current against wind

[girouette]

I have experienced that a current opposing the wind can make quite nasty waves. Is this somewhere discussed in depth? I am interested to know at what wind and current things become difficult to handle.

[boatman61]

Well I can tell you that 1.5kts S'bound stream in the Biscay against 60kts SE'ly will kick up 25+ft near standing waves.. 25-30kts will make life uncomfortable.

[girouette]

Originally Posted by boatman61

Well I can tell you that 1.5kts S'bound stream in the Biscay against 60kts SE'ly will kick up 25+ft near standing waves.. 25-30kts will make life uncomfortable.

BOATSMAN, this is 10 Bft, it is uncomfortable even without a current. But I am looking not for single personal experiences, but for a detailed discussion of this problem. Also graphs of wave forms for current against wind for different current and wind speeds would be helpful.

I am planning a trip in northern Britanny and the Channel Islands (Jersey ..), where you can expect strong winds and strong currents.

[Shrew]

Originally Posted by girouette

But I am looking not for single personal experiences, but for a detailed discussion of this problem.

1) A Forum Thread is nothing more than a collection of single personal accounts, opinions, and experiences.

2) In a Forum you will never truly get to dictate the responses or the direction of the discussion. Take it all in with a grain of salt, then cull from the responses that which you find interesting and informational.

[two-rocks]

There is no graph that will determine "difficult to handle".

Any graph is theoretical, the angles will never be exactly 'as predicted'. Eddies are abound, waves align, etc.

[Montanan]

References:

https://www.ec.gc.ca/meteo-weather/8...ndtheWaves.pdf

https://rmets.onlinelibrary.wiley.co...0.1002/wea.606

Snipet:


Wind against tide
The case of swell encountering a current in
the water appears to have been first treated
by Unna (1942). He considered the case of
a wave train from outside the current and
moving onto the surface of the opposing
current. As with the case for waves in shallow water treated previously, the wave
period will remain constant as the swell
enters the tidal stream. If the wavelength
and phase speed of the incoming waves are
λo
, co
and the same parameters within the
tidal stream flowing with velocity u are λ, c
then for the wave period τ to remain
unchanged at the interface:
Reference formula below.
This assumes that the boundary of the
current is sharp and that there is no reflection of part of the incoming wave. Note that
the wave phase speeds here are relative
to the water, not to the sea bed. It has been
seen previously that the wave speed c
decreases with wavelength λ . If this fact is
taken in conjunction with Equation (1) it can
be seen that if the tide is flowing against
the incoming swell (i.e. u is negative) then
λ can become much less than λo
so that the
wavelength may be considerably reduced.
It can also be shown from considerations of
energy transfer across the current boundary
that the wave height is increased. Overall
the steepness of the waves is greatly
increased. In many ways the situation is
similar to that of a swell entering shallow
waters treated above. As an example, if a
wave of wavelength 15m and speed 5ms–1
(10kn) enters an opposing stream of
strength 1ms–1 (2kn), its wavelength will be
reduced by 50% while its height is increased
by 75%, giving a dramatic increase in steepness. It can be shown that if the opposing
current is great enough so that the current
speed is no greater than co
/4 (i.e. 1.25ms–1
in this case), then the wave becomes
infinitely steep and will break. In fact opposing currents of only a few knots will cause
most waves encountered to exceed the
steepness limit and partially break. If u is
positive (tide moving with the swell) then
the steepness of the swell is decreased, so
that the change when the tide turns is very
pronounced.

Given this explanation it can be seen that
the phrase ‘wind against tide’ is something
of a misnomer and it should really be ‘swell
against tide’. However the swell is often
moving in a similar direction to the wind
when it has been generated in waters
adjacent to the tidal stream so that the
phrase normally used is reasonably accurate. For the western coast of the United
Kingdom, swells generated at distant locations usually approach from the prevailing
wind direction and so in this case, too, the
swell may be aligned with the wind.
When the tide first turns against the wind,
the existing waves in the flow do not steepen.
However, waves from swell entering the flow
from outside it will become steeper as they
do so. The area of current covered by these
modified waves spreads upwind from the
down-current boundary and eventually
extends over the whole current.
In combination with the effects of shallowing depths, described earlier and often
encountered in tidal races, such seas can
become extremely confused and broken.

