Cruising Anchor Chain Length

[Dockhead]

Originally Posted by Auspicious

Well jeepers. It's Boat Show time here in Annapolis so I'm not keeping up. Once again, get yourself a drink of choice and perhaps a snack. *grin*

Welcome back!

Originally Posted by Auspicious

I take issue with this. You got in. Why can't you get out? There was ice in the water when you entered the fjord, there is ice in the water when you leave (unless you're there so long there are seasonal issues, or a REALLY long time climate change issues *grin*).

That is not to say that slowing down to increase available reaction time is not good seamanship. How fast are you going hove to? Less than one knot?

I follow and agree with the rest of your post, but not with this. "When in doubt, go out." . . .

Well, if you had been there, I am sure you would agree with me.


The difference is that we entered in calm weather. In a storm, you would sure as hell not want to be out there with the ice. A growler with greater mass than your boat may be barely visible, and if a wave throws it on you you're toast. Plus a storm moves pack ice and you may find yourself stuck.


Sea ice adds a totally different dimension to all of this; the normal rules which work elsewhere don't necessarily apply. It is pretty hard to describe how terrifying it is, especially when you're up there in a plastic boat like I was.

[conachair]

Originally Posted by Auspicious

Not true at all. The equations are just the same. The implications of the numbers to seamanship may be different (less scope at deeper depths).

That was exactly the point, the effect on your boat is different with different depths. One size scope fits all doesn't work. The equation showing this was there in the link.

[Auspicious]

Originally Posted by Dockhead

Welcome back!

Still have two-and-a-half days of Boat Show left but I needed an afternoon off. *grin*

Originally Posted by Dockhead

Well, if you had been there, I am sure you would agree with me.

There is no substitute for being there. That doesn't mean that being there is a substitute for making good decision - not poking at you, saying in general. I do reflect on the people in get in big trouble by running for shore in weather instead of out to sea where in general and within broad limits it is safer.

Originally Posted by Dockhead

The difference is that we entered in calm weather. In a storm, you would sure as hell not want to be out there with the ice. A growler with greater mass than your boat may be barely visible, and if a wave throws it on you you're toast. Plus a storm moves pack ice and you may find yourself stuck.

I'll certainly accept weather as a limiting factor when evaluating options.



A growler of greater mass than my boat or yours thrown onto a boat is apocryphal. It just isn't. You may bump into it. It may bump into you. It isn't going to be thrown onto your boat.



The density of seawater ranges from 1020 to 1030 kg/m3 while the density of freshwater is about 1000 kg/m3. Glacial ice is essentially fresh - close enough for comparison. Cold sea water (e.g. WNA) is more dense and of higher salinity. Accordingly we can use 1030 and 1000. My boat is about 12 tonnes (real tonnes, not those little Imperial measure tons *grin*). That's 12 m3 of ice of which 3% will be exposed. That is a good sized beach ball. The submerged portion of ice has a lot of inertia. The energy in a wave has very little horizontal component. Now I'll give you that at dusk or dawn (night is easier than dusk/dawn with lights) and dark grey seas seeing that beach ball is a problem, and that the horizontal extension of that growler is a lot more than the nominal beach ball. I'll also give you that the volume of the beach ball could be pretty widely spread so that it is more like a sheet of plywood than a ball. That growler however is not going to be thrown onto your boat. The priority is not to hit the ice. I think that's all.



I think the valid argument you make is bad weather. The biggest deal is that we are bobbing around with a lot of windage and a lot more motion relative to a hunk of ice. If you HAVE to be out in that mess slow is a good idea (which includes heaving to).



It does take us back to your point, which I do agree with, of having the gear that allows you to anchor in deep water with funky bottoms rather than be forced out with no control over the timing.



I spent a number of winters in the Barents. I get you about ice. Not my favorite thing. It isn't going to be thrown onto your boat.



Purely for entertainment value, does anyone else know the current state of the art in ice removal on US Navy and Coast Guard ships? I can speculate on the RN analogue (please note spelling *grin*).

[Auspicious]

Originally Posted by conachair

The equation showing this was there in the link.

Except it did not account for the height of the bow roller over the water.

[conachair]

Originally Posted by Auspicious

Except it did not account for the height of the bow roller over the water.

[Psy at SEA]

Another link related to Jedi's post ....Crosby Twin Clevis Link S-249 Chain Connector


https://boiserigging.com/product/cro...is-link-s-249/


TY Jedi Capt.

