Is there a rule of thumb with regards to the effect of the tidal flow and water state given the same wind strength and an incoming and outgoing tide?
Guess another variable would be on-cross/onshore and offshore wind direction.
The following rules of thumb apply:
1) Tidal flow effects getting up on plane. Its easier to get up on plane in the direction of the tidal flow and harder against the tidal flow.
2) Once up on plane the effect is less.
3) When the wind is against the tidal flow, then the chop is significantly larger than if the wind is in the same direction as the tidal flow. In extreme cases, where you have large tidal flows and strong winds you can get standing waves
Select to expand quoteJohn340 said..
The following rules of thumb apply:
1) Tidal flow effects getting up on plane. Its easier to get up on plane in the direction of the tidal flow and harder against the tidal flow.
I disagree.
If you're moving in the same direction as the water (i.e. in the direction of the tidal flow) it is harder to get up on the plane as you need to be travelling much faster.
Edit - it's the same principle as why aircraft take off and land into the wind.
The main effect I have found is when waterstarting when wind is opposing the tidal flow. It can be really hard to get the clew out of the water when the current/tidal flow is pushing it down.
tide being the green arrow
i find what john says is right if the wind is right angles to the tide - if the wind is the yellow arrow, i find it easier to plane going in the direction of the tide. i'm guessing that with my ~18cm fin, the tide carrying me along and generating apparent wind in the sail probably out weighs the effect of water running over the foil of the small fin (minimal lift)? i too thought what flickyspinny suggests would have been what happens in this scenario as it seems logical and was surprised that it wasn't, even sailing somewhat diagonally
it's easier to plane if the wind is in the direction of the red arrow, and as john says, bigger chop or waves (pushing everything into the wind giving the effect that the wind is stronger than it really is)
as opposed to wind in the direction of the blue arrow which has the opposite effect of the above
Select to expand quoteFlickySpinny said..
John340 said..
The following rules of thumb apply:
1) Tidal flow effects getting up on plane. Its easier to get up on plane in the direction of the tidal flow and harder against the tidal flow.
I disagree.
If you're moving in the same direction as the water (i.e. in the direction of the tidal flow) it is harder to get up on the plane as you need to be travelling much faster.
Edit - it's the same principle as why aircraft take off and land into the wind.
Sailing a windsurfer against the tide is not the same as taking off into the wind in an aircraft. It works in an aircraft taking off into the wind because the wind (current) is acting directly on the foil (wing) and creats more lift. In the case of a windsurfer against the current, the only foil the current is directly acting on is the fin and the additional lift is insignificant. In addition the apparent wind on your sail is reduced because the current reduces your board speed, especially in subplanning speeds
When you travel with the current, your apparent wind is increased on your sail which often provides that little bit of extra lift you need to get onto the plane. As Haircut says the extra lift of the increased apparent wind on the sail when sailing with the current is much more significant that any extra lift you might get out of your fin when sailing against the current.
Once onto the plane, the surface area of the board affected by the current is significantly reduced and hence the effect of the current is much less.
Hey John, sorry mate unless I misunderstand your take on this you are 100% wrong
Sailing with wind and tide going the same way kills your apparent power, smashes your speed and turns what could of bean a good session into ****e!
If you want to test my argument go to Caloundra river mouth, Maroochy, Noosa river mouths and test your theory!
None of us bothered sailing after 3.30pm at GB today because the tide was flooding in with the wind, killed it!, those that turned up late couldn't get going even though it was windy as, and ended up drifting down wind, god bless them for trying though!
Ever wondered how kites at the above places get going in really light winds....they work the opposite wind/tides as it creates more apparent wind and gives massive boost! Same for kites also, once the tide floods in same direction as the wind, it's pack up time.
Wind + Tide same direction =
Wind + Tide OPPOSITE direction = 
Cheers
All you're sailing in is the differential velocity between the water and the air. All your gear sees is that difference. It's only the rider who looks at the land and tries to complicate the situation.
Chop is well known to be exaggerated if the wind is against tide but I haven't been able to find an explanation on the internet. I suspect that it is due to a combination of finite water depth and differential speeds of the current across the width of every stream. Waves generated in the slower water have to shorten wavelength and jack up when they move into faster water. Then with the wavelength and relative wind now in disharmonious proportions it all possibly just gets amplified even more. Has anyone found another explanation for this well documented observation?
Select to expand quoteIan K said..
All you're sailing in is the differential velocity between the water and the air. All your gear sees is that difference. It's only the rider who looks at the land and tries to complicate the situation.
Chop is well known to be exaggerated if the wind is against tide but I haven't been able to find an explanation on the internet. I suspect that it is due to a combination of finite water depth and differential speeds of the current across the width of every stream. Waves generated in the slower water have to shorten wavelength and jack up when they move into faster water. Then with the wavelength and relative wind now in disharmonious proportions it all possibly just gets amplified even more. Has anyone found another explanation for this well documented observation?
I assumed it was just the extra relative air to water speed.
Are you saying there's more chop produced by 5kts of wind directly against a 5kt current, than there is for a 10kt wind over stationary water?
