John the kiwi
Well-Known Member
Here you go:
"Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%."
Shame we cant fix the other definition so easily!
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
The "lee bow effect"
- Thread starter bdh198
- Start date
Here you go:
"Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%."
Shame we cant fix the other definition so easily!
Kerenza
Well-Known Member
It's getting a bit boring going round in circles.
No one disagrees the weather forecasters use true to differentiate from magnetic.
When I'm running downwind at 14knt over the ground in 4 Knts tide I want to know what is going to happen when I turn left at the mark.
That wind is going to be something different to what I am experiencing and the manufacturers have chosen to use the term true for it for a very long time.
In another world of mine we would refer to the wind pressure in the bellows of an organ in terms of pieces of old gravestone placed on top. The important thing was we knew what we were referencing to.
Mr raymarine etc al have given us a term I find very appropriate and there is no way he's going to change it.
Ivw lived a long time with peoples misuse of the term decibel, and I'm sure most people can find alternative uses of a word in different situations.
No one disagrees the weather forecasters use true to differentiate from magnetic.
When I'm running downwind at 14knt over the ground in 4 Knts tide I want to know what is going to happen when I turn left at the mark.
That wind is going to be something different to what I am experiencing and the manufacturers have chosen to use the term true for it for a very long time.
In another world of mine we would refer to the wind pressure in the bellows of an organ in terms of pieces of old gravestone placed on top. The important thing was we knew what we were referencing to.
Mr raymarine etc al have given us a term I find very appropriate and there is no way he's going to change it.
Ivw lived a long time with peoples misuse of the term decibel, and I'm sure most people can find alternative uses of a word in different situations.
iLens
Well-Known Member
Sorry to add another complication, but a book I'm reading* points out that the wind at the top of the mast can differ by "up to 300% in speed and 20-30 degrees in direction" from that experienced on deck. As the anemometer is usually at the top of the mast, we now have two versions of apparent wind.
The book also refers to "true wind" as the wind experienced by "a mast fixed in the water" - that is what people here have been referring to as "ground wind". That means we need another term for the "computed wind", as shown by a Raymarine** wind instrument set to display "True" rather than "App". This "computed wind" is the dot product of the boat's speed and direction relative to the water and the wind relative to the anemometer, and as the angles are based on the boats fluxgate compass, its direction it is relative to magnetic north. To determine the ground wind, you need to include the vector of the water relative to the ground - the "cause" of the lee bow effect - which brings us back to the original subject of the thread.
Finally, the "Actual" wind as experienced by the helmsman is either too little or too much and usually in the wrong direction
*"Weather at sea" by David Houghton p23
** other brands of wind instrument are available
The book also refers to "true wind" as the wind experienced by "a mast fixed in the water" - that is what people here have been referring to as "ground wind". That means we need another term for the "computed wind", as shown by a Raymarine** wind instrument set to display "True" rather than "App". This "computed wind" is the dot product of the boat's speed and direction relative to the water and the wind relative to the anemometer, and as the angles are based on the boats fluxgate compass, its direction it is relative to magnetic north. To determine the ground wind, you need to include the vector of the water relative to the ground - the "cause" of the lee bow effect - which brings us back to the original subject of the thread.
Finally, the "Actual" wind as experienced by the helmsman is either too little or too much and usually in the wrong direction
*"Weather at sea" by David Houghton p23
** other brands of wind instrument are available
lw395
Well-Known Member
That's completely wrong. A dot product of two vectors is a scalar, e.g. force.distance=work..... This "computed wind" is the dot product of the boat's speed and direction relative to the water and the wind relative to the anemometer,
[
force and distance are vectors with both magnitude and direction, work is a scalar with no direction.
Sailing wind (vector) is apparent wind (vector) plus boat velocity through the water (vector)
Kerenza
Well-Known Member
[QUOTE=iLens;6270376]Sorry to add another complication, but a book I'm reading* points out that the wind at the top of the mast can differ by "up to 300% in speed and 20-30 degrees in direction" from that experienced on deck. As the anemometer is usually at the top of the mast, we now have two versions of apparent wind.
One thing that hasn't been contentious is the standard 10m height reference.
The book also refers to "true wind" as the wind experienced by "a mast fixed in the water" - that is what people here have been referring to as "ground wind".
No, ground wind would be a mast fixed to the ground.
That means we need another term for the "computed wind", as shown by a Raymarine** wind instrument set to display "True" rather than "App". This "computed wind" is the dot product of the boat's speed and direction relative to the water and the wind relative to the anemometer, and as the angles are based on the boats fluxgate compass, its direction it is relative to magnetic north.
Bit of gobbledygook but addressed in previous post.
To determine the ground wind, you need to include the vector of the water relative to the ground - the "cause" of the lee bow effect - which brings us back to the original subject of the thread.
Finally, the "Actual" wind as experienced by the helmsman is either too little or too much and usually in the wrong direction
Don't think we'd ever go sailing if that we're true.
One thing that hasn't been contentious is the standard 10m height reference.
The book also refers to "true wind" as the wind experienced by "a mast fixed in the water" - that is what people here have been referring to as "ground wind".
No, ground wind would be a mast fixed to the ground.
That means we need another term for the "computed wind", as shown by a Raymarine** wind instrument set to display "True" rather than "App". This "computed wind" is the dot product of the boat's speed and direction relative to the water and the wind relative to the anemometer, and as the angles are based on the boats fluxgate compass, its direction it is relative to magnetic north.
Bit of gobbledygook but addressed in previous post.
To determine the ground wind, you need to include the vector of the water relative to the ground - the "cause" of the lee bow effect - which brings us back to the original subject of the thread.
Finally, the "Actual" wind as experienced by the helmsman is either too little or too much and usually in the wrong direction
Don't think we'd ever go sailing if that we're true.