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Old 02-01-2022, 02:58   #31
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

@Pete7
Thanks very much, good to know sources.

I am trying to understand the forces involved with respect to the ABYC wind tables for different length boats. This table just covers wind loads due to sf of windage on the hull and rigging?

Peter Smith says they are to conservative and there are others loads to be accounted for:
1 Wind on hull and rig
2. Waves on hull - surges
3. Current
4. Forces due to sailing on ground tackle, including impacts.
Hope I havent left anything out.

How can we calculate for those forces? It appears Mathias has done a lot of that for us in his calculator which I am going to purchase.

In using his calculator with 50 knot winds and all-chain rode with something entered for waves I am getting just loads of 850 lb at the anchor which is much less than the ABYC wind table alone suggests. I am finding it difficult to determine the real loads on anchor gear so that I can balance out the components.

Right now I think the weaker link is my need to usr a rope due to my concern about the weight of 200' of chain.

I wish there was some way to use MathiasW anchor calculator for chain-rope too!

Also for the calculator
What is an excellent snubber or quality?
What is the typical horizontal speed from waves in various winds. I need some idea of this to be able to run some trials and understand the relationshipd better.

Thanks
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Old 02-01-2022, 06:22   #32
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

Quote:
Originally Posted by rgleason View Post
@Pete7
Thanks very much, good to know sources.

I am trying to understand the forces involved with respect to the ABYC wind tables for different length boats. This table just covers wind loads due to sf of windage on the hull and rigging?

Peter Smith says they are to conservative and there are others loads to be accounted for:
1 Wind on hull and rig
2. Waves on hull - surges
3. Current
4. Forces due to sailing on ground tackle, including impacts.
Hope I havent left anything out.

How can we calculate for those forces? It appears Mathias has done a lot of that for us in his calculator which I am going to purchase.

In using his calculator with 50 knot winds and all-chain rode with something entered for waves I am getting just loads of 850 lb at the anchor which is much less than the ABYC wind table alone suggests. I am finding it difficult to determine the real loads on anchor gear so that I can balance out the components.

Right now I think the weaker link is my need to usr a rope due to my concern about the weight of 200' of chain.

I wish there was some way to use MathiasW anchor calculator for chain-rope too!

Also for the calculator
What is an excellent snubber or quality?
What is the typical horizontal speed from waves in various winds. I need some idea of this to be able to run some trials and understand the relationshipd better.

Thanks
If your concern is weight, you can go down a size in chain when you go for G70 grade chain. I.e. of you normally have 3/8 G40 you can go down to 5/16 G70 with big weight savings.

We are 64 long ketch weighing 25 metric tons and use 3/8 G70 chain.
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Old 02-01-2022, 07:43   #33
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

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@Pete7
Note that the Safety Factor that is normally used is 3 (or 1/3) instead of 1/4!
-- Pete You are making a good point here, with regard to what Steve s/v Panope actually measures for break out loads. Where are you getting the figures for the 50 knot loads on your boat and Franziska's boat? I am very interested!!
I have seen 3:1 advertised in the USA, but in Canada, and most other places, I've always seen 4:1 as the wll.

Franzeska is in the a
EU, so Id expect she will find the 4:1 is the wll.

I think SWL advertised as 3:1 is just a sales pitch, to show higher numbers.

Cheers.
Paul.
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Old 02-01-2022, 09:26   #34
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

From recent experience, the shock load can be the entire boat weight times the FPS of it drifting in the current until it reaches the end of the chain slack.

To get Feet per second multiply MPH by 1.618.

SO a 2 MPH drift on a 10,000lb boat is up to 32,000 lbs of force if stopped instantaneously, minus the weight of the chain times the catenary angle divided by the feet of slack, and drag of the slack chain. So up to around 12,000 lbs. in worse case scenario, if the anchor is snagged on solid rock, and you don't have a chain snubber.

Just to give an upper end of forces the chain can see.


3/8 G7 has a breaking strength of 19,800 pounds.

Probably the weakest link would be the cleat, followed by the swivel, followed by the anchor itself.

I've read stories about broken anchors, and broken swivels, and even torn cleats, but not one about a broken anchor chain, yet.

SO the chains commonly used are probably overkill, with the extra weight helping keep the anchor down with a good catenary.
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Old 04-01-2022, 04:30   #35
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

If you get Mathias W Anchor chain calculator, his instructions show that the speed entered for surges etc is seldom over 1. [Later 1 knot]

But your calc shows how high the loads can be without the elasticity of the chain catenary and snubber in a good current with waves.
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Old 13-01-2022, 18:38   #36
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

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Originally Posted by capn_billl View Post
From recent experience, the shock load can be the entire boat weight times the FPS of it drifting in the current until it reaches the end of the chain slack.

To get Feet per second multiply MPH by 1.618.

SO a 2 MPH drift on a 10,000lb boat is up to 32,000 lbs of force if stopped instantaneously, minus the weight of the chain times the catenary angle divided by the feet of slack, and drag of the slack chain. So up to around 12,000 lbs. in worse case scenario, if the anchor is snagged on solid rock, and you don't have a chain snubber.

Just to give an upper end of forces the chain can see.


3/8 G7 has a breaking strength of 19,800 pounds.

Probably the weakest link would be the cleat, followed by the swivel, followed by the anchor itself.

I've read stories about broken anchors, and broken swivels, and even torn cleats, but not one about a broken anchor chain, yet.

