Radar Arch Fail - Cautionary Tale

[montenido]

Hi folks,
I installed a kit radar arch a couple of years ago on my boat. I also installed davits and solar panels, as well as a radar antenna. Today, after more than 3000 miles in all kinds of conditions, it failed and fell off the back of my boat. I was moving my boat to a broker's dock in order to sell it. I had 10+ knots of wind about 30 degrees off the bow, with some waves.
I heard a strange noise from the stern, nothing dramatic, and when I looked back the arch was in the water.

Now, I have never carried my dinghy with the outboard on it, as I don't like the weight back there. I also lash my dinghy (Caribe 10X) tightly to the arch so that it doesn't swing or move around. When it fell into the water, both legs of the starboard side had detached from the boat, while one leg on the port side stayed attached. Since I was single-handing, this caused quite a bit of stress and trouble for me. I secured each side to stern cleats using docklines, and then cut all the cables away (radar and solar). I also chose to call vessel assist, since I needed another set of hands in the windy and bumpy conditions. Once they were on scene we cut the entire thing away and tied fenders to it to keep it afloat. Vessel assist then towed the arch, solar panels, radar, and dinghy back to my slip. The arch was so well secured to the dinghy that they didn't have to secure it any further, which is funny. If I'd had someone else on board I might have been able to tow it home myself and save $450.

Once I arrived back in the marina I took a look at things. It appears that all four 1/4" bolts holding one leg to the hull sheared off, causing the others to fail. The reason I am posting all of this is that I have a suspicion that one or more of the bolts might have already been sheared, as today's weather was no big deal. In fact, I would venture a guess that some of the other bolts on the other legs might be sheared.

Please take a few minutes to check the mounting bolts on your arches and other deck hardware. All of mine appeared normal and all were in place.

I am including a few pictures below for your information.

Comments are always welcome. I'm really glad that this did not happen one month ago while I was returning from La Paz, BCS, to Los Angeles, some 1100 miles.

Cheers, Bill

[montenido]

Pictures. Before and after.

[montenido]

Oops, here is the before picture.

[onestepcsy37]

As a fellow CSY owner, I know as well as you how strongly these boats were built.

This is just my humble opinion (JMHO) but I think 1/4" bolts were insufficient for this application. I don't know if you also used backing plates under the deck but that would have probably helped too.

Also, don't know about California, but here in Florida a lot of the so called "stainless" bolts are made in China and are substandard. Hard to find bolts NOT made in China nowadays...

Hope you don't think i'm being a monday morning quarterback about this. Your having chosen a CSY it's obvious to me that you know how to select a boat..

[Boatguy30]

I considered buying one of those arches last fall, but couldn't get past the lady's pushy hard sell full of lies and BS.


I ended up getting a one piece arch made in same town in NJ reportedly by a former employee. Its not perfect but was less delivered for a 110" wide arch shipped 800 miles than the box of pieces that apparently only stay in one piece for so long.

[Tayana42]

Bill, so sorry to hear of the problem you had with your arch, particularly as you were getting ready to offer your boat for sale. Your cautionary advise is worth heeding. Hope you get it sorted out quickly and can move ahead.


S/V B'Shert

[model 10]

You should have used 5200.

[MarkJ]

Maybe a prospective buyer won't notice.






Sorry for your misfortune.


Mark

[Steadman Uhlich]

Hi bill..

Thanks for posting the advisory and photos. That does help others consider risks and posssible failures.

Truly unfortunate.

What follows is written in a friendly curious tone of voice.

I am curious about the total weight of the:
Arch structure
Dinghy
Solar panels
Radar dome
Etc.
Total all that stuff up. How much does it weigh?

Just looking at all that stuff, and also wondering if the dinghy was carried there on the arch during 1100 mile offshore voyage you mentioned.

Also, has anyone else ever reported an arch failure like this? I have only been here a year, but have not heard of a collapse like that before.

[DeepFrz]

It looks like a lot of weight way up high. Long lever arm.

[montenido]

Hi folks,

Thanks for the replies. I will try to add more information. The arch came with its own mounting hardware, hence the 1/4" bolts. It does have backing plates, and having to do it again I would use more robust fasteners. I think the arch failed due to the fasteners failing (shearing), not due to structural weakness.

I carry 3 solar panels on top, which is a fair amount of weight with a long lever arm, as was mentioned. However, this is a pretty standard arrangement on many different boats and arches. My dinghy weighs about 150, but is supported on davits sold by the same company to be used with this particular arch. I don't believe that the arch was overloaded, but I could be wrong about that. I did carry the dinghy on the davits for the trip down to La Paz, which was downhill. I carried it on deck when I returned, and will carry it on deck for any future voyages.

I have enough confidence in the arch construction that I will consider ordering another and use larger fasteners. I believe the smaller fasteners were the culprit causing the failure.

Thanks again for the great posts.

Cheers, Bill

[Greenhand]

Am I understanding correctly that this was attached at the side of the hull, so that the bolts were supporting all of the weight?

[montenido]

Yes, that is correct. The arch was bolted to the sides of the boat per the instructions that came with it. Too much shear force for the supplied fasteners apparently. I'll have to re-think this when I replace it.

Cheers, Bill


Sent from my iPad using Cruisers Sailing Forum

[Wotname]

Sorry for your misfortune and in many ways you where very lucky. Had it failed in less benign conditions, the outcome could have been ugly.

Hindsight is great, those bolts were way too small

[Sandero]

If the bolts sheared then the forces on them were too much. This means the engineering was wrong. In addition to the static load (dead weight) you have dynamic loads created from the boat's movement and these sorts of loads are much greater than static loads. That is to say, this rig sitting at the dock would likely not fail. But take it out to sea in all manner of waves and you introduce forces which exceed capacity of the bolts. There are also different grades of bolts and you might have had the lowest grade which didn't help.

The design looks poor as well. The rear post is in compression and the forward one is in tension. Once the starboard side failed and the structure detached and fell... the remaining apparently pinned port connection was no longer in compression and the reduced weight was carried by the floating dinghy. So it seems.