How much (all) chain for North Brittany Anchoring?

[Babylon]

Renewing all my ground tackle in advance of spending a month or longer on the North Brittany coast, with lots of overnight anchoring expected.

Fitted a 25lb Manson as new best bower (old 25lb CQR with 25m 8mm chain spliced with 50m anchorplat to be kept as spare) plus installing a windlass. Boat is a 27ft long-keeler displacing 9,000lbs.

I expect to need a total rode of 80m for that coast. Is all-chain prudent given the big tides and rocky nature of the place, or will I simply be adding a lot of weight in the bow for nowt? What if I find myself in a position where I'm unable to enter some sheltered river or harbour?

 

[John Barry]

Presumably you're sticking with 8mm chain.

50m will weigh about 70kg (60kg in water). 80m will be over 100 kg.

Weight matters in the rode - it keeps the pull on the anchor horizontal, but it's a pain on the foredeck. As always you have to compromise.

I'd go for 50m plus 30m or 40m of warp. And you should have a warp spring to attach (15-20m) for when you don't have more than 50m out to counter snatch loading.

The Manson will tolerate angulation much better than the CQR, so shorter rodes are possible.


Waiting for the fight to start...

 

[KellysEye]

Get a chart of the area and look at the depths where youn intend to anchor. The key to the length of chain is that the weight of the catenary should be such that the chain puts no load on the anchor. Thus the amount of chain is variable for diffferent depths. For example 5 meter depth at low tide needs 10 x depth, 25 metres needs 4 x depth.

 

[John Barry]

As an addendum to my earlier post,

For a 27ft (8.2m) boat with 50m of 8mm chain and 30m of warp you should still get a horizontal pull at the anchor with 10m depth and 40kn of wind (static load from constant wind), or in 17½m depth and 30kn of wind.

Let me know if you want help modelling rode behaviour.