I'm a new owner of a CD-33. Yesterday we anchored for lunch in a scenic, though not very protected spot. There was a 20 knot wind blowing against a 2 knot tidal current. Much to my amazement the boat lay stern to the wind with the anchor lying upwind. I can rationalize this considering the wind was blowing the bow while the current was pushing the stern, but is this normal behavior for a Cape Dory? Getting the anchor back up was a considerable adventure. We tried raising the main to the 2nd reef position (not an easy task facing downwind), and that only brought us around broadside to the wind. Is there anything we can do to avoid this?
sharphat@mind.net
Anchoring: wind vs. current
Moderator: Jim Walsh
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Ken Coit
Re: Anchoring: wind vs. current
Tom,
Congratulations on your new boat and getting out for a spin. Wish we had been so fortunate.
As for the current or wind acting on the boat, here are some rough numbers:
In a 2 knot current, the boat is being struck by a wall of water about 4 ft. high and 25 ft wide if it is broadside to the current. Every second, a molecule in the water will move about 3 ft at 2 knots. Thus, the boat broadside to the current is being struck by 3 ft x 4 ft x 25 ft of water, or 300 cubic feet of water. A cubic foot of water has a mass of about 62.5 pounds. Someone else can tell you what force a 20 Kt. wind will present to your topsides and rigging, but I believe you will understand that the impact of about 18,000 pounds of water every second is going to win out. The boat is going to swing head to the current to minimize the force on the hull unless you anchor from the stern.
If the wind and current are not directly opposed, then the wind may cause the boat to swing slightly to one side of the current or the other, but it won't be much.
Someone will undoubtedly want to refine my numbers, but I think they are in the ballpark.
Keep on sailing,
Ken Coit
CD/36 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
parfaitNOSPAM@nc.rr.com
Congratulations on your new boat and getting out for a spin. Wish we had been so fortunate.
As for the current or wind acting on the boat, here are some rough numbers:
In a 2 knot current, the boat is being struck by a wall of water about 4 ft. high and 25 ft wide if it is broadside to the current. Every second, a molecule in the water will move about 3 ft at 2 knots. Thus, the boat broadside to the current is being struck by 3 ft x 4 ft x 25 ft of water, or 300 cubic feet of water. A cubic foot of water has a mass of about 62.5 pounds. Someone else can tell you what force a 20 Kt. wind will present to your topsides and rigging, but I believe you will understand that the impact of about 18,000 pounds of water every second is going to win out. The boat is going to swing head to the current to minimize the force on the hull unless you anchor from the stern.
If the wind and current are not directly opposed, then the wind may cause the boat to swing slightly to one side of the current or the other, but it won't be much.
Someone will undoubtedly want to refine my numbers, but I think they are in the ballpark.
Keep on sailing,
Ken Coit
CD/36 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
Tom Keevil wrote: I'm a new owner of a CD-33. Yesterday we anchored for lunch in a scenic, though not very protected spot. There was a 20 knot wind blowing against a 2 knot tidal current. Much to my amazement the boat lay stern to the wind with the anchor lying upwind. I can rationalize this considering the wind was blowing the bow while the current was pushing the stern, but is this normal behavior for a Cape Dory? Getting the anchor back up was a considerable adventure. We tried raising the main to the 2nd reef position (not an easy task facing downwind), and that only brought us around broadside to the wind. Is there anything we can do to avoid this?
parfaitNOSPAM@nc.rr.com
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John MacArthur
Re: Anchoring: wind vs. current
Yup. It makes things really interesting in an anchorage where there are several (or many) boats, especially around the time when the tide and current change. Especially if there are multihulls involved, you will have boats pointing every which direction, and swinging round and round as the wind pipes up and down, as it temporarily overpowers the weakened current at these times. In LaPaz, Mex. this is called "The LaPaz Waltz", and is quite unnerving.Tom Keevil wrote: the boat lay stern to the wind with the anchor lying upwind. I can rationalize this considering the wind was blowing the bow while the current was pushing the stern, but is this normal behavior for a Cape Dory?
John MacArthur
CD-30 "Stork"
Taos, NM
jmac@laplaza.org
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Boyd
Re: Anchoring: wind vs. current
Tom...
Let me welcome you to the unique world of full keel boats. Ken's comments are right on. This is very normal behavior for a full keel baot. I have experienced the phenom you describe and it can have some other rather dangerous consequences.
Tern "hunts" or sails around her anchor extensively anytime the current is opposite the wind. She will typically lie stern to the wind in a current. This will drive other boaters nuts to watch. This is especially true for powerboats that present almost no resistance underwater and will be pointing bow to the wind and lying very still. I think my binini and dodger play a big role in provoking the movement. The wind will catch the bimini, force the stern to the starboard and the current will then act on the keel sailing the boat over to port until she reaches the limit of the anchor line. The pull from the anchor line and the inertia of her movement will then turn her nose in the opposite direction and the current will then pull the boat to the starboard side of the anchor till the anchor line pulls her nose back again to port. The proscess continues on ad infinitum... People who do not have bimini's report much less of this effect.
