Subj : Re: Fastest path through a sharp bend? To : rec.sport.rowing From : carl Date : Tue Feb 09 2021 03:58 pm On 09/02/2021 13:59, lin...@gmail.com wrote: > On Tuesday, February 9, 2021 at 12:30:39 PM UTC, Andy McKenzie wrote: >> On Monday, 8 February 2021 at 10:20:39 UTC, lin...@gmail.com wrote: >>> What is the fastest path for a rowing boat through a sharp bend? A car or motorcycle going trough a bend maximises the radius of the bend by going from outside to inside of the bend back to the outside again. >> Assuming no current I can't really see that it would be different for a boat, the fastest corner is the 'racing line' which maximises the radius of the curve and avoids sharp rudder movement. The main difference to a car is, unless turning around a buoy, you aren't de-accelerating into the curve and accelerating out so the path should be more symmetrical. If you watch crews on windy courses like the Charles that's the line they take if they can. > > I think it's not so clear cut. If you are walking, the shortest line would be the fastest because you almost don't have to slow down into a tight bend. A boat does slow down in a tight bend because of sideway drift which creates drag and because of centrifugal forces. So the fastest line depends on this slowdown. I still suspect that you are correct but it's only a hunch. > Leeway drag is a significant cause of speed loss when steering into & around bends, because it is the only way in which a shell can resist sideways movement under the centripetal force generated by the changing direction, & then there's the energy absorbed in rotating the long shell with its high moment of rotational inertia. Proper control foils (e.g. our HyperSteer system) considerably reduce turning & cross-wind leeway losses, & enhance directional control at all times. On a river there will usually be local variations in flow velocity & direction due to influences on the flow from a little way upstream, but on bends there will also be an overturning (spiral) flow, with the surface waters moving towards the outside of the bend & carrying the boat outwards. This transverse element may continue for a short distance below the bend, generating noticeable steering issues, including forcing you over to the outer bank In principle, one should take the broadest arc around a bend when rowing upstream, going from the outside, crossing to close to the inner bank & then back to the outside, which imposes the slowest rate of rotation of the boat itself about its own vertical axis and the smallest amount of centripetal force, but that course passes twice through the swiftest flow. However, going into shallows on the inside of the bend (rivers tend to be deepest towards the outsides of bends) may incur additional drag. Unfortunately, upstream rowing puts the faster water under the blades that are closest to the mid-stream, making it hard to stay in the slower water, whereas rowing with the stream means having to fight to stay in the fastest flow. And when taking downstream bends you tend to get pushed to the outside and find yourself in the slow flow on leaving the bend. So coxing on river courses is far more of an art (& a science) than most rowers appreciate when blaming cox for their poor performances, & there are few hard & fast rules, as different rivers, & bends, may behave differently. I hope that's spread enough confusion? Cheers - Carl -- Carl Douglas Racing Shells - Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK Find: tinyurl.com/2tqujf Email: carl@carldouglasrowing.com Tel: +44(0)1932-570946 Fax: -563682 URLs: carldouglasrowing.com & now on Facebook @ CarlDouglasRacingShells --- This email has been checked for viruses by AVG. https://www.avg.com * Origin: SportNet Gateway Site (24:150/2) .