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  • 1 Post By St Anna
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Old 03-22-2012
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My Brain is Anchored

So, you only have so many boat bucks and you need a new anchor and really want to make a good decision, so how do you proceed?
I previously posted that I was considering a new anchor and rode for my 28 foot 7850 lb disp pearson, and that it would be a Manson Supreme 35 pound anchor, 30 feet of 1/4 inch hi tensile G4 chain and 200 feet of 1/2 inch 8 plait nylon anchor line.
Then I read this report: http://www.alberg37.org/Project%20DB...AnchorTest.pdf
which lead me to further question my proposed set up. In this test it seems a pull of 5,000 pounds is considered the upper limit for a 30 something foot boat (Manson Supreme 35s are recommended for 35 - 40 foot boats).
1/2 inch 8 plait nylon line (Yale) has a breaking strength of 8300 lbs
1/4 in G4 high test chain (Acco) has a working load of 2600 lbs.

Does this mean that the chain will break before the anchor pulls free or the nylon line separates?

Or that I should use 3/8 inch chain (5400 lbs load)?

I understand that nylon will deteriorate over time, but how much and how fast given that it will spend most of its life out of the weather in the locker?

I guess in the past most anchors would drag before the chain actually broke, but now with all these new generation anchors holding at far greater loads, maybe I need to use a larger chain that previously recommended.

I know that everyone is really tired of anchor discussions, but I hope you will take up the gauntlet one more time and help me understand the physics of loads and working strengths, etc.

John
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Old 03-23-2012
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Re: My Brain is Anchored

John

First you are comparing the breaking strength of the line with the working load of the chain. 1/4" G40 has a breaking strength of 7750 lbs.

I am in the same situation as you but with a lighter boat - 27'CS, design weight 6100. Currently I have a 25 lb CQR and want to upgrade. I was thinking Rocna 33lb but that has changed to Manson Supreme 35lb for obvious reasons.

I think the chain length is about right - I will go with 30' to 40'. I do not have a winch and will not have one. I think a 35 lb anchor and 30 to 40' of chain @ 3/4 of a pound a foot is about max without a windlass.

I believe there is no substitute for anchor weight. The chain is there mainly for chafe protection.
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Old 03-23-2012
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Re: My Brain is Anchored

Well I support your views for a larger anchor. I would also go all chain if you can store it and get it back up. 8mm chain will be sufficient for your boat.

Keep the nylon rode for spare/second anchor/drogue or use it to tie to a coconut tree.

Most manual windlass' can have rope/chain gypsy - (electric is better for many reasons - but on my first boat - 30ft, I had manual setup). I firmly believe a good windlass is also very good seamanship - If you are too tired pulling up the anchor, you are useless for anything else. Just my view and based on a lot of time pulling up rotten anchors!

I have oversized anchor/s, more chain than you'd expect and an oversized windlass. When the anchor is set, I am confident that I can sleep at night and have done in places blowing 65kn. So oversized ground tackle works for me.

On a few occasions, a good while ago [ and with a different type of anchor and setup] , I have dragged anchor in nasty places and needed to get the thing up and get out of the situation before it became a situation. Now I try and get more choosy where I anchor as well as the heavier gear.

You will get a the whole gamut of advice - so pick out what works for you, ignore the rest.
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Last edited by St Anna; 03-23-2012 at 03:09 AM.
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Old 03-23-2012
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Re: My Brain is Anchored

It depends where your likely to be anchoring, if you know the area, ask around about what gear other people use then adapt that information for your needs.

I have two anchors because the heavy anchor is a pain in some areas and my light anchor is useless around coral and rubble bottoms.

Its a bit like antifouling, what works for locals may not be very useful in other areas.

I have learnt that light anchors like the Fortress with limited chain are outstanding and do outperform modern heay anchors with lots of chain when used with suitable bottoms.

