Here is one possible answer to the circumnavigation contest. Assignment: Smallest boat for a two person nonstop circumnavigation on one tank of fuel. Given: Estimated distance travelled is 24,000 NM. Six lbs. food/water per person per day. Qualifications: A circumnavigation is traditionally considered complete when the returning boat crosses its line of departure after traversing 360 degrees of longitude. The actual travelled distance can vary. If the circumnavigator hugs the contenential shoreline the way the early explorers did, the distance can be 40,000 miles or more. On the other hand, a start and return from Capetown with an eastward passage around the Southern Ocean at a latitude of about 60' S would reduce the distance to about 10,000 very uncomfortable miles. The distance of 24,000 NM basically corresponds to the equatorial distance with a bit of manuevering room. The use of currents to provide assistance is a legitimate technique since that is what most low powered vessels (sailboats, rowers, rafts, etc.) do. Most oarsmen who have rowed across the Atlantic and Pacific actually drift across the oceans using their oars to stay in favorable currents. Finally, the use of renewable energy sources like solar power and wind are not quite legitimate for this contest. We already know that wind works pretty well to move small boats across large bodies of water. The Atlantic has been crossed in a 6' sailboat. Solar power is a great idea if the route is chosen carefully but at its current stage of development only the most optimistic or foolhardy sailor would trust his future to a small solar powered boat in the middle of an ocean. While I have had a number of lovely days at sea, I have also sailed in overcast conditions where the sun was obscured a week at a time. A solar powered boat would need sufficient energy storage capacity not only for night time power but for several days of bad weather. At the moment, internal combustion engines seem the only practical mechanical energy source for a small boat circumna vigation. That is until cold fusion comes on line. Possible answer: Lets start with an assumed speed of 4kt. With no favorable lift from wind or current the 24,000 NM trip would take 6000 hours or 250 days. This requires 3000 lb. of food and water for the two crew members. Also assume a LWL of 36 ft. and a boat structure weighing 12,000 lbs. A hull could be constructed this light with sufficient strength to withstand the rigors of a circumnavigation although not providing many creature comforts. If we average 10 NM per gallon of diesel fuel, the total fuel load would be 2400 gallons or about 17,000 lbs. The gross weight of hull, supplies and fuel would be about 32,000 lbs. Using Keith's formula, the fully loaded boat would require 5.62 hp to make 4 kt. A well tuned diesel engine will generate 1 hp per .06 gal. of fuel per hour. This is .34 gal. per hour or 11.86 NM per gal. This is better mileage than anticipated so we can either shorten the boat or carry less fuel. If we choose to skimp on the fuel, we need only 2000 gallons for a fuel weight of about 14,400 lbs. Also, the boat will require 5.6 hp only when full loaded. As the fuel is consumed, power requirements drop. If we use a watermaker operating off mechanical power or waste heat, 2000 lbs of water can be eliminated at the cost of a little additional fuel. Rainwater collection and fishing are additional sources of provision without a weight penalty. Aluminum construction will permit a lighter hull structure, say 10,000 lbs. The total gross weight is now 24,400 lbs and the boat requires only 4.3 hp to average 4 kt. The new fuel consumption estimate is 15.5 NM per gallon or only 1548 gallons. If we go with the 2000 gallons, we will have reserve fuel for unanticipated conditions. Alternatively, we can decrease the length of the boat to 30 ft. LWL. Maybe we can even take a case of beer for an Equatorial celebration. The 2000 gallons of fuel will need about 260 cu. ft. of tankage. A tank 9 ft. long by 5 ft. high and 6 ft. wide will suffice. It would be better if the tank were divided into several compartments and occupied the bilge area for most of the length of the boat. The weight when full would add stability and water ballast could be added to keep the boat stable as compartments were emptied. Most small diesel engines are conservatively rated for 5000 hours between overhauls. Hence the boat should use two diesels coupled to a large, slow turning propellor for maximum efficiency. Either engine could be clutched to the shaft, allowing for maintenance on the standby engine. Engine hours would be shared yet both could be coupled to the shaft for emergencies. Thus the circumnavigator would be a 30 to 36 LWL boat of about 10 ft. beam, powered by two small (about 10 hp each) diesels, driving a single large diameter slow turning screw. The fuel would occupy compartments under the sole and living quarters of the crew would be above. For safety, the shape should resemble a Coast Guard surf boat, capable of handling rough seas and surviving a rollover. Top speed with both engines operating at peak power would be 7 kt, hence there is little possibility of outrunning bad weather. If the circumnavigator were really clever he would take advantage of the prevailing currents and might be able to gain a free ride much of the way. After all, if a message in a bottle cast adrift in the middle of the Pacific can find its way to Cape Cod, an intelligent boater, using those same currents might be able to cut fuel consumption even further. Of course if we used sails the fuel requirement drops to zero. Any volunteers for the trip? Larry Zeitlin PUFFIN (not a circumnavigator) Cortlandt Manor, NY

