KayakPro Red JET

[subaruguru]

My yearning to paddle faster on 3x/wk flatwater workouts on the Mystic Lake resulted in finally getting a Chinese KP Jet a couple of weeks ago. This quasi-racer dumped me twice in two minutes on the maiden tryout, but I managed to then go 3 mi at 2 knots before dumping another 5 times in 10 minutes once I hit a 10 know wind and just a ripple of current. As this 'yak is a baffleless design, I had to swim/tow it to the Medford Boat Club ramp to put out. Unfortunately their premises were fully padlocked for the season, so I was a cold prisoner for about an hour, wondering whether to break a window to find a phone or attempt to throw me and the Jet over a 6 ft fence and then walk miles around the lake to retrieve my Subie!

I finally figured out that I could portage through the lower end of the dam and climb back up to the Tufts put-in, wherein I paddled back to the Sandy Beach put-in with only one additional capsize.

My buds at Charles River gave suggestions re float bags and West Systems epoxy to repair the broken seat panel (oy), so my recent two excursions have been easier. I mounted my GPS and yesterday managed 5mi in 2 hrs. I seem to barely keep afloat the first 1/2 hr, averaging 2 mph for the first hour, eventually crising around 4mph, building to spurts in the 5 mph range. Torso rotation is just a fantasy as I'm glued to the centerline for balance, so my arms eventually grow tired. (Lean turns happen with the slightest provocation, which may eventually be seen as a positive attribute.

By contrast I now completely understand and appreciate my Looksha IV's rock-hard secondary!)

The Jet, like the Necky, turns upwind, hence the interesting combined skeg/rudder design I'll someday dare budge with my paralyzed feet.

I've attempted to adjust seat position, adding pads for seat and knee bracing (supposed to be unnecessary!), and realize that I prefer to sit far enough back to keep my knees fairly low AND my back in contact with the rear cockpit combing for stability (there's no backband).

On the positive side this Jet glides very quietly with almost no effort, easily jumping to 5mph before my stability is threatened.

By contrast it's a lot of work to get the Looksha IV to 5mph, with 5.5mph as my max. I'm hoping the Jet will cruise in the 6-7mph range someday.

Weighing under 30lbs with float bags is a real plus, allowing one-arm carrying.

The cockpit is a bit forward, so the narrow deck seems a bit short, even at 17'3".

The bow-view appears as a very slightly ballooned pure conical "missile" coming to a sharp point. More Jetson-like than Flash Gordon.

KP describes the JET as haing a "6"/10 for stability, in contrast to their racers at "1" and all intermediate quickies at 3-5. Phew!

Anybody else have one of these...or the Simon River equivalent? Could you share tips in determining seating geometry and learning curve?

I managed to survive 5-6ft seas at CRCK's Ocean Skills clinic a couple weeks ago in the Looksha, finally dumping only once when learning about smashing through an invisible-to-me eddyline.

But this Jet has me feeling like a complete novice again...even in mirror-flat conditions.

If any of you are game to try this fast semi-racer I'll continue to paddle on the Mystic Lake until early December on selected afternoons, and would really welcome some company out there.

Oh...I bought the special zippered skirt for it, so if anyone (Peter B?) wants to try to roll it....

Will there be any more Level 2/3 trips this fall? Gotta try out that new Kokatat SuperNova drysuit.

Cheers.

[Christa]

Hi Ernie,

I have a Jet. Here is a picture of Elizabeth McBride sitting in one so you can see her leg and back position. http://pg.photos.yahoo.com/ph/christarotol...3a3.jpg&.src=ph

You want to sit up straight with your knees bent and fairly close together. Your back should not be touching anything. Backbands prevent torso rotation which is why racing boats don't have them. In Ben Lawry's Forward Stroke class, he makes the students take their backbands out of their sea kayaks. The knee padding will hinder your leg movement. Don't try to make the boat fit like a sea kayak.

Sit up straight and get used to your core muscles holding you erect. If your legs are straight then you can't be using them effectively. Try this exercise from Ben's Forward Stroke class. Sit on the ground with your legs in paddling position. Ask a partner to stand in front of you with their foot against yours. Bend your leg at different angles and push against your partner's foot. Try it with a straight leg. Then have them give you feedback on what leg position gives the most push.

Adjust the foot bar so that your feet fit through it and it's fairly snug. You should only be able to get your toes through it. Originally I had mine so that my foot slid all the way through, but Ben showed me where it should be on my feet and that helped.

