G'Day Dave, John and Paddlewise, As a follow on, thought I'ld test my assumed knowledge in case its wrong. Here's an approximation, not to scale, of a chined boat cross section with letters at the corners for reference. Boat X section A E # # # # B D # # ....................C......................X If the section CD is aligned with the wave surface, is it the design aim, for a chined boat that this is nearly the point of initial (primary) stability. Would the point of secondary stability be when section CDE is roughly aligned with the wave surface. Clearly this is an over simplification depending on the centre of gravity of the boat and its load, but the presence of such well defined planes in this style of boat suggests that its not a bad approximation. If the assumptions are correct then wouldn't chined boats have to be edged beyond their point of initial (primary) stability to remain vertical in a choppy sea where the wave face is at a greater angle than XCD? All the best, PeterO *************************************************************************** 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/ ***************************************************************************
Peter, Primary stability has almost nothing to do with the cross sectional shape of a boat. Chines, no chines, makes no difference. It is the shape of the water plane and the height of the center of gravity that will determine initial stability. Secondary stability starts to have some relation to hull shape, but what matters as much as anything is the volume of the boat above the level waterline which begins to get submerged as you lean or tip the boat. For more discussion on the subject I have an article on my website: http://www.guillemot-kayaks.com/Design/StabilityArticle.html Nick On May 10, 2005, at 9:15 AM, PeterO wrote: > G'Day Dave, John and Paddlewise, > > As a follow on, thought I'ld test my assumed knowledge in case its > wrong. > Here's an approximation, not to scale, of a chined boat cross > section with > letters at the corners for reference. > > > Boat X section > A E > # # > # # > B D > # # > ....................C......................X > > If the section CD is aligned with the wave surface, is it the > design aim, > for a chined boat that this is nearly the point of initial (primary) > stability. Would the point of secondary stability be when section > CDE is > roughly aligned with the wave surface. Clearly this is an over > simplification depending on the centre of gravity of the boat and > its load, > but the presence of such well defined planes in this style of boat > suggests > that its not a bad approximation. > > If the assumptions are correct then wouldn't chined boats have to > be edged > beyond their point of initial (primary) stability to remain > vertical in a > choppy sea where the wave face is at a greater angle than XCD? *************************************************************************** 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/ ***************************************************************************
Nick wrote: - >For more discussion on the subject I have an >article on my website: http://www.guillemot-kayaks.com/Design/StabilityArticle.html Matt wrote: - >I like a progressive secondary stability that >doesn't peak until a large angle of lean combined >with a low initial stability. Effortless to lean >at first but much more secure feeling when leaned >than a kayak with high initial stability (or one >with low initial and low secondary stability). G'Day Dave, John, Nick, Matt, Robert et al, Your explanations were appreciated. And Nick that web page of yours is an excellent, clear description of stability curves, thank you! I strongly suspect that in the wooden chined boat I am confusing the feel of initial stability with the feel of secondary stability. PS Three Days Later I started to write this email on Friday and since then have been surfing in the wooden chined boat and can confirm that the effect I was experiencing was one of high initial stability. Also the feeling of conscious effort required to keep the boat vertical disappeared after a couple of days so I guess it was just a question of getting used to the boat. Was it important? Well not as much as lack of volume in the bow and its tendency to submerge, as I can attest after a number of spectacular endo's, some of which I survived. Only time I've ever had a crowd on the shore cheering and it was all by accident! Anyway the subsequent discussion on stability is keeping me off the streets and I'm particularly interested in trying to understand Robert Livingstone's point on the nebulous nature of secondary stability. Its going to take a while to think through all the correspondence though. But I really appreciate your debate, All the best, PeterO *************************************************************************** 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/ ***************************************************************************
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