Hard Seabeds

[Neeves]

I don't experience hard seabeds, so hard they are difficult to anchor in. I do read of hard seabeds, in the Caribbean. I also read of seabeds that have a thin layer of sediment but rock beneath.

In one of our cruising guides (Oz) one bay is described as hard (Shoal Bay, Port Stephens) but we often stop there and never have had an issue - and maybe some bays have hard patches. The advise is to deploy more chain (I'm not convinced that in a sustained strong wind that would be the answer - but as we have never found anywhere hard - don't know).

I'm assuming, or defining, hard seabeds as hard, possibly scoured, sediment, not solid rock nor solid rock overlain by a thin layer of sediment. I'd have to guess these sediments have been very well compacted or have some cementitious component holding the seabed together.

'Normal' seabeds in which one might anchor and particularly those in cruising guides and the Pilot books are commonly sand or mud (or combination) sometimes with stones, shells and weed.

I wondered how common were hard seabeds where attempts at anchor need much more patience than normal or even where an anchor might be defeated. I'd include in a hard seabed those seabeds when an anchor might engage but actually getting the anchor to bury is needs all the tension developed by engine power.

The Navy remedy for hard seabeds was to sharpen the anchor toe - visions of men sharpening 10t anchors with files or angle grinders seems unlikely and possible with our anchors, if you don't mind using more gal.

Jonathan

 

[Old Bumbulum]

An old fashioned Fisherman's anchor is often better than the usual modern designs on rocky and hard bottoms though nothing will grip on smooth rock of course.

 

[Tranona]

Very common in the Med - of both types, that is heavily compacted sediment and thin layer of sand over rock.

This is probably the reason why many visitors from the UK find their CQR which was excellent in the UK rather ineffective as it just slides over the top of the first type of bed. The second is more difficult as the sand is often not deep enough for any anchor to get a grip.

 

[NormanS]

One of my arsenal of anchors is a 20kg fabricated Fisherman type. It has largish palms on the flukes, and has quite sharp tips. To be honest, it's probably years since it's been in the water, but at least I know it's there, and as we say in Scotland, "It's no eatin' a piece".

Yes, it's home made, but galvanised, probably saved my previous boat on one occasion, and certainly gave a good night's sleep to folk on a wee boat, who simply couldn't get a grip in the weed in Canna, to whom it was lent.

Handling it is awful 'cos it's full of sticky-out bits, but if it's going to save the day, I can live with that.

 

[RupertW]

Very common in the Med - of both types, that is heavily compacted sediment and thin layer of sand over rock.

This is probably the reason why many visitors from the UK find their CQR which was excellent in the UK rather ineffective as it just slides over the top of the first type of bed. The second is more difficult as the sand is often not deep enough for any anchor to get a grip.

Found both types many times and I suspect my 15kg Delta (copy) has struggled with the first type compared to modern designs as it sometimes fails to set a couple of times before digging in properly (then never drags at least in my first 8 years of use). But the second type is where a good hard reverse to dig in is essential. If it's sand over rock then every anchor type will drag once force is applied so you get to find out straight away that you need to move, as the alternative is finding out in the middle of the night when a big gust comes in.

 

[noelex]

Very common in the Med - of both types, that is heavily compacted sediment and thin layer of sand over rock.

This is probably the reason why many visitors from the UK find their CQR which was excellent in the UK rather ineffective as it just slides over the top of the first type of bed. The second is more difficult as the sand is often not deep enough for any anchor to get a grip.

+1 That is my observation as well.

Those accustomed to anchoring in much easier, softer substrates cannot understand why in some parts of the Med their anchor, which they have trusted for so long, will not set. Fortunately in the Med there are also many anchorages with lovely mud, or soft sand where nearly all anchors work well.

Australia is quite different. Much of Australia has beautiful soft sand beaches and the substrate is often similar. It is near perfect for anchoring. Almost any design of anchor will set. Although the substrate is occasionally soft enough that the convex plough anchors with their limited surface area can slowly creep back in stronger wind.

Consequently, the uptake of new generation anchors seems very slow in Australia.

Of course Australia is a big place and there are some anchoring challenges. A few that spring to mind. The heavy weed in some parts of SA deserves respect, and anchoring in locations with coral and/or large tides can be a challange although the actual holding is not the problem. There are naturally some rocky anchorages, but only very rare pockets of thin sand over rock. There is very little hard sand.

