The radius of gyration is the distance k from the axis of rotation at which a single point mass equal to the object's mass M would be put to have the same moment of inertia I as the object. Found this definition at http://www.unb.ca/web/physics/1040/torque.htm I have just looked at a lot of warship pictures on the web and they range is from reverse rake on some early 1900's battleships to near 45 degrees of rake on some modern U.S. anti aircraft missile cruisers and over 45 degrees of rake on some Russian ships. Way more rake still on one Russian aircraft carrier. The majority had modest rakes of 75 to 60 degrees. Looks to me that the ship designers haven't reached agreement on this issue yet either. Couldn't find the Gerritsma research though (in less it was in one of his research papers that SNAME's website wanted $30 for). I'm still betting that he moved weight around to change the gyradius of the sailboat rather than testing various rakes. I don't know but I'll bet he found that the lower the gyradius for a given hull the faster it was through the waves. If I am right it may be evidence to support the lift over the wave advocates rather than the punch through the wave advocates as to which is faster into seas. I'm betting on the "pitch as little as possible but at the same time don't let water wash over the deck" compromise school of though on this one. So far I have lacked much beyond subjective evidence and Sea Kayakers 1986 very limited wave tank towing tests to back up my theoretical speculations. Even if I'm proved wrong I have a lot of subjective personal evidence that a compromise between the extremes is the most comfortable for me the paddler. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
On Sun, 25 Jul 1999, Matt Broze wrote: > The radius of gyration is the distance k from the axis of rotation at which OK, which axis, the vertical(yaw), long axis of the boat(roll), or beam axis(pitch). (Hope I got those right, Pat Moss will be at me if not....) e *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Elaine Harmon wrote: > On Sun, 25 Jul 1999, Matt Broze wrote: > > > The radius of gyration is the distance k from the axis of rotation at which > > OK, which axis, the vertical(yaw), long axis of the boat(roll), or beam > axis(pitch). (Hope I got those right, Pat Moss will be at me if not....) e Each has its own radius of gyration. For a long, skinny kayak, the pitch and yaw values will be similar in value. The roll radius of gyration will be small. Mike *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Matt wrote; (SNIP) >I have just looked at a lot of warship pictures on the web and they range is >from reverse rake on some early 1900's battleships to near 45 degrees of >rake on some modern U.S. anti aircraft missile cruisers and over 45 degrees >of rake on some Russian ships. Way more rake still on one Russian aircraft >carrier. The majority had modest rakes of 75 to 60 degrees. Looks to me that >the ship designers haven't reached agreement on this issue yet either. I don't think anyone should get the idea that one and only one rake works. Designers consider a lot of factors. How the volume is distributed vertically, how the volume gets distributed longitudinally, requirements for longer flight decks on aircraft carriers, aesthetics and the need to cram lots of cabins in a shorter space (see some of the Carribbean cruise ships) that avoid heavy weather at all costs to keep passengers happy, whether the boat must stay at sea indefinitely etc. etc.. What angle did you use here, Matt? Cheers, John Winters Redwing Designs Web site address, http://home.ican.net/~735769 *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
At 02:38 AM 7/25/99 -0700, Matt Broze wrote: >I have just looked at a lot of warship pictures on the web and they range is >from reverse rake on some early 1900's battleships to near 45 degrees of All the negative rake on the turn of the last century battleships was because the bows were actually rams. The designers in those days weren't all that confident about gunfire against armor, and designed the potential for a ramming battle into the ships. -- Wes *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Michael Daly wrote: > Elaine Harmon wrote: > > > On Sun, 25 Jul 1999, Matt Broze wrote: > > > > > The radius of gyration is the distance k from the axis of rotation at which > > > > OK, which axis, the vertical(yaw), long axis of the boat(roll), or beam > > axis(pitch). (Hope I got those right, Pat Moss will be at me if not....) e > > Each has its own radius of gyration. For a long, skinny kayak, the > pitch and yaw values will be similar in value. The roll radius of gyration > will be small. Further to my own message: Actually, as far as the similarity in value of the pitch and yaw radii of gyration, this is true if you consider the kayak without a paddler in it. With a paddler, the pitch gyradius will be greater than the yaw. This is because the paddler sticks up from the kayak. The exact value would be difficult to agree on, since one assumes a rigid object. Paddlers have a nasty habit of keeping their bodies vertical while the kayak gyrates with the waves. Thus their legs would be relatively static WRT the kayak, but their torso would be quasi-independent. The paddle would affect the yaw gyradius as well, depending on the length, weight, position held etc. On a big ship, you can ignore the "live" load somewhat, as it is not as dynamic as a paddler. That is, compared to the size and mass of the overall vessel, the live contents don't move around much. Paddlers move a lot and would complicate the analysis of boat motion and interaction with waves considerably. Here's a slightly counter intuitive fact, variations of which are used to trip up engineering students in exams: The roll radius of gyration is less in a fully loaded kayak than in an empty one, even though the angular inertia is greater. Mike (whose only experience in naval architecture is reading Marchaj and doing dynamic analyses of ice breaker hulls) *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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