Viking tumblehome sterns

Okay, what ever you say . . .

 

Well now we're into it, I agree with PAR in that it was a design feature(it benifited the crew) but while doing so i again go back to my former logic in that it also added stregth to the overall stern area whether or not this was the origional reason. It could have been the other way around. I well know the benifit of a waist high body brace when leaning over the side hauling cod and salmon nets.The key reason here is Design not Astetics, which are the two opposing poles of this debate. Regarding tumblehome on freight or aramament carrying vessels I always read historically it was to move the weight inward toward the longitudional center of the ship to improve "Inital Stability" thru "Hull Form". I can also see this working to the benifit of the vessel in the case of the typical war maneuver "Raking". Typically this war maneuver destroyed and removed alot of weight from one side of the vessel creating an amount of transverse imbalance which without tumblehome would be greater.(Blasted away large chunks of wood, drove cannon both inward and overboard.) Without tumblehome the opposite side of the ship would be farther out from the normal transverse center of balance creating a longer lever force. Many of these high sided ships with their heavy rigging and aramenent were never highly stable to begin with and the loss of even moderate amounts of weight on one side could easily subject the opposite side gun ports to intake of sea water or a sudden gust of wind knockdown. The same could be applied to a merchant ships freight shifting in a storm. Hey i'm not an engineer but I do have years of experience on fishing boats where one develops a 6th. sense of survival in load distribution ( balancing out the fast incoming weight of tons of new cargo (fish).-Geo.

A yacht is not defined by the vessel but by the care and love of her owner

 

That's precisely correct Viking, though strength has to be assumed or they'd use a different approach. They didn't care about anything other then function, until absurd wealth made such, a plausible concept. These were the most high tech contraptions of their era, so thoughtful consideration was applied to every element, for load sharing, crew safety (to a limited degree by today's standards), ultimate strength, etc. This was a requirement of the owner, who wanted the most bang for their buck. I'm not even going to get into the debate about massing armaments and cargo nearer the centerline, as it's too well documented.

 

Tumblehome as described by PAR would be authentic "wooden walls" practicality.

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

http://www.thedockyard.co.uk/Plan_Your_Day/Wooden_Walls/wooden_walls.html

PAR has forgotten more about naval architecture than I have learned. Regard his numbers. I have followed his contributions since I joined this forum. I'm a "nowhere man" by comparison.

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Tumblehome on a Knarr stern,as viewed on a model, is a "non sequitur". The Norse did what they did in ship design for seagoing reasons. They came to England for a bit of **** and pillage and some stayed to pop down the pub.

http://www.theploughandsail.co.uk/

Regards,

P

 

Centered at rest only. Greater beam at a high, old fashioned gundeck seriously degrades stability due to CG shift. The guns do not balance each other out when the ship heels, but shift the CG to the lee side excessively due to fact that lee guns are significantly farther from C/L than would in narrower beam at same heeling angle, while windward guns are on the wrong end of the lever moment to completely compensate.
Anyone studying European harbors before the Industrial Revolution should see that the dense shipping of all types and sizes, rough stone quays and tidal conditions make tumblehome a very good thing along with thick oak planking. A Scottish harbor in the herring season in the 1880s was so full of double ended fishing boats you could walk across from one side to the other. They nested like herring in a can and transoms would have been ground to dust, so the double ended tumble home shapes fitted perfectly.
As to what does best in a crashing breaking sea assaulting you from behind? From extensive practical use of CG surfboats I can say that a light buoyant stern balanced by a light buoyant bow will get you a long way. The shape matters little as evidenced by Amoy Fishers, rough junks that work some of the roughest waters in the world, the Strait of Formosa. The keyword is "light", as in keep all the heavy stuff out of the ends and have a shape with sufficient buoyancy to lift under all conditions.
Viking shipbuilders used split from the tree planking and did not saw it. This gives a wonderfully supple piece of oak that can take a severe bend without breaking, especially if steamed or boiled. The easiest shape to build with the available materials and techniques to the early Norse also gave a very beautiful and sea kindly ocean vessel. Easiest just means economics, like cheapest. These were industrial and military constructions, and followed the rules of societal economics like anything else, so their shapes are the result of many factors, not just one or two.

