Dave -- My best estimate of a sea anchor size for your 42 ft/43000 lb semi-displacement boat would be a minimum 18 ft para-anchor with a 3/4 in three-strand nylon rode 300 ft long extendible (in some fashion) to 600 ft. The critical aspects of this standard installation would be how to adjust the rode length without losing a finger<g> and how to prevent chafe. Both would be boat-installation dependent. I would recommend you read Dan Shewmon's book "The Sea Anchor and Drogue Handbook" (Fax # 813-797-5708) and Victor Shane's "Drag Device Data Base" <VicShane@compuserve.com> for details. My own book "Understanding Sea Anchors and Drogues" details how to calculate size and loads, but unfortunately it is out of print at the present. Shewmon makes and sells sea anchors as does Don Whillden at ParaTech Engineering <paratech@rof.net>. Try all three of these sources for more information. I said minimum size above because having too large a sea anchor only makes it more effective, but it also is more stuff to handle and is costlier. With the sea anchor deployed, you will experience primarily head seas and head winds. Cross seas may occur and you can rig a Pardey bridle to hold your bow at a comfortable compromising riding angle to the seas and wind. Too small a sea anchor could put you at a significant angle to the seas and enhance the rolling and undesirable sternway when a wave strikes. There is little experience on powerboats riding to sea anchors at winds above about Force 8, but I am not sure you want to plan to get into such weather. Earl