When we discussed the power required for a 50' trawler, we neglected to discuss the efficiency of the propeller. That makes all the difference between requiring a 100 hp engine and a 200 hp engine. The weather has been miserable in the Northeast recently and I have a lot of time on my hands. Just for fun I calculated prop specifications for my Willard using a range of engine and speed variables. For the 13 years I've owned the boat, I've kept accurate logs of trip speed and fuel consumption so I have good baseline information. The usual screw propeller is not a very efficient device, On most trawlers the propeller efficiency ranges from 30% to 50%. Less than half the engine power is used to move the boat forward. The rest is wasted in churning the water and (very slightly) heating the ocean. Most formulas used to specify boat propellers make an arbitrary generous assumption of 50% efficiency. In many cases the actual efficiency is a good deal lower. Of course listees remember the 40' Nordhavn circumnavigation where the boat almost ran out of fuel on the first leg to Hawaii. Fuel consumption was estimated on the basis of a 50% efficient prop. In actuality the prop efficiency was closer to 40% and the boat used considerably more fuel than anticipated. My Willard Horizon is 30' LOA and has a waterline of 27.5 ft. It displaces 16,000 lbs. Power is provided by a venerable Perkins 4-107 driving an 18x14 prop through a 2.57 BW Velvet Drive reduction gear. Hull speed is almost exactly 7 knots. The power required to reach this speed is 22.4 hp, a figure confirmed by fuel consumption over several long cruises. At an engine rpm of 2000 with my current 18x14 prop, the efficiency is approximately 42% and the static thrust is 665.5 lbs. Maximum efficiency with my current setup would be realized with a 23x14.8 prop. With the engine turning at the same rpm the efficiency would be 54% and the static thrust would be 793 lbs. The five inches of additional diameter would gain me a 28% boost in efficiency and would be the equivalent of adding a number of extra horses to my hard working engine. Alternately it would reduce my fuel consumption by about 25%. If I should reduce the prop diameter to 16", the efficiency would drop to 38% and the static thrust would be 612 lbs. If I should choose to swing a 30" prop, using a 3.5 reduction ratio, the efficiency would rise to 61%. With a 36" prop the efficiency would be 67%. I doubt that such a prop would fit on my boat but the general idea is clear. For displacement boats we can see that prop efficiency is very dependent on diameter. The engine should be turning the largest prop that will fit the hull. The gear ratio and prop pitch should be adjusted to achieve hull speed. Theoretically is is possible to get up to 75% efficiency with very large, very slow turning props. So the range of powers suggested for that 50' ft. trawler, from 100 to 200 hp, are correct. It all depends on the efficiency of the prop. I hope the weather gets better so you won't have to put up with any more of this drivel. Larry Z ************** Ideas to please picky eaters. Watch video on AOL Living. (http://living.aol.com/video/how-to-please-your-picky-eater/rachel-campos-duffy/ 2050827?NCID=aolcmp00300000002598)