An unlucky Vulcan

[s/v Jedi]

Originally Posted by Sonosailor

Folks: I am sitting in my little boat, in Grand Anse D’Arlet, watching one boat after another come in between the snorkelling turtle watchers, drop 3:1 or less, and drag their anchor hundreds of feet back out to sea, ripping up the turtle grass that brings them all here in the first place. They try again and again, plowing long cuts; each time varying only where they start. Why do we think we can do the same thing and get different results? Why are we so closed to advice? What a stupid species we are. They each do it until they either grab some random coral or end up in another anchorage, or get so close to shore their method works. Then we watch out for them - sometimes picking our anchors up from behind them and move. No sense talking to them. Where are you in this?

You are wrong to form an opinion on what you see in Martinique. What you see is probably the hordes of charter boats that are a pest in the Eastern Caribbean.

I always set my Bruce at 3:1 and it always sets at the first try, even at 20’ depth. I have been doing this for 20 years and never dragged, not even during hurricanes.

When depth is less than 20’ I still set 60’ of chain, which is the minimum. When depth is 40’ or more, I set 3:1 regardless of conditions and experienced 60+kts wind without trouble. When there is less than 40’ depth, I set 5:1 when wind is over 20kts or when staying overnight and room around us allows.

We actually view boats like you as suspect to dragging. Setting excess chain with anchors that don’t set otherwise is a big red flag.

[hpeer]

Originally Posted by noelex 77

The large roll bar of the Mantus presents the tip at a more aggressive angle to the seabed than the Rocna. This aids the penetration in difficult seabeds. I have owned and extensively used both of these models.

The Mantus roll bar is significantly larger than the Rocna roll bar. The first photo shows a Rocna anchor with an identical weight Mantus roll bar placed on top. The difference is significant and more than people realise simply viewing most photos of these two models.

The second photo shows the initial setting position and aggressive attitude of the Mantus. This sharp downforce helps the anchor initially penetrate difficult substrates such as weed and hard sand. The thin tapered fluke also helps. The smaller roll bar of the Rocna makes the anchor less wide and therefore the setting angle is less. The tip is presented at a shallower angle and therefore is less likely to penetrate.

The advantage of the Rocna is that it significantly less wide than the Mantus therefore it is easier to fit on many yachts, an important factor, but the setting angle and therefore the performance is poorer. The Rocna is still an excellent anchor but the Mantus M1 is better in my view.

Thanks for the side by side comparison.

Elsewhere I have heard criticism of the Rocna, and hence all roll bar anchors, for the ability to “plug” in a grass bottom and then not reset with a wind turn. My suspicion is that the Mantus, with its much bigger roll bar, is far less susceptible to this type of failure, the “plug” would push through.

I have no proof of this, and I have not anchored in that type if bottom, but it seems reasonable to me.

The only weed problem I have ever had is on my smaller boat, the chain and hence anchor got fouled miserably in a kelp drift. I’ve little experience with kelp, and after that would appreciate no more. I can imagine it could screw ip any set, given the right circumstances.

[Pete7]

Originally Posted by hpeer

Elsewhere I have heard criticism of the Rocna, and hence all roll bar anchors, for the ability to “plug” in a grass bottom and then not reset with a wind turn.

I think that should be taken in context and yes it did happen to us, just once in 6 years. We anchored in a seagrass bed and the anchor clogged and then pulled out. Likely because this has been a very small popular anchorage for 5 decades and very busy all summer long so frequently ploughed. Lifted and cleared the Rocna roll bar, then reset nearby in a clean area of thin sand over mud.

However, the Rocna hasn't clogged in sand or shingles. It does clog in mud as do other rollbar anchors. However, to replicate the concern about the roll bar, you then need a wind shift, or presumably a change in tidal direction. So mud+change in wind means it may not work, might, but may not. Sand and shingle, great anchor never had a problem. Did work in large pebbles, but hardly testing as it was a very sheltered location and didn't push our luck.

Yes we did swop out our 10kg Rocna roll bar anchor for a 12kg Vulcan, but that was to maximise anchor weight for a size that would fit in the anchor locker, oh and Amazon almost giving away Vulcans at nearly 50% of the chandlers price.

