Peter wrote; > A few clarifications I think are in order, I never wrote that secondary > stability was meaningless, I just speculated that it could be something not > relevant to large commercial vessels since you can not rapidly shift the CG > to alter the ships response like you would on a kayak. Fair enough but it still applies as important in ship design. While people may not always run from side to side they do sometimes and the results include capsized ferries, swamped tour boats etc. Freighters and tankers must have enough overall stability to absorb shifts in cargo soametimes quite rapid. One can spend many hours reading such entertaining topics as damage stability and free surface effects that deal with rapid changes in CG. (SNIP) > > I would also think that if the curve had a sharp peak, it would feel less > forgiving since the correcting moment would drop off rapidly with little > warning once you pass a certain roll angle. This makes sense to me. > > In fact I would say the higher the peak of the curve on the chart (i.e. > highest absolute rolling resistance) would have more influence over the > perceived secondary stability than the location of the inflection point. > And the overall rate of increase, or average slope, would also have a > powerful influence of the perceived secondary stability. I would add the slope behind the maximum as well since the more righting force you have after the maximum the more help you get from the boat in getting back to upright. > I do not claim to be anykind of an expert on hull design but I have spent > many years analyzing aircraft stability and control curves know well how to > read a chart and its derivatives, you have to look at how the changes > affect the "human factors", hard to predict from purely a mathematical > stand point. > I would suggest someone get together a group of paddlers of various skill > levels and compare perceived secondary stability with all kinds of curve > properties in various hull designs. If you can find any kind of > correlation (which you may well not find) then we might have a working > definition, and something to look for in a cure (maybe an article idea for > SK mag?). As one of my engineering professors used to say, one simple > experiment is worth a thousand expert opinions. Unless I read Nick incorrectly, he (and I) would rather see quantifiable physical parameters that would allow a paddler to get an idea of how a boat might feel. I get the feeling that some people want a definition in human terms rather than physical terms. I do not believe this would ever have a lot of value since such information only tells us what some people think. With a quantifiable (and reproducible) method of presenting stability characteristics germane to the paddling experience a paddler could paddle several boats, compare their curves and from that discover how the curve applies to his perceptions. John Winters Waveform Plastics Technologies Ltd. 15 Ena Ave. South River, Ontario P0A 1X0 *************************************************************************** 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 Tue Nov 21 2000 - 14:06:34 PST
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