[Paddlewise] Re: [Paddlewise] RE: [Paddlewise] Leaning in Surf vs Riversþ

All good Matt!!

Not the same without John W's counterpoints, but hey, at least we can leave 
lots of bandwidth for other topics, supppose. :-)

Sorry about some posts not always making it to the regular list. That Kirk, 
imagine, taking holidays and going off kayaking without asking us, leaving 
his list-Dad duties by the way side...;-)


> Last Saturday I sent the following to Paddlewise. It has not yet appeared 
> on the Paddlewise Digest (that I get). I'm sending it again to give it 
> another try for the Digest folks like myself to read if they want to. 
> Those of you not on the Digest may or may not have already had the chance 
> to look at how long this post is and delete it. If that is the case, you 
> can delete it again.
>
> RE: [Paddlewise] Leaning in Surf vs Rivers~
>
>
>
>
>
> From:
> MATT MARINER BROZE (marinerkayaks_at_msn.com)
>
> Sent:
> Sat 8/29/09 4:41 PM
>
> To:
> Paddlewise (paddlewise_at_paddlewise.net)
>
>
>
>
>
> On Aug 27, 2009, at 11:48 AM, Craig Jungers wrote:
>
>> This is what's confusing for me. The dynamics of a standing wave
>> seem far
>> simpler (to me) than ocean surf and I'm having a hard time picturing
>> all the
>> motions.
>
> Nick responded:
>>>>>........Typically we use the river/ocean bottom as our frame of 
>>>>>reference, but
> to the water both surf and river waves are traveling through the water.
>
> Instead of thinking of approaching a wave in a river, think of the
> wave approaching you and you will see you deal with exactly as you
> would in surf.<<<<<<
> Thanks Nick, you just saved me a long explanation. I'm glad I read all the 
> digests (as mixed up and out of order they remain) before jumping in here 
> again.
>
> Relative to your boat, a standing wave is identical to a moving wave. In 
> one the water is moving through the wave and in the other the wave is 
> moving through the water but given they are the same size and the same 
> kind of water density and viscosity about the only difference you might 
> detect is the wind in your face (and a fan could probably remove that clue 
> from the test in a double blind study.) I might add that they act the same 
> even when the waves are both breaking. So for controlling the kayak when 
> surfing either kind of wave it makes no difference at that point in time 
> when everything is the same. The beach break wave does change as it 
> approaches shore and a boat wake will change along with your position in 
> relation to the wave's source (or changing the speed of the source). 
> Standing waves can change too but the surges in a turbulent stream are 
> less predictable.
>
> I think on closer examination Duane will find it isn't usually the chine 
> in the fore body that is helping him turn on a wave using a tilt to the 
> outside of the turn. When surfing a sea kayak the bow is usually not even 
> in the water at the point you can easily turn it. It is the stern chine 
> and/or the shape of the stern which is most important. The combination of 
> the hull shape (and mostly the chines, tubes, keels, V-bottom, skegs, 
> fins, or rudder of the kayak--and their location) with the viscous fluid 
> and the side (skidding) motion of the kayak down the face of the wave 
> (powered by gravity) that what will determine how the boat handles. The 
> placement of the kayak on, or in, the wave and where it is located on the 
> wave (and the wave size) will also be factors. The "trim" of the 
> symmetrical object at the time will also be a factor. The tendency of any 
> long symmetrical object in waves is to rotate until it is sideways to the 
> wave direction (even if it is perfectly round in all
>  ways except for length). Even just floating free, the end of the 
> symmetrical object the wave contacts first gets moved more by the wave 
> that the other end. There may be more to it, but the combination of 
> gravity and the orbital motion of the water molecules in a wave (forward 
> at the crest and backwards in the trough) is enough to cause this.
>
> Once the object starts skidding on the water (surfing) a lot of variations 
> in the shape of the object (that effect how easily different parts 
> skid--fins, chines keels etc.) will have a big effect on what the long 
> object does. Since the tendency is to broach and since one has to fight a 
> tendency constantly the more you can make the kayak neutral going in the 
> direction you want it to go the more control of the kayak will shift to 
> the paddler and away from the tendencies and the environment. If your boat 
> broaches you wouldnt want to put a fin or rudder up near the bow (even 
> turned completely in the direction of sideways motion it is still adding 
> drag to the bow end that will increase the broaching). So think about what 