I don't think you can roll it just with a zippered spray-deck - unless those knee braces you added are really quite large. There's nothing for get your knees under so without a thigh belt it would be pretty tough.

Christa

[cathyfoley]

Ernie:

I'm planning on paddling Sunday afternoon Oct 30 up this way somewhere (Rye, Portsmouth area or great bay if ocean is too choppy). You

are welcome to join me. Cathy

[subaruguru]

The sun sparkled briefly this afternoon, so I couldn't resist another Jet-trip. Still took a good 1/4 hour of slow paddling before I got up to 4+ mph. I tried to keep my back off the rear combing, while reducing knee-contact bracing. Knees-up-parallel seems far a far off goal. But I managed a tight circumference of the Mystic (3.7 mi) in an hour, so I'm getting used to it. Glasslike conditions helped. Hitting a submerged concrete step crunched the bow and pissed me off sufficiently to cause my only capsize.

Thanks for the tips, Christa. I'll try sitting a bit more forward. Will that result in a more squirrely bow...especially in wind? I have a sense that sitting farther back results in more stability, but that may be only a temporary result due to my back bracing against the coaming. The Jet does seem more responsive when sitting a bit forward, but indeed more tender, too.

I DO like the 3/16" (4.5mm) hogh density soft foam pad I made for the hard carbon seat. If you or Gray want to try one I'll make a second. Velcros on/off easily....

Interestingly I notice I'm better able to brace against a moderate lean with an opposite-side strong (desperate?) forward stroke than a same-side low brace...which seems to result in overkill to the other side, given the low stability. Stern rudders are easy...bow rudders much trickier.

OTOH whereas I can't scull much with the Looksha I notice that light sculling is pretty effective for counteracting the Jet's soft hulls.

There just isn't much righting moment here, so it's interesting to see that the stroke formulae differ from the Looksha. Or maybe I'm just not stable enough yet.

Gray at KayakPro confirmed that body contact is to be ONLY at the seat and foot-panel, so as to allow free torso rotation. Maybe in 2006.

Anybody want to show me how it's done?

[Christa]

You shouldn't need to do turns like bow and stern rudders -use your tiller bar to turn the boat. The faster the boat is going, the tighter the turns will be. If you find it is not turning fast enough, then you can adjust the pins on the rudder. Move them in closer to the center and then when you get used to the Jet, you can move them back out.

I spent a few months in flat water before I ventured out in chop. If you do go out in chop, make sure you have the float bags in bow and stern and that whoever is paddling with you is able to rescue a rec boat.

I have to start coming to Boston fairly regularly for work and I'd be up for a paddle. I'll let you know once my trips start.

Ben adjusted my boat so I never had any issues with being too far forward or back and that affecting the bow. Maybe you should ask one of the racer types like Alex L, Binks, or Ken Cooper for some help.

Christa

[Guest guest]

Ernie,

If you got the boat at CRCK you must know about the racing club they support. http://www.ski-paddle.com/racing.html

At this point we are just paddling on Sunday mornings at 10 am up until it freezes over. Most or all of these padders are in ICF racing kayaks and Pro boat C-1's and C-2's....this is the group to get involved with your new boat. There are 3 or 4 paddlers in Jets like yours and they run them as they were manufactured without any of the pads you're adding...the boat is meant to be ''balanced'' and paddled forward with a wing, turning is via slight hip tilt and rudder.

If your not interested in racing and developing a modern forward stroke with a wing, I'd say go ahead and pad the boat out like a sea kayak and have fun experimenting with it. If you really want to be stable, take out the seat and mounting plate and sit on a foam tractor seat right on the bottom.

look at this video...this is how you should paddle that boat.

http://www.kayaksport.net/technique/movies/k1_500_final.wmv

why do you call yourself..subaru guru ?

[subaruguru]

Hi.

Thanks much for the info and video!

Mark @ CRCK might have mentioned the Sunday racers' group in the past, but I may have forgotten. I've delayed introducing an Epic midwing into JET use as I'm still bracing with the Ikelos a lot.

The padding I mentioned was just a thin 3/16 seat pad and 1/2" foam pads on the rear coaming and knee-sides; the back pad I've removed, as I've become used to very light occasional contact there, but the side-pads act as bump-guards for my outer knees. So except for seat comfort I'm running farely "naked", as you say.

I DO find myself low-bracing and what I guess is a combination forward-stroke/highish-brace when hitting the soft secondary.

Is an Epic wing ok for that, or should I forestall purchasing one until I've mastered the JET with the Ikelos?

Thanks again.

