A little more on this design from an old discussion on the woodenboat forum:
Excuse me, but I just noticed the "Double-Ender" entry, and read the replys.
I just can't resist:
To begin with, Scott Russel was the Englishman whose "Wave Line Theory" Colin Archer read, believed part of, and revised as he felt necessary. That theory, and Russels's, mainly go on the presumption that since a moving vessel makes a bow and a stern wave, it would allow the vessel to move more easily if the volumes of the ends corresponded to the increased water
pressure due to the wave buildup along the hull
at the ends; in other words, make the vessel fit the hills and holes in the water
that vessel itself causes by its movement. This makes sense to me, even in the year 2000, but more impressive is that boats designed to comply with the theory do move slightly faster, and with less horsepower expended while moving the same displacement
than their non-wave form theory sisters. I leave the tank-testing of John Hannah's "Caroll" and the design that later became the "Tahiti" ketch
hulls, against comparable Archer hulls, to others. I know it works, and that's good enough for me. My own North Sea Fisherman, built in 1917 in Risor, Norway
, utilizes the same principle, as do most of the boats of the period built on the South Coast of Norway
To those who say there is no difference in seaworthiness provided by the double-ended shape, I can only say that I very much doubt whether they have experienced a real North Sea storm in such a vessel, when the waves are vertical, breaking, and from three directions at once. Then it isn't just how the vessel is shaped to the waterline, because the effective waterline is often nearer the deck
than where is usually is. The North Sea is a place like no other, at such a time, and anyone who has seen it like that would know it again. The double-enders were shaped to try to live in those conditions, and live they usually do. Many other designs often do not. That such a stern better facilitates leaving the side of a larger vessel, or a quay, is a spinoff. The real reason for the shape is seaworthiness, and I maintain that the sort of boat LFH and the others designed has little to do with that shape, except that both are at least somewhat pointed at both ends. I think William Atkin and William Garden came the closest, with"Eric", the two "Bullfrog"s and "Seal". The others, in my opinion, aren't very close in concept
It isn't just the shape that makes the difference, but the blend of shape, displacement
, and disposition of weight both vertically and longitudinally that make similar vessels differ. Archer, like everyone else, designed boats for particular jobs, and with very different priorities. His pilot boats would have been a bit more seaworthy
for the average cruising sailor had they been, on the average, a little fuller in the stern. They were not intended to be cruising boats for the average cruising sailor. They were intended to be fairly seaworthy
, but for professionals whose livelihood depended upon getting to the ship to be piloted first, before the other pilots beat them to it.
And get there first they very often did, making them very successful pilot boats, and safe enough, usually, in the hands of professionals. The obvious morale is, " If you want a good cruising boat, design a boat to do that. If you want something else, design that. Don't generalize about a shape, without talking about the other factors involved with that shape, and don't expect shape alone to solve the seaworthiness problem." I also maintain that the double-ended shape, be it full enough where it counts, and fine enough where that counts, when coupled with the correct amount of correctly-located weight and total displacement, is the best solution to the seaworthiness problem, in very severe conditions.
Those who say that double-enders lack volume in the ends haven't really experienced a North Sea fisherman---my boat, with a deck
length of 49 1/4', must have eighteen tons of just ballast, distributed well strung-out, also toward the ends, just to keep her from pitching one off the foredeck in a head
sea. Volume she has, in the freeboard of the ends, much more than most, and yet is quite fine underwater. For her 45-ton displacement, she is remarkably easily driven. Archer concentrated the ballast of his Redningskoytes toward the center of buoyancy, and in the keel
, so that they would pitch
unmercifully in ultimate conditions, and have great righting moment, but keep their decks as free of green water as possible. That's great for the North of Norway in the winter, but very tiring for the usually small crew of a cruising sailboat. Again, design the boat for the job. And trust a heavy, well-designed double-ender, when the sea becomes really windy and lumpy. They survive, as do their crews. I have owned two of them, for a total of over forty years, 32' and 49+' on deck, mostly in the North Sea but also in the Caribbean
and Eastern U.S., and found the above to be true when it really counted, every time.
Cheers, Jeff Lane