Folding Kayaks Forum

The user forum for FoldingKayaks.org
It is currently Tue Jan 23, 2018 3:54 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 8 posts ] 
Author Message
PostPosted: Sun Aug 21, 2016 1:46 pm 
forum fan

Joined: Fri Aug 19, 2016 6:39 am
Posts: 17
hi all,
I'm not sure if this is put the right place and with right subject-text. It's associated with the post "Rudder?".
I've written it at home and makes a copy/paste:

Hi constructors.
I just arrived from another test-tour in my newly constructed kayak. It was not a success.
The wind was light with fresh gushes. Unlike my previous kayak, which would position itself perpendicular to the wind when not paddling, this one would position itself differently. Its probably no wonder: the sidewards drag is stronger on the frontal part as it has a more pointed profile where the rear half has a round profile. What does not differ between the two is, that, once in rest relative to the wind, its extremely difficult to change this orientation.
In a previous post in the old forum I tried to describe my after-rationalisation of what happens for the boat that lies perpendicular to the wind, but the post got no responses.
It's obvious that it's the same phenomena that's at work on the latest kayak. When paddling again after a rest, it strikes me as odd, that the kayak will swing it`s snout up against the wind (on symmetric paddling ); so, to get the right orientation I`ll have to take ~5 strong strokes in the wind side, and eventually I`ll get the right heading. But now, it is as if the water has stored the vain power in the first 5 strokes and now releases it - with the result that the kayak now swings way out of course to the other side. And the paddling will continue like this.
Ok. I know that I sound like an observant newbie that just hasn't got it right from the paddling instructor. I have in fact spent 8 years rowing and is not a newbie on the water - but in the kayak, yes (~200 km in total).
From some of the posts I've read in the old forum, I know that the wind is something of a nuisance to some of you. As a kayak-constructor I'm not done until I've found an acceptable solution to this problem. And it would be very appropriate to attempt to express the formal physics that is at play.
In the previous kayak I considered the mikro-turbulence in the curved-in skin between the stringers as the culprit. Once they have aligned in the sideways movement, they do contain a rotational momentum (as a gyroscope) and as such could be able to keep the kayak orientation fixed in a none intuitive way. This consideration cause me to build the current kayak with boards between the stringers (to support the skin from curving in), to obtain a smooth bottom. Well .. the symptoms changed with the kayak, but both seems to get somewhat locked in position by the wind.
If you recognize the problem, then, what would be the most effective solution? This is probably silly to ask as the combined wind & paddle-direction could call for different solutions.

I've thought out a harness for a rudder, something that can be strappe on (around the rear-most section) without moderations to neither skin nor boat-structure. A minor (velcro) removable finn on the keel is another option with minor overall disturbance. The option to not use the solution in perfect weather is called for as there are a lot of seaweed at the surface of my local water (googl Aalborg, Danmark).

I look forward to read your input


Top
 Profile  
 
PostPosted: Sun Aug 21, 2016 9:10 pm 
paddler

Joined: Sat Aug 13, 2016 3:17 pm
Posts: 9
Perhaps the weight distribution is too far forward?

_________________
Folbot Super


Top
 Profile  
 
PostPosted: Tue Aug 23, 2016 2:52 pm 
Site Admin

Joined: Thu Apr 14, 2005 12:34 pm
Posts: 1694
Location: Southeast Michigan
Yes, just move the seat to get more neutral handling. It's also the case that with more practice you'll find that your paddling and leaning skills can make any kayak feel more neutral. A friend bought a Nautirad single as his first kayak and could not get it to point straight ahead. I got in, and couldn't figure out what the problem was. It just went where I wanted it to.

But I remembered that when I bought my Feathercraft K1 I was sure the frame was misaligned, as it kept veering off one way or another. After more practice and more awareness of my body position, it seemed to point al out intuitively. So it was with my friend. By the end of the day, with a little coaching, his boat went where he wanted it to go.

_________________
Michael Edelman
FoldingKayaks.org Webmaster


Top
 Profile  
 
PostPosted: Tue Aug 23, 2016 2:52 pm 
Site Admin

Joined: Thu Apr 14, 2005 12:34 pm
Posts: 1694
Location: Southeast Michigan
Yes, just move the seat to get more neutral handling. It's also the case that with more practice you'll find that your paddling and leaning skills can make any kayak feel more neutral. A friend bought a Nautirad single as his first kayak and could not get it to point straight ahead. I got in, and couldn't figure out what the problem was. It just went where I wanted it to.

But I remembered that when I bought my Feathercraft K1 I was sure the frame was misaligned, as it kept veering off one way or another. After more practice and more awareness of my body position, it seemed to point al out intuitively. So it was with my friend. By the end of the day, with a little coaching, his boat went where he wanted it to go.

