Which way??

from the Osculati website.....

"The fixed eye is connected to the anchor with a shackle."

I would have reservations about the strength of the swivel end. The kink is going to produce a wringing stress in that rather small joint when the anchor is under load.

Perhaps another triumph of design over engineering ?
 
Yes, got to admit I have my doubts, seen other swivel arrangements, but on boats that rarely leave the marina let alone anchor up. We do it at least 300 times a year, when fishing. I think I will stick to the present arrangement, and live with the 30% upside down bit.
 
I've used one for 5 years, and it works faultlessly, and is robustly built. We anchor overnight all the time (10 times in last two weeks for instance) and I have full confidence in it. The swivel end attaches to the anchor chain, and the fixed end to the stem of the anchor. Use a narrow shackle that fits snugly around the anchor stem for best operation.

Also check you have enough distance between the end of the anchor stem and the windlass gypsy with the anchor stowed, to allow for the length of the "Twist" and the shackles you attach it with.
 
Craig

I don't have access to any of the section drawings of the device, so my cautions are based on my lack of x-ray vision.

Do you have a section of the swivel end which you can share with us, please ? I'm concerned lest there be a discernible weak link in the way that the swivel is retained within the body of the device.

Alternatively, do you know if the device has been load tested to destruction under tension, and if so what figures they have achieved pls ?

TIA
 
Sarabande, this is a very rough section of the swivel end. As there is little clearance between the height of the T section on the main body, and the corresponding gap in the two cups that enclose it, the load is always in tension, not shear, and intuitively there seems plenty of metal there to provide the strength.

twist.jpg
 
The T head, whether it's pressed or upset forged, is the weak link. Without running some finite stress analysis on it, the red lines are the weakest points - especially the one on the opposite side to the bend in the link.
 
Last edited:
sarabande said:
The T head, whether it's pressed or upset forged, is the weak link. Without running some finite stress analysis on it, the red lines are the weakest points - especially the one on the opposite side to the bend in the link.
Click to expand...


I share your general concern, though if it is sized appropriately and manufactured the right way it ought not to be a problem so far as nominal strength of the material is concerned

Incidentally, when people consider this kind of gear they worry I think whether the kit will break in the middle of the night while they're anchored+asleep and let them drift onto rocks or something. I think that's the wrong view though. The danger you need to worry about (on a mobo especially) is whether the item will fail thru fatigue cracking, at much lower stress levels than the nominal strength of the component. The stress cycling that causes fatigue occurs mostly as the boat is motoring along with the anchor stowed, not when the anchor is deployed. The danger is that the component cracks, so releasing the anchor into the oggin at 25kts, and it then thwacks the props and (in extremis) makes you lose a shaft or P bracket which usually means you sink.

So, imho, you need to replace these st steel things, and always the shackles, every say 3 years or 5000nm (I'm kinda guessing those figures), even if they haven't failed.

The remaining components in the system, namely the anchor shank near the eye and the chain, are mild steel so should last many years before cracks are of any concern. Stress cracking is much more likely on the s/s components

It's also a good idea if the anchor's safety retainer attaches directly to the anchor shank as opposed to say a link in the chain

I may be being super-cautious here. Not wishing to be a scaremonger, and (to quote Wiggo) I do sometimes run while carrying scissors :-)
 
Bear in mind this was a 30 second sketch, and done from memory of something I last fitted 3 years ago, so don't read too much into the exact proportions. Also, as stated above, the clearances are not excessive, which reduces the shear loads on one side of the head. The reference to the "opposite side to the bend in the link" makes me think you need to see one of these in operation. It doesn't lift the whole anchor out horizontal and upside down, and then spin round with a big clatter, it gradually turns as the twist goes over the bow roller. The biggest loads will be in use in high winds and/or heavy seas, when the load on the neck is entirely in tension, and any shear loads on the head are distributed equally.
 
there is a bending moment generated between the anchor end and the swivel end, as the link has a kink in it. The distance (couple) may only be 50 mm or so, but the tension is not going directly along the stem of the T, but along the line between the anchor shackle attachment point and somewhere roughly in the stem of the T.

It would make more sense if the T stem were in alignment with the anchor shackle slot, so that the loading would be linear.
 
You must log in or register to reply here.

Share this page

Top