Chopping bits off anchors

[prv]

I know I'm almost certainly going to regret asking this question, but some kind of morbid fascination drives me to ask anyway . And just maybe, someone might have some factual information rather than gut feeling...

So, here goes: is it a really daft idea to cut about three inches off the end of the shank on a bog-standard knockoff Danforth, used as a kedge on a 34 foot boat?

I ask because I really have nowhere else to put it except in the dedicated kedge locker built into the stern, and the 10kg Danforth I've just bought will not quite fit. The boat crams a full-width aft cabin into 34 feet, and the casualty is cockpit locker space, hence lack of alternative stowage. I don't want to switch to a smaller anchor as I don't reckon the fluke area would be sufficient.

I wouldn't dream of messing about with a carefully-engineered new-generation anchor, but this is a relatively crudely (though strongly) made copy of a generic design, and I suspect the dimensions are not all that critical. In any case, I can't really see that the length of the shank makes much difference to the operation of the anchor, since the pull of the chain (I have 10m of 8mm chain) is always in line with the shank when the anchor is in use. The shackle will still be well outside (about 4" outside) the tips of the flukes, and holding the anchor at both the old and new positions it doesn't seem to appreciably change the angle of dangle (shank hangs straight down in both cases due to the weight of stock and crown). I guess there's slightly less leverage to pull the flukes out when lifting the anchor, but I'm willing to live with that.

I have some zinc-rich paint which claims to be almost as good as galvanising, which I'll apply to the cut edges. The thing's rarely going to be put in the water anyway.

Fire away...

Pete

 

[vyv_cox]

Sorry, no factual information but I would not hesitate. It is my perception that an equivalent Britany or FOB are both quite a bit shorter than a Danforth in the shank. For a kedge I would think it will be fine.

 

[winsbury]

I had to do something similar myself on a CQR that was slightly over sized for my boat and consequently was too tight for the jaws of the largest swivel that would go though the bow fitting. A bit of grinding and zinc paint later it fit the swivel properly yet still has a very substantial thickness of metal at the connection point. Clearly it must be less strong than originally but given the size of my boat is unlikely to ever be stressed even vaguely close to its maximum yet provides the extra security of greater holding power and easier setting versus the tiny Danforth that came with the boat which is now relegated to kedge duties.

Its remarkable just how strong good metal is but I would hesitate to modify a cheap Chinese copy that might be made with inferior metal to start with.

 

[prv]

Its remarkable just how strong good metal is but I would hesitate to modify a cheap Chinese copy that might be made with inferior metal to start with.

No strength issues here - the shank is a flat bar of constant cross section. I would just be sawing it in two, drilling a hole, then rounding off all the corners (including edges of the hole) and painting with the zinc.

Glad to have Vyv's blessing on it

Pete

 

[winsbury]

No strength issues here - the shank is a flat bar of constant cross section. I would just be sawing it in two, drilling a hole, then rounding off all the corners (including edges of the hole) and painting with the zinc.

Glad to have Vyv's blessing on it

Pete

Provided the machining processes don't heat the metal too much I would imagine you would have no problems with that approach. Shortening it will reduce the leverage and hence turning moment so if anything will make the overall anchor more resistant to deformation though as you say might make breaking it out to retrieve a little more difficult.

 

[NormanS]

I can't see that it would make any significant difference by shortening the shank of your Damforth. For many years my main anchor was a fabricated plough with a considerably shorter shank than the same size of regular CQR. It worked very well, the main advantage being that it self stowed better on the bow roller. It takes quite a force to bring a 140lb anchor over the bow roller.

Winsbury. I'm not sure why you need a swivel at all, but it is very poor practice to fit it direct to the anchor. Better, if at all, to be a few chain links away.

 

[prv]

Provided the machining processes don't heat the metal too much

"Machining"? There's posh . I was just going to use a hacksaw and a file

(Yes I know these will still warm the metal up a bit, but hopefully nothing like enough to change its properties.)

I still reckon it's unlikely that a £35 anchor has much in the way of advanced metallurgy...

Pete

 

[winsbury]

Winsbury. I'm not sure why you need a swivel at all, but it is very poor practice to fit it direct to the anchor. Better, if at all, to be a few chain links away.

Its one of those heavy duty all stainless double swivel thingies that both bends and swivels, ie it is more articulated than a chain and shackle termination, it is specifically designed to attach directly to the anchor and allows the anchor to retrieve smoothly over the bow roller the correct way up (well, most of the time it ends up the right way round anyway! )

 

[vyv_cox]

I would be amazed if it was made from anything other than a length of flat bar, which comes normalized, i.e. allowed to cool down in air after hot rolling in a bundle with thousands of its mates. It will have a carbon content of maybe 0.1%, which means you could heat it to red heat and let it cool with only a very minor effect on its microstructure.

 

[SaucySailoress]

Thanks. I have been trying to get information about this sort of thing from another forum, with little success. Captai has chopped off the ends of the shanks on our two sand anchors... his post is:

Sorry just assumed it was a spade anchor - have learned that spade anchors could even be ploughs! So majority from internet search it is a FLUKE ANCHOR



So assuming ground conditions are sandy / muddy anchor should land flat.

as tension comes on the end of the shank, provided it is not too short for leverage, the spades will start to dig in.