As of this time I dont have an answer except to use the biggest baddest and heaviest anchor I can find in these situations. And keeping a constant watch. I have tried adjusting the rudder in all positions with no improvement. Some on this board have suggested a riding sail. Have not tried it myself and I dont see how it would help this situation. Maybe it can hold the stern in one direction allowing the whole system of forces to reach an equalibrium..?
What is happening with current and your keel is something to always be aware of. It crops up in other situations that can have very bad results if you are not aware. When there is current running from stern to bow and the boat is turned... say to make a U turn in a tight situation... the boat will be caught in the current and swept down stream very rapidly. She tends to respond very sluggisly even under max power in the last half of the turn. She just does not want to point her nose back into the current very fast. I got pinned on a bridge bulkhead and have had some docking disasters as a result of this. It does not seem to take much current to cause it either. Fin keel boats are much less affected and can be turned very quickly.
Congratulations on your new boat. Take her sailing as much as possible.
Boyd
s/v Tern
Fort Lauderdale, Fla
Tern30@aol.com
Let me welcome you to the unique world of full keel boats. Ken's comments are right on. This is very normal behavior for a full keel baot. I have experienced the phenom you describe and it can have some other rather dangerous consequences.
Tern "hunts" or sails around her anchor extensively anytime the current is opposite the wind. She will typically lie stern to the wind in a current. This will drive other boaters nuts to watch. This is especially true for powerboats that present almost no resistance underwater and will be pointing bow to the wind and lying very still. I think my binini and dodger play a big role in provoking the movement. The wind will catch the bimini, force the stern to the starboard and the current will then act on the keel sailing the boat over to port until she reaches the limit of the anchor line. The pull from the anchor line and the inertia of her movement will then turn her nose in the opposite direction and the current will then pull the boat to the starboard side of the anchor till the anchor line pulls her nose back again to port. The proscess continues on ad infinitum... People who do not have bimini's report much less of this effect.
As of this time I dont have an answer except to use the biggest baddest and heaviest anchor I can find in these situations. And keeping a constant watch. I have tried adjusting the rudder in all positions with no improvement. Some on this board have suggested a riding sail. Have not tried it myself and I dont see how it would help this situation. Maybe it can hold the stern in one direction allowing the whole system of forces to reach an equalibrium..?
What is happening with current and your keel is something to always be aware of. It crops up in other situations that can have very bad results if you are not aware. When there is current running from stern to bow and the boat is turned... say to make a U turn in a tight situation... the boat will be caught in the current and swept down stream very rapidly. She tends to respond very sluggisly even under max power in the last half of the turn. She just does not want to point her nose back into the current very fast. I got pinned on a bridge bulkhead and have had some docking disasters as a result of this. It does not seem to take much current to cause it either. Fin keel boats are much less affected and can be turned very quickly.
Congratulations on your new boat. Take her sailing as much as possible.
Boyd
s/v Tern
Fort Lauderdale, Fla
Ken Coit wrote: Tom,
Congratulations on your new boat and getting out for a spin. Wish we had been so fortunate.
As for the current or wind acting on the boat, here are some rough numbers:
In a 2 knot current, the boat is being struck by a wall of water about 4 ft. high and 25 ft wide if it is broadside to the current. Every second, a molecule in the water will move about 3 ft at 2 knots. Thus, the boat broadside to the current is being struck by 3 ft x 4 ft x 25 ft of water, or 300 cubic feet of water. A cubic foot of water has a mass of about 62.5 pounds. Someone else can tell you what force a 20 Kt. wind will present to your topsides and rigging, but I believe you will understand that the impact of about 18,000 pounds of water every second is going to win out. The boat is going to swing head to the current to minimize the force on the hull unless you anchor from the stern.
If the wind and current are not directly opposed, then the wind may cause the boat to swing slightly to one side of the current or the other, but it won't be much.
Someone will undoubtedly want to refine my numbers, but I think they are in the ballpark.
Keep on sailing,
Ken Coit
CD/36 Parfait
Hailing Port: Raleigh, NC
Sailing from: Beaufort, NC
Tom Keevil wrote: I'm a new owner of a CD-33. Yesterday we anchored for lunch in a scenic, though not very protected spot. There was a 20 knot wind blowing against a 2 knot tidal current. Much to my amazement the boat lay stern to the wind with the anchor lying upwind. I can rationalize this considering the wind was blowing the bow while the current was pushing the stern, but is this normal behavior for a Cape Dory? Getting the anchor back up was a considerable adventure. We tried raising the main to the 2nd reef position (not an easy task facing downwind), and that only brought us around broadside to the wind. Is there anything we can do to avoid this?
Tern30@aol.com
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Randy Bates
Re: Anchoring: wind vs. current
You might want to try the "Bahamian moor". One anchor up wind, one anchor up current. The bow then stays in one spot and the boat simply pivots into the stronger force.
rtbates@austin.rr.com
rtbates@austin.rr.com