_________________
Michael Edelman
FoldingKayaks.org Webmaster


Top
 Profile  
 
PostPosted: Wed Aug 24, 2016 5:26 am 
forum fan

Joined: Fri Aug 19, 2016 6:39 am
Posts: 17
hi mje & skyl4ark,

Tuff luck that I don't have a moveable seat. I use the cockpit rear section to lean up against, so I can move forward only. The way the kayak positions to the wind is not perpendicular .. but it will position itself into SOME position even if I'm not at center, and that's the core problem.
It struck me, that I had not added a longitudinal curve to the hull and that this probably would focus kayak water-drag midships, and thus swinging easier. If this would change anything, then there certainly must be a balance since I've deliberately kept bow and stern out of winds reach. The hull has been screwed together (as a triangular prismatic succession), so it should theoretically be possible to add o-rings at lower section's screw to add a cumulative curve (rubber-rings for a 'soft', dynamic bending) .. if the skin allows.

And, .. I suspect that rowers pondus does make a difference. I haven't been paddling for a year, but last year I had/chose to beach 10 kilometers before home, in very fresh wind - on a 50 km tour.

Anyway, I did make a small rudder last night .. it 'must' make a stable course much easier once you are up and running.


Top
 Profile  
 
PostPosted: Wed Aug 24, 2016 7:52 am 
lord high faltbotmeister

Joined: Thu Sep 06, 2007 8:05 am
Posts: 804
Location: atlanta, georgia
I am afraid you will be disappointed with results from your attempts to change hull shape below the water line in order to effect the helm behavior, it just does not make that much of a difference. The freeboard area and, most importantly, the center of effort created by how the kayak is loaded is what makes the most difference. Think of your kayak like a weather vane. If you suspend the weather vane with a post in the middle and present the vane to the wind then the vane will be very unstable and will sometimes spin, sometimes point into the wind (weather helm) and sometimes off the wind (lee helm). Now think about how the vane would behave if you suspend it from a post near the front of the vane. The vane will then always point into the wind. Conversely, a vane suspended near its back will point away. Now, think of your weight distribution in the kayak as the suspension post of the weather vane. I hope that makes sense.
Finally, you can use water bag(s) to change the weighting if you can't achieve the distribution you want by just moving your seat.

Best,
g

_________________
"There is nothing--absolutely nothing--half so much worth doing as simply messing around in boats"

1990's A1 Expedition
2010 Klepper Quattro
Kayaksailer
Balogh sail rig, 24 + 36 HP
Torqeedo outboard
1938 Sachs-Fichtel seitenbordmotor


Top
 Profile  
 
PostPosted: Fri Aug 26, 2016 4:36 am 
forum fan

Joined: Fri Aug 19, 2016 6:39 am
Posts: 17
hi gbellware,
You've given me food for thought.
As for the weather vane with the post in the middle .. in stable wind and ideal conditions, it will line up perpendicular to the wind. If wind changes so the vane.
I'll not present the physics .. I think that it is a bit difficult: the sum of forces on each side of the pole depends not only on area-size, but also on how far away from the pole the incremental area lies. Anyway, the forces acting tends to bring the kayak into some alignment with the wind - I think that we agree on that - and that compensating for this will take some paddling-action.

My initial question was also about the forces acting when starting in the wind after a rest. My kayak gears strongly up against the wind in an unintuitive way. The analogy in your post made me figure out why: drifting along the wind sets the water below the kayak in motion. Start paddling and the front of the kayak will enter water that does /not/ drift alongside the kayak, whereas the rear end will move in upon water that is moving along with the drift .. for and aft are thus pushed in each direction making a notable twist/gearing, one that vanes off once you are up in speed as the water below the boat is exposed to drag in a shorter interval.

I'm contend with this. It gives me a reasonable explanation.
Thanks for helping me think


Top
 Profile  
 
PostPosted: Fri Aug 26, 2016 12:35 pm 
forum fan

Joined: Fri Aug 19, 2016 6:39 am
Posts: 17
Went to test the rudder.
It's been perfect kayak-days, warm and quiet, but the wind rose to fresh wind with strong gushes when I was ready. Went out a mile up against the wind on one of our shallow flats. The rudder functions well .. kind of slow, but not really mixing with the seaweed. Steering through the rudder is kind of an abstraction where I use my head and not my instincts - that's confusing, but .. after turning around for home I had my fastest kayak-tour ever ;o).
I lock myself to the kayak by my fore-foot, knee and back and can respond quickly and precisely on imbalances. Adding my two unexperienced big toes into this controle-mix made me kind of prepare for a dip in the drink. When going downwind the kayak are 165 degrees out of it's rest-position - when it decides to take the rest-position, it not only gears fast, but also tilts. I don't understand this tilt and suspect that it's my own unconscious action from 50 years on a bike.
Gee, I could hear the rudder cut through the water...


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 8 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group