Assuming there is sufficient "holding power" in the ground it will continue to dig in until either the shank is pulled more vertically or the drag is greater than the holding power.

All that the shank length does is determine the angle of the "dig, the shorter it is the steeper the angle of dig as there is less leverage between the flukes and the chain. Too sort however then you are creating a reverse "vertical" situation where you are at risk of pulling it out or it not even digging in at all - at a guess shortening the shank considerably less than the ends of the flukes - which would be rather stupid as the probabilities increase that chain would then get tangled in the anchor!

Does anyone have anything to add to this? Or arguments against it - I am not quite satisfied with the situation yet!!!

 

[vyv_cox]

Sounds like a load of tosh to me. The critical component, not mentioned in your post, is the amount of rode that has been deployed. If there is plenty, 5:1 with all chain, more with mixed rope/chain, the pull will be almost horizontal along the seabed. Think of the shank as an extension of the rode (more or less). The load provided by the boat, either by engine or the wind, will set the anchor in the bottom.

Spade is a very effective new generation, concave anchor, not a plough. There are so many incorrect uses of specific terms that it is difficult to understand exactly what he means.

 

[TradewindSailor]

Vyv ..... if you think of the effects of no shank at all, and the blades aren't aligned, you may then understand that it may not be a 'load of tosh'.

 

[vyv_cox]

Vyv ..... if you think of the effects of no shank at all, and the blades aren't aligned, you may then understand that it may not be a 'load of tosh'.

The angle of penetration, somewhere around 35 degrees on a good anchor, is determined by the connection between the shank and the flukes. There clearly has to be a shank of some sort to control this angle but, as said earlier, provided the rode is pretty much along the bottom it is not necessary for the shank to be very long. The explanation given above has little credibility for me and contains several basic errors of terminology.

 

[Greenheart]

Not sure if this has been covered already, with the swivel mentioned earlier...

...but how hard would it be to have a shortish bolt-on section, which when added to the shank, returns it to its designed length? You might make the bolt-on section permanently attached, but free to loosen from its in-use position, so it can swing round to fit inside the limited-locker dimension.

Hardly ideal if it added lots of weight at the wrong end, but not difficult to make effective.

 

[prv]

how hard would it be to have a shortish bolt-on section, which when added to the shank, returns it to its designed length? You might make the bolt-on section permanently attached, but free to loosen from its in-use position, so it can swing round to fit inside the limited-locker dimension.

Hmm, that's an interesting idea. Obviously a freely-pivoting extension is pointless, because it's no different to a piece of chain. But I think you're suggesting one that can be locked into place? I can't see why that wouldn't work, as long as it was strong enough which could be a challenge for the DIYer with limited metalworking facilities.

I'm not going to bother though, just chop the end off mine and have done with it

Pete

 

[Greenheart]

...I think you're suggesting one that can be locked into place?

Exactly. In fact, having cut the end off, just put two new holes in the lower end of the cut section, which will line up with another two in the remainder of the shank...

...one hole can be bolted-through permanently so the extra bit can be swivelled for compact storage...the other holes line up with another bolt, for anchoring.

Pretty simple, no? Domed-head bolts for minimal snagging.

 

[prv]

Exactly. In fact, having cut the end off, just put two new holes in the lower end of the cut section, which will line up with another two in the remainder of the shank...

Given the small length I'm planning to cut off, by the time you've added that overlap you'd be left with practically none of the original end sticking out.

Pete

 

[Greenheart]

Given the small length I'm planning to cut off, by the time you've added that overlap you'd be left with practically none of the original end sticking out.

I believe you. But I think I've worked out how to bring my danforth back from France, in very compact cabin baggage!

 

[winsbury]

Given the small length I'm planning to cut off, by the time you've added that overlap you'd be left with practically none of the original end sticking out.

Pete

If its only a short section I cant see there would be any [measurable] degradation either in holding power or ability to set the flukes provided sufficient chain is out to hold it horizontal.

As to a locking joint of some sort, that's over engineering the solution imho, that said there are various ways that could be achieved but not necessary in this instance.

Personally I think there is a case for a kedge design that can be taken apart/ reassembled for easy stowage. This would also suit dinghy sailors that like to anchor off too ( On our Wayfarer the Danforth anchor is a constant cause of scraped ankles and gouges out of the paintwork) edit: yes I know there are collapsible grapnels but these have such poor holding in most conditions I don't see them as a realistic solution.

 

[NormanS]

If its only a short section I cant see there would be any [measurable] degradation either in holding power or ability to set the flukes provided sufficient chain is out to hold it horizontal.

As to a locking joint of some sort, that's over engineering the solution imho, that said there are various ways that could be achieved but not necessary in this instance.

Personally I think there is a case for a kedge design that can be taken apart/ reassembled for easy stowage. This would also suit dinghy sailors that like to anchor off too ( On our Wayfarer the Danforth anchor is a constant cause of scraped ankles and gouges out of the paintwork) edit: yes I know there are collapsible grapnels but these have such poor holding in most conditions I don't see them as a realistic solution.

A Fortress anchor does just that.