Luxury Guide

Overview

My name is Norm Mosher. I am a retired Navy Captain, and I have spent a good part of my adult life at sea in command of ships. My experience has taught me that bad weather should be avoided. Sounds simple, but riding out two typhoons in a minesweeper left an indelible impression on me. That was a slow ship with short legs. After retiring, my wife and I sailed to the Caribbean aboard our 42' ketch. Again, a slow boat, and, we had to endure bad weather from time to time. That is part of the package in offshore sailing, but after a certain age the fun/work ratio starts to drift in an unfavorable direction. When it happened to me, I decided to search for a powerboat that would have a good turn of speed and would have good range so I could continue cruising.

When I started searching for the proper boat, I was quickly reminded that all displacement hulls are subject to the tyranny of the speed/length ratio. That ratio is determined by multiplying the square root of the waterline length by 1.34 to arrive at a theoretical maximum speed before the hull starts piling up a resistance wave that requires an exponential increase in power to overcome. Because it is not fuel-efficient to run around at maximum hull speed, most displacement boats cruise at a more efficient 1.1 or 1.2 speed/length ratio.

A few years ago a popular and authoritative boating magazine ran an article listing the boats the author considered capable of ocean passage-making. There were eighteen models from 39 feet to 75 feet, and the prices were spread between $319,000 and $2 million. Interestingly, the differences in size and cost failed to translate to a similar difference in performance. Maximum speeds (S/L of 1.34) ranged from 8.1 to 11.2 knots, and cruising speeds (S/L of 1.1 or 1.2) ranged between 7.3 and 10 knots. Clearly, pouring money on the problem was not the answer to increasing operational speed in a significant way.

As I pondered the question of how much range a power boat should have, I was reminded that Captain Robert Beebe gave us a useful guide for power passagemakers when he identified in his classic book, Voyaging Under Power, that in the smallest ocean the longest leg is 1850 miles between Bermuda and the Azores. He concluded that if a motorboat is not capable of making that run, it could not lay claim to being an ocean passagemaker. Of course, one really needs more range than that if you are to have the capability to avoid unfavorable weather along the way.

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