Ernie

PS The SubaruGuru is a moniker given to me years ago as Boston's independent used Subie procurer/servicer. My daughters overheard customers' use of it and presented biz cards as such 1/2 dozen years ago, so it stuck. If you want to learn my perspective on AWD non-SUVs see my post on craigslist.org

[subaruguru]

Sorry I mssed ya, Cathy, but the inch of snow kept me away!

[subaruguru]

Christa,

Thanks for your replies, and the demo back in June.

As I mentioned, the only padding I'm using is 1/2" on the coaming sides for knee-bumping (now that I'm trying to avoid knee-bracing) and that nifty thin-but-comfy seat pad I made.

I rimmed the inner coaming with sturdy 1" velcro band so that popping on thin padding strips (like for a shoulder-portaging area) are easy to try. Makes the coaming less slippery when carrying.

I also added a 3/4" rubber tube (heater hose) over the naked aluminum tiller, capping with a perfect-fitting auto cigaret-lighter/12v dummy plug. Greatly improves tiller feel with neoprene boots. Let me know if you want any of these ergo bits.

Cheers.

Ern

[binks]

>Is an Epic wing ok for that, or should I forestall

>purchasing one until I've mastered the JET with the Ikelos?

Ernie, you may find paddling the Jet easier with a wing. It will have a firmer 'bracing' feel.

To give an example, surfskiers try not to brace when the ski gets tippy - they paddle harder because (a) primarily, a brace slows the boat and ( perhaps more relevant for you, increasing forward speed changes the vector of inertia closer to the longtitudinal axis of the ski; i.e. away from the perpendicular axis needed for a swim.

[Nick Schade]

>increasing forward speed changes the vector of inertia

>closer to the longtitudinal axis of the ski; i.e. away from

>the perpendicular axis needed for a swim.

Can you explain this please. I have never heard of a "vector of inertia" and can't imagine how it could move from one axis to another.

[bob budd]

Ah yes, the dormant brain cells. Angular momentum it is.

Consider the paddler sitting upright with a longitudinal vertical plane slicing the boat and paddler in half. As you execute a stroke more of your weight is on one side of the vertical plane than the other, thus the tendency to tip. If you do nothing as you descend toward the water you tip over like the tricycle rider in Rowan and Martin's Laugh-In. I recall one of my early learning trips with the AMC...

When you brace you push off the water, when you hip-snap you shift the boat underneath you; both are methods to impede/arrest your descent. Both of these take energy otherwise applied to moving forward motion and impede the establishment or maintenance of rhythm.

Now consider the paddler in motion. You stroke on one and then the other side, leaning across the other side of the plane and reversing your descent as you initiate each stroke. Gravity has its hand on you and is a constant acceleration, the extent of your descent as the square of the time you spend on a given side.

When you paddle harder you increase your cadence, apply more force to the water, or both. When you increase your cadence you spend less time on one side of the plane decreasing the distance you descend. When you apply more force to the water part of that force works against gravity ("bracing feel"), further impeding your descent.

Inertia is the tendency for an object to stay in place or continue on its current direction of motion. I can't explain how inertia of the forward motion of the boat would contribute to remaining upright, they seem uncorrelated to me.

[djlewis]

I thought the stability of a bicycle is due to *angular momentum*, that is, the gyroscope effect of the spinning wheels.

So maybe Andrew is saying that paddling faster generates more angular momentum, as your arms and paddle move in a roughly circular path parallel to the direction of travel, like bicycle wheels. Somehow, that doesn't seem like enough to make a big difference -- are arms+paddle massive enough and/or move fast enough to make much difference?

So, the question (in my mind anyway) does linear momentum (which I think is what the vector of intertia describes) add any lateral stability, the way angular momentum does? I tend to doubt it, but I'm no physicist.

In fact, we should all probably wait for the real physicists in the neighborhood to chime in before making fools of ourselves -- Jeff, John?

--David.

[Guest guest]

Wow, you really have to be careful here on this web site !!

Hey web master, please remove my ability to post here so I won't be tempted again.

Ernie, again, come next spring to the CRCK group, we paddle the boats, we don't argue about why they're tippy. In fact the saying is "There are no tippy boats, just tippy paddlers in them."

[Nick Schade]

>The path of the paddler's head and top heavy upper body when

>falling over to the side, (while not moving), is

>perpendicular to the long axis of the boat. Once the paddler

>is moving forward, the path of the head and upper body while

>falling over, now also has a forward component to it.