[boatman61]

Originally Posted by girouette

BOATSMAN, this is 10 Bft, it is uncomfortable even without a current. But I am looking not for single personal experiences, but for a detailed discussion of this problem. Also graphs of wave forms for current against wind for different current and wind speeds would be helpful.

I am planning a trip in northern Britanny and the Channel Islands (Jersey ..), where you can expect strong winds and strong currents.

Well if thats your specific area you will have strong currents in opposing directions every 6hrs but strong winds will be much less frequent.
Considering the hazards that exist in that area I would hope you are heading for shelter if the forecast is over F7, remember the rise and fall is 30ft and more or a tad less in places.
With areas like the Alderney Race where the currents can hit 6kts plus in places its not a fun place to be.. remember making the run from Alderney to St Peters Port before a NE F8 hit luckily the tides were in our favour.. 9 of us got kicked out of what would have become an untenable anchorage.
Good luck with getting a graph other than tidal.

[girouette]

Originally Posted by Montanan

References:

https://rmets.onlinelibrary.wiley.co...0.1002/wea.606

Thanks Montana, this is exactly what I was looking for.
Girouette

[bwindrope]

Those of us who cruise around the Salish Sea could each write a thesis on this topic. Since our currents are crazy strong, and our winds potent, it is just a nasty fact of local cruising. Don't get me started on the Straits of Juan de Puca, or Deception Pass ebbing against a strong westerly, or Rosario Strait ebbing against a winter SE.

I agree with the person who posted that it is so locally variable due to the eddies of water and wind around local peaks, and underwater topography. There is a spot, for example, not far from Seattle near a place called Foulweather bluff that is just a nasty stretch of water because of the way local currents and local winds contradict each other around headlands. Steep and close 6-8 foot waves kind of stuff. On the outside of Vancouver Island, for those who have rounded, if you have a strong summer NWesterly when the current is ebbing out of the one of the large Sounds, you are in for a very nasty ride. I've had those waves swallow my Gulf 32 so fully that my wife sitting in the cockpit saw waves well over my head looking at me at the helm.

I can only imagine what Tierra Del Fuego and such places are like, or the southern tip of Africa is notoriously hellish.

Nice walk down memory lane, thanks for the topic!

[Tillsbury]

There aren’t a lot of places where it’s not an issue. The prevailing westerly against a decent spring west-going tide at the Needles can get interesting, particularly since a lot of sailors consider that fairly protected waters. Most headlands will give you enough current at certain times that the combination of that and a decent wind makes for a pretty nasty situation.

Around the Channel Islands and the nearby coast of France things can get hairy with hardly any wind if it’s spring tide. Plan to be at the most exciting places close to slack water, neaps if possible. Remember that 8kts of tide even in your favour requires concentration — it takes a while to get used to remembering that you need to steer pretty much 90 degrees to port in order to avoid a rock that’s coming up...

I’d not want to be in those places with more than 2-3kts of current against say 20 kts plus, for two reasons: one is that any non-sailors with you won’t be enjoying things at all, and the second is that even if you’re all gung-ho there’s no point in bashing around putting significant additional stress on your boat if you don’t have to.

[Pete7]

On more than one occasion we have gone out and changed our minds returning for 24 hours before trying again. Its not just when the wind is blowing hard but there will be an uncomfortable slop left afterwards possibly with a change in wind direction with other waves that can make life really unpleasant. You can manage it, noting Tillsbury's comment above about non sailors. However, if something went wrong like the fuel filter blocked or the dinghy goes over the side then fixing it becomes just that more difficult problem. We go cruising, not endurance trials.

Pete

[Jenneau Owner]

If you are planning to sail Brittany and the Channel Islands, everything is dominated by TIDE heights and flow. You can not fight them but it is possible to use them to great advantage.
Wind against tide can and will cause lumpy seas.
There are numerous tidal flow diagrams available and are essential to have on board. They are very often based on HW Dover or Cherbourg. If you are not used to the process of Standard and secondary ports etc study up. Knowledge of GMG/BST and French Standard time is also required.
Working the tides is one of the most satisfying aspects of cruising this wonderful area.
Enjoy and I apologise if I am “Teaching you how to suck Eggs” !!
If possible don’t miss out SAN Malo well worth a visit.

[Group9]

Read about the Gulf Stream when strong north winds opposed the north flowing current. I've been on it a couple of times in those conditions, and it was hellish.