The assignment is to optimize the boat for minimum size. I would interpret that to apply to displacement rather than to length, so I could build a fairly long trimaran with a SWATH-type main hull. Such a boat, about 46 feet in length, has already made the San Francisco to Honolulu run at ten knots averaging ten miles per gallon; and then went on to Australia on less than 400 gallons. I don't have the exact numbers handy, but that is greatly increased at lower speeds. His drive system was twin Yanmar diesel outboards, so they could not have been terribly efficient. If you were to properly optimize the drive system, you should be able to approach or exceed the 30 mpg mark at very low speeds, which would make it reasonable to carry the fuel in the SWATH keel. You would just need a water bag in the fuel tank for ballast. Paul Kruse paulkruse@cfl.rr.com > -----Original Message----- > From: owner-trawler-world-list@samurai.com > [mailto:owner-trawler-world-list@samurai.com]On Behalf Of > LRZeitlin@aol.com > Sent: Tuesday, April 10, 2001 11:37 AM > To: trawler-world-list@samurai.com > Subject: TWL: Circumnavigation without refueling > > > Here is one possible answer to the circumnavigation contest. > > Assignment: Smallest boat for a two person nonstop > circumnavigation on one > tank of fuel. > > Given: Estimated distance travelled is 24,000 NM. Six lbs. food/water per > person per day. > > Qualifications: A circumnavigation is traditionally considered > complete when > the returning boat crosses its line of departure after traversing > 360 degrees > of longitude. The actual travelled distance can vary. If the > circumnavigator > hugs the contenential shoreline the way the early explorers did, > the distance > can be 40,000 miles or more. On the other hand, a start and return from > Capetown with an eastward passage around the Southern Ocean at a > latitude of > about 60' S would reduce the distance to about 10,000 very uncomfortable > miles. The distance of 24,000 NM basically corresponds to the equatorial > distance with a bit of manuevering room. The use of currents to provide > assistance is a legitimate technique since that is what most low powered > vessels (sailboats, rowers, rafts, etc.) do. Most oarsmen who have rowed > across the Atlantic and Pacific actually drift across the oceans > using their > oars to stay in favorable currents. Finally, the use of renewable energy > sources like solar power and wind are not quite legitimate for > this contest. > We already know that wind works pretty well to move small boats > across large > bodies of water. The Atlantic has been crossed in a 6' sailboat. > Solar power > is a great idea if the route is chosen carefully but at its > current stage of > development only the most optimistic or foolhardy sailor would trust his > future to a small solar powered boat in the middle of an ocean. > While I have > had a number of lovely days at sea, I have also sailed in > overcast conditions > where the sun was obscured a week at a time. A solar powered boat > would need > sufficient energy storage capacity not only for night time power but for > several days of bad weather. At the moment, internal combustion > engines seem > the only practical mechanical energy source for a small boat circumna > vigation. That is until cold fusion comes on line. > > Possible answer: Lets start with an assumed speed of 4kt. With no > favorable > lift from wind or current the 24,000 NM trip would take 6000 hours or 250 > days. This requires 3000 lb. of food and water for the two crew > members. Also > assume a LWL of 36 ft. and a boat structure weighing 12,000 lbs. > A hull could > be constructed this light with sufficient strength to withstand > the rigors of > a circumnavigation although not providing many creature comforts. If we > average 10 NM per gallon of diesel fuel, the total fuel load > would be 2400 > gallons or about 17,000 lbs. The gross weight of hull, supplies and fuel > would be about 32,000 lbs. > > Using Keith's formula, the fully loaded boat would require 5.62 > hp to make 4 > kt. A well tuned diesel engine will generate 1 hp per .06 gal. of > fuel per > hour. This is .34 gal. per hour or 11.86 NM per gal. This is > better mileage > than anticipated so we can either shorten the boat or carry less > fuel. If we > choose to skimp on the fuel, we need only 2000 gallons for a fuel > weight of > about 14,400 lbs. Also, the boat will require 5.6 hp only when > full loaded. > As the fuel is consumed, power requirements drop. If we use a watermaker > operating off mechanical power or waste heat, 2000 lbs of water can be > eliminated at the cost of a little additional fuel. Rainwater > collection and > fishing are additional sources of provision without a weight penalty. > Aluminum construction will permit a lighter hull structure, say > 10,000 lbs. > The total gross weight is now 24,400 lbs and the boat requires > only 4.3 hp to > average 4 kt. The new fuel consumption estimate is 15.5 NM per > gallon or only > 1548 gallons. If we go with the 2000 gallons, we will have > reserve fuel for > unanticipated conditions. Alternatively, we can decrease the > length of the > boat to 30 ft. LWL. Maybe we can even take a case of beer for an > Equatorial > celebration. > > The 2000 gallons of fuel will need about 260 cu. ft. of tankage. > A tank 9 ft. > long by 5 ft. high and 6 ft. wide will suffice. It would be better if the > tank were divided into several compartments and occupied the > bilge area for > most of the length of the boat. The weight when full would add > stability and > water ballast could be added to keep the boat stable as compartments were > emptied. Most small diesel engines are conservatively rated for > 5000 hours > between overhauls. Hence the boat should use two diesels coupled > to a large, > slow turning propellor for maximum efficiency. Either engine could be > clutched to the shaft, allowing for maintenance on the standby > engine. Engine > hours would be shared yet both could be coupled to the shaft for > emergencies. > > Thus the circumnavigator would be a 30 to 36 LWL boat of about 10 > ft. beam, > powered by two small (about 10 hp each) diesels, driving a single large > diameter slow turning screw. The fuel would occupy compartments under the > sole and living quarters of the crew would be above. For safety, > the shape > should resemble a Coast Guard surf boat, capable of handling > rough seas and > surviving a rollover. Top speed with both engines operating at peak power > would be 7 kt, hence there is little possibility of outrunning > bad weather. > > If the circumnavigator were really clever he would take advantage of the > prevailing currents and might be able to gain a free ride much of > the way. > After all, if a message in a bottle cast adrift in the middle of > the Pacific > can find its way to Cape Cod, an intelligent boater, using those same > currents might be able to cut fuel consumption even further. > > Of course if we used sails the fuel requirement drops to zero. > Any volunteers > for the trip? > > Larry Zeitlin > PUFFIN (not a circumnavigator) > Cortlandt Manor, NY