How does this forward component effect the paddler's tendency to capsize? Does it somehow effect the acceleration of gravity? I.e. if someone is less likely to tip the side when they are moving forward, it can only be because that forward motion creates a force perpendicular to the motion. How does this work?

>

>Dr. Binks is referring to this part of Newton's First and in

>this case the "vector (direction of force) of inertia

>(tendency to stay in motion) is moved closer to the

>longitudinal axis" and this is how ( direction of momentum )

>changes via forward movement from where it was while sitting

>still.

How does forward momentum effect side-to-side inertia? I can find no references to inertia being a vector. Inertia is related to mass and it can have a center or moment, but is not changed by velocity and it does not have a direction. Momentum is related to inertia but has the added factor of velocity and with that it has a direction and is a vector. But the fact that a paddler may have forward momentum does not mean that his inertia is changed by the motion.

The simple fact of forward motion is not on its own enough to make you stable. All forward momentum provides is the tendency to keep moving forward. It does not effect your tendency to move towards the side.

Try balancing a yard stick on your finger. Do it while standing still and again while walking forward. If there is a "vector of inertia" it will be easier to balance the stick while walking forward. I'm sure you will find that walking does not make it any easier.

I am not saying paddling faster doesn't help you stay upright, just that the "vector of inertia" has nothing to do with it.

[Guest guest]

It's the "balance" of the paddler, not stability of the boat that changes when moving forward. The boat is what it is. There are no tippy boats, just tippy paddlers.

It's like running; a state of controlled imbalance, falling forward onto one foot placement and the next. You can't just sit comfortably in a K-1 as you do in a sea kayak. In a K-1, you fall onto one paddle stroke then the next. With skill development, you fall less and less and learn to control this with each paddle stroke, to get a steady glide phase.

I'm talking about a K-1 here. That was the original question of Guru's.

It's not a physics problem as much as it must be a physiological problem of the human balance mechanisms.

If it was a physics problem, the boat never would "become" more stable, yet the paddler adapts his balance mechanisms to deal with this problem and becomes comfortable.

[bob budd]

For me Ken's posting demonstrates that the paddler is best served by compensating weight on one side of the vertical plane with weight on the other side (weight centered). This seems like what Ernie was originally looking for.

I would agree with your contention that simple forward motion has nothing to do with your ability to remain upright. If you want to learn about vector of inertia you can Google (is it capitalized as a verb?) the phrase in quotes and you'll get links like

http://www.csiberkeley.com/Tech_Info/12.pdf

[bob budd]

Angular momentum goes as the product of the velocity of a point on the circumference and the radius of the wheel. When the scooter is travelling at the same velocity as the bicycle its smaller wheels are rotating faster so angular momentum would be comparable. Ken, keep those cards and letter coming.

[Suz]

You are so right Ken! I think that as the days get shorter and we don't get on the water as often as we would like, paddlers get cranky. Just wait until February and we will all be stir crazy!

Suz

[subaruguru]

Hi Folks!

Managed three more trips around the Mystic Lakes this week, capsizing only once, saving myself with strong low braces maybe 1/2 dozen times. Getting there....

While passing the Tufts crew where slight waves were piling (fetched as a passive verb??) I hollered to their coach Ken that I was having trouble with stability in this new JET. This man of few words only yelled that "maybe you should go faster". Ha!

I'm trying to sit more perfectly upright so as to not touch the rear coaming, as well moving knees gingerly closer together, thus reaching for a more-forward purchase, but this results in bonking my right knee once in awhile in my stroke flattens if I lose stability.

My current Sat AM pre-caffeinated synthesis suggests that if I can figure out how to adjust the foot-rest forward a bit I can both lower my center of gravity a bit and obtain a more relaxed geometry that still keeps me off the rear coaming.

As part of my Subaruguruness I teach AWD handling skills to all prospective clients. As they learn to stay on throttle THROUGH twisties, thereby engaging a REAR-centered forward vector (rear wheel drive part), they quickly experience the more solid "on-track" stability inherent in manipulating the angular moment around its polar moment of inertia. This most-satisfying "throttle-steering" is often mentioned by REAR wheel drive Porsche/BMW/etc fans as the primary reason for cornerning preference over FRONT wheel drive...but it only works when carefully applied on a dry surface.

AWD allows mere mortals to VERY confidently control forward acceleration through turns even on wet surfaces.

So I try to correlate this behaviour with my "center-wheel" drive in the Jet, but I get fuzzy with the long-forgotten physics.

Since the rear part of a sweep stroke seems to have little effect upon steering the Jet (compared to leaning), nor achieving stability.

