A while ago somebody was after one of these. Don't remember who. I took this one out of my boat today and I will be having the hole glassed in.

If anybody wants it (free), just PM me with name and address and I will send it.

I am going to let the GPS tell me how much fun I am having.

On it's way mate.

Likewise. What method using to patch hole?

Bit worried about this trend to rely only on SOG and ignore BWS when the comparison between the two is one of the best navigational planning tools.

lydia said..
Bit worried about this trend to rely only on SOG and ignore BWS when the comparison between the two is one of the best navigational planning tools.

They are handy for detecting current or for racing and adjusting sail trim etc. The downside is l keeping the paddle wheels clean. I reckon it's two years since I even took the cover off mine. Commonsense and knowing how fast your boat really travels through the water in the conditions is probably enough for most people when using GPS.

lydia said..
BWS (or same systems use BSD) but boat water speed or speed through the water as opposed to speed over ground.

Difference on the east coast can be over 70 miles day if you are using this properly.

I don't use put the log in every time I sail but on a long passage I always put it in

Couldn't agree more. I use mine when passage making and consider it very important. I pull it back out to keep it clean when I'm not using the boat. (the bung is not meant to roll around in the bottom of the hull gathering dust).

The log is also required by your wind instruments to determine "apparent wind"

The log is also required by your wind instruments to determine "apparent wind"

No,no,no a thousand times no. The true wind calc MUST be made from SOG.

You are at anchor, zero wind speed, 3 knot current by your paddle wheel. You vector add the paddle wheel speed to indicated wind speed to get true wind speed, answer 3 knots. False result. You vector add the speed over ground ( 0 ) to apparent wind speed and you get the correct answer - zero.

Sorry cisco, I'm just getting over the dreaded coughing disease and I have become a grumpy old man.

Raymarines speed /Temp transducer is around the $150 saves me filling in the hole

The masthead sensor measures Apparent wind. The Raymarine system calculates True wind, relative to the boat, based on Apparent Wind and speed through the water. There's no option (at least, in the ST60) for using SOG from a GPS instead - I seem to remember reading somewhere that this is due to the formal definition of the various NMEA parameters. I don't know what other manufacturers do.

I wouldn't be without a paddlewheel and the data it provides. I pull mine out and give it a coat of this stuff every couple of months:
www.whitworths.com.au/transducer-paint-92ml

It's all a matter of definitions. This version of True Wind, which has been around since pre GPS days, is "True" relative to the water surface, whether that is moving due to currents or not. It is calculated from Apparent speed and direction, with appropriate vector offset by speed through the water.

There's another parameter, which I believe is called "Ground wind", which as you might expect is relative to earth's surface. Calculating that would require SOG.

You could probably make a case for either option being the more useful under various circumstances. However, as currents rarely get over 2-3 knots, and wind is rarely of any relevance unless it's several times that, it's hairsplitting in my view.

fills a hole anyway
I've a belly full of wind at the moment
I guess that's true wind and Sog

That is just wrong
Try again.

Thanks Phoenix Star it just clicked

cisco said..

If we are using a wind instrument to achieve more efficient sailing, why would we be concerned with "True" wind speed and direction??

Surely if the boat is sailed to the best "Apparent" wind direction relative to the course we want, that is as good as it gets isn't it??

You will end up chasing the AWA with boat speed changes.

FreeRadical said..

PhoenixStar said..

QLDCruiser said..
It's all a matter of definitions. This version of True Wind, which has been around since pre GPS days, is "True" relative to the water surface, whether that is moving due to currents or not. It is calculated from Apparent speed and direction, with appropriate vector offset by speed through the water.

There's another parameter, which I believe is called "Ground wind", which as you might expect is relative to earth's surface. Calculating that would require SOG.

You could probably make a case for either option being the more useful under various circumstances. However, as currents rarely get over 2-3 knots, and wind is rarely of any relevance unless it's several times that, it's hairsplitting in my view.

True wind is something of a misnomer in that it is shown relevant to the boats heading, as is apparent wind and is never dependent on current. If you know SOG you don't need to know about the interaction between boat speed through the water and current.

True wind is found by vector addition of SOG to Apparent wind and is shown as speed and direction relevant to the boat. And current is only relevant in that it affects SOG. If you need to know the current then you need a paddle wheel and GPS to do another vector addition.

I don't know why this is so confusing. It's just the way it is.

You say true wind is not dependent on current (correct), but then say true wind is calculated from SOG, which is dependent on current. Makes no sense.

true wind is calculated from apparent wind and boat speed.

ground wind is calculated from apparent wind and SOG.


www.sailingworld.com/what-are-my-electronics-telling-me-about-boatspeed-and-heading/?image=0

Of course SOG is dependent on current but only SOG is used in the calc, ie after current has had its effect on boat speed.

To use a simple example, you are anchored in 3k current, no apparent wind, no true wind. If you use speed through the water (3k) with apparent wind (0) you would get a true wind of 3 knots, obviously false. If you use SOG (0) with apparent wind (0) you get the right answer, true wind 0. Ground wind needs input from the ships COG for its calc. and is not shown on a wind instrument hooked up to NMEA or a proprietary net.

True wind is mainly useful for planning the next leg, knowing how you will be placed for the mark and your best sail set or as an indication if you will be over canvassed coming off a run.

Stuart Quarrie "Race Navigation" published by Stanford Maritime Limited in 1982 is as good an authority as any.

PhoenixStar said..

FreeRadical said..

PhoenixStar said..

QLDCruiser said..
It's all a matter of definitions. This version of True Wind, which has been around since pre GPS days, is "True" relative to the water surface, whether that is moving due to currents or not. It is calculated from Apparent speed and direction, with appropriate vector offset by speed through the water.

There's another parameter, which I believe is called "Ground wind", which as you might expect is relative to earth's surface. Calculating that would require SOG.

You could probably make a case for either option being the more useful under various circumstances. However, as currents rarely get over 2-3 knots, and wind is rarely of any relevance unless it's several times that, it's hairsplitting in my view.

True wind is something of a misnomer in that it is shown relevant to the boats heading, as is apparent wind and is never dependent on current. If you know SOG you don't need to know about the interaction between boat speed through the water and current.

True wind is found by vector addition of SOG to Apparent wind and is shown as speed and direction relevant to the boat. And current is only relevant in that it affects SOG. If you need to know the current then you need a paddle wheel and GPS to do another vector addition.

I don't know why this is so confusing. It's just the way it is.

You say true wind is not dependent on current (correct), but then say true wind is calculated from SOG, which is dependent on current. Makes no sense.

true wind is calculated from apparent wind and boat speed.

ground wind is calculated from apparent wind and SOG.


www.sailingworld.com/what-are-my-electronics-telling-me-about-boatspeed-and-heading/?image=0

Of course SOG is dependent on current but only SOG is used in the calc, ie after current has had its effect on boat speed.

To use a simple example, you are anchored in 3k current, no apparent wind, no true wind. If you use speed through the water (3k) with apparent wind (0) you would get a true wind of 3 knots, obviously false. If you use SOG (0) with apparent wind (0) you get the right answer, true wind 0. Ground wind needs input from the ships COG for its calc. and is not shown on a wind instrument hooked up to NMEA or a proprietary net.

True wind is mainly useful for planning the next leg, knowing how you will be placed for the mark and your best sail set or as an indication if you will be over canvassed coming off a run.

Stuart Quarrie "Race Navigation" published by Stanford Maritime Limited in 1982 is as good an authority as any.

We'll have fun assessing your performance against polar plots using a SOG derived TWS!