True Wind - your definition.

[johnalison]

The problem didn't arise from any nefarious motives on the part of manufacturers. Long before Raymarine came along, when the people who were able to connect wind information and log information to calculate the wind over the water, it was natural for them to think in terms of a frame of reference centred on the boat. In terms of wind angle, the differences are usually so small that in practice, most of us ignore them, though they have an effect in relation to lee-bowing. The strongest tides that I normally sail in for long periods are about 2 1/2kn, making the difference in wind speed significant, with a 5kn range according to tide direction. This affects my sailing choices at the time, but there are few occasions when the difference in discussion matters much, except perhaps when recounting the horrors of one's last trip up the Wallet.

 

[Fascadale]

I want to fit a wind instrument to my boat. It will display apparent wind speed and I would prefer it to give ground wind speed rather than (manufacturers' definition) true wind speed.

Is there any system on the market that can do this?

I don't want another hole in the hull for a paddle wheel. I don't have one now and I'm not particularly interested in water speed. I have plenty of GPS information giving me SOG and COG

 

[lw395]

The problem didn't arise from any nefarious motives on the part of manufacturers. Long before Raymarine came along, when the people who were able to connect wind information and log information to calculate the wind over the water, it was natural for them to think in terms of a frame of reference centred on the boat. In terms of wind angle, the differences are usually so small that in practice, most of us ignore them, though they have an effect in relation to lee-bowing. The strongest tides that I normally sail in for long periods are about 2 1/2kn, making the difference in wind speed significant, with a 5kn range according to tide direction. This affects my sailing choices at the time, but there are few occasions when the difference in discussion matters much, except perhaps when recounting the horrors of one's last trip up the Wallet.

It goes back before wind instruments.
A quick look in my library finds True and Apparent wind defined in Hinton's 'Dinghy and Small Class Racing, published 1938.

Manfred Curry in his 1928 book 'Yacht Racing' uses the terms 'Real Wind' and Apparent Wind. Whether we can draw anything from True vs Real in something translated from German, I wouldn't know

In both cases the frame of reference is the boat, i.e the apparent wind is the True/Real Wind vector plus the boat speed vector.

 

[Mark-1]

What do you call the wind experienced by a boat drifting with the tide?

Never had a term for it. I'd probably have called apparent without the boat movement vectors. Or true wind with tide factored in.

Do you see any value in that information?

In the recent Bramblemet under reading thread it would have been very important - but nobody mentioned it there. (Care to guess why?)

Other value. Well, I once sailed through the Sound of Sleet in a gale and took some comfort that for part of the day apparent windspeed would drop by 9kts. (Although it didn't because the funnel effect of the Mountains was far more than the tide.) I've occasionally been crossing the channel in light stuff and thought "When the tide changes we'll have 4kts extra wind and a lift assuming nothing else changes.".

Have I never made a sail change decision or a go-no go decision base on anticipated wind increased or reduced by tide? Nope.

Have I ever used Ground wind with tide factored in for tuning? Nope, and now I've thought about it and I'm surprised anyone else does. Apparent works better for comparative tuning because it ignores all the values you don't care about. Wind direction and speed and STW are the only factors that matter in boat speed. You'd go just as fast in a flat calm with a 10kt wind generated by 10kts of tide as you would at slack tide with 10kts of Ground wind. You just don't care.

My own planing is done with Ground Wind Forecasts which I never correct for tide and I've never known anyone correct forecasts for tide.

On the water I only care about apparent wind because that's all I can detect at the time. Yes it possible that if I'm the tide changes I'm going to get 4 knots change - but I won't because I'm very likely to be staying out of the tide if any component of it is against me - that's two knots difference. So something that I'm aware of but not something that would change my actions.

So far nobody has stated the "killer app" of factoring tide into ground wind (or factoring tide out of Apparent wind) I'd be interested to know. Everything stated so far has been unconvincing.

 

[Lucky Duck]

Whether its a weather going tide or not has played a substantial part in when or if to make a passage or more than one occasion.

 

[RichardS]

I want to fit a wind instrument to my boat. It will display apparent wind speed and I would prefer it to give ground wind speed rather than (manufacturers' definition) true wind speed.

Is there any system on the market that can do this?

I don't want another hole in the hull for a paddle wheel. I don't have one now and I'm not particularly interested in water speed. I have plenty of GPS information giving me SOG and COG

I have a Raymarine ST60+ wind display which I can switch between True Wind and Apparent Wind with a single push of a button. I don't have a paddlewheel but I do have a CruzPro SOG-1 but the newer SOG-2 and GPS2 are even better.

I've no idea what the wind terms mean and I don't care in the slightest.

What I know is that if I'm motoring at 5 knots into a 5 knot headwind then the True Wind option will show 5 knots whereas the Apparent Wind option will show 10 knots. :encouragement:

Richard

 

[noelex]

I have a Raymarine ST60+ wind display which I can switch between True Wind and Apparent Wind with a single push of a button. I don't have a paddlewheel but I do have a CruzPro SOG-1 but the newer SOG-2 and GPS2 are even better.

That is a clever solution Richard.

The ST60 does not have the option to display ground wind but the CruzPro device fixes the problem. It looks like a good way of enabling the owners of older instruments to try a ground wind display. I think many cruising sailors will find this much better than the normal true wind or water referenced measurement.

 

[Yealm]

Yes I expect most if not all of them do. True wind is getting a bit old fashioned - I’m sure ground wind will the norm in the future and future sailors will look back on this forum with bemusement.

I have 10 year old tack tick instruments (now owned by Raymarine).

I blanked the paddle wheel aperture and instead feed in a GPS speed input- so it now reads ground wind and direction by default (instead of true wind).

