Cracked Davit :banghead:

[Dockhead]

I sail in quite a bit of fairly rough weather. I try to stay out of F8 and above, but F6 and F7 are more or less normal conditions if the English Channel is your playground, at least, if you sail in the Spring and Fall.

I usually have my dinghy with me, an Avon 340 rib with remote steering and 25 horsepower Mariner two stroke. The whole thing weighs around 150 kilos, I reckon, and it lives on a pair of Simpson-Cooney S175 electric davits. The davits are apparently sturdy and other than having to refine horizontal bracing of the dink to cut down on chafe, I've never worried too much in rough weather.

Recently I noticed that the port side davit seemed to be sagging. After I returned from a fairly brisk Channel crossing in October, it was really drooping. I thought the bolts were coming undone. Imagine my dismay when I saw that the davit had cracked at the base and was about to fall off! I rigged a spare halyard to take the load off and continued the cruise.

Now what to do? I'll have the davit welded by my wonderful metal guy in Cowes, over the winter. But obviously I need a way to prevent this from happening again.

I'm considering two measures:

1. Rig a sling to attach the halyard to, and leave the halyard on at sea. It's a spare aft-facing halyard which I was planning to use for my SSB antenna. I guess I could use the SSB antenna as part of the system, although it would mean running the feed wire along the davit - ick. I am thinking about putting on a frame between the davits for a solar panel anyway, so maybe all of this together will be no more ugly or inelegant than any one by itself

2. Lighten the dink. It has been great having a spacious, powerful dink which is more like a small motorboat, than previous sinks Ive had. I've even crossed the Solent - four times in winter, no less - in it. But occasions to use the 25 knot speed are exceptionally rare - in harbors there's always a speed limit. 97% of the time it's used for trips short enough even to row. Maybe it's time to simplify? Get rid if the remote steering and jockey console, and fit a regular tiller steered 15 horse two stroke? A tiller steered OB can be stored on the rail, further reducing weight, and so I can reduce load on the davits by half or more.


I wish I could ditch the davits altogether, and with them the ugliness and windage, but is is the eternal question, isn't it? I could probably store the dink (or a smaller one) on chocks on the afterdeck, but the that creates a different set of problems. Plus there goes the only reasonable place to put a solar panel.

What do you guys think?

[WindLove]

Looks like you are wanting someone to validate the opinions you have already developed, so I don't what you are asking. Davits with dinghies are really no good for heavy weather sailing in my opinion, and if you are sailing with the outboard on the dinghy, while on the Davits you are asking for trouble. It's not a smart way to sail. Did you know that?

These two sentences aren't coinciding with my logic.....

The davits are apparently sturdy and other than having to refine horizontal bracing of the dink to cut down on chafe, I've never worried too much in rough weather.

Recently I noticed that the port side davit seemed to be sagging

If the Davits were sturdy I don't think one would be sagging.


So maybe a little clarity would help some of us who have some experience and can offer you some good suggestions.

[Stumble]

How old is the davit? Is it possible that it's just an age issue? That size dingy doesn't sound like it is significantly oversized for the boat. Stainless is notorious for work hardening which can make it brittle. It is most likely to occur as a weld, or the flange where the pole mounts to the boat.

You may want to look at a motor mount. We have a seperate motor crane to house ours onto a dedicated bracket. This would help to remove some of the weight from the davit system.

[noelex 77]

It seems to be just a case of davit strength rather concern about excessive pitching due to the weight in the ends, or any concern about transom strength etc. If so the davits should be easy to reinforce, particularly as their durability up to now suggests they almost strong enough.

Some stainless gussets, or even a second additional base to distribute the load should be able to reinforce them.

[Dockhead]

Originally Posted by WindLove

Looks like you are wanting someone to validate the opinions you have already developed, so I don't what you are asking. Davits with dinghies are really no good for heavy weather sailing in my opinion, and if you are sailing with the outboard on the dinghy, while on the Davits you are asking for trouble. It's not a smart way to sail. Did you know that?

These two sentences aren't coinciding with my logic.....





If the Davits were sturdy I don't think one would be sagging.


So maybe a little clarity would help some of us who have some experience and can offer you some good suggestions.

I'm not looking for a validation of anything; I'm looking for ideas and experience of others. This Forum is a wealth of them. I'm sure there's something I haven't thought of; maybe someone has tried something I'm thinking about, or has some objection that I haven't thought of, or some different approach I haven't thought of. That's what this Forum is all about.


