Chain plates for a Jordan Series Drogue

[Rum Run]

I not currently a Jester challenger myself but am intending to carry a JSD or at some another sea - anchor system. This will require adding some hefty chain plates as none of the existing hardware in that area would do it.
The usual lengths of thin strip stainless I see won't do the job reliably because of side loadings causing fatigue so I designed some to be laser cut in 10mm 316. I was surprised that the un-polished blanks will be under £30 each! Being profiled, it is possible to get some taper and shape into it to reduce weight and ugliness. I'll try to upload pics when they are here

 

[G12]

I also thought about fatigue on the ones that oceanbrake sell for quite a bit of money. I thought maybe a proper set of chain plates with toggles to allow movement would do the trick.

I'm looking forward to seeing yours though, sounds pretty tidy.

 

[Triassic]

Do attachment points for a Jordon drogue need to be that substantial? I thought one of the main advantages of the Jordan over a conventional drogue/sea anchor/builders bag arrangement was that it is supposed to offer a soft progressive control over the boat rather than the snatch loads common with the others. Are the loads really likely to exceed those imposed by for example mooring ropes, in which case why are the stern cleats not sufficient (chafe issues aside)?

 

[Rum Run]

i have no experience in the real world in this area, but looking at seriesdrogue.com , Don Jordan gives single bridle loads of around 50% of the boats mass. Grant you his figures start at 10,000lbs displacement. Also he explains why winches etc are not ideal. Some people have used a bridle going all around the boat connecting winches and cleats etc but on my little boat they are pretty small and I can get stainless stuff made easier than making a rope assembly!
The thought also occurs that if the JSD carried away then the snatch loads of a conventional parachute sea anchor need to go somewhere.
Regarding toggles, I assume that the big shackles holding the bridle would do that job? I note that galvanised alloy steel shackles with a 12mm diameter pin are rated to 1500kg working load which will be plenty for my boat.
Fatigue in the chainplate should only occur if there was any significant flexing, so if it were stiff enough this should not happen.
The pic shows the pair I just got back from the laser cutter and they are unpolished as yet. At this thickness (10mm) the steel is hot-rolled so looks pretty rough. The fat end takes the shackle and it uses M10 bolts through the remaining 4 holes.

 

[ScallywagII]

Do attachment points for a Jordon drogue need to be that substantial? I thought one of the main advantages of the Jordan over a conventional drogue/sea anchor/builders bag arrangement was that it is supposed to offer a soft progressive control over the boat rather than the snatch loads common with the others. Are the loads really likely to exceed those imposed by for example mooring ropes, in which case why are the stern cleats not sufficient (chafe issues aside)?

The spec for a JSD has the first rope with a breaking strain greater than the boat's displacement to cope with exceptional waves in extreme conditions. It seems to me a false economy to have chainplates or shackles of lower rating. In practice the loads encountered when it is likely to be deployed in a "normal" storm will be a lot less. Read the report from the US Coastguard: www.seriesdrogue.com/coastguardreport

 

[Tim Good]

Rum Rum,

Did you get these fitted in the end? Where did you place them? Did you mount them right at the top of the hull under gunwale or slightly down? Also what sort of backing plate did you put on?

I have some oceanbrake chainplates on order which should be fine. The weakest thing in the system are the shackles which are Alloy Crosby types with a 1 inch pin diameter. Boat is 17-18t.

 

[Rum Run]

Hello Northcave.
I have not fitted them yet, since work is getting in the way of sailing, or at least fettling before sailing.
The plan is to fit them just under the gunwales so as to not disturb the rubbing band, and use backing pads of 12mm thick unplasticised PVC (I use this for work, and it won't rot or crush) bedded into epoxy / glass fibre tape patches.
My problems in this area are about 1/12 the size of yours- the boat only weighs about 1.25 tonnes all up! I did some FEA on the design and deflection under load was negligible.
I believe you are right to have a weak link in something as replaceable as a shackle. If the chainplate to hull connection where the weak link it would tear a chunk out of the hull on failure, whereas if a shackle goes you could potentially re-rig with spares. Also the shackle pin is easy to inspect for overload: if bent, then replace.
Presumably the main design factor in positioning the chain plates is that you must be able to reach them from deck level to couple everything up at sea. Leaving the bridle rigged all the time must be a fatigue and UV risk, so ease of deployment must be a factor. Not a problem on my 22' boat with low freeboard, but maybe with larger vessels.

 

[Tim Good]

Not a problem on my 22' boat with low freeboard, but maybe with larger vessels.

Gosh what sort of sailing are you doing to need a JSD on a 22' boat at only 1.25 tonnes!!!! And what type of boat is it?

I plan only to rig my bridle when we do significant passages where a JSD could be deployed... I.e. lots of sea room. As such they won't be in danger of UV long term.

 

[Rum Run]

The idea is to be able to take a rest during a North Sea crossing if I get the weather badly wrong. I generally sail on my own so fatigue is a worry. With a decent wind and sea astern she will surf, so while it's fun during the day for a few hours, too long could be iffy.
To be honest the prompt for making them at this point was that I had some work going to a laser-cutting firm that did not reach the minimum charge, so putting these into the order made them effectively "free"! And like most coastal boats of that size she lacks robust strong points aft so these plates can be used for JSD, parachute sea anchor or stern-to anchoring.
The boat is an Anderson 22 and the original owner used to sail across to buy lots of duty free booze (late 70's), hence the name.