Yes apparently that's the case. I haven't spent enough time at a tidal location to observe that the chop is more than for 10 knots over stationary water but those who have seem to be pretty convinced.
But anyway in your first situation there will always be water around the edges of this 5 knot current that is moving slower. Even stationary. The waves generated in this stationary water at 5 knots might have a 1 metre wavelength ( Of course they don't but stick with the relativity ) If they move into the centre of the current they have to bunch up, the wavelength must reduce to 0.5 metres. Now you've a recipe for a very messy chop in the middle of the channel where the windspeed over water is 10 knots.
If your sailing at 90 degrees to the current flow then wind against tide DEFINITELY produces more power and makes it easier to get planing. If you have say 3-4 knots of current flow then tide against wind is sort of pulling you towards the wind making it seem as though you've got 3-4 knots more wind speed powering you up where tide with the wind is de-powering you because it is pulling you away from the wind. Go and sail at Shearwater and tell me I'm wrong. That's why you can be having an awesome day at Shearwater planing on every run and within an hour or so with the same wind speed the tide changes and you're chugging around struggling to get going. That is unless the wind is really strong.
Found a diagram of streamwise velocity profile in a channel. The flow starts off even but the longer the channel the more the profile goes to the red set of arrows. Now you can imagine waves trying to form as wind blows against the flow. Waves forming in the centre of the flow will refract towards the bank as they move into slower water. Waves formed near the bank will refract towards the centre, wavelengths correspondingly stretch and contract. Nothing is ever going to line up. Wind against tide makes for very choppy water.
Select to expand quoteJonesySail said..
Hey John, sorry mate unless I misunderstand your take on this you are 100% wrong
Sailing with wind and tide going the same way kills your apparent power, smashes your speed and turns what could of bean a good session into ****e!
If you want to test my argument go to Caloundra river mouth, Maroochy, Noosa river mouths and test your theory!
None of us bothered sailing after 3.30pm at GB today because the tide was flooding in with the wind, killed it!, those that turned up late couldn't get going even though it was windy as, and ended up drifting down wind, god bless them for trying though!
Ever wondered how kites at the above places get going in really light winds....they work the opposite wind/tides as it creates more apparent wind and gives massive boost! Same for kites also, once the tide floods in same direction as the wind, it's pack up time.
Wind + Tide same direction =
Wind + Tide OPPOSITE direction =
Cheers
Jonesy
I'm not sure we are talking abiout the same thing. On my slalom board, I can only sail accross the wind from 60 deg to 130 deg. Hence the wind and the current are never in the same or opposite direction.
However depending on which direction you travel, the current either increases or decreases your subplanning board speed relative to the wind. This then in turn increases or decreases your apparent wind and hence lift on the sail.
When you sail golden beach in a NE wind and strong incoming tide, is it easier to plane sailing towards bribie or towards golden beach?
Is it the tide or is it the sailor?
When sailing with the tide you feel like you can afford to bear away by a few degrees and get on the plane. Sailing into the tide you might tend to pinch up a few degrees and making it harder to plane.
This an observation from a sail last week. Starboard tack was a lot easier to sail going with the water movement. Port tack was harder to get going and always remed to pinching to get back to the starting point.
More than likely its just my last of skill and technique but the bloke I was sailing with and a kiter had the same observations.
On boats whether displacement or planing there will always be an effect on the boat. One knot of tide or current is a fair bit of force to deal with. It just depends on what angle you attack that movement.
In sailing tide/current hitting your lee bow is more beneficial to your COG than tide/current hitting your weather bow.
I hope I haven't confused things more.
Select to expand quoteJohn340 said...FlickySpinny said..
John340 said..
The following rules of thumb apply:
1) Tidal flow effects getting up on plane. Its easier to get up on plane in the direction of the tidal flow and harder against the tidal flow.
I disagree.
If you're moving in the same direction as the water (i.e. in the direction of the tidal flow) it is harder to get up on the plane as you need to be travelling much faster.
Edit - it's the same principle as why aircraft take off and land into the wind.
Sailing a windsurfer against the tide is not the same as taking off into the wind in an aircraft. It works in an aircraft taking off into the wind because the wind (current) is acting directly on the foil (wing) and creats more lift. In the case of a windsurfer against the current, the only foil the current is directly acting on is the fin and the additional lift is insignificant. In addition the apparent wind on your sail is reduced because the current reduces your board speed, especially in subplanning speeds
This isn't exactly true. An aircraft flies off indicated air speed which is essentially the velocity of the aircraft accounted for air density. Ground speed is indicated air speed (IAS) with wind factored in. Into wind GS = IAS - wind velocity. Wind does not affect the IAS other than a microburst which is a sudden gust of around 30 kts.The reason aircraft take off into wind is not due to an increase in lift from the wind travelling over the wing but due to the decrease in ground speed. Allowing the aircraft to get to the necessary flying speed (IAS) in less distance.
Applying the same theory... A windsurfer can get onto the plane against the tide at the same forward velocity but in less distance due to tidal flow.
