Ralph wrote; (SNIP) > >When you are crossing the river, you have two choices...attempt to >paddle straight across to minimize your time in traffic or go across at >a ferry angle that keeps you out there somewhat longer. The prudent >thing to do is to ferry angle since it means you will get to where you >want to go and not get pushed down range by the currents (or winds, >plenty of them here). What happens if you try to rush straight across >is that you will have to stop at points to let a large boat by, and >broadside to the current, you will go downrange of your destination. >Then you will have to paddle back against the full current's force and >expose yourself even more with your speed and manueverability greatly >reduced (the channel is effectively as broad as the river, i.e. near >shore is not "safe" from roaring motorized traffic). Has anyone done any experiments on the ideal angle? I mention this because tank and wind tunnel tests have shown that the greatest leeway occurs at an angle of thirty degrees to the flow. In other words, one could be heading upstream but the net effect would not only keep one out in the channel longer but would make a person work much harder to get to the destination. I wonder if there may not be better approaches. For instance, paddling up stream along shore where currents may be less or even going in the favourable direction and then sprinting across the heavy current. I do some upstream paddling of rivers an have used the eddy hopping and sprint across technique with apparent success. Of course, different conditions will require different strategies so I am not suggesting this method for every condition. Obviously this tactic may be not practical in New York harbour. The surf thing is a good example. Some times getting out of the surf as quickly as possible may be the best attack. I have not had good luck backing through dumping surf possibly due poor balance or something. The loss of stability on the crest really throws me for a loop so I prefer to try to ride it in. I have had good luck using a sea anchor to slow the boat in surf. Incidentally, The Walleye Angler Speciality catalogue (Web site http://www.basspro.com) has some neat things. On page they have some inexpensive sea anchors that look good. On page 66 they have a barometer for $25.99. This is a superb price for a tool that can keep you out of trouble. On page 85 there is an adjustable shade umbrella that looks like it can clamp on to the boat. $29.99. I will report on how well these things work except the umbrella that I think is neat but is not something I would ever use. I have no connection with Bass Pro financial or otherwise. Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft http://home.ican.net/~735769/ A lot would depend upon the wind angle as well. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
> Has anyone done any experiments on the ideal angle? I mention this because > tank and wind tunnel tests have shown that the greatest leeway occurs at an > angle of thirty degrees to the flow. In other words, one could be heading > upstream but the net effect would not only keep one out in the channel > longer but would make a person work much harder to get to the destination. > I wonder if there may not be better approaches. For instance, paddling up > stream along shore where currents may be less or even going in the > favourable direction and then sprinting across the heavy current. Actually, I experiment with the ferry angle all the time when crossing the half-mile wide Hudson. You need different angles for different speeds of current and wind. When crossing from the New Jersey to New York side I am at different building such as the Empire State Building when the current is real strong. I get a sense of my progress across by the seat of my pants. If you get the right angle, you actually almost fly across. I have been with people who follow my angles and exclaim at how fast they are moving as various vector forces act on the boat. But often you can't hit the ideal whiz-across angle because you have to slow for traffic to let it cross. When I am on my own I manage to literally fly across, as I am master of my own domain; I know how to judge the speed of traffic and know my sprint speed for getting across ahead of it rather than be forced to wait for its passage across my path. But with groups I need to paddle with the LCD paddler pace, the least common denominator. I don't know how fast they can sprint and I don't want us stretched out like shooting gallery ducks. Most of the time I can convince people to paddle across in a chorus line. It looks neat and becomes kind of a game to keep the line straight. My objective is not to have the group blown down current from our destination as the slower people are also the weakest paddlers and not likely to do well against the full head on force of the current if they wind up downcurrent of the place we are going. Angles? I aim at 20 degrees generally. But, as I said, I vary the angle according to what is happening and to keep the group together and in a good position to make it to where we are headed. ralph -- ----------------------------------------------------------------------- Ralph Diaz . . . Folding Kayaker newsletter PO Box 0754, New York, NY 10024 Tel: 212-724-5069; E-mail: rdiaz_at_ix.netcom.com "Where's your sea kayak?"----"It's in the bag." ----------------------------------------------------------------------- *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
John Winters wrote: >Has anyone done any experiments on the ideal angle? I mention this because >tank and wind tunnel tests have shown that the greatest leeway occurs at an >angle of thirty degrees to the flow. In other words, one could be heading >upstream but the net effect would not only keep one out in the channel >longer but would make a person work much harder to get to the destination. >I wonder if there may not be better approaches. For instance, paddling up >stream along shore where currents may be less or even going in the >favourable direction and then sprinting across the heavy current. Gronseth pointed out (in his basic 5 day kayaking course) that the cosine of 60 degrees is 0.5 (adjacent angle divided by the hypotenuse), thus if you have to ferry at an angle 60 degrees, you have to paddle twice the distance.... which takes twice the time. Angles greater than 60 degrees, the rate of change in ferry distance increases exponentially. The Cos of 30 degrees is 0.86, therefore if you ferried at a 30 degree angle, your increase in distance would only be 14% greater. In summary, if you have to paddle at a ferry angle greater than 60 degrees, the effort and time spent might not be worth it. Robert *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Somehow the additional info did not get in my message, namely that: John Winters also wrote: > For instance, paddling up >>stream along shore where currents may be less or even going in the >>favourable direction and then sprinting across the heavy current. It may indeed be more favorable to eddyhop going in the opposite direction to the main flow out away from shore. Keeping in mind the cosine law adds a bit more information to deciphering out the varibles and making an appropriate decision. Robert *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Regarding ferry angles, John