RYA Yachtmaster question - help sought...

[Kukri]

A friend's girlfriend is taking the Yachtmaster course and was confronted with a question which she could not answer, so she asked him.

He is a Master Mariner with twenty years in command of very big tankers.

He could not answer it so he asked me.

The question is:

" As you approach a windward coast, will the wind tend to veer or to back?"

This is a slightly odd question because as he says it does not tell you what the source of the wind is - is it a sea breeze or is it generated by another weather system - and it does not specify which hemisphere you are in.

Our provisional answer after half an hour on Skype is:

"It will tend to veer in the Northern hemisphere due to the combined effects of the Coriolis effect and surface friction; in the southern hemisphere it will tend to back - in both cases the effect will be to cause the wind to blow more along the coast."

Right or wrong? A lot of male prestige is riding on this...

(My friend's view is that in 280,000 tons of tanker at 13 knots you don't want to go approaching any coasts at all... )

 

[Neil]

This is the consequence of the greater degree of friction of moving air over land as opposed to water. When the wind slows as a consequence, the Coriolis force causes it to back. So approaching a windward coast, you would expect the wind to back as you approach the coast. The southern hemisphere would experience the wind to veer.

I say this only because I've just done Yachtmaster theory, and I double checked in the book.

 

[Kukri]

Ah, thank you!

Back to the classroom for the two of us, then!

 

[bedouin]

This is the consequence of the greater degree of friction of moving air over land as opposed to water. When the wind slows as a consequence, the Coriolis force causes it to back. So approaching a windward coast, you would expect the wind to back as you approach the coast. The southern hemisphere would experience the wind to veer.

I say this only because I've just done Yachtmaster theory, and I double checked in the book.

I think I agree

IIRC the wind tends to blow with a direction about 15degrees from the isobar (in the direction of low pressure) over land and about 10degrees over water.

 

[Kukri]

So, the perfect student's reply is "the wind will back by up to five degrees in the Northern hemisphere!"

So this is about on the same level as tidal height calculations to the last centimetre.

What a lot of frightfully learned Yacht Masters there must be, these days!

 

[macd]

" As you approach a windward coast, will the wind tend to veer or to back?"

It's a dumb question: as you point out, it depends on the hemisphere.

So without qualifying the question, the correct answer is "Yes". i.e. it will tend to veer or back.

 

[Skylark]

The question is:

" As you approach a windward coast, will the wind tend to veer or to back?"

Is it a trick question? I've justed read through a couple of text books and refer you to David Houghton / RYA Weather at Sea; it says that there is no significant variation in the wind over the water when it's blowing onto the shore. All of the changes occur over land.

Wind blowing over the land is slowed by friction and this causes it to back.

Wind blowing offshore from the land will veer about 15 degrees and accelerate

 

[Poignard]

" As you approach a windward coast, will the wind tend to veer or to back?"

This is a slightly odd question because as he says it does not tell you what the source of the wind is - is it a sea breeze or is it generated by another weather system - and it does not specify which hemisphere you are in.

l... )

A windward coast is one from which the wind is blowing, therefore it could not be a sea-breeze.

 

[Kukri]

A windward coast is one from which the wind is blowing, therefore it could not be a sea-breeze.

True, O King.

It could be a land breeze, though.

 

[Simondjuk]

So, the perfect student's reply is "the wind will back by up to five degrees in the Northern hemisphere!"

So this is about on the same level as tidal height calculations to the last centimetre.

What a lot of frightfully learned Yacht Masters there must be, these days!

It's actually has a good deal more relevance than knowing the depth to within 10mm.

If you're expecting the wind to back as you approach a windward shore, you can plan your tacks from some way off in order to prevent finding yourself being headed as you near your destination. Do so and find yourself downtide to boot, and you can easily join the ranks of amateurs who motor the last couple of miles uptide and upwind to their destination.

Knowing of such effects also allows one to make the most of heavier or lighter airs (as required) found on opposite sides of channels parallel to which the wind is blowing as caused by convergence and divergence.

 

[Fantasie 19]

It's actually has a good deal more relevance than knowing the depth to within 10mm.

If you're expecting the wind to back as you approach a windward shore, you can plan your tacks from some way off in order to prevent finding yourself being headed as you near your destination. Do so and find yourself downtide to boot, and you can easily join the ranks of amateurs who motor the last couple of miles uptide and upwind to their destination.

