Dumb Anchoring Question

[Hillbillylad]

Originally Posted by AllezCat

to answer the question - the 5 foot depth.

This is sorta why it caused me confusion. To use that formula say at 5 to 1 you would be letting out 25 feet of rode. That would only be 5 foot more than the depth you would be in. So the angle on the anchor would be way off. I would assume that would be a usual reason for dragging.

[noelex 77]

Originally Posted by Hillbillylad

This is sorta why it caused me confusion. To use that formula say at 5 to 1 you would be letting out 25 feet of rode. That would only be 5 foot more than the depth you would be in. So the angle on the anchor would be way off. I would assume that would be a usual reason for dragging.

The angle of concern is the angle at the anchor shank. If you draw a diagram the effect is clear.
If the anchor is in 5 feet of water the boat can be in 100 feet of water, or more, without altering the angle of pull, but as others have said if the anchor is on a down slope the holding will be reduced

[Reefmagnet]

I gave a theoretical answer at the start of the thread to a theoretical question, but in a practical scenario with the anchor in 5 ft and the boat in 20 ft consideration needs to be given to what happens if the anchor breaks out. The potential consequences depend on a quite a few situational variables. Sometimes it won't matter at all, and other times it will be critical.

Here's a small twist that this thread got me thinking about. What about anchoring in areas of big tides. Say when tides are 20 ft and you anchor in 10 ft of depth at low tide. This means that the depth will change between 10 and 30 ft. In theory, currents within the anchorage will be strongest mid tide, but wind and surge will usually be stronger at high tide. What does one do in this scenario?

[Vasco]

Originally Posted by Hillbillylad

Yep they fall into a class of their own do Centaurs. I'll be making the best use of the keels to bag the sweetest spots next to the beach.

Hope you've got your bug screens in.

[jackdale]

Originally Posted by Reefmagnet

Here's a small twist that this thread got me thinking about. What about anchoring in areas of big tides. Say when tides are 20 ft and you anchor in 10 ft of depth at low tide. This means that the depth will change between 10 and 30 ft. In theory, currents within the anchorage will be strongest mid tide, but wind and surge will usually be stronger at high tide. What does one do in this scenario?

I do anchor in the situations; Desolation Sound gets 18 foot tides.

1) Big tides do not necessarily equate to large currents. Desolation Sound gets very little current. Further north in more restricted areas - huge currents in the passes.

2) Good anchorages are protected from currents.

Our biggest concern is that use the scope appropriate for the largest tide.

[familycruisers]

Save one for me!

[zeehag]

i cannot anchor in 5 ft of water. i will not anchor near a beach as it becomes 5 ft way too quickly.
i was advised yelapa is not for sailboats or anchoring. i know a fella brags on smuggling drugs from and to there, and now has a house there. bay was formed in 1911 by a major earthquake. not for me, ty.
i like 20 ft and 100-150 ft chain. so far, so good.....

"good anchorages" may allegedly be protected from currents, but ye wont find that in pacific coast. we have tidal currents and we have winds and we are a lee shore for hundreds of miles. we also have estuarial currents. now try to find a generalization in that.

[Surrymark]

So let's say the shore is shoaling at a rate of one inch per foot, which is quite gradual. And let's say you put out rode at 8:1, which would be about 40' in five feet of depth at the anchor. And let's say your boat is 26 feet plus about 30 feet of rode (roughly figuring the angles), which gives you an effective distance of about 50 feet from the anchor to the keel. So that's about 50 inches of depth you have lost, which puts you in ten inches of water when the wind or tide swings you around.

In ten inches of water your boat would, effectively, be an anchor. This means that the thread really should be discussing the pros and cons of two anchors.

[Vasco]

Originally Posted by Surrymark

So let's say the shore is shoaling at a rate of one inch per foot, which is quite gradual. And let's say you put out rode at 8:1, which would be about 40' in five feet of depth at the anchor. And let's say your boat is 26 feet plus about 30 feet of rode (roughly figuring the angles), which gives you an effective distance of about 50 feet from the anchor to the keel. So that's about 50 inches of depth you have lost, which puts you in ten inches of water when the wind or tide swings you around.

In ten inches of water your boat would, effectively, be an anchor. This means that the thread really should be discussing the pros and cons of two anchors.