Winters wrote: > > >Has anyone done any experiments on the ideal angle? ...SNIP... to which Robert C. Cline responded: > ...SNIP.. > In summary, if you have to paddle at a ferry angle greater than 60 degrees, > the effort and time spent might not be worth it. According to my calculations, this is pretty close. For a current of uniform strength, the break even point is about 57 degrees, which occurs when the ratio of paddling speed to current speed is approximately 1.19 . In other words, if you can paddle more than 19 percent faster than the current, your ferry angle will be less than 57 degrees, and it will take less time to ferry across than to paddle at a straight-across heading (with zero ferry angle, followed by a paddle up current). On the other hand, if your paddling speed is less than 19 percent faster than the current, your ferry angle would have to exceed 57 percent, in which case it will take you less time if you paddle a straight-across heading (zero angle), even though you have to paddle up current once you reach the other side. Now for the math! Using some fairly straightforward trigonometry, it can be shown (if I haven't made an "oops") that the ratio of the straight-angle time (including the upriver paddle) to the ferry-angle time, st/ft, equals (1+c/p)cos(a), where "c" is the speed of the current, "p" is the paddling speed, and "a" is the ferry angle (in degrees) which itself is a function of c/p. The necessary ferry angle "a" equals the inverse sine of c/p. In other words, the time ratio st/ft is a function only of c/p. This ratio equals one when c/p is approximately equal to .83867, which corresponds to a ferry angle of 57 degrees. If the ratio c/p exceeds .83867 (i.e., if p/c is less than 1.1924), then st/ft is less than one and ferrying will actually take more time than paddling at a straight-across heading, even though you have to paddle up current. (I have checked this against a few simulations, and this seems to work, but as always someone should check the math...) So there you have it. Next time you have to cross a current, ask yourself if you can paddle more than 19 percent faster than the current. If so, then you MIGHT save time by ferrying. I say that you might save time, because the above analysis assumes a current of constant strength. But I have never seen such a current. It is typically slower near shore, even in the absence of eddies. And with eddies it is, of course, a whole new ballgame. So actually, it is quite a bit more complicated than in the simple model above (it always is). Add your own fudge factor to the 19 percent rule. But perhaps the "rule" provides a crude staring point... Dan Hagen Belingham, Washington *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Dan , Ralph, and Robert commented on ferry angles; In my post I was speaking of the acute angle made by the course and the current direction. I suspect that Dan, Robert, and Ralph are talking about the acute angle between the course made good and the course normal (90 degrees) to the current. If so, the 60 degrees corresponds to the 30 degrees I was talking about (neat ehhh?) Not arguing over the comments but want to make sure I haven't confused anyone by using a different angle and talking about the increased resistance rather than the increased distance. I don't recall if Dan included the effect of the apparent current speed in his calculations. As he said it can get complicated. Hydrodynamic resistance can increase roughly by the fourth power of velocity and that may complicate the calculations a bit. In other words, the decision as to whether to ferry or not may include more than just the extra distance travelled. Any thoughts or experience with this on this? Paddling upstream in reduced current may take less effort than paddling at an angle to the maximum current. Good old Marchaj (Sailing Theory and Practice) has a chart relating velocity to depth and river slope that is interesting While speaking of currents some might be interested in the currents I experienced in the McLelan Strait in Northern Labrador. The current is strong so we waited till there was an outgoing (west to east) tide. In the center of the channel the tide was running west to east but along the shore the tide was still running east to west. If you got caught in one of the whirlpools you could find yourself outside the shear zone and paddling your butt off while the other boat coasted past at high speed. The 20 - 30 foot tides in Ungava Bay caused lots of current problems and we would usually sprint across and hop the eddies upstream. Mind, the current was often much faster than we could paddle in the center of the channels. Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft 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.gasp-seakayak.net/paddlewise/ ***************************************************************************
John Winters wrote: > Dan , Ralph, and Robert commented on ferry angles; > > In my post I was speaking of the acute angle made by the course and the > current direction. I suspect that Dan, Robert, and Ralph are talking about > the acute angle between the course made good and the course normal (90 > degrees) to the current. If so, the 60 degrees corresponds to the 30 > degrees I was talking about (neat ehhh?) > > Not arguing over the comments but want to make sure I haven't confused > anyone by using a different angle and talking about the increased > resistance rather than the increased distance. > > I don't recall if Dan included the effect of the apparent current speed in > his calculations. As he said it can get complicated. Hydrodynamic > resistance can increase roughly by the fourth power of velocity and that > may complicate the calculations a bit. In other words, the decision as to > whether to ferry or not may include more than just the extra distance > travelled. > > Any thoughts or experience with this on this? > > Paddling upstream in reduced current may take less effort than paddling at > an angle to the maximum current. Good old Marchaj (Sailing Theory and > Practice) has a chart relating velocity to depth and river slope that is > interesting > > While speaking of currents some might be interested in the currents I > experienced in the McLelan Strait in Northern Labrador. The current is > strong so we waited till there was an outgoing (west to east) tide. In the > center of the channel the tide was running west to east but along the shore > the tide was still running east to west. If you got caught in one of the > whirlpools you could find yourself outside the shear zone and paddling your > butt off while the other boat coasted past at high speed. The 20 - 30 foot > tides in Ungava Bay caused lots of current problems and we would usually > sprint across and hop the eddies upstream. Mind, the current was often > much faster than we could paddle in the center of the channels. > > Cheers, > John Winters > Redwing Designs > Specialists in Human Powered Watercraft > http://home.ican.net/~735769/ > Gee... I forgot my protractor I guess I'll have to go back to the put in and keep to paddling on the local pond. Robert Somerville Toronto PS Sewer surfers should try Mimico Creek in flood, Toxicity and odors are higher than the water *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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