added distance to our voyage but offered a convenient and safe port, the opportunity to arrange a convoy with other yachts headed up the Red Sea, plus, we could maintain maximum clearance from dreaded Socotra Island. The weather continued fair, and as each day passed we began to notice the air cooling slightly. The evenings were now into the high 70s and we found it was no longer necessary to run the air conditioning. Each night we were given a remarkable show of phosphorescence--brighter than any
I've ever seen. Maybe associated with this light phenomenon, the water teemed with flying fish and at night Nordhavn was pelted by them, leaving small marks where they hit the cabin and hull. Many stranded themselves on deck. Some, attracted by the light, would fly right into the open wheelhouse doors, and one even glided through the saloon and crashed in the lower passageway to the staterooms. Squid also attacked our
percent. At lower speeds, frictional or drag resistance is the primary force to overcome. As speed increases up to 1.2 to 1.3 times the square root of the waterline (speed-length ratios), the primary resistance force to overcome shifts to wave-making, thus, we see only a 12-percent reduction in performance at 7.14 knots. Drag from these appendages is not hurting us as much at higher speeds. Another big consumer of power are alternators, which are known to be very inefficient. I have heard it said that a DC alternator is only about 38 percent efficient—which means that for every horsepower consumed by the alternator, only 38 percent of that power is converted into wattage. In other words, to produce one horsepower of wattage (750 watts) 2.6 horsepower has to be delivered to the alternator. On our around-the-world boat, with the large freezer aboard, I estimated that we consumed an average of 70 amps of DC power, 24 hours a day: 70 amps times 14 volts equals 980 watts is 1.3 hp multiplied by 2.6 equals 3.4 hp, plus there is inefficiency due to the belt loss. I suspect that the alternator is drawing approximately 4 hp, again adding about a quarter of a gallon per hour top our fuel burn. As with the hydraulic draw—maintaining 1200 PSI of pressure, regardless of whether the fins are moving or not—the alternator draw is consistent and, at lower power settings, the draw becomes a larger percentage of the fuel consumption. At the long-range speed of 1,400 rpm, our 40 runs a little over 6 knots, burning about 1.9 gph. At this low speed, the power draw of the alternator and hydraulics account for over 27 percent of the fuel consumption. Out of the 880 gallons of fuel consumed on the Dana Point to Honolulu voyage, 237 gallons went to hydraulics and electrical demands! That certainly isn’t anything we learned from tank testing. Another area of interest lies within the propeller selection. We spin a 4-bladed 28-by-24-inch prop. A huge amount of effort has been put forth to make the boat as quiet and smooth running as possible. Over the years, we have done testing on propellers and found that a 3-bladed prop will give better performance at lower (ocean-crossing) speeds at S/L between 1 and 1.2. Above that, the 3-bladed propeller becomes more highly loaded and begins to cavitate. Normal-
boat after dark, with a particularly large one spraying the whole starboard side with reddish brown ink. A forensic review in the morning suggested he must have shot out of the water and hit the paravane pole, bursting on impact. It took an hour to clean up the mess. After eight and a half days of easy running we called for an entry clearance with the Salalah Port Authority, and were authorized to enter the inner har-
ly, Nordhavns are run at an S/L ratio of 1.3 (for the 40 this is just under 8 knots) and the 3-bladed prop offers no advantages and is quite noisy. We installed a 3-bladed prop on Salvation ll Visual fuel check backs up electronic metering. for the final leg of her circumnavigation from Hawaii to California. The 3-bladed prop gave a 20-percent increase in Salvation ll's range at 6.5 knots, however, it was subsequently removed and the 4-bladed prop was reinstalled for coastal cruising to reduce vibration and cavitation. I did order a new 3-bladed 30-by-24-inch prop and tested in on the 40 just prior to our departure. We noted an increase in performance of about 10 percent, but also noticed the characteristic vibration, which was anticipated. Despite the performance improvement, I reinstalled the 4-bladed propeller in the interest of a quiet and vibration-free boat. The point of this is that the BC Research predictions were based upon achieving propeller efficiency of 50 percent. I don’t believe we are achieving that with our present propeller selection and I don’t believe that we can, unless we’re willing to accept noise and vibration. To recap: We have a much heavier boat than what was originally tank-tested.It has a lot of drag because of the accessories we install to make voyaging safer, more comfortable and easier. We have been aware of the effect of weight and drag on all of our vessels and find that oceans are crossed at much lower speeds than what the same vessel makes during coastal passages. One of the reasons we took on the challenge of a circumnavigation was to develop better methods of prediction that take into account the true performance of the modern, wellequipped vessel but also to understand the effects on performance that the wind and sea have out on the open ocean. — Jim Leishman 2003 CIRCUMNAVIGATOR · 75