Is there validity to the notion that a pointy stern, a canoe stern, is safer at sea

[KCook]

So what is the reasoning for a mixed design, like the QM2?

http://i225.photobucket.com/albums/d...QM2SternSt.jpg

Kelly Cook

[robherc]

That one defo looks like an iceberg catcher to me...guess they're working on the S.S. Titanic again

Honestly, my guess there would be either A: extra space/balancing weight aft; or B: more overhang to keep the boat on top of extremely high seas (though I doubt it's necessary in THIS large a boat).

[Tad]

From Wikipedia....

http://en.wikipedia.org/wiki/RMS_Queen_Mary_2


One aspect of the QM2 that has been criticised is the contour of her stern. Payne's intent was to make the ship's stern profile similar to that of the QE2, with a spoon shape, but the mounting of the propeller pods required a flat transom. The compromise was a Constanzi stern – a combination of a more traditional cruiser stern with a contemporary box-like transom stern. The design of the stern has ironically been criticized from two diametrically opposed perspectives by liner buffs. Some feel that nothing but a traditional cruiser stern would be suitable for a true ocean liner, whereas others feel that his choice of stern represents a purely visual conceit that detracts from the quintessentially functional nature of a liner. In fact, Payne has specifically said that he would not resort to adding any non-functional elements to the QM2's design purely to make her appear more "liner-like". It can indeed be argued that the stern satisfies a mixture of functional and aesthetic requirements: A Constanzi stern provides the transom required for azimuthal pod propulsors, yet provides better seaholding characteristics in a following swell than a standard transom stern. The stern design, too, has been seen by some as a homage to earlier (especially Italian-built) liners such as the SS Eugenio C. and the SS Oceanic.

[KCook]

Thanks guys. A wide flat bottom stern to accommodate the aziuthal pods make sense. I'm not so sure about the spoon shape protuberance! Now I'm being thrown by "Constanzi"?

Kelly

[Tad]

Who the heck is this Constanzi guy anyways?

"better seaholding characteristics" Sounds like smoke and mirrors to me!

[KCook]

Plus, the QM2 does not exactly plug along! What is the max speed for a following sea? I kinda doubt a following wave would catch the QM2 ....

relativistic Kelly

[PortTacker]

Originally Posted by robherc

Realistically, I'm pretty sure a canoe stern would get pitched about a bit less by a large following sea than a transom on an otherwise identical ship...but you'll have trade-offs for that at higher speeds I guess...

My experience at sea has been just the opposite. Narrow sterns tend to make a boat want to 'death' roll down wind - as the bow and stern are in the waves and the bulk of the hull in the troughs, there's not much stability.
I FAR prefer a stern with some width to it.
But, not like (just to pick an example) the newest Hunters, which take width aft to extremes - great at the dock, horrible to sail.

Originally Posted by KCook

Plus, the QM2 does not exactly plug along! What is the max speed for a following sea? I kinda doubt a following wave would catch the QM2 ....
relativistic Kelly

"Typical" speed of waves at sea - 10mph on the slow end to 20 mph on the fast end, with storm waves approaching 30.

In sailing craft, it's only been the last few years than anything sailpowered actually overtook and passed open ocean waves on a regular basis. (For example Volvo boats or the big tris of Ellen and Francis et c.)

[timothy22]

W.A.Robinson actually had some tank testing done in hopes of finding the perfect stern for his new yacht, "Varua" in 1941.
Varua, which means "spirit" or "soul" in Tahitian, is considered by many
aficionados to be the most beautiful and functionally perfect sailing yacht ever
built. Based on his years of experience sailing the oceans of the world, the lines
were worked up to Robinson's specifications by W. Starling Burgess, famous
designer of the America's cup defender, Ranger, and numerous other fine ships.
The model was tested and refined by tank tests at the Stevens Institute, and the
hull was constructed of the (then) advanced composite steel frame and wood-
planking technique. She was launched March 19, 1942, just after the U.S. was
plunged into war with Japan and Germany. During the war, Robbie and his
wife lived aboard and made plans for the future. One weekend in 1943 they
had as a guest aboard, the famed circumnavigator Conor O'Brien, whom Robbie
found to be exceptionally charming and entertaining.

Varua's dimensions are: 66.2 feet overall, 60 feet on the waterline, 16.2 feet
in beam, with a draft of 6.6 feet, a net tonnage of 37, and a gross tonnage of
43. Her A.B.S. rating is *A I Y S.