The availability of different types of anchors and the performance of the different anchors convinces me there is not one single best anchor or tackle.
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Old 03-23-2012
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Re: My Brain is Anchored

I also am looking to purchase a Manson Supreme for my 35.5 Bristol and looked at these at the last Annapolis boat show. I had a chance to speak to the sails rep and discuss the size needed after realizing that 35 lb is a monster at the bow. The rep recomended 25 lb for the Chesapeake Bay and indicated that 35 was oversized for my vessel. Have you had a chance to look at these up close and personal?
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Old 03-23-2012
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Re: My Brain is Anchored

It appears that your concern is over breaking the chain. Unfortunately, one of the hardest things to predict is the load placed on an anchoring system. It has been shown that the ABYC guidelines overpredicts the load placed on your anchor by 2-3X in benign conditions and underpredicts the load in really bad conditions. This is because of dynamics where waves will throw your boat several feet backwards. To keep the loads down, it is necessary to have a shock absorber in the system which you do with the line. ABYC predicts a load of <2100lbs for your boat in storm conditions which is within the safe working load of the chain so you should be fine provided that the chain is in good shape. You would have to be anchored in a reasonably exposed location in extreme conditions to ever see this load so we are talking about an unlikely scenario. It might be a bit different if you were planning on this setup being your hurricane plan but anything short of that, you should be fine.

Both chain and line deteriorate over time which must be considered. You can prolong chain life somewhat by using a slightly larger size such as 5/16 G4 but that is a call that you need to make on how much weight you want to haul up versus how long you want it to last. Regardless, once it shows significant degradation, it needs to be replaced.

For reference, on my 30' 10000 lb boat, I use a manson supreme 35, 30' of 3/8" BBB and 250' of 5/8" three strand nylon. I would have used 5/16 G4 but I already had the other chain lying around so I am using it until it wears out. I do not have a windlass so this is all hauled up by hand in depths to 50'. It has worked through several severe thunderstorms and tropical storm Irene without a problem.

It would be great if someone would do an experiment with a couple of mooring fields of boats in storms and provide data on mooring loads but I doubt that this will happen anytime soon. Until then, I think that your proposed system is fine.
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Old 03-23-2012
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Re: My Brain is Anchored

Thank you guys.
All of this makes me think a 25 lbs Supreme would be enough for other than hurricane conditions and 1/4 high tensile is just fine. I prefer more nylon in the rode for its shock absorption and damping effects on the anchor, especially since we do not have any coral around here. I also plan to splice the nylon driectly on the chain and by pass the shackle and eyelet.
KLEM: can you post a link to the ABYC load preditions you mentioned?
Thanks again,
John
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Old 03-23-2012
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Re: My Brain is Anchored

Hi John,

A Manson Supreme 25lb with 30' 1/4" G4 chain and 200' of 5/8" 3strand nylon is the setup I have on our 30' Morris Leigh. 10,000# sloop.

I did a lot of research and believe it was the best setup for us. I think it should work for you also. Be aware that Manson sets "quickly" ...hold on.

Brian
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Old 03-23-2012
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Anchor system sizing tables

Here's the information on system sizing:

Ground Tackle & Anchor System Sizing TABLES & Swivels
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Old 03-24-2012
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Re: My Brain is Anchored

The tables are in the link provided by Stu Jackson.

Whether you go with a 25lb anchor or a 35lb anchor is a whole different debate. You need to figure out what the worst conditions you want it to reliably hold in. On the east coast, I generally recommend that it be sized to hold through any severe thunderstorm, I don't know whether this would still be the best way to size where you are. Also, you need to know what bottoms you will be anchoring in as this will determine how much holding power your anchor has. If all of the bottoms are hard sand, a 25lb anchor could probably hold your boat through a hurricane. However, if it is silt or soft mud, the 35lb anchor might not hold you even in a tropical storm. Obviously fetch has a lot to do with it so the more exposed the anchorages are where you sail, the bigger gear you need. Since all of these numbers are approximations, you may want some safety factor as well. If you always have good holding bottom and good shelter, the 25lb anchor should be fine for anything that you will run into short of a named event.
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