I posted awhile ago about a double ender I was designing just to do a little winter dreaming. Here's a rendering of it:
Double Ender
- Thread starter Roger Long
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The whole double ender in a following sea business is vastly overblown. A properly designed transom stern boat will be just as good in rough seas 95% of the time and few people will let themselves get into situations where the slight advantages of the double ender in the other 5% will become apparent. Most transom stern boats will be better than the typical double ender (like a Westsail) in the conditions most likely to create hazard such as facing a long beat to windward where fatigue becomes a danger. They will pitch less and get there a bit faster. I think that's a good trade off for being slightly less likely to broach on a rare nasty sea you may never see.
The reference points on discussions like sterns make most bar and Internet discussions pointless. Is a double ender a boat in which some buoyancy has been removed from the aft quarters or is it a transom stern boat with additional buoyancy add to the back end? I could go on for pages but my fingers are worn out from producing that rendering.
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AutoCad with curve coordinates exported into text files for import into Freeship. Long painful process but I wanted to learn how to do it.
The has the same basic dimensions as the L.F.H. Rozinante canoe yawl but with more displacement and form stability so I don't think she would be considered overly tender by people familiar with the type.
There's no future for a boat like this though, less room than a trailerable Hunter 22 and six more feet of length to pay for in dockage and winter storage. The real potential of this lines plan is being scaled up to 42 feet where it would have full headroom under the raised deck. She would still be small for a boat of her length. Beam and cross section space would be about the same as my Endeavour 32 and the sails, ketch rigged, would be about the same size. The thought of her reaching fast in a quartering sea stirs my imagination in a way that makes all the work of producing this lines plan and rendering worthwhile on a gray winter day.
Roger has answered but I'd like to add a simplistic additional response, as one who extensively sails a 'double ender' over long distances.
Consider the pointy stern as just a stylistic or cosmetic 'add on' to a hull. Imagine the same boat but with the pointy stern cut off entirely from the design and then imagine the remaining stern buoyancy --- 99% of the time you will visualize (or calculate) a 'standard form' with a slightly 'pinched stern' boat but still with adequate reserve.
OTOH - take a look at the plan view of the hull to visualize the real advantage of such a design: will be able to heel over almost over onto its beam ends (heeling to the max.) and not develop any increase in helm pressure. That alone will retard any 'broaching' moments and is definitely good for pointing; although Id prefer a much sharper bow angle. As Roger said, this will be a 'sweet sailing' boat (in comparison to a more modern "Fat Assed" design with a 'cranky helm').
Secondly the reserve buoyancy comes from the sections at near the stern waterline (the 'fanny') ... look at the 'rest' of the hull form - its 'symmetric', a sweet sailor!
When one looks at the record book of circumnavigators, surprisingly the predominant hull form is "the double ender" - Valiant, Passport, Tashiba, Baba, PSC, Tayana, Westsail, etc. !!!
One of the seldom talked about 'advantages' of a Double Ender is ... lack of stowage space in the stern end .... if you dont have the capacity to overload the stern with a lot of 'crap' that by itself will keep the stern end 'light' and will tend to prevent 'hobby-horsing'.
So when 'evaluating' a double ender, simply and imaginarily cut the stern end off with your eyeball and then see whats left ... usually quite a good hull form. Style.
Having built, owned and sailed one, the chief characteristics of today's double ender have already been mentioned, those being graceful appearance and limited volume aft.
Consider double enders are a traditional design. Back in a time of wooden boat construction, before resins, fiberglass, epoxies or even adhesives of any quality existed, boats were built with mechanical fastenings. A pointed stern, like the bow, could be constructed with vastly superior strength than a transom type. If you were planning a crossing and your boat was fastened with nails or nails and roves (actually rivets) you wanted the strongest system possible and the double ender provided such a design.
Consider double enders are a traditional design. Back in a time of wooden boat construction, before resins, fiberglass, epoxies or even adhesives of any quality existed, boats were built with mechanical fastenings. A pointed stern, like the bow, could be constructed with vastly superior strength than a transom type. If you were planning a crossing and your boat was fastened with nails or nails and roves (actually rivets) you wanted the strongest system possible and the double ender provided such a design.
The weakness of wooden vessel construction back when double enders developed their reputation is unimaginable from our modern perspective. If a steel or fiberglass hull today were found to have degenerated to the strength of trunnel fastened plank on frame vessel, it would be instantly condemned. The wracking and twisting caused by waves coming up under the quarters of a sawn frame wooden vessel could open up seams after many hours in severe conditions once the vessel was just a few years old. I think this had as much to do with double enders being considered the most "seaworthy" type as their motion response in waves.
It's funny, I favor transom stern boats and I've never cared for raised deck double enders because of the visual mass imbalance. However, when I set out to design this boat as an experiment in using a classic proportions system, it just seemed to work. That brings up the primary reason for building a double ender, you just like looking at it.
That's nice Roger, the raised deck reminds me of my old Cal 28 flat top, but yours is much better looking! My current boat is an Eric Jr., how would you compare your design to that?
The legendary Westsail 32 was actually William Atkin's Eric design, modified for fiberglass construction by William Crealock. It's ancestry goes back to Norwegian sailing lifeboats (Redningskoites) designed by Colin Archer that were usually dispatched in the worst conditions.
Roger,
I'm struggling with the beam dimension. Typically, cruising designs accommodate the weight of extensive stores without affecting sailing performance significantly. Your 6' beam seems to me to be at odds with that. The 11' beamed Westsail 32 suffers from a poor performance reputation that frankly I found to be untrue and later beamy designs, even racers, have shown respectable speed. So the question is, why the narrow beam? I'm sure you had a reason, hence the question.
I also noticed the little 'kick' in the sheer curve right at the stern, assume that's for looks?
Roger,
I'm struggling with the beam dimension. Typically, cruising designs accommodate the weight of extensive stores without affecting sailing performance significantly. Your 6' beam seems to me to be at odds with that. The 11' beamed Westsail 32 suffers from a poor performance reputation that frankly I found to be untrue and later beamy designs, even racers, have shown respectable speed. So the question is, why the narrow beam? I'm sure you had a reason, hence the question.
I also noticed the little 'kick' in the sheer curve right at the stern, assume that's for looks?
Isn't it fun what you can do with computers?
Note that wetted surface and sections are very similar. Although Eric Jr. has more beam, the difference is primarily on deck where it adds to deck structure weight. Down at the waterline where the sail carrying power is developed, it's only greater for a bit of the midships length. There is more waterplane area in my design. Sail carrying power would not be all that much different and my design with the greater waterline and shallower flow angles would just walk a way from the more traditional double ender. Add in greater pitch damping and you've got a faster boat that is every bit as seaworthy.
You have to understand that this boat can't be compared on length with anything that seems normal today. Something like a Hunter 22 has more room. She is a daysailer / overnighter very comparable to the L.F.H. "Rozinate" but with more sail carrying power and interior room.
The design actually started as a 36 foot centerboarder and I decided to see how she would work as a traditional canoe yawl, a type which is expected to be long, lean, and minimalist.
The best use of these lines would be as a 42 footer. Even at that length, she would be a long and lean"35 footer" in comparison with more modern types but that length would make her a real mover.
You can see the rational for the sheer in this thread:
http://forums.sbo.sailboatowners.com/showthread.php?t=124421
and you might find this interesting:
http://forum.woodenboat.com/showthread.php?104113-Expanded-sheer-lines&highlight=
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