> you could do to a kayak's shape to make it more neutral when it is facing 
> the direction (to the wave motion) you want to have it move. Now you are 
> doing the kind of thinking I was doing when I was designing a sea kayak.
>
> A perfectly round hull will not be easier to turn if you lean it. A lean 
> helps partly because you are pushing the wider more curved part of the 
> hull into the water which raises the ends of the kayak more out of the 
> water. The ends of the kayak are also more rockered on the sides than at 
> the keels when in that tilted orientation. Leaning either way will help 
> when the kayaks waterline width is wider than twice its draft (is not 
> round). Even Olympic Flatwater kayaks are not round but are about 3 to 1 
> (WL width to draft). However, just because you can lift the ends equally 
> leaning to either direction that doesn't mean they will work the same (or 
> be equally effective) in use. They might be in a perfectly symmetrical 
> kayak that is sitting in one place but an asymmetrical kayak that is 
> moving one way or the other is usually what we are trying to deal with.
>
> To further complicate things, the paddler wants to accomplish some goals 
> and uses strokes with a paddle to do that. One of the main things needing 
> to be accomplished is to keep the kayak from capsizing while we are 
> tilting it. Most likely we also want to keep the kayak moving at speed 
> rather than putting on the brakes (although when you want to put on the 
> brakes and turn at the same time the inside lean and a constant brace for 
> capsize prevention are often employed). A forward stroke and a high brace 
> are easily combined. A single reverse stroke and a low brace are easily 
> combined. A braking high brace (or sculling brace) can work especially if 
> you have some momentum to play with but you wont be able to use any 
> forward stroke effectively enough at that time to maintain your momentum. 
> Therefore, if you want to keep going forward and turn your kayak quicker 
> you will lean it to the outside of the turn.
>
> With most kayaks there are several other advantages to leaning to the 
> outside of the turn as well. When water is flowing past the hull and you 
> make one side more curved than the other side (by leaning it) you create a 
> wing shape in the water (the "lift generated by this moving wing will be 
> to one side). Add to that, the fact that the stern of a forward moving 
> kayak is a lot freer to move sideways (than the bow) because there is less 
> water pressure at the stern. When moving forward, water is being pushed to 
> the side by the bow half of the kayak. It has momentum to the side (and 
> up) and is having to reverse direction again to fill in the hole the boat 
> left as its stern withdraws. Therefore, there is a lot more water pressure 
> over the area of bow (which is doing the pushing aside) than over the rest 
> of the kayak. So far what I'm saying all works even on well rounded 
> symmetrical hulls (as longer as they are more curved on the sides than at 
> the bottom). For example, take an old
>  fashioned rounded slalom type kayak. Anyone who has paddled such a kayak 
> knows how difficult it is to keep it going straight at first. What I wrote 
> above is the reason for the river kayaks tendency for the stern to skid 
> out to one side or the other. Complicate the shape more (as is the case 
> with most sea kayaks) and you can counteract or enhance these tendencies 
> depending on how you modify the shape. One way to get the kayak to go 
> straighter might be to add a fin, drop skeg or more keel to the "loose" 
> stern end to prevent it from going sideways so easily. Once you have done 
> that you will find that it is a whole lot easier to turn the kayak by 
> leaning it to the outside so that water sheds off the fin or keel easier 
> in the stern half (rather than to turn the fin into more of a hook 
> snagging the water by tilting the kayak to the inside of the turn). You 
> have to lean the kayak far more to the inside to get the fin or keel 
> enough out of the water not to snag than you have to l
> ean to the outside. Your brace will be even more important then and ev
> en it you use a high brace you will be constantly braking with it rather 
> than doing forward paddling.
>
> Now, if you are a budding kayak designer, think about how you might be 
> able to change a kayaks shape to enhance the performance in the desired 
> direction without hurting it too much in other respects. In boat design 
> everything is a compromise, but your job as a boat designer is to learn to 
> be good at negotiating with Mother Nature. You want to be a lawyer looking 
> for loopholes in the laws of physics you can squeeze your kayak through.
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