G'Day, Can anyone tell me if all (sea) waves travel at roughly the same hoizontal speed (relative to the current of course). I've been trying to observe if this is the case for some time and am coming to the conclusion that they do but am not sure if they speed up when approaching shore? All the best, PeterO *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Peter Osman wrote: > Can anyone tell me if all (sea) waves travel at roughly the same hoizontal > speed (relative to the current of course). I've been trying to observe if > this is the case for some time and am coming to the conclusion that they do > but am not sure if they speed up when approaching shore? [The following is based on Bascom's "Waves and Beaches," 1980 edition, pages 32-34 and 69-73.] The answer to your question depends on whether you are dealing with "deep water waves," or "shallow water waves." For waves in "deep water" -- water so deep the waves do not "feel" the bottom (depth is greater than half the wavelength), the translational velocity is proportional to the square root of the length, and directly proportional to the period. This means that swell in deep water running with a 12-second gap between crests will travel twice as fast as swell with a 6-second period, for "ideal" waves. Real waves will be close to this. When these same waves approach shore, however (the depth is less than half the wavelength), where we are more likely to be paddling, they become "shallow water waves," whose translational velocity is essentially **independent** of period (and hence wavelength). In "shallow water," their speed is proportional to the square root of the depth of the water, and does not depend (much) on their period or wavelength. This means that the 14-second swell and the 7-second swell will approach the surf zone with essentially the same speed. NOTE that these period values will change some as the waves steepen up as they reach shallow water and begin to "peak up" preparatory to breaking in the surf zone. Some wave velocities, as a function of period: 6 seconds (21 miles/hr); 12 seconds (42 miles/hr); and [the longest period swell ever recorded] 22.5 seconds (78 miles/hr!!). All these are for "deep water." But, even the 6-second swell has to be in at least 92 feet of water to be a "deep water wave." The 12-second swell needs 369 feet of depth! My apologies if this is more than you wanted to know. <g> -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Dave: There is an adjective missing here... the translational velocity is directly, or indirecdtly proportional to the sq.rt. of the length? Robert > From: Dave Kruger <dkruger_at_pacifier.com> > Date: Fri, 07 Apr 2000 23:51:23 -0700 > To: PaddleWise <PaddleWise_at_lists.intelenet.net> > Subject: Re: [Paddlewise] Wave Speed - (totally trivial question!) > > For waves in "deep water" -- water so deep the waves do not "feel" the bottom > (depth is greater than half the wavelength), the translational velocity is > proportional to the square root of the length, and directly proportional to > the > period. *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
"Robert C. Cline" wrote: > There is an adjective missing here... the translational velocity is > directly, or indirecdtly proportional to the sq.rt. of the length? Sharp eyes, Robert -- thanks for spotting the omission -- should be **directly** proportional to the sq. rt. of the length. I inserted the additional "directly" in your quote below -- that's what I should have written. > > From: Dave Kruger <dkruger_at_pacifier.com> > > Date: Fri, 07 Apr 2000 23:51:23 -0700 > > To: PaddleWise <PaddleWise_at_lists.intelenet.net> > > Subject: Re: [Paddlewise] Wave Speed - (totally trivial question!) > > > > For waves in "deep water" -- water so deep the waves do not "feel" the > > bottom (depth is greater than half the wavelength), the translational > > velocity is [directly] proportional to the square root of the length, > > and directly proportional to the period. -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
They don't travel. It's an up and down rotating motion. A molecule of water is not displaced horizontally to any great extent. Richard Smith ----- Original Message ----- From: Peter Osman <rebyl_kayak_at_hotmail.com> To: <PaddleWise_at_lists.intelenet.net> Sent: Saturday, April 08, 2000 12:32 AM Subject: [Paddlewise] Wave Speed - (totally trivial question!) > G'Day, > > Can anyone tell me if all (sea) waves travel at roughly the same hoizontal > speed (relative to the current of course). I've been trying to observe if > this is the case for some time and am coming to the conclusion that they do > but am not sure if they speed up when approaching shore? > > All the best, PeterO > > *************************************************************************** > PaddleWise Paddling Mailing List - All postings copyright the author and not > to be reproduced outside PaddleWise without author's permission > Submissions: paddlewise_at_lists.intelenet.net > Subscriptions: paddlewise-request_at_lists.intelenet.net > Website: http://www.paddlewise.net/ > *************************************************************************** > *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Richard wrote; > They don't travel. It's an up and down rotating motion. A molecule of > water is not displaced horizontally to any great extent. Waves do experience translational motion or "travel" as it were. The water. however, moves in what we call general motion (i.e. translational and rotational) even though the translational aspect may not amount to much. The rather neat thing about waves it that they do travel for if they didn't, I would not hear my wife announcing that coffee and pie is ready and I have to stop mucking about on the Internet. Cheers, John Winters Redwing Designs Web site address, http://home.ican.net/~735769 *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
This is EXACTLY what I was trying to say!!! Richard G. Smith ----- Original Message ----- From: 735769 <735769_at_ican.net> To: <PaddleWise_at_lists.intelenet.net> Sent: Sunday, April 09, 2000 7:01 PM Subject: Re: [Paddlewise] Wave Speed - (totally trivial question!) > Richard wrote; > > > They don't travel. It's an up and down rotating motion. A molecule of > > water is not displaced horizontally to any great extent. > > Waves do experience translational motion or "travel" as it were. The water. > however, moves in what we call general motion (i.e. translational and > rotational) even though the translational aspect may not amount to much. > > The rather neat thing about waves it that they do travel for if they didn't, > I would not hear my wife announcing that coffee and pie is ready and I have > to stop mucking about on the Internet. > > Cheers, > > John Winters > Redwing Designs > Web site address, http://home.ican.net/~735769 > > > > > > *************************************************************************** > PaddleWise Paddling Mailing List - All postings copyright the author and not > to be reproduced outside PaddleWise without author's permission > Submissions: paddlewise_at_lists.intelenet.net > Subscriptions: paddlewise-request_at_lists.intelenet.net > Website: http://www.paddlewise.net/ > *************************************************************************** > *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
From: Peter Osman > > Can anyone tell me if all (sea) waves travel at roughly the same horizontal > speed (relative to the current of course). I've been trying to observe if > this is the case for some time and am coming to the conclusion that they do > but am not sure if they speed up when approaching shore? > I knew that I had this written down on a card somewhere, and have finally found it (reference unknown): "For waves in water deeper than half the wavelength, Period (secs) Wavelength (metres) Speed (knots) 4 25 12 5 39 15 6 56 18 7 76 21 8 100 24 9 126 27 10 156 30 11 189 33 12 225 36 So Wavelength equals 1.56 times the square of the Period, and Speed in knots is three times the Period in seconds. When the depth is less than half the wavelength, the length decreases, the height increases and the period remains the same (i.e. the wave goes slower). At a depth of one tenth the deep water wavelength the height increase is marked, the wave is unstable and ready to break." So you can sit out at sea bobbing up and down and time the period (easy enough). Working out the wavelength might be more than you want to attempt, but multiplying the period by three to get the speed is not too difficult. Then you can turn towards the shore and see if you can paddle at wave speed! Allan Singleton Hamilton NZ And I hope the table formatting survives. *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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