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Old 28-09-2015, 08:02   #1
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Lightbulb Davits failed

Davits failed on on my 2001 bahia. Last owner did a reinstall with no backing plates.
I need to repair and do 110% for doing RIGHT AND STRONG !!!
Open to suggestions and ideas
Thanks
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Old 28-09-2015, 08:54   #2
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Re: Davits failed

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Originally Posted by johnnyforu View Post
Davits failed on on my 2001 bahia. Last owner did a reinstall with no backing plates.
I need to repair and do 110% for doing RIGHT AND STRONG !!!
Open to suggestions and ideas
Thanks
When you say failed, do you mean the davits themselves failed, or they pulled through the area they were bolted to?

If it's the latter, nice big backing plates is your best answer - inch thick hardwood sized 50 - 100% bigger than the davits base should do the trick. You could also use 6mm stainless if that's more your cup of tea.

n
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Old 28-09-2015, 09:18   #3
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Re: Davits failed

Pulled through the the fiberglass. He had 3" SS pipe davits, 1 1/2" face plate on outside, 3 SS bolts through face plate a small washer on the inside. Also had 2 bolts into a inside thin side wall. Have a 11' RIB with 30 hp Yamaha.

So, when I repair I want to be SURE it's good to go what out question.

I'm used to rope rescue and rope rigging and safety factors...
New to the boating and fiberglass stuff.
Ty for reply
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Old 28-09-2015, 09:23   #4
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Re: Davits failed

That's frustrating... makes you wonder why people don't just install things properly the first time!

Ok, you're going to want to check the surrounding fibreglass for any damage (esp. cracking) that might have happened. Once that's all good, get the backing plate in there (with a healthy dose of 5200 to watertight and secure it) and you should be gold.

n
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Old 28-09-2015, 10:14   #5
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Re: Davits failed

Ty! Think it was just flip of boat as other stuff unfolded. Friend found the posting here for sale n SUGGESTED it was a good boat. Live n learn and move forward. Fix this time will be STRONG and if it comes to my standard, should never be an issue again.
I questioned it from the beginning... My bad for not doing repair before it failed ! Didn't look right.. He even had 3 deck boards to shim it out as it was still out of square.
Ty again
Johnny
Is there a brand of davits you suggest?
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Old 28-09-2015, 11:23   #6
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Re: Davits failed

In addition to repairing & replacing the glass that was already there, plus that that got damaged, you're going to need to heavily beef up the laminate in that area in general.
I'd say, by adding at least 10mm - 12mm of epoxy/glass laminate, in a pad FAR larger than the davit's footprint themselves. Like at least by a factor of 4, if not far, far, bigger than that. Using proper laminating practices, & tapering the reinforcing pad to be thinner & thinner, out toward it's edges.

In addition, you can glass in some stiffening ribs as well, up to & including some glassed in framing, to tie in the loadings from the davit's new reinforcement pad, into some of the boat's primary structure... like connecting the hull sides to the deck in that area.
And to also possibly include stiffeners glassed into/inside of the new (glass/epoxy) reinforcing pad, in the way of cores. Be they; high density foam, balsa, plywood, G10, or aluminum.

The reason for so much of the extra reinforcement being glass, is that it then becomes integral to the structure of the vessel. And everything is working together to help to support your loads. So you get a lot more bang for your buck, than by just adding a backing plate.

Once you've added more primary structure to that area of the vessel, THEN, look at adding under deck backing plates. Aluminum or G10 might be easiest & best (you can make the latter yourself). As they're machineable without special tools. And both can be easily bonded with epoxy, right to your boat's laminate (although some fasteners too, wouldn't hurt).

Some of my stressing the points of both; bonding things to the boat's structure, & adding more laminate thickness is 2-fold.
- You're thus adding strength, in the monocoque sense, to the hull & deck. Where as when just adding backing plates, they only act to spread a load.
- You're adding integral stiffness. And stiffness increaseas with the cube of thickness. Which greatly reduces flexing.

Adding stiffness is key in an application like this, where you have a load which inherently wants to flex things, cyclically. Because cyclical flexing weakens structures over time, in exactly the same manner as bending a piece of wire back & forth.

Hope that that helps, & isn't a case of TMI, or preaching to the choir. And some of my simplifying things, & laying them out in a bit of detail, is for the new guys. Who may not have been exposed to this kind of thing before.

PS: Also make sure to taper the edges of any backing plates, regardless of what material they are. So as to reduce stress concentrations at their edges.
- That, & I forgot to state that adding supportive/stiffening plates to the outside of the deck/area ain't a bad practice either. So as to help balance out the loads (and laminate strength).
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Old 28-09-2015, 11:28   #7
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Re: Davits failed

Thanks for the detailed reply...
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Old 28-09-2015, 13:56   #8
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Re: Davits failed

We had Simpson Lawrence 150 stainless davits on our motorsailer - 6 x M10 bolts holding each one down; can't rate them enough. Easily took our dinghy and 8hp outboard. If you can pick some up second hand, they've got a good, simple ratchet mechanism and will easily outlast the boat.

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Old 29-09-2015, 15:37   #9
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Re: Davits failed

I don't have the specs for the Bahia in front of me, but I would guess the original davits were rated somewhere in the 100-150kg per side. Hence, you current dinghy is probably over the design spec.
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Old 29-09-2015, 15:45   #10
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Re: Davits failed

1st it's good to hear from you. I left Sara and filed for divorce. I'm at Calusa now.
Last owner did a repair and my guess he come up short of original spec.
His repair was ruff!
Hope all is well with you two.
Any suggestion as to rebuild as this is time to upgrade !
John
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Old 30-09-2015, 13:48   #11
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Re: Davits failed

I think if you shoot for "100% right" you hit your goal...
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Old 30-09-2015, 15:39   #12
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Re: Davits failed

Quote:
Originally Posted by johnnyforu View Post
1st it's good to hear from you. I left Sara and filed for divorce. I'm at Calusa now.
Last owner did a repair and my guess he come up short of original spec.
His repair was ruff!
Hope all is well with you two.
Any suggestion as to rebuild as this is time to upgrade !
John
I know a local who can rebuild it the right way.....PM me....
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