In "To The Great Southern Sea" ..Robinson talks about the conventional stern being revised on the board with aid from Stevens Institute testing tank till they had what they called a "double chin" stern...they being he and S. Burgess.
Talking of the model with the conventional stern being tested in the tank...Robinson said ,"Special apparatus had been devised to simulate following seas.At first her stern had been more conventional; but she had a tendency to pull the following seas over on top of her and even to broach to. Little by little the stern was changed and the rest of the underwater lines accordingly, untill one day we had a model that did not disturb the form of the following sea,that did not trip, that ran true before it at all speeds".
This design was just a typical counter stern with the lower half of the transom cut away. The upper half was normal, the cutaway portion slightly convex. This slightly unorthodox design fulfilled its promise in a survival storm.

[kb1one]

The Pinkies and Block island boats of the Northeast maritimes were double enders, "pink sterned" as they were then referred. Pinks were known in these waters for nearly three hundred working boat years, and only two were ever lost. One was run into a rocky shoal by a drunk helmsman; we cannot blame the design for that. The other went off and never returned. Something about the accounting of it smelled like an impromptu divorce to me. Longevity of a concept among the working boats is not something I tend to discount, personally. More recently, a very nice pink crusier was built here in Maine. I do not remember the issue, but it was featured in Wooden Boat Magazine a couple years back. The boat is named Elf, and it migrates southward throu open water and back every year. I will not call the design fast, but it is "weatherly". And is speed really everything?

[kb1one]

The Pinkies and Block island boats of the Northeast maritimes were double enders, "pink sterned" as they were then referred. Pinks were known in these waters for nearly three hundred working boat years, and only two were ever lost. One was run into a rocky shoal by a drunk helmsman; we cannot blame the design for that. The other went off and never returned. Something about the accounting of it smelled like an impromptu divorce to me. Longevity of a concept among the working boats is not something I tend to discount, personally. More recently, a very nice pink crusier was built here in Maine. I do not remember the issue, but it was featured in Wooden Boat Magazine a couple years back. The boat is named Elf, and it migrates southward throu open water and back every year. I will not call the design fast, but it is "weatherly". And is speed really everything?

[Tad]

Originally Posted by kb1one

Pinks were known in these waters for nearly three hundred working boat years, and only two were ever lost.

There's an easily substantiated claim!

Having sailed more than a few miles in a big pinky, I would say they can relatively comfortable offshore in big ocean swells. They can also be real pigs and pitch themselves to a standstill in steep chop inshore. All around slow, but comfortable in the right conditions.

[harlemriverman]

Originally Posted by TeddyDiver

It's more relevant issue on shoals and coastal waters with "sharper" wave patterns, and then a double ender is (in my opinion) more comfortable. In small open boats without reserve boyancy also safer..

roger that.

i might consider a dory shaped stern or fan tail if, for example, my slip was in an inlet with usually following seas that break on shoals or shallower bottoms and that may otherwise tend to swamp the boat from aft. the design makes life simpler, as would a powerful motor. a ketch addresses the same challenge but its rigging may prove more complicated to manage in general.

[BOATMIK]

Danishbagger is getting close.

From sailing canoes and dinghies a relatively narrow boat with a canoe stern does not tend to round up much when heeled heavily.

I think this is basically because the forces are symmetrical.

Also you see that wide sterned boats push the bow down as they heel ... I have a strong hunch that this makes them tricky at speed in waves. If you imagine something wide heeling heavily there starts to be a lot of depth forward and very little aft, which is generally the opposite of what you want if a boat is expected to track without excessive rudder input.

whereas a boat with a more balanced volume distribution (whether canoe sterned or not) when heeled and more symetrical waterlines forward compared to aft is much easier to control.

A canoe stern is just one way of making sure the volumes and centre of buoyancy stay in about the right place as the boat heels.

With Australian International Scow Moths they had a lot of trouble with nosediving and control issues in rougher water, until in the early '80s they started pinching the last couple of feet of the boat in very sharply so the stern buoyancy would not overwhelm the buoyancy of the bow. The transoms were much narrower than the bows. Wardi who appears here from time to time was in the centre of this development, so can probably fill in the detail ... I was hearing about it all second hand.

Before this the tendency was to go for big wide powerful sterns with the hope they would provide lots of speed downwind, but the control issues became much greater.

This fed into a lot of the antipodean restricted class designs. You can see a general trend of pushing stern widths out until the early '80s and then suddenly the wide sterns are gone and they are getting more speed from straightening out the rocker.

Best wishes
Michael