[tgradyv7m]

It just really comes down to how well will you sleep if you have anchor with 35 knots of wind in the forecast (or 40, or 50)? 100m and 30 m min rode. As big of chain as your boat can handle. Me'z think

[Gerrit Coetzee]

Originally Posted by CAVOK

Is there any consensus about what is the ideal anchor chain length to carry on a cruising yacht. We intend to cruise the Med then over to the Caribbean and possibly further, so there isn’t any specific cruising area. I intend to have only chain as I will be anchoring out as much as possible. Ideally the more the better, but cost, weight and it’s distribution also have some bearing. Thought there might be some long-term cruisers that may have an opinion based on experience.

You don't say what vessel you will use:
I have been sailing with a 45' Sea Ray and a 44 Catamaran side by side for a year in the Caribbean (why I did it is irrelevant for this scenario, but have very relevant application), so here goes -

Both vessels have 40m chain and the same stainless Steel lewmar anchor. In most conditions and calm weather it is perfect fine for the Catamaran. I would prefer to have had more chain and would not mind the extra weight, as we are only 3 people on the Cat.

In the exact same conditions, in the very same areas, things were different with the monohull. Same length and almost same weight, the 3:1 ratio was a no go, not even 4:1. The Sea Ray could barely be tamed with a 7:1 ratio in modest weather conditions. Thus the type of boat has an impact.

The monohull pulled its anchor out more than once. So when it bend its anchor in grassy anchorage (avoid sea grass anchor spots - two types of anchor would not catch grip and does not allow for the anchor to turn like it would in the sand), we took the loan anchor, re-anchored in the sand and added rope to increase the rode to depth ratio. At night (always at night), the increased rationed rope rode caught on a reef spot when the boat turned in changing winds. This cut the new 1" rope and given the gust, the boat was on the reefs before we realised what was happening. The damage was done.

Thus, rope is a good alternative in normal circumstances, but for this horse, anything but chain is an accident waiting to happen. I would love the flexibility and stretching capability of rope, but I hasten to warn consider your boat! In a perfect world I wouldn't mind rope, but chain on this powerboat is a better alternative .

[Dockhead]

Originally Posted by tgradyv7m

It just really comes down to how well will you sleep if you have anchor with 35 knots of wind in the forecast (or 40, or 50)? 100m and 30 m min rode. As big of chain as your boat can handle. Me'z think

Sleep at anchor with a gale blowing? I don't. Regardless of what kind of chain I'm on.

[s/v Jedi]

Originally Posted by Dockhead

Sleep at anchor with a gale blowing? I don't. Regardless of what kind of chain I'm on.

All hands on deck to fend off the draggers, then off with the dinghy saving them, then finally hot coffee and sleep. By that time we go to sleep even if it’s 35kts wind

[jmh2002]

Yes it is great to be able to have so much confidence in your own setup that you can run around the anchorage helping other people during a blow.

I often did this too in the Caribbean, because we had a big dinghy with a 25hp honda on it, which wasn't very common 25 years ago. Apart from affording us some serious convenience it also really enabled the possibility of helping others in times of need too.

Some of this was self preservation as well of course, since being one of the deeper draft boats we were always further out in the bay, but this also meant that many of the potential draggers might be bearing down on us...

But what goes around comes around. If people need help, try to help.

[jalea]

Originally Posted by noelex 77

It is based on the underwater observation that even with all chain the catenary will effectively disappear at around 30-35 knots.

Therefore if the substrate is adequate to provide enough ultimate holding ability with your chosen anchor, the advantage of all chain rode in terms of holding ability is small. However, if the substrate is poor and the chosen anchor cannot obtain enough grip to hold the boat at this type of windspeed, at lower windspeeds the anchor of the boat with all chain rode will be more horizontal and therefore have higher holding ability, if all other things are equal.

Here is a photo of a boat with a Rocna and an all chain rode in about 25 knots of wind (higher in the gusts). You can see the chain is essentially straight in the gusts with no beneficial catenary:

What anchoring depth? What chain length?

[noelex 77]

Originally Posted by jalea

What anchoring depth? What chain length?

5m depth of water with an all chain rode with a scope of 4:1. So about 25m of chain. The average wind was 25 knots (higher in the gusts).

[Yellow bird]

Originally Posted by noelex 77

5m depth of water with an all chain rode with a scope of 4:1. So about 25m of chain. The average wind was 25 knots (higher in the gusts).

4:1 scope in "25 knots of wind (higher in the gusts)"??
The issue is not the catenary or all chain vs chain+rope rode;
it's just a poor scope!!

[kas_1611]

Originally Posted by Black Eagle

4:1 scope in "25 knots of wind (higher in the gusts)"??
The issue is not the catenary or all chain vs chain+rope rode;
it's just a poor scope!!

4:1 with a modern anchor is good for 25kts if you set it properly. Hell I've hung on at 25kts with 3:1 down albeit only for an hour or so. Anchor was well dug in by the end of the wee blow.

Can one humbly ask how much you think should be down at 25kts if you have a correctly sized, new gen anchor and all chain in 5m of water?