SO the chains commonly used are probably overkill, with the extra weight helping keep the anchor down with a good catenary.
I was thinking the same thing, never heard of a chain breaking. Has anyone ever known someone that had a chain failure?
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Old 14-01-2022, 09:36   #37
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

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I was thinking the same thing, never heard of a chain breaking. Has anyone ever known someone that had a chain failure?
Mooring chains break all the time, but I do remember one boat that broke their anchor chain in Bahia Santa Elena during a Papagayo. They had recently left California on a circumnavigation and didn't think the chain needed replacing.
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Old 21-01-2022, 14:55   #38
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

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Mooring chains break all the time, but I do remember one boat that broke their anchor chain in Bahia Santa Elena during a Papagayo. They had recently left California on a circumnavigation and didn't think the chain needed replacing.
Because cheap chains used, often even used ones and they are permanently in the water compared to an anker chain.
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Old 22-01-2022, 07:52   #39
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

In the 15 years I spent cruising full time, my chain was in the water at least 2/3 of the time. The reason mooring chains break is that they are not inspected for wear.
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Old 22-01-2022, 09:01   #40
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

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In the 15 years I spent cruising full time, my chain was in the water at least 2/3 of the time. The reason mooring chains break is that they are not inspected for wear.
Doubt that most boats its 2/3, if its a Caribbean one i would estimate approx 50/50, if its med where you stay in habours more like 1/3.
Every day not in water is less wear, especially if it get cleaned from time to time.

Sure mooring chain break at the end because its not inspected and inspection what you do automatically when you deploy or haul the anker chain in and you see it lying in your anker locker, especially on cats. So you see the condition and damage.
Most of us also dive every time we deploy the anker to check if anker sits so we check chain too. And thats what i do on mooring chains too, dive and check its condition.
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Old 22-01-2022, 09:25   #41
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

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Most of us also dive every time we deploy the anker to check if anker sits so we check chain too. And thats what i do on mooring chains too, dive and check its condition.

I wouldn't say most. It's very location dependent for that one, and even in places with warm, clear water, not everyone dives. It's certainly rare up north. Even if the water is clear enough, I'm not diving 50 feet down (in some cases) to look at my anchor. Even when the water is 75* at the surface, it may only be 50* (or even colder) once I get down to the anchor.
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Old 22-01-2022, 09:48   #42
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

Regarding anker chain length, i have now 50m and will add 35m for my around the world tour 10mm G4 which is slightly oversized for the 8.5t loaded 40ft Lavezzi. Till now i deployed minimum 5x depth till 5m,4x depth till 10m an 3x till 15m, i went till 17m depth with the 50m chain. When 3x out i shackle in a 15kg weight (in German called Reitgewicht) after 10m of chain. Keeps the chain down and i can shakle it in through the net as my anker sits back between the bows. Never dragged till now, even in 45kn. So with 80m i should be good till 25- 30m depth.

Happy to learn new.
As i have enough rope on board happy to learn how you actually use/handle a rope and chain combination when it switches from rope to chain: how do you handle it regarding the windlass . If i let my 80m 10mm chain out there is no way you can hold this and then switch from the nut to the "drum" and put 2 or 3 turns of rope around. could theoretically lock the chain with the chain lock but that sits 25cm behind the chain nut and i can easily overshoot and the the rope runs freely out till i lock it. Even harder how to get in?
Is there a video that shows how to handle that on cat with anker location retract between bows?
Have a lofrans cayman windlass where its a 90-100 degrees angle chain in out of the chain nut, so quite a small patch where the rope is on the nut.
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Old 22-01-2022, 09:55   #43
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

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I wouldn't say most. It's very location dependent for that one, and even in places with warm, clear water, not everyone dives. It's certainly rare up north. Even if the water is clear enough, I'm not diving 50 feet down (in some cases) to look at my anchor. Even when the water is 75* at the surface, it may only be 50* (or even colder) once I get down to the anchor.
You're right, absolutely location dependent.. didn't thought about eg up north and there is also conditions you can't see ground and dive.
Then i choose a different location when possible and if not drop what i have, drive it in properly plus have a person as anker watch if close to shore or other obstacles.
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Old 22-01-2022, 12:04   #44
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Re: Chain length Caribbean & tropical waters on a 35ft cat??

I thought really long and hard about my anchor set up for my Atlantic circuit (now only a year away) mainly with the Caribbean in mind.

The boat is 6ft draft 43ft long and 11mt lightship. She has a bow platform with a roller built into it. The platform is rated for up to a 20kg anchor.

I went with a 20kg Vulcan on 40m of 10mm chain spliced to 45m of 18mm triple braid nylon rope. Due to concerns about the strength of the platform and windlass, due to snubbing, and due to my hatred of swinging at anchor, I always attach a bridle to the chain back to deck cleats. Both arms of the bridle are 40m of 12mm multiplait.

All parts of the system are rated at 4mt or over.

I didnt go all chain mainly due to wanting to avoid weight at the bow and because I was always going to have a bridle anyway.

The bridle is a bit of a faff to set. I typically just let out all the chain and a bit of the rope and then scoop the rope with a boat hook up and make it off to a bow cleat and sit like that until Im confident the anchor has set. Then its easy to hook the bridle on and set it. Bringing the rode in I use the windlass on the rope to take the load off the bridle. In theory this then falls off the chain. More often than not though I have to whack it with the boat hook to get it off. Then the rope and chain just come in on the windlass. That handles the rope, splice and chain just fine.

In extremis I add the bridle to the end of the rope to get 125m of rode. The is my storm setup, good for in excess of 4mt of load with loads distributed to 2 big cleats and with plenty of shock absorption built in. In lighter airs I can connect the arms of the bridle in series to get a rode of 165m good for up to 2mt of loading.

Again. Unless expecting really heavy weather I have always only put out at most the same length of rope as my depth gauge tells me is under the boat. As this is 2m less than the distance from my roller to the bottom I avoid chafe on the rope and bridle. However the idea of a float at the splice is a good one I am going to experiment with in the future.
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