If anything, it would seem that any angular vector applied at the stern would cause MORE instability if applied on the tilted side, as gravity would have a cleaner (vertical) path if the JET is sliding away from the center-line.

I think that applying a strong forward stroke tends to thwart a capsize in part because of the counterbalancing upward force applied as the stroke becomes a "mini-scull" as pulled to my side. (I'm told that a wing paddle automatically accomplishes this by rising upward as a stroke matures). But this "front-center-wheel drive" vector group can only halt gravity temporarily.

So the question of why stability is possibily enhanced BY SPEED ALONE

remains. I think I understand that a faster cadence can seem to be less prone to capsize by having a higher frequency of counterbalancing angular vectors so that there simply isn't quite enough time for gravity to work, but my aerobic endurance isn't there yet.

Can anyone out there finetune this analysis?

Now for that java.

[jeffcasey]

Sorry to chime in so late - as soon as I see our hard-core colleagues chiming in about the finer points of high performance racing kayaks, my eyes glaze over - similar to how many of you feel when the physicists start arguing about angels dancing on pinheads, etc. I'm not a racer, nor do I aspire so...I'd be happy if I could get out for more long aesthetic tours in moderate weather. In short, I haven't been following this thread much.

Without commenting on long skinny boats, I can confirm David's intuition -- linear momentum won't prevent you from tipping, and doesn't add any lateral stability. This is a purely textbook answer, and doesn't take into account any of the minor effects that a good paddler almost certainly learns to account for intuitively. We all know that minor body english can tweak the boat's position (lean, nudging the bow angle, etc etc). Any effects that interplay with the stream of water will certainly be accentuated at higher speed. So while a textbook answer that linear momentum and angular momentum are decoupled may be correct, it could easily be in conflict with the gut feel of an experienced paddler -- and that experienced paddler would be right.

Also, whatever angular momentum is generated by the whirling arms and paddle is probably negligible -- the speed isn't great, and the mass isn't distributed well to make for a large moment of intertia. Also, there isn't really a mechanism to couple whatever angular momentum there is to self-righting of the kayak, like there is in the steerable front wheel of a bicycle.

I ***GOTTA*** stop working so hard and get out and paddle. Who's gonna tempt me to play hookey?

[jeffcasey]

"who's gonna tempt me to play hookey?"

THAT didn't take long. This is why NSPN is such a great orgy of anarchy...there are always bohemians around to keep one away from work and family. I sleep well knowing that so many of us have our priorities knickered up spicily.

Yee-haw!

[donperry]

Water molecules accelerating against the advancing hull stabilize the watercraft. They also limit the hull speed. Long & narrow hulls with a minimal wetted area move fewer molecules to the side than short & wide hulls do at the same speed. The molecules don’t have to move to the side as quickly. Even so, at some higher speed, the power required to displace the water is more than you have on board, limiting your speed in the water. With enough speed, the water being displaced will potentially force the hull upward as it does when a wave is pushing things along.

It’s similar to sailing a board in very light wind. There is little force acting on the sail to balance the sailor. The water is exerting only a buoyant force and the hull is a difficult platform. Then the wind picks up and things get moving. Now the board moves forward and accelerating water molecules provide resistance and stability. At some speed, the (downward) force required to displace the water becomes greater than the weight of loaded board and the hull begins to plane. A powered up sail adds an upward component and the entire rig can become airborne.

When a kayak is dead in the water the only resistance to rotation about the long axis is primary and secondary buoyancy in the hull profile. Rocking the hull from side to side has no tendency to turn the boat or move it fore or aft. When there is forward speed there is equal resistance on each side that changes as the hull is tipped. Leaning forward and to starboard for a port turn slightly changes the equilibrium, increasing force on the starboard bow, causing CCW rotation about a central vertical axis. This also develops a reactive rotational moment on the long axis… impossible without forward speed. The lateral reaction against moving water gives the paddler some more stability in addition to the paddle strokes.

But forward momentum transposed to rotational moments or used for turning reduces the forward speed.

I agree with Nick & Bob that momentum by itself does not translate to perpendicular axes without a change in its direction. It’s a fundamental tenet of inertial guidance that the three axes are mutually independent. This would all have Charles Draper rolling over in his kayak.

“Familiarity Breeds Contempt”

-Aesop

[jonsprag1]

I've always suspected that North Shore Paddlers were primarily MIT graduate students(or at least undergrads)---Now I know it for a fact--lol

[Rick crangle]

It’s just cheating to use gyros for stability. Nice thinking Don.