Windward or Leeward side of banks?

[svseachange]

If you see a bank on your chart where the depth rises from, say 4000 feet to 100 feet theen drops again to 4000 feet do you prefer to pass a ten or so miles windward or leeward of the bank? Why?

[Pelagic]

Is this s trick question.... What is your draft?

[colemj]

If there is no problem with ground swell standing up on it, we would just go right over the bank. If we did decide to go around it for whatever reason, 10 miles is way out there - we would be much closer than that. As for windward/leeward, it only makes a difference if the sailing angle is bad or uncomfortable.

Mark

[Andrew Troup]

Leeward, for sure, in any conditions where it mattered.

Or, if there was a strong tidal stream or ocean current: possibly down-current, but that's not so simple. Lots of variables. Can't answer.

[svseachange]

We were having this discussion over a few beers last night.

I have been going leeward, figuring I don't want to go over banks due to turbulence, it is easier to do that leeward and the sea state would tend to be calmer leeward after the initial turbulence subsided.

The other two sailors, more experienced than I, said they prefer windward, the reason being the turbulence created by the banks disturbs the sea state for quite some distance.

We were talking about the many such banks in the western Caribbean sea. For arguments sake lets say we there is no current (although they tend to set with the prevailing wind direction in the area of interest).

[Hud3]

Right over the banks, trailing a fishing line.

[svseachange]

Originally Posted by Hud3

Right over the banks, trailing a fishing line.

On a calm day, that's a good plan!

[colemj]

We actually seek out sea mounts and banks for the fishing!

In the Western Caribe, just sail right over the banks. Even in the deeper water, the seas are mostly turbulent - they are piling up in this part of the ocean and being refracted off and around all the land masses for hundreds of miles. We have rarely found any difference between 1000' and 100'. Keeping all of those banks 10nm away makes you sail much further and in strange route patterns. If you are not catching fish, that doesn't make any sense to me.

Mark

[MarkJ]

I always go to the leward side of banks. Not ten miles. I would go quite close to them.

At that depth of 100 feet you can go right over the top anytime except for really bad weather, even then you'd need pretty big waves before stacking up.

Assuming you mean shallower depth where waves could interact with the bottom, then I would always go to leward. To do to windward adds a little danger as any lee shore does. But there could be current effect too. Water moving at one knot 1,000 feet below and hitting a rise could well make stuff quite weird on the surface. Even the 100 foot depths would have that current effect. But there could be no real difference between upcurrent and down current sides as the water still averages the same speed.... Except for whirlpools.

All in all its gunna be safer staying in the 4,000 foot depths. But I wouldnt be going ten miles out of my way for it!

[barnakiel]

But a bank can generate very confused seas on its lee side. So the question stands open.

b.

[Andrew Troup]

The difference for me is the VERTICAL component of currents. I think it's misleading to think only in terms of what you see on your GPS; that's strictly horizontal.

Steep underwater features extending hundreds or thousands of metres create strong vertical currents when an essentially horizontal mass transit system passes across them. In some cases, it's an unperceived bottom current being forced to the surface, and this can be truly problematic.

I am mistrustful of the influence of upwelling currents on wave form.

To me that's likely to be the missing "elephant in the room", one of several which have always caused some sailors to look askance at the textbook rules of thumb originating from oceanographers.

Few of these sailors attempt a satisfactory explanation; they're simply observing the difference between theory and reality.

[Andrew Troup]

There is (I think) minimal interaction (unless the minimum depth over the bank is quite shallow) between the 'wind drift' (mass transportation of surface water due to friction coupling) and the bank, because the wind drift layer is rather shallow.

However the waves created by that wind will surely interact with perturbations to OTHER currents resulting from their interaction with the bank. But for me it is the lee side in respect of the strongest such CURRENT which is the crucial factor, and that can be difficult to predict without actually going there.

So when strong winds coincide with strong currents I thing it is prudent to stay well away from undersea cliffs and canyons, unless their ridges are a long way down.

[Pelagic]

I think it is important to put this question in to
perspective!
Normally if the chart doesn't indicate dangerous overfalls or disturbed waters at a 100ft. seamount, I don't worry about it.
However, in survival storm/typhoon conditions if caught outside I would be staying in deeper water, staying away from converging currents and focused on one wave at a time.
Since the OP did not specify those conditions, I believe fishing is the best answer

[svseachange]

With respect to conditions they can be hard to predict when you plot the course. That's why the question was unqualified. Andrew is probably right, the effects of banks and associated currents has not been studied enough to answer the question.

[colemj]

Well, I can tell you from experience of having travelled over many of the banks in question that only the roughest weather would make any noticeable difference in traveling over them vs around them. And in the roughest weather, 10miles on either side is way too much.

The banks you are discussing are very large and going around them would add a lot of mileage and require a twisted route just to avoid 100-200' of water - which you would be happy with in other circumstances, but seem shallow now only in relation to the 2000' preceding them.

These types of banks in other areas may certainly require a different approach, but the banks in the Western Caribe are as I describe.

Mark