PilotWolf
Well-known member
Yep, not one jot of evidence to support his childish argument.
Or anyone's here.
Kind of sad that a leisure sailor has gone to the extent of all this. No longer what would be my idea of leisure.
PW
Yep, not one jot of evidence to support his childish argument.
If the ansatz is reasonable to work out the load on the anchor caused by the engine as f = ? p / v, then I can apply the same principle to work out the load caused by a head-on tidal stream. Only head-on, not from the side!
I do the same procedure as before, but now with engine with full thrust forward. ? and v may be slightly different, but p will be the same.
Then I use the - Bernoulli ? law - of quadratic dependency of the resistance in a laminal flow to scale this force / load to the speed of the tidal current, v_c. This gives me the anchor load due to the tidal current as f_c = ? p / v (v_c/v)^2.
As said, only an approximation for when the tidal stream is coming head on. Normally, wind and tide will mean the vessel is at an angle for both of them, meaning windage area is enlarged, as well as the under-water hull. This will mean the anchor load to the tidal stream will normally be larger than what I have estimated above. It'll make for a factor 2, 3, 4?
Anyway, just toying around with the concept.
So everybody who responded to you is wrong and your right? There isn't a single contributor to this thread that agrees with you but your right? Wake upOr anyone's here.
Kind of sad that a leisure sailor has gone to the extent of all this. No longer what would be my idea of leisure.
PW
I would love to see someone work up the math on wind vs. tide.
Assume the boat pivots around the rode. A safe engineering simplification, because a rode can only function in tension. It cannot push to the side.
Assume there are only 3 forces, each acting in sum on a single point.
Remember that the rode is not aligned with either the current or the wind. It is at an angle, because neither the wind or water force act exactly in opposition to the flow (the water moving over the keel will push to the side).
a. If the wind and water forces act on the same point the boat will not swing to one side (no torque moment around the rode).
b. Each must act on a center of effort. The water COE is typically several feet farther aft of the air COE, which is why boats can yaw.
c. The angle will be determined by the ratio of forces and the ratio of distances from the rode.
d. The actual effect on rode tension will not be that great. If one is much more than the other it will override the other force the boat in line with it. In no case will the rode feel a strong tidal force on its flank, because the ONLY way it can be stable in that position is if the forces are nearly balanced.
e. The resulting tension is probably actually less than either separate force, but you can show us with a vector drawing showing wind and water direction, and resultant force directions and magnitudes.
I'll have to do this when bored some night. While watching an old movie, perhaps.
What is surprising that despite this refreshing improvement we still see CQRs, Deltas, and Bruce on bow rollers - many on yachts whose owners claim to be liveaboards or long term cruisers.
So everybody who responded to you is wrong and your right? There isn't a single contributor to this thread that agrees with you but your right? Wake up
With reference to your statement that tales of dragging anchors were common place fifteen years ago, and aren't now. It may be that the same people who were dragging then, are now using the increasing number of marina berths and commercial moorings, and now simply don't anchor. You don't see the anchors on boats that are anchored. The anchors that you see on bow rollers, are the unused anchors on the boats tied up in marina berths.Sticking with the topic raised by the OP.
Reverse thrust on the engine to set the anchor confirms that the anchor is set, not fouled, and that it will withstand whatever tension is developed by the engine were that tension be developed by the wind.
Whether the anchor will foul at a higher tension, if the wind tension is higher than the engine tension, is unknown. There maybe a small piece of wood 1mm beyond the toe of the anchor that will foul the anchor if the tension were increased beyond the set tension. You simply don't know.
When testing anchors you learn what sort of hold to expect. Sometimes the hold is much less than expected and when you dig the anchor out carefully you commonly find a fouling element, piece of wood, seaweed, shell - impailed on the anchor toe.
The other problem that can arise is that the reverse engine tension differs from the wind direction and then the anchor will need to re-align to the new wind direction. If the change is minor the anchor will simply re-oreintate - if the direction is major the anchor may change direction but commonly will list to do so - and until the anchor sets more deeply again then its hold have been compromised.
The biggest issue with a large change in tension direction is that some seabed will have been embedded in the fluke and this embedded seabed alters, completely, the characteristics of the fluke (it becomes convex instead of being concave) and will never develop as high a hold as it should. Think of Morgan's Cloud damning of concave anchors. Though I have also tested for this and agree with Morgan's Cloud there has been no reports of dragging concave anchors, almost, since Morgan's Cloud raised the issue. For those who have invested in a Knox - though it is a concave anchor the slot seems to ensure that the fluke stays clean, my testing would agree with this. The slots of a Viking also help to keep the fluke clean - I'm not sure what the mechanism might be.
Anchoring will always remain a lottery. You don't know what is hidden just below the surface of the seabed. Reverse engine setting increases your chances of success (and safety). The more tension you apply the better will your anchor set. Its not a case of knowing what wind speed your engine tension equates to - go for maximum tension if you want maximum re-assuarnce.
A deep set will also bury some chain and buried chain will increase hold, slightly, but more important will reduce the impact of yawing, up to a point.
Adding a decent snubber will also increase the security of a set anchor as the snatch loads and veers are partially absorbed by the elstciticy of the snubber. Similarly if you have room and the chain then increase the length of your rode will also offer more chances of success (nothing new here).
The increased installation of modern windlass have changed the anchoring environment - if we find our chosen location is more subject to wind and chop than another location it is relatively easy to retreive the anchor and move a few 10s of metres to somewhere offering more shelter.
15 years ago tales of dragging of anchors were common place - now with the high populations of newer anchors the reports of the new generation anchors dragging have reduced, almost completely. What is surprising that despite this refreshing improvement we still see CQRs, Deltas, and Bruce on bow rollers - many on yachts whose owners claim to be liveaboards or long term cruisers.
Jonathan
...
On your other point about a slot in the flukes preventing a build up of mud, someone should tell my Fortress, as when deployed in mud, it frequently comes up absolutely full of the stuff. I've no complaints about its hold.
We are a diverse lot and anchor threads bring out some of the differences.
It is a refreshing change that despite a bit of thread drift we have almost, so far one exception, unanimity.
Jonathan
Good luck!
Love being the butt of ridicule. Boys and their toys Play on.
PW
Hi PW,
I’m slightly surprised by all of this. I’ve been another random guy kicking about these fora for slightly longer than you have been and I can’t say that I’ve ever noticed you previously getting in to this kind of negativity. in fact the opposite, I’ve always thought your posts worthy of a glance as I might learn something.
I’m not at all interested in anyone being the butt of ridicule (well maybe Johnson our PM, but he deserves it!) but I’m interested to know more of your theory and practical experience, I ’d Just be grateful if you could provide supporting information to your statements so that I could better understand how your opinions are formed.
Rob
Yeh, and you don't even need an anchor on the end of the chain?Now that anchoring has become so complicated and technically demanding, is it surprising that so many people choose not to, and instead use marina berths and commercial moorings?
Anchoring used to be straightforward and simple. Now it seems that you have to be a techie nerd. ?