I want to fit a wind instrument to my boat. It will display apparent wind speed and I would prefer it to give ground wind speed rather than (manufacturers' definition) true wind speed.

Is there any system on the market that can do this?

I don't want another hole in the hull for a paddle wheel. I don't have one now and I'm not particularly interested in water speed. I have plenty of GPS information giving me SOG and COG

 

[pyrojames]

I don’t think anything to do with marketing.

It’s just standard terminology. You need to have terms to distinguish wind speed calculated with a paddle wheel from wind sped calculated with GPS..

For the (wrong) majority who think True wind is defined relative to a fixed point in the earth, what do they call the wind speed on their instrument display using a paddle wheel (which the manufacturers call True Wind)?

It's only standard terminology for people with raymarine/simrad etc kit on a boat. I care about the true wind forecast, and the apparent wind that I feel while sailing. I can look at what simrad suggest is "true wind" but I know that it is their best estimation. For everyone else, meteorologists, pilots et al, the true wind has nothing to do with the tide.

 

[lw395]

I have a Raymarine ST60+ wind display which I can switch between True Wind and Apparent Wind with a single push of a button. I don't have a paddlewheel but I do have a CruzPro SOG-1 but the newer SOG-2 and GPS2 are even better.

I've no idea what the wind terms mean and I don't care in the slightest.

What I know is that if I'm motoring at 5 knots into a 5 knot headwind then the True Wind option will show 5 knots whereas the Apparent Wind option will show 10 knots. :encouragement:

Richard

That's still true wind relative to the bow of the boat though?
To get true wind with a compass direction, you need heading information.
Or are you taking that from a digital compass or autopilot?

 

[lw395]

It's only standard terminology for people with raymarine/simrad etc kit on a boat. I care about the true wind forecast, and the apparent wind that I feel while sailing. I can look at what simrad suggest is "true wind" but I know that it is their best estimation. For everyone else, meteorologists, pilots et al, the true wind has nothing to do with the tide.

No it is what nearly everybody with a jib and a compass has been calling true wind for the last 80 years at least.

 

[RichardS]

That's still true wind relative to the bow of the boat though?
To get true wind with a compass direction, you need heading information.
Or are you taking that from a digital compass or autopilot?

It gets that from the autopilot/fluxgate. I gave the simplest example but if I was motoring at 5 knots and the wind was 5 knots on the beam then the True Wind would still read 5 knots but the Apparent wind would read approx 7.5 knots.

Richard

 

[Yealm]

It’s got nothing to do with Raymarine.

ALL manufacturers and EVERYONE involved in wind calculations uses the same terminology!

True wind speed uses a paddle wheel (STW) input.
Ground wind speed uses a GPS (SOG) input.

You are out of date!!

It's only standard terminology for people with raymarine/simrad etc kit on a boat. I care about the true wind forecast, and the apparent wind that I feel while sailing. I can look at what simrad suggest is "true wind" but I know that it is their best estimation. For everyone else, meteorologists, pilots et al, the true wind has nothing to do with the tide.

 

[RichardS]

True wind speed uses a paddle wheel (STW) input.

Post #86 is your friend.

Richard

 

[johnalison]

Boat-centred True wind may be old-fashioned, but so am I, and it is what I want to know when sailing or motor-sailing downwind, or when motoring generally. A typical example is when motor-sailing in a slowly rising wind, when I will want to know when it is worth my while stopping motoring and continuing under sail. It is hard to judge this by eye and feel, or from the apparent wind, and the Ground wind is irrelevant.

 

[lw395]

It gets that from the autopilot/fluxgate. I gave the simplest example but if I was motoring at 5 knots and the wind was 5 knots on the beam then the True Wind would still read 5 knots but the Apparent wind would read approx 7.5 knots.

Richard

But if you were to stop head to wind (lets say N wind over the water for example), with the tide taking you West at 2 knots, your SOG would be 2 knots, your apparent would be 5 knots on the bow and Mr Ray Moron will think the true wind is North 3 knots . But the ground wind is actually 5.4 knots from 336deg

 

[Yealm]

In your example, how do you know it’s a slowly rising wind? Only ground wind will tell you.

True wind changes could be due to changes in atmospheric wind or tide.
Apparent wind chances could be due to changes in atmospheric wind, tide or boat speed.

Boat-centred True wind may be old-fashioned, but so am I, and it is what I want to know when sailing or motor-sailing downwind, or when motoring generally. A typical example is when motor-sailing in a slowly rising wind, when I will want to know when it is worth my while stopping motoring and continuing under sail. It is hard to judge this by eye and feel, or from the apparent wind, and the Ground wind is irrelevant.

 

[lw395]

In your example, how do you know it’s a slowly rising wind? Only ground wind will tell you.

True wind changes could be due to changes in atmospheric wind or tide.
Apparent wind chances could be due to changes in atmospheric wind, tide or boat speed.

Have you done any sailing?

 

[Yealm]

Yes I do the similar (tacktick allow you to simply substitute SOG for STW - it still labels it True wind I think even if it’s effectively now measuring ground wind)

Post #86 is your friend.

Richard

 

[RichardS]

But if you were to stop head to wind (lets say N wind over the water for example), with the tide taking you West at 2 knots, your SOG would be 2 knots, your apparent would be 5 knots on the bow and Mr Ray Moron will think the true wind is North 3 knots . But the ground wind is actually 5.4 knots from 336deg

No tide where I sail is the simple answer.

But yes, it's not 100% accurate in tidal areas but hopefully for most of us cruisers, most of the time, the wind speed and boat speed are such that the tidal induced error is not worth worrying about.

(I know that the Swellies surfers or the Corryvrecken whirlers will probably pile in now ..... but please relax and chill )

Richard