A prudent sailor motors around the anchorage to determine if there's sufficient water when the boat swings. Very few just drop the hook and hope for the best.

[Ex-Calif]

Originally Posted by Reefmagnet

I gave a theoretical answer at the start of the thread to a theoretical question, but in a practical scenario with the anchor in 5 ft and the boat in 20 ft consideration needs to be given to what happens if the anchor breaks out. The potential consequences depend on a quite a few situational variables. Sometimes it won't matter at all, and other times it will be critical.

Here's a small twist that this thread got me thinking about. What about anchoring in areas of big tides. Say when tides are 20 ft and you anchor in 10 ft of depth at low tide. This means that the depth will change between 10 and 30 ft. In theory, currents within the anchorage will be strongest mid tide, but wind and surge will usually be stronger at high tide. What does one do in this scenario?

This is a great theoretical discussion by all prompting lots of good thinking.

- large tidal change ~20 feet
- significant slope
- exposed to wind
- exposed to >2 knots current
- dodgy bottom

All great things to consider. One anchor, two anchors, bahamian moor, med more.

However, sometimes one must eventually think about anchoring somewhere else...

At some point the elements no longer are a challenge to be overcome but a risk to be avoided...

[Bash]

Originally Posted by zeehag

i cannot anchor in 5 ft of water. i will not anchor near a beach as it becomes 5 ft way too quickly.

You know, I think Zee is onto something here. I was originally pondering the question according to how the scenario was proposed, but in reality I'm just not going to anchor in 5' of water. Not with a draft of 7'.

Duh.

[TEE]

Also, when figuring scope, add in your freeboard, for instance, if you are in 12 feet of water, but your rode at the bow has four fee of freeboard, you need to figure it out like you were dropping in 16 feet. Then think about the fact that if you drag, all of a sudden you won't reset. so under these circumstances, I would start out with about 80 feet of chain for a five to one, then add about 20% to improve chances of resetting, for about 100 feet. If anybody disagrees, please let me know. I won't be offended. But that's how I would do it.

[Palarran]

Originally Posted by Ex-Calif

However, sometimes one must eventually think about anchoring somewhere else...

At some point the elements no longer are a challenge to be overcome but a risk to be avoided...

That is really good....

[jackdale]

Originally Posted by TEE

Also, when figuring scope, add in your freeboard, for instance, if you are in 12 feet of water, but your rode at the bow has four fee of freeboard, you need to figure it out like you were dropping in 16 feet. Then think about the fact that if you drag, all of a sudden you won't reset. so under these circumstances, I would start out with about 80 feet of chain for a five to one, then add about 20% to improve chances of resetting, for about 100 feet. If anybody disagrees, please let me know. I won't be offended. But that's how I would do it.

Only one caveat - do you have sufficient swing room?

[Ex-Calif]

Originally Posted by TEE

Also, when figuring scope, add in your freeboard, for instance, if you are in 12 feet of water, but your rode at the bow has four fee of freeboard, you need to figure it out like you were dropping in 16 feet. Then think about the fact that if you drag, all of a sudden you won't reset. so under these circumstances, I would start out with about 80 feet of chain for a five to one, then add about 20% to improve chances of resetting, for about 100 feet. If anybody disagrees, please let me know. I won't be offended. But that's how I would do it.

I dont see lots of chain marked in 20 foot increments. I am sure someone will say they do. I see them at commonly at 100, 200, 300

Keel to cleat runs 15-20 feet on most boats. Tides run zero to ten. Max depth cleat to bottom = 30 feet X 5 = 150. 30 X 7 = 210 for a blow.

200 feet works to 20 foot high tide depth. 300 works to 40.

For those worried about swing room dont forget 200 feet of rode does not a 400 foot diameter circle make. For a given rode the circle gets smaller as the depth gets deeper until you are right on top of the anchor swinging in your LOA.

It is sort of a right triangle with base = depth, hypotenuse = rode and height = circle. Or something like that. The formula is basic but put of my feeble brain and replaced by "where I put my car keys when I got home." But you can look it up, there are many online calculators, and plug your numbers in. And yes I know the rode doesn't draw a straight line to the anchor but close enough and a bit more conservative.

Bottom line - throw out 200 feet in any water up to 20 feet under keel and sleep soundly.