Robert Livingston wrote: >>>>>I am surprised how little I can find on the Web about Volumetric Coefficient relevant to boats.<<<<< Most folks probably use the dimensional displacement-length ratio which is basically the same thing. >>>>>>Is this part of the formal definition that SALT water density be used. And for that matter is there an official density of SALT WATER that everyone uses? (Baltic Sea a lot less salty than other places for example)<<<<<< No, the Volumetric Coefficient is defined as the displaced volume divided by the waterline length to the third power see: http://66.102.7.104/search?q=cache:bemFpJWxVRgJ:wseweb.ew.usna.edu/nahl/ITTC /ittcst99.pdf page 11. Therefore the volumetric coefficient will be different for different densities of salt water, for fresh water (about 62.5 pounds per cu. ft. rather than 64) or for a boat floating in mercury for that matter. There is a density of salt water (probably the average for sea water in the oceans) at 59 degrees F. that is used as a standard for tank testing (even though most towing tanks are now fresh water). Tests performed in other densities and temperatures of water can be corrected to that standard with relatively simple formulas. The temperature has far more effect on drag than the density. Density sort of controls for itself to a large extent in its effect on drag. Yes, salt water is heavier and harder to push apart but then since it also floats your boat higher there is less of it to push aside and less wetted-surface friction as well. Temperature adds roughly 2.5% to the drag for every ten degrees colder the water gets. Of course, at some point along the temperature drop the drag suddenly approaches infinity ;-) [Note: I don't see "fatness ratio" in the 1999 ITTC list of terms (above link) at all and I can only find three instances of "fatness ratio" used in regards to boats on Google. All three were written by John Winters. I tried to get to the source John mentioned where "fatness ratio" was proposed, "Explanatory Notes for Resistance and Propulsion Data", published by SNAME, but the $25 entrance fee to buy it brought me up short. It wasn't you who proposed this term was it John? In any case, I'm betting the term wasn't adopted but was only proposed.] The Volumetric Coefficient is defined as the displaced volume divided by the waterline length to the third power http://66.102.7.104/search?q=cache:bemFpJWxVRgJ:wseweb.ew.usna.edu/nahl/ITTC /ittcst99.pdf page 11. John wrote: >They also include the >displacement/length ratio (They call it the fineness ratio - go figure) for >North Americans more familiar with the dimensional term. Looking up "fineness ratio" on Google, it appears to be mostly used in aerodynamics to mean the ratio of length to diameter. In the relatively few instances it was used in surface craft it seem to be used as the waterline length to waterline width ratio rather than as the displacement/length ratio. John, if you have a copy of "Explanatory Notes for Resistance and Propulsion Data" could you tell us the exact definition given these terms "fatness" and "fineness" ratios as written there and if they have been adopted or rejected or are in limbo (that is, merely proposed)? Paul Grant said: > Before the Toksook thread dies out, can anyone explain the > technique D. > Hutchinson uses in rolling (or not rolling) the control wrist > while paddling with a 90 deg. offset blade? > I think I read someplace that there was something special he > advocated. Steve Holtzman replied: >>>>>The wrist is kept straight and the entire forearm of the control hand is raised up by bending at the elbow. This causes the blade to be put in the water with the correct orientation without subjecting the wrist to all of the problems associated with bending the wrist.<<<<<< Steve, could you (or anyone) describe this technique to me in more detail? This isn't the technique that I call the "George Peck technique" is it? Derek paddled with George (then the magistrate of Seward--later the unicycle mtn. biking originator) Peck in AK back in the late 70's or early 1980's. Robert Livingston was up there then as well and knows about this. George would continually rotate the paddle forward a quarter turn with each stroke (which is possible to try with any feathered paddle but works best with an 90 degree flat blade paddle with no asymmetry--like a Toksook). In other words with each alternate stroke on the same side the back and power face of the paddle is switched. I saw this on the video Derek had made of his Expedition to Prince William Sound and noticed something weird about George's stroke. Upon replaying it to look closer I finally saw what George was doing. With the right paddle this technique seems to work pretty well. After that expedition, Robert bought Derek's Umnak Icefloe and sent it to some of his friends down here in Seattle. It was the first Icefloe I tried, way back in 1982. Tying some threads together here now, my understanding is that the Icefloe was modified a little in Australia sometime prior to 1991 and renamed the Pittarack. Robert Livingston got his start in kayak "designing" by modifying Derek's Baidarka (for his own use) but later returned to the straight and narrow and developed his own unique designs (with the help of a 4K computer and his programming skills). The length and the bow sections of his Ursa Micro model look suspiciously similar to a Coaster's. That's because we asked Robert if he would have any objection to us making a kayak with those similar features (short with a big buoyant bow). Although the Coaster was designed from scratch by Cam we credit Robert as the godfather of the Coaster in our website's history section since it was the breaker surfing ability of his Ursa Micro that inspired Cam to design the Coaster with some similar features. Matt Broze (110/77) www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Fri Sep 03 2004 - 21:48:01 PDT
This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:31:17 PDT