Anchor Specs

[webcraft]

Re: Weight

I have never understood this argument.

According to the weight fanatics my 10kg anchor is a little on the light side or maybe just big enough. OTOH if I had a 20kg anchor it would be bombproof, and the shape (according to weight junkies) is largely irrelevant.

I'm sorry, but there is no way I would leave my boat on even a 50kg mooring . . . which is all a non-dug-in anchor is. Relying on weight is a mugs game IMHO - if your anchor is not set properly and it comes to blow then you WILL drag unless it sets itself when it begins to drag.

So shape and design are paramount, and weight gives a false sense of security. I do not want someone who doesn't care whether his anchor is set or not anchoring next to me, no matter how heavy his gear may be.

BTW, the table in the MCA code is specifically for HIGH HOLDING POWER ANCHORS - but why anyone should use any other sort when they are available is quite beyond me.

- Nick

 

[Ships_Cat]

Re: Weight

According to the weight fanatics my 10kg anchor is a little on the light side or maybe just big enough. OTOH if I had a 20kg anchor it would be bombproof, and the shape (according to weight junkies) is largely irrelevant.

I did not read that as being said at all.

But I would certainly tend to agree that if you had a 20kg anchor of reasonable design it would indeed be much more bombproof than one of the same design at half the weight. That not only because of its greater weight but also because it would have bigger presented area and be structurally stronger - so depends how bomb proof you want to go for the boat's service (we have specified miniscule anchors for commercial vessels never expected to anchor, and convinced Class to accept them).

Nigel's photo of the chain in a curve on the bottom has always interested me (he has shown it before). We usually anchor in exposed areas with swirling type winds and I have found that the boat will generally range around a circle much less than the scope let out (am talking about up to 35-40 knot force swirling gusts). Then if a stonger and sustained gust of longer duration comes along, over a minute or so the boat will range back much further as the chain is slowly pulled straight through the bottom and straightened out.

I suspect that the chain bedded in the sea bottom has a great deal to do, under those conditions, with preventing anchor breakout due to rotation of the boat around it. It obviously takes quite some force, a surprising amount to me, to actually pull the chain around when part of its length has been buried.

John

 

[GMac]

Re: To Hylas ...

Anchor threads... don't ya just luv em.

I have a theory which I would like to test the waters with which goes a bit like this;

The WEIGHT of the anchor is more important than the area to smaller boats than larger boats.
The AREA of the anchor is more important than the weight to larger boats than smaller boats.

I'm thinking the cutoff or '0' point is around an average 9m/30fter size boat. Of course this will vary between boats/windage and etc but as an average point 9m.

Smaller boats, generally, are over anchored in relation to bigger ones if you do a 'gear sizing to boat length/displacement' sort of ratio thing. This is due to, in big part, the 'feel good factor' i.e a 3mm chain will hold 500kg ruffly which is a awful lot for a smaller boat but who would be sitting there happy on 3mm, not many I suspect, hence 6mm is quite a small chain actually found on boats.

Smaller boats don't have anywhere as much exposure to windage, tide and so on hence have to rely more on WEIGHT for holding as the boat does not have the 'pull' to set the anchor well.

In bigger boats we have more windage (some new designs have heaps more), are effected by tidal flows more, have smaller (lighter) anchoring gear in relation to boat 'bulk'. Due to these bigger forces bigger boats do have the 'pull' to set an anchor well and then the AREA is very important.

This is based on lots of diving (I always go down the rode and back up at the end of the dive. Just nosey I guess) and having a big personal and professional interest in anchoring systems for many years.

Using this theory you may have the situation (and it is actually strangely a bit like that in real boating) where a 25fter is happy on a 25lb clump of anything and a 45fter is equally happy on a 20lb Alloy anchor with a big surface area.
Assumptions: Boat driver is not a nutter, correct chain/rope sizing combo is attached, average weather conditions, the anchor is not 'set' by the skipper on deployment (as most aren't sadly).

Just my thoughts but I sort of quite like them

 

[vyv_cox]

Re: To Hylas ...

Fully agree. I have a Fortress on chain plus rope, which according to 'advice' should be the greatest combination available. It isn't. I have dragged it several times and it often fails to set. I would never sleep on it or leave the boat on it. In soft mud/sand it holds very well indeed but I cannot guarantee to only anchor on this type of bottom.

On the other hand my Delta plus chain has never dragged and failed to set only once in exceptional conditions, which backs up what you say. The bottom was very hard sand, on a surf beach. The Delta simply skipped across the surface without digging in. May I suggest, at the risk of castigation from above, that a Spade would not have set there either.