 

Here's a VASA look alike we had to wrestle with for months in the Bahamas at the whim of Production and studio heads. Almost lost it on the reef late one night when they made us do a long list of not-nautically-smart things.

 

Early man powered Warships used " Tumblehome " amidships to get maximum beam for the oarlocks of the oarsman.

I always assumed that "Tumblehome" aft on a double enders was simply a way to generate additional buoyancy ....a wineglass aft section also generate buoyancy aft.

 

Tumblehome means less beam at sheer than w/l so would seem to give less beam for oarlocks and less buoyancy, since you are decreasing above water line displacement when building in tumblehome. Most 'Fatness' with least weight generates buoyancy, no matter what the shape. A wineglass section has more fatness/displacement/buoyancy above the w/l, a tumblehome shape has more fatness at the w/l and less above.

 

War ships were rowed from under deck...sometimes three layers of oarsman.

 

war ship

 

warship

 

Battan, how was that prop built, was it an actual replica tormented into what we see or was it a shell built over an actual boat. Whatever it was the designer must have one hell of an imagination. I always thought it was a studio prop set on hydrolics and computer fitted into the film.
Michael I can see that as a functional design for human powered ships. It would effectively move the fulcrum point of the oar further out (more mechanical advantage) but at the same time reduce the stroke (water sweep) so there must have been some pratical design trade off there.( This of course assumes the oars pierce the hull at the max. beam of the vessel) When you say tumblehome at the stern adds additional boyancy, is your comparison between two identical hulls with the exception one stern has no tumblehome but just a curved stern that ran straight up to the sheer edge(deck edge) and the other formed into tumblehome but allowing the reverse curve to finish to the same height as the non tumblehome vessel. In other words both hulls are identical up to the point where one chooses to start the reverse tumble home curve. In that case wouldn't both vessels have the same displacement and boyancy. OR was your idea that in order to develop the tumblehome feature the hull stern section would be extended(bulged out) to form the curvature of the reverse curve to form the tumblehome. In that case the tumblehome boat would be of greater LOA and this would result in more displacement and boyancy, The same idea when comparing tumblehome with a transon stern, the bulged out section would in effect go beyond and cover what would have been the flat section of the transom. Not trying to be a smart a-- here but my sponge brain wants to progress from hands on to brains on and i really appreciate the feedback from all you more qualified members. Example PAR was kind enought to take time and confirm my thinking was in the right direction earlier up the post.--Tnx. Geo

P.S. Upon posting i see several people have beat me to a response to Michaels post #22 so Michael consider this my response to your post #22

A yacht is not defined by the vessel but by the care and love of her owner.

 

Rowed warship. I see no tumblehome.

 

A 'prop' is something an actor holds in their hand, 'set dressing' is what they sit and lean on, a 'set' is where this all happens, so the FLYING DUTCHMAN here was a set, not a prop. At almost 130' long on a purpose-built steel hull and $5 million she was quite a piece of work. Handling sails and anything else was a challenge due to the tons of vinyl 'seaweed' on everything. All the cannons fired and recoiled hard and very realistically, though they were fiberglass and operated by the SFX department.

 

Nope that Greek looking vessel of the Med. doesn't have any tumblehome being set up with three levels of oars it possibly wouldn't work so well. The top set of oars would have to be that much longer if at gunnel level. I can't recall any of the Med. Roman era boats having tumblehome. Different culture different designs I guess.
Being that Gorden Pincent( famous Canadian actor) is my first cousin and Wylie Stateman of SoundDelux Studios in Hollywood is one of my best friends you would think I would have more knowledge of those labels, however i'm not totally wrong you are holding that prop boat in your hand. ---Geo.