[Muaddib1116]

To the OP, if you decide that you've lost confidence in the Vulcan, that's fine and that's up to you, but it doesn't seem like it will be a decision based on much objective evidence. Two of your three examples have strong mitigating factors that are not the fault of the anchor. One was an anchorage that no anchor would perform well in, and the other is that your anchor was fouled by debris that would have compromised other designs as well. The third example is by your own admission likely due to poor technique.

Originally Posted by ThereAndBack

Generally speaking I put out a 5 to 1 scope as measured by:
Depth x 5 + tide + 3ft (which is the height of the attachment points for bridle above the waterline).

I do wonder about your scope calculation though. Assuming you are using normal mathematics equation standards, you don't factor in your bridle height and tide into your multiplication? To me, it's only logical to calculate scope at X*(depth at high tide + bridle attachment height).

[Lodesman]

Originally Posted by rslifkin

By conventional wisdom, 3:1 scope has you down to about 40 percent of optimal holding power. Anchor size and conditions will determine if that's enough. 5:1 isn't enough for maximum holding either. With most anchors that'll require somewhere between 7 and 10:1, although the amount will be lower in deep water with an all chain rode.

If that's the conventional wisdom, I don't get it. Oversize or not, why would you want to deliberately reduce the anchor's hold to less than half of its potential, except if just stopping for lunch?

[rslifkin]

Originally Posted by Lodesman

If that's the conventional wisdom, I don't get it. Oversize or not, why would you want to deliberately reduce the anchor's hold to less than half of its potential, except if just stopping for lunch?

It's all about what you've sized the 100% case for. If you sized the anchor for 60+ kts of nasty thunderstorm in a questionable bottom and less than perfect protection from sea state and the current conditions are 20 kts of wind, calm seas and a good bottom, then 40% holding power still leaves a pretty big reserve for a stronger than expected wind.

In a situation like that, you can sacrifice holding power by shortening scope to allow you to fit into a tighter anchorage that you might otherwise pass up (if the weather were worse or you had less capable ground tackle).

Having excess holding power beyond what the current conditions demand is the only reasonable way to anchor, but there's a limit to how much excess you need before you're making sacrifices elsewhere (like an excessively large swing circle) to get more safety margin.

Keep in mind that most of us carry far more capable (both better design and larger size) anchors than many of the conventional "rules" about anchoring assume. Before windlasses were commonplace, etc. then unless someone was deploying a "storm" anchor, they were likely to be using something much smaller than most of us have on the bow. Which means they had far less excess holding power to work with.

[ThereAndBack]

Originally Posted by Muaddib1116

To the OP, if you decide that you've lost confidence in the Vulcan, that's fine and that's up to you, but it doesn't seem like it will be a decision based on much objective evidence. Two of your three examples have strong mitigating factors that are not the fault of the anchor. One was an anchorage that no anchor would perform well in, and the other is that your anchor was fouled by debris that would have compromised other designs as well. The third example is by your own admission likely due to poor technique.

I do wonder about your scope calculation though. Assuming you are using normal mathematics equation standards, you don't factor in your bridle height and tide into your multiplication? To me, it's only logical to calculate scope at X*(depth at high tide + bridle attachment height).

Yes, I do factor it in. I typed that formula wrong and it was corrected later in the thread.

[noelex 77]

Originally Posted by rslifkin

It's all about what you've sized the 100% case for. If you sized the anchor for 60+ kts of nasty thunderstorm in a questionable bottom and less than perfect protection from sea state and the current conditions are 20 kts of wind, calm seas and a good bottom, then 40% holding power still leaves a pretty big reserve for a stronger than expected wind.

In a situation like that, you can sacrifice holding power by shortening scope to allow you to fit into a tighter anchorage that you might otherwise pass up (if the weather were worse or you had less capable ground tackle).

Having excess holding power beyond what the current conditions demand is the only reasonable way to anchor, but there's a limit to how much excess you need before you're making sacrifices elsewhere (like an excessively large swing circle) to get more safety margin.

