having done even a little surfing
I know what you mean. It is not easy, but skegs do work in current to anchor the stern in order to give better control over where the kayak is going. I don’t personally use mine, I use a stern rudder stroke, which is a more effective skeg than the drop down variety, but the principle is the same is it not?
you’re getting
it, Glasshopper!
I like the hanging sandbags!
I think we’ve beat this horse long enough.
whew!
steve
I wouldn’t say
more effective when talking stern strokes vs retractable skeg. The retractable skeg is most effective at giving the hull a balance that is needed, by moving the pivot point. The stern stroke is most effective at moving the stern to a new position, using your muscle and leverage.
Like the wheels on your car are better at keeping it on the road and giving you direction control but the motor has to be pushing to get 'em to spin.
;^)
let’s move on!
steve
Skegs DO work in currents…
– Last Updated: Jan-06-04 11:51 AM EST –
...as long as you're paddling rather than drifting.
If you're just sitting still and being carried along, you're correct that it won't make any difference.
However, paddling forward creates a high pressure zone at the bow and a low pressure zone at the stern, which tends to anchor the bow and release the stern. Deploying a skeg affects this balance and therefore the attitude of the boat relative to the water. Also, skegs and rudders work by producing lift, which occurs when the boat is moving and water is flowing over the blades.
Have you never used a skeg to help maintain a ferry angle?
There will be some angle to the current (probably close to 90 degrees) where the skeg would have no effect, but as soon as you begin to move at an angle to the water flow in the current, it will begin to work.
REALLY???
;^)
steve
What you describe
is no different than in a no current situation. As you said, the pressue difernce in generated by your motion realtive to the water. The skeg has effect relative to YOUR motion in the water, not that water’s motion over land. That is not counter to anything I’ve said.
Relative motions seem to confuse the heck out of people. Think enough has been said. More would seem like an argument, and that’s not what this is.
nope
Unless the water is moving faster at the depth of the skeg then the current isn’t going to drag the stern any faster than the bow. Effects you were seeing were due to the waves and wind unless the current had boils.
The effect of current on waves (open water here, Chesapeake Bay is my reference) is that a current opposing the wind magnifies the wind stress on the surface water and increases the wave height. It also increases the effective fetch by moving the water into the wind which increasing the time it takes for the wave to get from point A to B. It slows the propagation of the wave relative to a stationary object but not relative to the a parcel of water or an object in that parcel of water.
Sandbags hanging above our imaginary walk way are like pier piles sticking up through the current and not analogous to waves in open water. The frame of reference is off. Waves in moving open water (discounting effects from bottom interaction) are like sand bags sitting on the walkway (well rolling slowly in some direction or other but you move relative to them as if they were rolling along a stationary floor.
Waves
– Last Updated: Jan-06-04 2:04 PM EST –
Of course a skeg is usefull in beam, quartering, and following seas (surfing being the extreme).
That is a rather different thing, and applies with or without being in a current.
skeg and ferrying
Yep, I’ve used my skeg to maintain a ferry angle for 5miles crossing the James river many times. But I set the orientation of the boat. On one crossing, I had the bow pointed at the Lions Bridge the entire time and landed at Hilton School a little over a mile downriver. Tide was ebbing hard. The reason I used the skeg was that there was a light SW wind (rear quartering on my desired heading) that was trying to point my bow down towards the JRB. The current moveing from my left to right did not affect the orientation of the boat but required that I adjust my heading to land as the correct point. With no skeg deployed the boat just wanted to swing around and point back towards the wind, just as if there was no tide moving at all.
When the wind is dead, the boat points where I want with no skeg or with skeg. I can point the boat straight cross current and it stay pointed that way, skeg or none.
whitewater and open water currents not
– Last Updated: Jan-06-04 2:25 PM EST –
""Even a very slight angle to the current will have a huge effect on a hull.""
Only in very shallow water where bottom friction causes a very rapid decrease in current velocity with depth.
For this to apply in deep water, the water at the bow and stearn would have to be moving at different velocities.
A solid understanding of current comes early on to anyone who paddles whitewater, a highly recommended pastime for any sea boater!
Boils, eddies, and such don’t effect those of use paddling wide estuaries to often except maybe around bridge abutments. Most current we encounter can be treated as essentially laminar.
current interaction with the bottom new
New kink when you throw in the current interacting with the bottom. At the mouth of the York, waves often come from multiple directions because the shoals redirect them.
and…
in the scenerio you describe “When the wind is dead, the boat points where I want with no skeg or with skeg. I can point the boat straight cross current and it stay pointed that way, skeg up or skeg down”
Would you be paddling ‘exactly’ the same, skeg up or skeg down in this cross current boogie??