As to the sagging -- I wrote that the port side davit was cracked. That was why the davit turned out to be sagging. As to whether or not it is a good idea to sail with a dingy cum outboard in the davits -- I think everyone knows that the less weight you have on your davits the better, but on the other hand, leaving the outboard on is the usual practice with large cruising boats like mine (my boat is 54 feet on deck, 60 feet overall, and 31 registered tons). Anyway, you have no choice with a remote-steered outboard because you cannot rig and unrig the remote steering in a reasonable amount of time for every launch/retrieval of the dinghy. These Cooney-Simpson davits are pretty massive and are designed for the load of the dinghy with the motor on.


This 150 kg dinghy and davit setup was original to my boat, which was launched in 2001, and has served for about 15,000 miles at sea, 10,000 of which I have put on myself, in weather up to a F10. One approach to the problem is just to chalk up the crack to age and metal fatigue, weld it up, and forget about it for another 15,000 miles. Or one or both of the approaches above. Or something I haven't thought about.

It's a constant dilemma on a cruising boat, because there is no way, short of having a dinghy garage, to have both convenient launching and retrieval of a good size dinghy, on the one hand, and low windage and sleek lines and no worries in big weather, on the other hand. There is always a dilemma.

[Dockhead]

Originally Posted by Stumble

How old is the davit? Is it possible that it's just an age issue? That size dingy doesn't sound like it is significantly oversized for the boat. Stainless is notorious for work hardening which can make it brittle. It is most likely to occur as a weld, or the flange where the pole mounts to the boat.

You may want to look at a motor mount. We have a seperate motor crane to house ours onto a dedicated bracket. This would help to remove some of the weight from the davit system.

Thanks. Yes, the crack is where the base is welded to the plate which attaches to the transom.

Yes, getting the motor off is an obvious way to halve the loads. But it will require giving up remote steering, which is soooooo nice. I have unrigged the remote steering before, and it is not something you would be willing to do every time you launch or retrieve the dinghy.

[Dockhead]

Originally Posted by noelex 77

It seems to be just a case of davit strength rather concern about excessive pitching due to the weight in the ends, or any concern about transom strength etc. If so the davits should be easy to reinforce, particularly as their durability up to now suggests they almost strong enough.

Some stainless gussets, or even a second additional base to distribute the load should be able to reinforce them.

Yes, the dinghy is small enough in relation to the mass of the boat, that I don't notice any difference at all in trim or pitching with the dinghy on or off. I didn't even notice the difference when I added 330 kg of chain to the extreme bow end of the boat. That being said, theory dictates that every bit of mass off the ends of the boat will make her behave better, so there's certainly nothing wrong with getting weight off there.

The windage is not good for performance, but on the other hand, windage back there counteracts the bow-weathercocking effect. My boat has amazingly little of that, which makes her amazingly easy to maneuver at low speeds in strong winds. I suspect the windage of the dinghy is a positive factor there.


The davits are strong enough, I think. The boat was designed for them and they are mounted to massive knees behind the transom which are tied into the structure of the boat. There is no cracking or signs of stress on the transom. I do think just welding it back up would probably work, and adding gussets is a good idea. Still, I think about taking strain off.

My father's boat has a guy which runs to the masthead of his boat down to the davits. His setup is different, because his dink is a soft one weighing a fraction of what mine does, and his davits are light Garhauer ones, so not comparable, but the idea of taking some of the load to the masthead intrigues me. One question I have, however, is whether that might not affect the tune of the rig.

[Stumble]

My guess is you have a confluence of a heavy boat, work hardening, and possibly inter granular corrosion. Frankly I would just have it rewelded, and possibly reinforce the section that broke.

15,000 miles and almost 15 years is a lot of time and miles to put on a system. Since it made it to this point I doubt the system was significantly undersized from the get go, it just wore out.

[Dockhead]

These are my davits, by the way:

http://www.cooneymarine.co.uk/PDF/Series-8-Davits.pdf

Simpson Davits Series 8 Davits

[Dockhead]

Originally Posted by Stumble

My guess is you have a confluence of a heavy boat, work hardening, and possibly inter granular corrosion. Frankly I would just have it rewelded, and possibly reinforce the section that broke.