Knowing of such effects also allows one to make the most of heavier or lighter airs (as required) found on opposite sides of channels parallel to which the wind is blowing as caused by convergence and divergence.

...and the example we used in this years YM coastal was the Solent where if you know the effect it can help considerably on a transit east to west in a prevailing SW'ly and having to tack... I think...

 

[Resolution]

This is the consequence of the greater degree of friction of moving air over land as opposed to water. When the wind slows as a consequence, the Coriolis force causes it to back.

Sticking to offshore winds in the Northern hemisphere for now, surely the answer as to whether it veers or backs will also depend on whether the initial wind direction is from the North or the South?

 

[Simondjuk]

...and the example we used in this years YM coastal was the Solent where if you know the effect it can help considerably on a transit east to west in a prevailing SW'ly and having to tack... I think...

Whilst pretty certain that the effects will be almost entirely undefined in the confines of a mile or so of water, any way of escaping the Solent a little quicker has got to be worth a shot I suppose!

 

[Simondjuk]

Sticking to offshore winds in the Northern hemisphere for now, surely the answer as to whether it veers or backs will also depend on whether the initial wind direction is from the North or the South?

It matters not. Anticlockwise is anticlockwise, regardless of which way your reference is.

 

[chinita]

A friend's girlfriend

Of course, you mean your girlfriend

 

[Plomong]

A friend's girlfriend is taking the Yachtmaster course and was confronted with a question which she could not answer, so she asked him.

He is a Master Mariner with twenty years in command of very big tankers.

He could not answer it so he asked me.

The question is:

" As you approach a windward coast, will the wind tend to veer or to back?"

This is a slightly odd question because as he says it does not tell you what the source of the wind is - is it a sea breeze or is it generated by another weather system - and it does not specify which hemisphere you are in.

Our provisional answer after half an hour on Skype is:

"It will tend to veer in the Northern hemisphere due to the combined effects of the Coriolis effect and surface friction; in the southern hemisphere it will tend to back - in both cases the effect will be to cause the wind to blow more along the coast."

Right or wrong? A lot of male prestige is riding on this...

(My friend's view is that in 280,000 tons of tanker at 13 knots you don't want to go approaching any coasts at all... )

Along the north coast of Spain, it would just turn to run more nearly parallel to the coast.

If the wind has any west in it, it gets more westerly near the coast.
If the wind has any east in it, it gets more easterly near the coast.

But then the hinterland beyond the coast is often high mountains, and the coast itself cliffs of not inconsiderable height.

Plomong

 

[bedouin]

Along the north coast of Spain, it would just turn to run more nearly parallel to the coast.

If the wind has any west in it, it gets more westerly near the coast.
If the wind has any east in it, it gets more easterly near the coast.

But then the hinterland beyond the coast is often high mountains, and the coast itself cliffs of not inconsiderable height.

Plomong

Does that even apply with an offshore wind?

 

[mcframe]

It's actually has a good deal more relevance than knowing the depth to within 10mm.

If you're expecting the wind to back as you approach a windward shore, you can plan your tacks from some way off in order to prevent finding yourself being headed as you near your destination. Do so and find yourself downtide to boot, and you can easily join the ranks of amateurs who motor the last couple of miles uptide and upwind to their destination.

I was going to say "Oooh! +10 points, who do you think you are?" but then I saw who had posted it ;->

Thanks again for all your WX posts, Simon - looking forward to more this year.

 

[Searush]

It's actually has a good deal more relevance than knowing the depth to within 10mm.

If you're expecting the wind to back as you approach a windward shore, you can plan your tacks from some way off in order to prevent finding yourself being headed as you near your destination. Do so and find yourself downtide to boot, and you can easily join the ranks of amateurs who motor the last couple of miles uptide and upwind to their destination.

Knowing of such effects also allows one to make the most of heavier or lighter airs (as required) found on opposite sides of channels parallel to which the wind is blowing as caused by convergence and divergence.

Bollox, I'd just start the engine if headed.

 

[Kukri]

Of course, you mean your girlfriend

Actually, I don't! This is perfectly straight.

The lady in question has done plenty of sailing but its all been in either the Pacific or the Med.