Keep in mind that most of us carry far more capable (both better design and larger size) anchors than many of the conventional "rules" about anchoring assume. Before windlasses were commonplace, etc. then unless someone was deploying a "storm" anchor, they were likely to be using something much smaller than most of us have on the bow. Which means they had far less excess holding power to work with.

What he said .

The only factor I would elaborate on is at times it is convenient or safer to anchor on a shorter scope. For example, we are currently anchored at 3:1. The main reason is that this reduces the room ahead of us and discourages shallow draft vessels from anchoring in a position where they may drag into us. There are a lot of charter cats with questionable skills and equipment, so this risk is significant. I would argue that with our equipment we are safer at shorter scope.

When people think of upgrading their anchor equipment to enable the safe use of shorter scopes (as well as other advantages) they tend to think only about making use of shallow scopes to enable using anchorages or locations within an anchorage where a shallow scope is a necessity. This advantage does come into play, but there are many other times when it is just more convenient or actually safer to use a shallower scope. It is nice to have the option.

[Panope]

Originally Posted by hpeer

Thanks for the side by side comparison.

Elsewhere I have heard criticism of the Rocna, and hence all roll bar anchors, for the ability to “plug” in a grass bottom and then not reset with a wind turn. My suspicion is that the Mantus, with its much bigger roll bar, is far less susceptible to this type of failure, the “plug” would push through.

I have no proof of this, and I have not anchored in that type if bottom, but it seems reasonable to me.

The only weed problem I have ever had is on my smaller boat, the chain and hence anchor got fouled miserably in a kelp drift. I’ve little experience with kelp, and after that would appreciate no more. I can imagine it could screw ip any set, given the right circumstances.

The "plug" issue affects straight line holding power as well as when resetting. It is highly dependant on substrate type - not just a weed thing.

Yes, the Mantus M1 is less susceptible to this than the Rocna.

Steve

[malbert73]

The effect of scope is very reliant on depth. So you cannot claim certain scope is right without defining depth.
Yes, the catenary effect disappears with enough wind at all chain lengths, but the more chain you have, the higher the wind and snatch loads to lift the chain off the seabed. It’s why I have comfortably anchored in 20 knots in the deep hole in Block Island with 3.5:1 and nearly 200 feet of chain deployed but would never consider that in 10-15 feet of water where a gust of wind and a boat wake could easily pluck the anchor out of seabed at same scope.
So those who claim never to anchor with < 7:10 or 10:1 likely never anchor in deep water or have an inordinate amount of chain.

And yes, that means with only 220 feet of chain, if planning for a gale I will find a shallower harbor

[Lodesman]

Originally Posted by rslifkin

It's all about what you've sized the 100% case for. If you sized the anchor for 60+ kts of nasty thunderstorm in a questionable bottom and less than perfect protection from sea state and the current conditions are 20 kts of wind, calm seas and a good bottom, then 40% holding power still leaves a pretty big reserve for a stronger than expected wind.

Let's be realistic. There is no 100% solution. You simply can't carry around a deadweight large enough to hold you in the absolute worst case scenario. So any time you anchor, it's an act of faith. You can know what the strength limit of your rode is, and know what sort of hold your particular anchor has been tested to achieve in particular circumstances; you can calculate load based on measured cross-section, wind speed and current; and you can even make assumptions based on reports or previous experience in a given anchorage, but you will never know with 100% certainty, the amount of hold you'll get from the specific piece of dirt in which your anchor sits presently. Even if you've tested it with full-power reverse (which you can then assess as equivalent to wind up to a particular strength) you can't know if you'll have the same "hold" on subsequent pulls, especially after a shift in the wind direction.

Originally Posted by rslifkin

Having excess holding power beyond what the current conditions demand is the only reasonable way to anchor, but there's a limit to how much excess you need before you're making sacrifices elsewhere (like an excessively large swing circle) to get more safety margin.