15,000 miles and almost 15 years is a lot of time and miles to put on a system. Since it made it to this point I doubt the system was significantly undersized from the get go, it just wore out.

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.

[poiu]

Just another bust thing that needs fixing. Your set up sounds otherwise perfect in my view. Give Cooney a call; they will probably have seen this before, analysed the problem and worked out the best fix - possibly a gusset. Also ask them if they can do the job and match or specify the weld wire for your welder. A less than perfect match of the wire may cause a failure later. They should be embarrassed by this, it shouldn't happen, is their fault and they may be happy to do it for free.

[BriaF]

Stainless is a metal know to suffer from fatigue !!!!!!!!!!

If you have a crack this is a sign of fatigue
Assuming that the welds were well made.
To last 10 yrs plus they must OK

The rest of your Davits will also be suffering from
fatigue in high stress areas.

If you just weld it, it will just crack somewhere else!!!!!!!

You need to additional support to share the load & reduce
stress levels.
How you do this will depend on the design of your Davits
& boat.
If it was my boat I would be reluctant to tie it to the mast,
loose one it may take the other with it ???????

Methods to achieve this would include
Gussets
Extra pipes welded in
Extra pipes taken to an appropriate place somewhere else
On the boat
Seek advice from other boaties & local tradesmen welders
engineers.
Some one who can see your set up & needs.

Think twice weld once

Good luck

[WindLove]

Originally Posted by Dockhead

leaving the outboard on is the usual practice with large cruising boats like mine (my boat is 54 feet on deck, 60 feet overall, and 31 registered tons).

I am glad you have a large boat and I am sure you are proud of it. Still, I would reconsider the idea of Davits offshore or in anything above 20 knots. I have not yet seen any commercial davits that I would trust offshore with any kind of sea. One big wave can poop the whole boat. Even a big one like yours! And the question of "standard practice" surprises me, as no one I know that cruises seriously would carry a dinghy (WITH AN ENGINE,) on Davits offshore.

I can go from a dinghy deflated on deck to in the water with an engine on in about 10 minutes. I weigh about 120 pounds.

These Cooney-Simpson davits are pretty massive and are designed for the load of the dinghy with the motor on.

Apparently not strong enough if one is cracked and sagging. Sounds like you averted a disaster or are possibly headed for one. Davits with a dinghy and engine should not be used offshore in my opinion. Again, you already have your opinions as I suspected.

[TeddyDiver]

FirstSorryMissingSomeKeyOnMyLaptop

WindLowe:PleaseStayOnTopic...IfNotSureReadTheOPAga in!

Dockhead:FatiqueIsOneThingThouTheWeldsMightCorrode d.TakeAGoodLookAtThemIfSoMustReweldAllTheJoints.Th enGoodForAnotherDecadeOrMore.
RegardsTeddy

[colemj]

Originally Posted by WindLove

I am glad you have a large boat and I am sure you are proud of it. Still, I would reconsider the idea of Davits offshore or in anything above 20 knots. I have not yet seen any commercial davits that I would trust offshore with any kind of sea. One big wave can poop the whole boat. Even a big one like yours! And the question of "standard practice" surprises me, as no one I know that cruises seriously would carry a dinghy (WITH AN ENGINE,) on Davits offshore.

I can go from a dinghy deflated on deck to in the water with an engine on in about 10 minutes. I weigh about 120 pounds.



Apparently not strong enough if one is cracked and sagging. Sounds like you averted a disaster or are possibly headed for one. Davits with a dinghy and engine should not be used offshore in my opinion. Again, you already have your opinions as I suspected.

I'll bet you can't do that with his dinghy. I can put one together and in the water in 3 minutes, but I get to choose the dinghy/engine combo.

Whether it is safe or good practice to carry a dinghy/engine offshore in davits is completely dependent on the davits and boat they are attached to. Yes, I have seen a few dinghies swinging from 1" tubing 2' above the waterline. I have also seen many boats with quite rugged davits that carry the dinghy in a manner which is safe in all seas. Dockhead's davits certainly look robust - and although I haven't seen how they are mounted on his boat or how they hold the dinghy, I suspect that it carries quite safely on his large boat.

Likewise, our davits are rated for >1,000lbs and our large dinghy rides rock-steady in them with no problems at all in our offshore passages.

Mark