It is a large country so it is difficult to generalise, but overall the anchoring is easy and there are some beautiful places to explore.

 

[Neeves]

So - concluding from limited posts - hard seabeds (where the sediment is hard) are common in the Med - but not elsewhere . I assume the Med 'stands out' because sedimentation is low as there are few rivers and the sea is not as aggressive at developing sand/mud because it is more benign than the ocean.

But ignoring the reasons (as being irrelevant) no-one suggest their anchors are defeated (excepting Tranona's comment of CQRs).

The HM Navy solution to sharpen the toe has logic but I find it odd that Spade developed by a Frenchman (who must have known the Med) and popular on French yachts has a particularly blunt toe (and I've always thought a bit if attention (with a file or angle grinder) might pay dividends).

Fishermen's in weed (over rock) or simply rock is a solution we have never tried in anger (mainly because of all the 'sticky out bits' and the weight needed to achieve a result. Another idle thought - I wonder if a one fabricated from high tensile steel might reduce the weight (though the 'sticky out bits' would still remain).

This is not a sales pitch - but Anchor Right now sell their steel Excels with a stainless toe plate - specifically to allow the toe to be sharpened without damaging the galvanising. Whether this is necessary in Australia, given Noelex' comment, I don't know (but assume they have made the change for a reason) and I have no experience of these newer models (as we find alloy more than adequate.. Fortress always emphasised their sharp toes - but most other anchors makers ignore that facet - suggesting its not a big issue.

Jonathan

 

[noelex]

Sharpening the toe of any anchor significantly improves its performance, but particularly in the substrates indicated, in my view a fundamentally excellent design is the critical factor.

 

[Kukri]

Some "Fisherman" anchors are more equal than others. For rock and kelp, the Thomas and Nicholson pattern is usually thought to be the best. This is the one that you will see on RNLI lifeboats (because they do sometimes need to anchor on rock and kelp - which nobody else does).

 

[RichardS]

I've anchored in hard flat seabeds in Croatia, sometimes with a layer of soft sediment maybe a cm thick which offers no help at all, but where there are a few large boulders on the seabed. By dropping the anchor very carefully and laying the chain by hand by diving down, you can wind the chain around a couple of boulders so that it can't pull itself free in the direction of the boat. I wouldn't risk it in strong winds though.

We once anchored on what, in the fading light, looked like sand. I pulled back using the engines and the Rocna held firm so we retired to bed. Next morning I got up and looked over the side and the anchor was clearly visible under the boat, as it usually is in the morning, but on this occasion I could see almost the entire anchor, so I dived down to have a close look.

We were anchored on a massive sheet of flat rock covering hundreds of square metres which was sand coloured but had no sediment covering at all. However, there were a number of large cracks in the sheet rock, about a couple of cms wide and the sharp point of the Rocna was stuck down into one of these cracks and was holding firmly in the direction. Had their been any change of wind direction in the night, I reckon we would have been as free as a bird. :ambivalence:

Richard

 

[noelex]

We were anchored on a massive sheet of flat rock covering hundreds of square metres which was sand coloured but had no sediment covering at all. However, there were a number of large cracks in the sheet rock, about a couple of cms wide and the sharp point of the Rocna was stuck down into one of these cracks and was holding firmly in the direction. Had their been any change of wind direction in the night, I reckon we would have been as free as a bird. :ambivalence:

Yep. This is a good warning, Richard. There are anchorages like this and it is easy to get caught out. The anchor can grip very well between the sheets of rock, giving the illusion of a solid set, but with a change in wind direction the anchor can let go. This is an example:

Excellent anchor design does not help much in this kind of bottom (altough a Fishman or similar is probably the best choice) . However, in other challenging substrates such as hard sand, or even a thin layer of sand over rock anchor design has a major influence on your chance of success.

 

[alan_d]

We once anchored on what, in the fading light, looked like sand. I pulled back using the engines and the Rocna held firm so we retired to bed. Next morning I got up and looked over the side and the anchor was clearly visible under the boat, as it usually is in the morning, but on this occasion I could see almost the entire anchor, so I dived down to have a close look.

