If you're up short, the chain is vertical relative to the bottom. Is that 1:1 scope, or actually zero "scope?" That would form a rt triangle with zero legs and thus a zero hyptenuse, etc.
Is There Such a Thing as 1:1 "Scope?"
- Thread starter Kings Gambit
- Start date
Sounds like 1:1 scope - 1 foot of rode for every 1 foot of depth. Unless it’s a mushroom anchor or something just so heavy that it won’t move I don’t expect that to do much good though.
1 to 1 is a 45 d angle. I believe the format is horizontal to vertical. The hypotenuse isn't a factor in the nomenclature. At least that's how ground slopes are defined, which I think the slope of an anchor line mimics, if I'm not mistaken. Roof slopes are the opposite, usually defined by the vertical measurement in inches over 12.
So, a vertical chain would be 0:1.
So, a vertical chain would be 0:1.
Come to think of it, we typically measure out the rode as if it is a hypotenuse. However, with all the sag in the rode, I have a very difficult time recognizing it as a hypotenuse! I guess a 1:1 could be a vertical set (if you could call it a set). I tend to consider the horizontal distance to vertical distance as my guide for anchoring.
Veer out c amount of rode at depth reading. Aft 25 ft depth, you’d have to veer out 35 ft of rode for geometric 1:1 scope.
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Interesting point. In most land based things we measure the ratio as horizontal run : vertical run. I presume that’s because from a surveying standpoint you have coordinates on the horizontal plane and altitude, so you use those to determine the ratio. But when anchoring it’s much harder to get the horizontal coordinate than count out lengths of line (forming the hypotenuse). In places like Chapmans I’ve always read the anchoring ratio as length of rode to depth, not the harder to measure horizontal length.
It’s hard to tell students that 1:1 “scope” is 25 ft veered out in 25 ft of water. It does not make sense b/c it confounds our understanding of the meaning of “scope”, as we’ve noted here. I’m attending an anchoring workshop today. Have find a hard question for the teacher! Similar to a point of sail question. One thing tied to the dock where there is only the true wind.. A different challenge when the boat is moving and there are true and apparent wind directions. If student trims to the apparent wind, the actual point of sail does not match what the student was told at the dock.
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jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 21,478
If I understand the math correctly, on a still day I drop 10 ft of chain and anchor to the sea bed. The boat drifts to a position 5ft from the position of the anchor. Then in theory I am at a .5 to 1 slope.
Even though I would need to let out more than 10 ft to allow for drift or the boat would be pulled downward into the water.
Even though I would need to let out more than 10 ft to allow for drift or the boat would be pulled downward into the water.
Yep, my tendency is to estimate the length of rode payed out for the desired scope and then pay out some more. That must be my instinctive reaction to a land-based scope projection. We typically anchor in such shallow water that the length of rode just seems very short in just about any circumstance, so I am usually putting out more just for good measure.
I always thought the scope was the amount of rode/chain compared to the depth. There is no hypotenuse because it ain't really a triangle. The whole point of the amount of scope is to provide enough flexible sag to allow the anchor to remain dug in so the forces on it remain horizontal. So, if you're visualizing your ground tackle as the hypotenuse of a theoretical triangle, and the two sides of your right triangle are the water depth and the distance the boat is from being directly over the anchor.... forget about it.... you're a gonner
. So... I'd try to think of your ground tackle as something other than just a triangle. I'd be more inclined to think of it as a shock absorber, instead of coils or compressed gas, using the weight of the rode to smooth out the motion of the boat so the anchor isn't disturbed. Hope that makes sense to y'all.
. So... I'd try to think of your ground tackle as something other than just a triangle. I'd be more inclined to think of it as a shock absorber, instead of coils or compressed gas, using the weight of the rode to smooth out the motion of the boat so the anchor isn't disturbed. Hope that makes sense to y'all.
Yes, John. But I’m looking at a diagram which is idealized, to explain to a student the meaning of 1:1 scope, plus other scopes. The “text” definition has the chain vertical at 1:1. I have a hard time seeing that as “scope.” Functionally, there is no “scope”, IMO.
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In my opinion you must also visualize it as when the rode is fully stretched out in strong wind, where it approaches the hypotenuse of a right triangle. The more horizontal the resultant vector, the less likely the anchor is to pull out. Which is your point.I always thought the scope was the amount of rode/chain compared to the depth. There is no hypotenuse because it ain't really a triangle. The whole point of the amount of scope is to provide enough flexible sag to allow the anchor to remain dug in so the forces on it remain horizontal. So, if you're visualizing your ground tackle as the hypotenuse of a theoretical triangle, and the two sides of your right triangle are the water depth and the distance the boat is from being directly over the anchor.... forget about it.... you're a gonner
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When you drop a Danforth anchor, lower it until it just touches bottom. This is 1:1. Then wait to drift a bit before letting it down further. This ensures the flukes lay down in the desired direction and helps avoid possible fouling.
It is a simple ratio of depth to rode length. Nothing more.
The only time a triangle is formed is when the rode is bar tight. That triangle then helps define the swing circle.
Trying to apply math will just confuse students and make it difficult and mysterious.
The only time a triangle is formed is when the rode is bar tight. That triangle then helps define the swing circle.
Trying to apply math will just confuse students and make it difficult and mysterious.
Yes, that is the definition we all use. This is very simple math; basically 8th grade algebra/geometry, if even. Tough concept, a right triangle.
It is a RATIO of depth to length of rode. Triangles have nothing to do with it...although Ralph's picture makes it appear to do that, but when you think about it, it really doesn't because it is only comparing two distances/lengths.
If teaching this, I wouldn't worry about teaching a right angle or trying calculate this. Just demonstrate it and leave the math out. It would be simple to build a little model to demonstrate the concept. High levels of precision are not needed in this application.