What is "excessively large"? I get there are crowded anchorages, and get why people want to be in them, but if you do, then there is a much higher risk right off the bat. Sensibly, you anchor far enough away from other vessels and navigational hazards, that you could veer to your full scope, if necessary. Assuming chain here, most of us would at most have a 100 yd +/- radius swinging circle. With rope or mixed rode, it becomes a question of trig, with minimal advantage to going beyond a certain scope, but is likely rarely going to be beyond that 100 yd radius, except in really deep water, in which case you won't be near other vessels.

Everyone has their own anchoring philosophy, but I would never hamper my anchoring system and leave the boat, or go to sleep. If stopped for lunch or whatever, then sure. Personally, I want to go with 100% anchor performance, or as close to that as I can get, and then set the anchor alarm. Because you can never trust that 100% is enough.

[Muaddib1116]

Originally Posted by ThereAndBack

Yes, I do factor it in. I typed that formula wrong and it was corrected later in the thread.

Ah, ok, good. This thread has been pretty fast moving, so I must have missed the correction. Thanks.

[Muaddib1116]

Originally Posted by noelex 77

What he said .

The only factor I would elaborate on is at times it is convenient or safer to anchor on a shorter scope. For example, we are currently anchored at 3:1. The main reason is that this reduces the room ahead of us and discourages shallow draft vessels from anchoring in a position where they may drag into us. There are a lot of charter cats with questionable skills and equipment, so this risk is significant. I would argue that with our equipment we are safer at shorter scope.

When people think of upgrading their anchor equipment to enable the safe use of shorter scopes (as well as other advantages) they tend to think only about making use of shallow scopes to enable using anchorages or locations within an anchorage where a shallow scope is a necessity. This advantage does come into play, but there are many other times when it is just more convenient or actually safer to use a shallower scope. It is nice to have the option.

This is great, I've never thought about it like this before. I want to read Noelex's Tactically Defensive Anchoring for Dummies guide book.

[noelex 77]

Originally Posted by Lodesman

Sensibly, you anchor far enough away from other vessels and navigational hazards, that you could veer to your full scope, if necessary. Assuming chain here, most of us would at most have a 100 yd +/- radius swinging circle. With rope or mixed rode, it becomes a question of trig, with minimal advantage to going beyond a certain scope, but is likely rarely going to be beyond that 100 yd radius, except in really deep water, in which case you won't be near other vessels.

A nice philosophy, unfortunately it is not feasible in some parts of the world.

[rslifkin]

How much safety margin you need to leave yourself depends on how much you know about the bottom in question. If you know it's pretty much homogeneous mud with not much else down there and you got a good power set, I'd see no reason to worry about it. But if you don't know what's down there, or it fouled on some junk the first attempt and took a second try to set, then I'd certainly want a whole lot more margin for error.

An excessively large swing circle depends on the situation and what's around you (and what scope other boats in the anchorage are using, if there are others). In some cases, you could have that 100yd radius on your swing circle and it would be no problem. In other cases, that would have you swinging into something. So your choices are either to determine if you can anchor with less scope to reduce the swing circle, or to go elsewhere.

As you mentioned, how long and when you're there also impacts how much margin you leave yourself. I'm certainly willing to push the limits more if we're just out for the day than if we're staying overnight.

And seeing the behavior during the day (both when power setting as well as if some wind comes up) gives an idea of how it all behaves to set future expectations. There are some places where I've learned to shorten up a bit because the holding power has been determined adequate in that bottom, but the rest of the boat behavior was better at shorter scope. One is an anchorage with some cliffs right up against it, so the winds can get pretty screwy in there. It's also close to 50 feet deep. Because the winds get screwy, having too much scope out means the boat sails off that much further (and faster) when that random wind gust from a different direction hits. Less comfortable, and the more violent pull on the ground tackle to stop the boat isn't a benefit either. I used to routinely drop 250+ feet of rode in there if we were spending the night, but at this point there would need to be some pretty strong winds in the forecast for me to put out more than 200-ish feet (which is about 3.7:1 scope).


That last point is a big one though: you can't just go shorten scope everywhere because someone else said it works. You have to get a feel for how your setup reacts to it, assess whether a smaller swing circle is actually useful or not in the places you typically anchor, etc. And you certainly can't go too short in shallow water, so in many places it's just not an option.