We were anchored on a massive sheet of flat rock covering hundreds of square metres which was sand coloured but had no sediment covering at all. However, there were a number of large cracks in the sheet rock, about a couple of cms wide and the sharp point of the Rocna was stuck down into one of these cracks and was holding firmly in the direction. Had their been any change of wind direction in the night, I reckon we would have been as free as a bird. :ambivalence:

Richard

The other problem that can arise with this sort of bottom is if the anchor wedges in a fissure it can be the very devil to recover it. I can recall a lunchtime anchorage in Anguilla where the pilot book advised a tripping line because of this. We duly used one and were glad of it, the boat next to us had to get someone to dive on their anchor and attach one before they could move on.

 

[thinwater]

On the Chesapeake Bay we get hard seabeds in a few places, where underlying hard clay is either covered with thin sand or naked. However, typically it is so hard that no anchor could penetrate it. A screwdriver barely penetrates and even stomping on an anchor does not help. Yet it is not quite stone. Other places it is weak stone.

You either move or focus on hooking/friction strategies.

I suspect there are few places where the bottom is unusually hard, but where a specialized anchor would help.

 

[vyv_cox]

The only place the Delta I owned at the time totally refused to set was immediately outside Pwllheli marina. The bottom here is hard sand, at times with breaking surf rolling over it. We tried four or five times but the anchor simply skidded over the surface.

 

[Neeves]

The only place the Delta I owned at the time totally refused to set was immediately outside Pwllheli marina. The bottom here is hard sand, at times with breaking surf rolling over it. We tried four or five times but the anchor simply skidded over the surface.

Obviously not a place I know - and certainly cannot pronounce.

Are you aware if anyone else has tried in the same place with any success? Or is it simply a lost cause?

Jonathan

 

[vyv_cox]

Obviously not a place I know - and certainly cannot pronounce.

Are you aware if anyone else has tried in the same place with any success? Or is it simply a lost cause?

Jonathan

Quite probably not. It was a long time ago before the marina was established. It is probably too close to the busy approaches for anyone to try today.

 

[thinwater]

The only place the Delta I owned at the time totally refused to set was immediately outside Pwllheli marina. The bottom here is hard sand, at times with breaking surf rolling over it. We tried four or five times but the anchor simply skidded over the surface.

There are a number of places on the Chesapeake with very firm sand where a Delta requires some finesse. It tends to glide over the top unless you feel it in. NG anchors bite right in and hold at very high capacity. A Fortress would break something (I've gave up at 750 pounds with a 2# Guardian because I didn't want to damage it). Some places this sand is over smooth rock at variable thickness and then you don't know what you've got; boats drag on to the beach in these places. It's really hard to tell the difference without taking a core sample.

 

[Neeves]

So if a sharp toe is one answer to hard seabeds, and if hard seabeds are common (as reported, say, in the Med) how many people would sharpen the toe of their anchor?

Or is the toes of existing anchors sharp enough and hard seabeds are really not an issue

Or is the idea of a sharp toe (for hard seabeds) lacking in credibility such that people are not convinced it would make difference (to their existing NG anchor).

Jonathan

 

[noelex]

I have seen a few convex anchors that have been modified by their owners to give them a sharper toe. There are also examples of other (usually misguided) modifications, for example adding roll bars.

There are also a couple of commercial convex anchors where the manufacturer has made the last 5 -10mm of the tip sharp and thin, presumably in an attempt to improve the performance of these anchors in hard substrates. Unfortunately, given they not the most common popular models, I have also seen a surprising number of examples where this fine tip has been bent, probably from hitting rocks while setting. I suspect these bent tips will significantly effect the performance. So there are some drawbacks to a very fine sharp tip.

Overall, I think modifying some of the older anchors and giving them a sharp thin tip is worth some consideration. The convex anchor models generally struggle in harder substrates. A sharper tip will not transform the performance, but it will help.
The chance of serious problems from dragging is higher than the rIsk of bending the tip, even with a very fine tip. So I think this is a worthwhile trade off. Very few anchors are bent, but lots of boats drag.

However, modifying new generation anchors is very rare and is not something I would normally recommend.

 

[RichardS]

So if a sharp toe is one answer to hard seabeds, and if hard seabeds are common (as reported, say, in the Med) how many people would sharpen the toe of their anchor?

Or is the toes of existing anchors sharp enough and hard seabeds are really not an issue

Or is the idea of a sharp toe (for hard seabeds) lacking in credibility such that people are not convinced it would make difference (to their existing NG anchor).

Jonathan

I sharpened the point of my Rocna after a few years of anchoring. I did it with a drill and sanding disk as the galvanising on the tip had already worn away. I've only done it the the once because in recent years I have learned to avoid the hard seabed anchorages.

Richard