DIY- make your own anchor

NormanS said:
And your point is? What has that to do with a competent person making their own anchor?
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I agree with you, boating seems to be the last bastion of DIY, but insurance companies increasingly seem to be taking a different view (here at least). But there is that example of a credible anchor design being made indecently - by people who should have known better.

Try not to get too upset, the idea is to share opinions and experiences not to get upset when one's view might provoke an alternative aspect.

Jonathan
 
As an inveterate DIYer myself, I see no difficulty in producing a decent low-tech anchor. As several posters have said, it doesn't matter too much if it comes out rather heavy and perhaps slightly less good at setting than a professional one. Where the difference comes, and if I read the OP correctly, is making a high-tech one. New Generation anchors are all high tech to some extent, using more complex manufacturing techniques and materials that may require advanced welding techniques.

I weld quite a lot myself, but only in mild steel, and draw the line at anything needing pre and post weld heat treatment. Many modern materials need these, or weld methods that limit thermal input as far as possible. Rocna cut their shanks using high pressure water jets to avoid thermal input, for example.
 
With regard to the insurance angle, it is worth remembering that a Fisherman's anchor would be perfectly easy to produce as a DIY effort - after all, the majority of them were probably made by local blacksmiths using forging and fire-welding skills. A DIYer who was a competent welder could easily produce something as strong and effective as the best Fisherman anchor. Materials no problem - mild steel or wrought iron! No insurance company could argue it wasn't a well-established design; probably the oldest still in more-or-less current use. Neither could they argue that it hadn't been made to appropriate standards (barring blatantly faulty welds). I'm not recommending that people use a Fisherman's anchor (except in rocky ground), but I suggest that this simple and easily made design provides counter-arguments to the idea that only bought anchors are good enough for insurance.
 
sailbleu said:
Not really showing off here guys , but maybe this could help someone on his way to make his own anchor.
It can be done and dont need to be a superman.
http://jeanneau.proboards.com/thread/2814/diy-rocna-anchor

Best regards
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Nit picking mode.
If I had been doing that, I would have slotted the plate so that the shank went right through, and was then welded top and bottom. I'm not sure that your shank is very strongly connected with the fillet welds. But, well done anyway.
I've made several anchors, but as yet, not a rocna copy.
 
sailbleu said:
Not really showing off here guys , but maybe this could help someone on his way to make his own anchor.
It can be done and dont need to be a superman.
http://jeanneau.proboards.com/thread/2814/diy-rocna-anchor

Best regards
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Very nice workmanship.

Have you considered shank strength? Your shank thickness is slightly more than the equivalent Rocna (25 and 33 kg Rocna 16 mm) but 316L has only slightly more than a third of the strength of Bis80, the original design material. The bendy Rocnas were around a third stronger than 316L. Unfortunately 316 has a very low yield strength relative to its UTS, so bending is a distinct possibility, provided the admittedly unusual conditions needed for a strong lateral force were met.
 
This is mine.I made it some six years ago from mild steel.
anchor2_zpsb1f56e25.jpg
 
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I do hope the squabbling has died down now. I started by thinking how strange it is that the subject of anchors always causes a fight, but then realised that everyone seems to start from the premise that a single perfect design of anchor should be possible, therefore differing designs of anchor can be ranked according to their ability. Unfortunately any one anchor may be called upon to set in a wide variety of bottoms and for each the ranking changes. As mentioned above, on rocks you can't beat a fishermans. Ships get around the problem by simply dropping a bloody great lump of metal as an anchor, the design being only to allow it to be stowed in the hawse pipe. Yachts require a more elegant concept as they simply don't have the buoyancy to carry a sufficient weight in the bows, so unless you carry several designs and select for each anchorage, then you can only hope to select the best design for the most likely bottom you'll encounter and sometimes that will be a low-tech design, for some a high-tech design.

I hope John has fun exploring anchor design and maybe building one that suits his own area and boat.

Rob.
 
Thanks for the respons and comments guys , I was slightly aware of the bending caracteristics of sss , but how does Rocna deal with the lesser strenght of that material ?
They also do ss types is it not? Is the shank thickness that much more than what I used ?

Edit : Oh yes , I should add this anchor is for a 40 foot yacht , so I guess I'm ' overanchored ' anyway . That could ease down the comparison with the original design dont you agree ?


Thanks
Regards
 
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Of course you are right Rob , but I think many of us try to find a shallow and sandy anchorage most of the time no ?
Atleast that's what I try to do , using the charts and pick a good spot.
Well , in many cases you dont even need a chart , just look out for a concentration of anchored yachts ;)

Regards
 
sailbleu said:
They also do ss types is it not? Is the shank thickness that much more than what I used ?
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When Rocna made a stainless steel anchor, not sure whether they do now CMP own them, the design calculations were carried out on a duplex version, AISI2205. Duplex is a heat treatable grade of stainless steel with strength about 150% of 316. The design calculations show the bending strength with the duplex to be around 4000N whereas with Bis80 they are nearly 7000N. Both with 16 mm shank thickness. Even using duplex ss the bending strength was marginal, as demonstrated by the 'bendy' Rocnas that were made from a steel with similar strength.

For comparison, here are some typical yield strengths:
Bisplate 80 - 780 MPa
Duplex 2205 - 450 MPa
316L - 170 - 200 MPa
Failed Rocnas - various measured values, 350 - 400 MPa
Mild steel - around 250 MPa
 
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sailbleu said:
And , are you happy with it sofar ?
Hard to tell by the picture , but what are the sizes and thickness you used ?

Regards
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I'm very happy with it.The performance in sand and mud is fantastic.I anchored on a rocky bottom the other day and the anchor performed well despite not being able to dig in.I used 15mm plate and made the shank as an I beam.Theoretically this should impair penetration but in real life it makes no difference.The anchor works so well that's a bit like hitting a wall when it digs in which is almost instantaneous .
If I ever make another one I'll use thicker plate for the blade,20mm or so.
 
Thanks vyv-cox for this technical explanation.
I'll try to remember to let you , and others on this thread of course , know whether my shank is/was strong enough for the task.

Regards
 
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