davits, with one end stronger? Seems so obvious.
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Old 06-11-2013, 13:07   #28
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Quote:
Originally Posted by CaptForce
I'm dealing with less weight and on a smaller vessel, but I have similar concerns with my davits offshore. My davits are 2&1/2" diameter SS pipe. For increased support I tied my davits into the frame of my rigging with added shrouds from the distal ends of each davit to my mizzen masthead. My ketch rig includes a triatic that carries this "frame" across to my main and returns to the hull at the stem. I understand those that might suggest that any failure would now compromise more of my rig; however, I'm pleased with the "unibody frame".
.....
Here, you can see the two metal tangs leading down from the aft of my mizzen,- each cabled to a separate davit.


You may be able to view the cable attached to the aft end of each davit in this last photo. I have turnbuckles on each davit connection to adjust tension. This has been serving me well
That's interesting. Looks very well done. I'm considering something like that, although it would be simpler - just a halyard and a sling, not the slick permanent setup you have here

Surely taking some of the stress off like that, distributing it wider, could be nothing but good.
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Old 06-11-2013, 13:28   #29
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Quote:
Originally Posted by thinwater

Granted you are not over the limit, but certainly you are close on the motor end. What with the sea, the WL may have had less in mind.

I'm not going to suggest going lighter or hauling the thing on deck; you have enough boat and all of that is a lot o work. I might go with simpler dingy (I don't care for remote steering even on large dinghies; it eats up too much space--I prefer good seats and a tiller extension). But assuming you want to stay with what you have, which is valid...
* Was the dingy struck heavily by any waves? if so, something needs to change because the forces are too great. a lighter dingy won't help much. You may need to go higher and perhaps further in.
* Why not go one size larger? Yeah, I know... $$$.
* Tricing-up the dinghy will help quite a bit. Not just strapping it against sway, but straps going around and up.

I'm not sure I would try to weld it up. You'll just worry about it. I don't think I would try a cable lift; the stiffness (stretch) in the cable vs. the structure of the davit means the davit will still see shock loads before the cable can help, and think of the complexity if the masthead is pumping even a few inches? Bad idea in my engineer's opinion.

Why don't they build asymmetrical davits, with one end stronger? Seems so obvious.
Dinghy and davits have been through 12 years and 15,000 miles in some of the world's toughest waters, leaving aside the Southern Ocean. I've been in F10 and 50-ish foot confused seas. Nothing close to ever being pooped - lots of buoyancy in the stern. But 15,000 miles of bouncing around in that turbulent water will naturally stress the davits to the limit of their useful lives. No need to raise the dinghy.

I'm impressed by your knowledge of subtle nautical terminology like "tricing up" Yes, my non-engineer brain vaguely comprehends the importance of preventing swinging around and attendant shock loads. I have only recently started to do it reasonably well, and my past of doing it poorly probably contributed to the stress failure.
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Old 06-11-2013, 13:30   #30
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Quote:
Originally Posted by beverley
Just a quick question - if the left davit is failing from fatigue, what about the starboard davit? They are the same age so surely it should be equally fatigued?

It might be worth checking it just in case and having them both fixed at the same time.
Thanks; great tip! I'll do that.
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