thinwater
Well-Known Member
A few thoughts on two anchors. I've done this a lot.
1. You really don't need chain on the second rode. It won't be rubbing on the bottom because the pull direction is consistent in most cases. Anyway, there is another anchor. Without chain it is WAY easier. With chain it is often too much work. Hard work if it is blowing and you are doing it singlehanded.
2. The direction of pull change WILL be zero if the angle is wide enough that there is never complete single leg loading or slack. This will not be true if there is a front passage, but it will be otherwise. Simple geometry that depends on how widely they are spread. About 90-120 degrees is optimal. Many people set them either too close together or too far apart.
If you expect radical shifts, there is always the Bahmian moor strategy, though you really need to keep the angle below 120 degrees to avoid force multiplication. Personally, since I nearly always know where the strong wind is going to come from, it's enough to set the second anchor a little wide of that direction; when it shifts, you will be in the V.
3. There is typically CONSIDERABLE increase in holding capacity for three reasons. First, if the boat is nervous (my cat and my tri are not because of bridles) eliminating yawing reduces rode tension 2-4 times the static value as compared to a boat that is yawing the typical 60 degrees. The exact amount depends on water depth and rode type. This is due both to snatch effects (chain rode) and increased windage (rope rode) when the boat is sideways. In other words, for the single big anchor to be equivalent, it needs to be not just a sized larger, but as much as 3 times as heavy. Also, it means you can use Fortress anchors, which hold a ton in the right bottom. Second, in soft mud (where holding is commonly a problem) the anchors can shift to share the load, although this takes special rigging (asymmetric lengths). Again, it allows one of the anchors to be a Fortress, with the NG anchor serving primarily to buffer changes. This is a VERY effective combination, greater than the sum of its parts; it can be stronger than a larger anchor, since it allows the optimum use of a Fortress. Not guesses, I've done a good bit of load testing on this topic. Finally, pulsation and twisting liquefies the mud around the anchor, reducing holding capacity. Variable, but perhaps 30-60% reduction in holding capacity in mud (more testing, but only 2 mud locations).
4. In-line tandems don't work. Smith posted something different, but if you look at the photos you will noticed two things: in no case are both of the anchors actually set, and the pull is never at any angle. Try it, dive on the anchors, and I will give you 10:1 the lead anchor will roll out within an hour, leaving you hanging from the smaller trailing anchor. I'll give you 3:1 that even after multiple efforts, you can't get both well set at the same time period. I succeded a few times, but it's not easy. Every other anchor manufacturer says "bollox." Additionally, even Rocna admits that in-line requires 2x scope and keeping the chain on the bottom 100%. That means at LEAST 20:1 scope for storms. The ONLY time in-line is smart is if the bottom is non-burying. Is it stronger than a single anchor of 2x weight? I've seen it go both ways, but that is a complicated explanation.
Is a single anchor better most of the time? Yes. But the whole yawing and reset topic area is complicated. I look at V-anchoring as a useful skill, but not a normal method.
1. You really don't need chain on the second rode. It won't be rubbing on the bottom because the pull direction is consistent in most cases. Anyway, there is another anchor. Without chain it is WAY easier. With chain it is often too much work. Hard work if it is blowing and you are doing it singlehanded.
2. The direction of pull change WILL be zero if the angle is wide enough that there is never complete single leg loading or slack. This will not be true if there is a front passage, but it will be otherwise. Simple geometry that depends on how widely they are spread. About 90-120 degrees is optimal. Many people set them either too close together or too far apart.
If you expect radical shifts, there is always the Bahmian moor strategy, though you really need to keep the angle below 120 degrees to avoid force multiplication. Personally, since I nearly always know where the strong wind is going to come from, it's enough to set the second anchor a little wide of that direction; when it shifts, you will be in the V.
3. There is typically CONSIDERABLE increase in holding capacity for three reasons. First, if the boat is nervous (my cat and my tri are not because of bridles) eliminating yawing reduces rode tension 2-4 times the static value as compared to a boat that is yawing the typical 60 degrees. The exact amount depends on water depth and rode type. This is due both to snatch effects (chain rode) and increased windage (rope rode) when the boat is sideways. In other words, for the single big anchor to be equivalent, it needs to be not just a sized larger, but as much as 3 times as heavy. Also, it means you can use Fortress anchors, which hold a ton in the right bottom. Second, in soft mud (where holding is commonly a problem) the anchors can shift to share the load, although this takes special rigging (asymmetric lengths). Again, it allows one of the anchors to be a Fortress, with the NG anchor serving primarily to buffer changes. This is a VERY effective combination, greater than the sum of its parts; it can be stronger than a larger anchor, since it allows the optimum use of a Fortress. Not guesses, I've done a good bit of load testing on this topic. Finally, pulsation and twisting liquefies the mud around the anchor, reducing holding capacity. Variable, but perhaps 30-60% reduction in holding capacity in mud (more testing, but only 2 mud locations).
4. In-line tandems don't work. Smith posted something different, but if you look at the photos you will noticed two things: in no case are both of the anchors actually set, and the pull is never at any angle. Try it, dive on the anchors, and I will give you 10:1 the lead anchor will roll out within an hour, leaving you hanging from the smaller trailing anchor. I'll give you 3:1 that even after multiple efforts, you can't get both well set at the same time period. I succeded a few times, but it's not easy. Every other anchor manufacturer says "bollox." Additionally, even Rocna admits that in-line requires 2x scope and keeping the chain on the bottom 100%. That means at LEAST 20:1 scope for storms. The ONLY time in-line is smart is if the bottom is non-burying. Is it stronger than a single anchor of 2x weight? I've seen it go both ways, but that is a complicated explanation.
Is a single anchor better most of the time? Yes. But the whole yawing and reset topic area is complicated. I look at V-anchoring as a useful skill, but not a normal method.
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