I leapt to the cockpit and quickly got the 16 lb bruce clone anchor over the windward rail and stood there holding the loose rode to play out scope as we drug.  Not long after deploying the bruce, the storm cell moved east and winds abated.  The rode on the bruce never came up hard.  We had just made the anchorage and backed down the 13 lb danforth as the storm approached. 

I estimate winds well exceeded 50 mph.  My reasons is that when I reached the cockpit, raindrops stung my face like sleet though they were not frozen.  There was not the degree of cold rush that accompanies hail or sleet and there was no other indication that it was sleet.  I would have felt ice under my bare feet as I moved around the cockpit getting the bruce and the bitter end secured and setting the anchor over the side.

I have since held my arm out the car window while its has been raining and at 70 mph do not feel the impact that I felt from the storm. 

My reason for offering this information is to hopefully save another owner from the peril I came close to.  The c250 when anchored in high winds will turn a bow quarter to those winds.  I recall another owner mention that they watched their C250 on a mooring do the same.  In my case I had a little more than half of the 200ft  half inch rode out so I had a little better than a 7:1 scope.  The boat sailed up on the wind.  The rode bore away from the boat on its beam and the wind came at a 45 degree angle to the bow and a 45 deg angle to the rode..  That means the boat had lifted into the wind and where in lighter wind it would have turned and sailed the other tack, in these winds it held up and strained at the rode.

Mariners have long known that many sailboats hunt on their rode and some have used riding sails to discourage this.  Previously I felt that it was a convenience issue, that it made sleeping easier.  In fact I really thought that in a strong wind the boat probably wouldn't hunt but be forced to vein itself into the wind.  Wrong!  The stronger the wind, the more lift the hull provides.

I'm not sure what the answer is to this.  Using two anchors has discouraged the boat from hunting in much lesser winds.  That one will display these tendancies on a mooring may be relative to a little swing in the mooring that two anchors don't offer.  I don't know but I do know that there are times when two anchors are not an option.  The other answer seems to be a riding sail.  They have the effect of providing drag aft to force the hull and its foil to vein into the wind or have nuetral lift.  Riding sails come in at least three flavors. 

• Traditional, a flat sail hanked to the backstay and drawn forward at the tack on the center line of the boat.  It has two known drawbacks.  They are noisy when filling from the opposite side and they allow some hunting until drag increases to the point of influence.  So, they decrease hunting by a percentage.
• V or wedge shaped are fairly new designs.  They are actually two sails tied together or having a common luff.  They have some amount of drag all the time, don't luff with the acompanying noise and are claimed to reduce the hunting percentage greater than a single sail on center line.
• Offset,  are a single sail like the traditional and hanked to the backstay but the forward tack is led to one side or the other.  They work by ballancing the lift and drag and because they are supposed to dissalow tacking, they stay filled on one side and don't luff and produce noise.
• There is a fourth design that is an offshoot of one of the other designs and it uses some stiffening members to deploy aft of the backstay.
  

I  built a heavy air riding sail for testing that is a combination of two of the above so it is a 5th design.   It is made from sunbrella and uses the V design with an aft of the backstay deployment and has stiffening members.  It uses two snap hooks on the tack to cleat to each of the split backstays and one at the head to cleat to the backstay and main halyard.  The foot of each sail has a 1/4 inch aluminum dowel sewn in.  The two clews have a 1/4 inch line that cleats to the stern cleats.  Between the two sails at the clew is a line which adjust the spread of the two sails.

During the 2002 summer cruise, a thunderstorm provided straight line winds that brought R&R close to peril.  The high winds on the leading edge of the storm caused her to sail (hunt) on her anchor rode and forced her on her starboard bow quarter to the wind placing great strain on the rode and dragging her anchor about 1,000 yards. and within  400 yards of a rock infested outcropping.   I was on the boat and at first oblivious through mental error to the dragging as I was watching the depth sounder which showed the whole time a depth between 13-14 feet.  I knew the portions of the bay we had anchored in were fairly uniform in depth...but not that the entire bay was so flat bottomed.  I mentally failed completely to make the uniform depth application and  think there might be a problem.  In fact, it was when I finally relaxed after a couple of minutes watching the sounder that I felt confident to move from the from my crouched position watching the sounder to the settee to get more comfortable that I discovered the dragging.  There, I glanced out the windows and because it was near dusk and the storm cloud and rain were heavy,  it was quite dark and I saw the lights from cabin windows ashore and new instantly that they were too far off...we were dragging.

                                                                                                                                                                    

Testing

The riding sail was used each evening at anchor for the 24 days of cruising during 2003.

What worked well  

•  completely quiet (very important) 
•  easy to set and douse. 
•  reduced anchor rode hunt by about 40%
•  roles up and stores easily in a locker without removing the stiffening members
  

Problems

• The aluminum shafts inserted into the hems of the two foot sections  experienced some bending when the clew lines were drawn too tight in an effort to hold the aft spread.  They should be fiberglass. 

• The spread of the delta design would work a little better if a rigid section was provided between the two clew points instead of relying on the clew lines to each stern quarter to hold the shape.  As noted just above, too much tension on those lines adds stress to the foot sections.

Changes

• I'm thinking 25% more area would provide a little more reduction in anchor hunting though I keep reminding myself that one design goals is to withstand the very high winds off a thunder head and too much canvas showing might not be a good thing either.  Also, a prime requirement is that it all roll up around the sewn in stiffening members and store in a locker 
•  fiberglass shafts instead of aluminum
•  trade the line section between the clews for a rigid shaft but designed in such a way to continue to allow the sail to roll into a very small bundle

Conclusions

I'm not sure that a ridding sail can be expected to completely overcome the problems caused by an anchor rode which is fed through a chock off center from the bow.  It seems to me that the off center chock, starts the process of swinging which once started, is perpetuated by momentum and force issues.  Consequently, anchor rode hunt in my opinion needs to be addressed on two fronts, a riding sail as discussed here and the use of an anchor rode bridle  which has the effect of shifting the anchor load always on the leeward bow chock and arresting the bow from sailing off.  A combination of riding sail and bridle has proven to be quite effective.