And would you finish at the same point B??
steve
since when
did pier piles swing back and forth like a sandbag on a rope??
steve
since when
Since when is a deep water wave stationary? The deep water wave is moving relative to the medium. The sandbags in the analogy would be stationary, maybe like a really flimsy pier piling but still not going anywhere.
yep
""Would you be paddling ‘exactly’ the same, skeg up or skeg down in this cross current boogie?? “”
Yep I would. I use the skeg to correct orientation relative to the effect of wind and waves. The current dicates what heading I choose but doesn’t affect the orientation of the boat relative to that heading. Paddling cross current isn’t like having a beam wind. It isn’t flowing under the hull creating a sideways friction force and a turbulent eddy on the downstream side of the boat as will wind moving across the deck. You’re simply moving sideways with the current.
I’m not discussing eddy grabs, and river running. Maybe you are.
The 0.75-2kt current in the wide tidal estuary that is the lower James or the Chesapeake Bay or the lower York River can be treated as essentially laminar. When there isn’t any wind or waves I point the boat to some target upcurrent of my destination, let the hull run flat, and “boogie”. It there’s a crosswind I either lean into it or put the skeg down. The boat doesn’t orient into the current, away from the current, or otherwise.
It’s not like a shallow, fast white water river where the top few inches of water are moving way faster than the layers underneath which are moving way faster than the next layer, etc…until you get to the stationary boundary layer. In an estuary the flow in the top meter of the water column is pretty uniform except over shoals on strong tides.
What if I’d had a rudder?
Sorry, just kidding .
Seriously, I’ve enjoyed the discussion. Even though there’s not a strong consensus on some of this, my awareness and powers of observaiton will certainly be hightened, next time I’m out in the wonderfull world of weather and water.
Paul S.
so…
you’re telling us that regardless of skeg deployment, paddling the same heading, exactly the same on both sides (as in NO corrections) the boat will go on the same exact course across the current?
what kinda magic boat ya’ got??
what’s the diffenence between what we’re talking about and river running theory?
water in movement. hull in interaction. different hull shape/ different interaction. plain and simple.
steve
nope
sandbags are free to swing. If in proper sync with each other they might resemble wave/ swell energy.
steve
so…
What exactly is supposed to be exerting the turning moment on the hull crossing in a unidirectional deepwater flow?
Wind causes weather cocking because it’s blowing across the deck and the boat isn’t skidding downwind at the same velocity as the wind so there’s lateral stress applied to the hull. The part of the boat that skids downwind faster in response to the windstress turns the boat. We all know this is compensated for by have nothing back aft for the wind to grab or by having a skeg to “anchor” the stearn.
Paddling straight across the current or angled 45degrees so it or what ever, water is passing under and around the hull as if paddling straight through still water or a wavy lake but no current. No water is moving sideways under the hull as with wind passing over the hull. The difference is that the entire system is moving sideways relative to whatever stationary target you’ve got that you’re trying to reach. The hull “sees” a molecule of water pass the bow to the right simultaneously with one on the left and they both pass the stearn at the same time. So what if both molecules and the boat are moving downstream at 2kts? The fact that the velocity of water is equal on both sides of the hull means that there’s no turning moment.
Find a wide river on a calm day. Paddle straight across. Note whether or not there’s more turbulence on the downstream side of the hull. Angle upstream a bit. The result will be the same. If you look down at the water as you move briskly forward provided you’re holding one heading you’ll see the same wave shape and turbulence pattern on both sides of the boat.
I logged 30-60miles per week this year on the lower york. I think I know how my boat behaves and what is necessary to get the desired heading.
skeg and wind
Wind and water do not affect the hull in the same way. The skeg simply stops the stearn from sliding downwind faster than the bow. The alternative of course being to find a way to reduce the windstress aft to match the water pressure’s ability to hold the stearn.
In a current the entire boat is moveing down current at the same rate. There is no current slideing sideways under the hull (unless you’ve just entered the current from still water) so there’s no opportunity for different lateral stress at the bow and stearn. Excepting entering/exiting eddies, the starboard and port side below the water line see water passing at the same rate.
Waves have the effect they do because of the water velocity differences in differency pieces of the wave. A uniform current is just like being on a giant swell, the entire boat experiences the same velocity of water.
“”“current coming at an angle 45 degrees off from the bow to starboard your tail will skid, if you drop a skeg then your stern is more anchored”""
Here it seems that you’re telling us that current is trying to push the stearn around so that you face into the current. Were that the case, putting the skeg down would make that tendency worse, kind of like having a rudder up increasing the wind stress on the stearn.