myHanse.com - Hanse Yacht Owners Website myHanse.com - Hanse Yacht Owners Website myHanse.com - Hanse Yacht Owners Website myHanse.com - Hanse Yacht Owners Website

Welcome to myHanse.com the forum for Hanse Yachts owners throughout the world.

Forum Home Forum Home > Hints and Tips > 370 / 375
  New Posts New Posts RSS Feed - Has anyone tried moving the speedo to centerline
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Has anyone tried moving the speedo to centerline

 Post Reply Post Reply Page  <12345>
Author
Message
Johan Hackman View Drop Down
Admiral of the Fleet
Admiral of the Fleet
Avatar

Joined: 24 August 2005
Location: Sweden
Status: Offline
Points: 3753
Post Options Post Options   Thanks (0) Thanks(0)   Quote Johan Hackman Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 14:20
A couple of years ago I looked at a sensor called CS4500 but it does not seem to be in the market anymore.

Johan
Back to Top
Johan Hackman View Drop Down
Admiral of the Fleet
Admiral of the Fleet
Avatar

Joined: 24 August 2005
Location: Sweden
Status: Offline
Points: 3753
Post Options Post Options   Thanks (0) Thanks(0)   Quote Johan Hackman Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 14:21
Back to Top
Johan Hackman View Drop Down
Admiral of the Fleet
Admiral of the Fleet
Avatar

Joined: 24 August 2005
Location: Sweden
Status: Offline
Points: 3753
Post Options Post Options   Thanks (0) Thanks(0)   Quote Johan Hackman Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 14:23
Puuhhh! It took me four posts two rewrite the post that was sent to the Moderator instead of the forum.

Anyway, the link above is to a sensor I find very interesting. I will read about it for sure.

Johan

Edited by Johan Hackman - 07 July 2017 at 14:53
Back to Top
samuel View Drop Down
Admiral of the Fleet
Admiral of the Fleet


Joined: 26 December 2004
Location: United Kingdom
Status: Offline
Points: 2009
Post Options Post Options   Thanks (0) Thanks(0)   Quote samuel Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 14:46
Many years ago I had 2 paddle wheels fitted on my earlier boat. One each side of the hull.This was because the paddle wheel one side would often come too near the surface as the boat always sailed on its ear.
There was a mercury switch rather like a horizontal egg timer that was pivoted in the middle. When the boat heeled one way the mercury ran to one side & the egg timer tilted & set an electrical connection to one paddle wheel. On the opposite tack the opposite would happen.
Could you have 2 paddle wheels & a change over switch.
 That way you could get 2 wrong readings rather than one correct & one incorrectThumbs Up



Edited by samuel - 07 July 2017 at 14:50
Daydream Believer- Hanse 311- No GBR9917T- Bradwell Essex
Back to Top
High Time View Drop Down
Rear Admiral
Rear Admiral


Joined: 04 September 2012
Location: Portsmouth UK
Status: Offline
Points: 628
Post Options Post Options   Thanks (0) Thanks(0)   Quote High Time Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 17:08
True wind is the wind speed and direction measured by a stationary (wrt the ground) sensor. 

The only way to fully allow for all vectors affecting the motion of the boat is to subtract the SOG vector (i.e. including COG) from the apparent wind vector.

Any mathematical function using STW will not always eliminate all the motion of the boat (current, leeway etc).

It is disappointing that only high end wind instruments allow the option to use SOG/COG to give TWS/TWD.
Roger

High Time (415 #038)
Back to Top
Johan Hackman View Drop Down
Admiral of the Fleet
Admiral of the Fleet
Avatar

Joined: 24 August 2005
Location: Sweden
Status: Offline
Points: 3753
Post Options Post Options   Thanks (0) Thanks(0)   Quote Johan Hackman Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 17:21
On a boat, True Wind is the wind that blows across the water. The electronics have traditionally been designed to show you this from the beginning.

If you want the wind in relation to the ground you need to find another name for it. It will however be less helpful kind of information when you are sailing.

Mathematically it is not enough to subtract the velocity over ground from the apparent wind. You will also have to make a relation between the boat's centreline and the rest of the calculation, so to speak.

I have been discussing this for years, both in this forum and Panbo.com but I have had a hard time convincing people I am right. Either I am the new-born Einstein or the village idiot.

Johan

Edited by Johan Hackman - 07 July 2017 at 17:28
Back to Top
High Time View Drop Down
Rear Admiral
Rear Admiral


Joined: 04 September 2012
Location: Portsmouth UK
Status: Offline
Points: 628
Post Options Post Options   Thanks (0) Thanks(0)   Quote High Time Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 17:29
Originally posted by Johan Hackman Johan Hackman wrote:


There is a 10 knot Southerly wind and a 10 knot Northerly current, i.e. the wind blows in exactly the same speed and direction as the water is flowing. You will not have any wind at all while there will be a 10 knot wind across the nearest land. Standing on the shore will be windy but drifting in your boat will be windless. That's because one wind information is the wind across land and the other wind across water.

Therefore 18 knots is correct as long as you want the wind across the water, and that is going to be the information you are looking for if you are sailing.

Johan

Johan

In your example above, the TWS is always 10 knots. It's the AWS that is zero, assuming your STW is also zero. As soon as you have some motion relative to the water, your AWS will not be zero but the TWS will remain at 10 knots.
Roger

High Time (415 #038)
Back to Top
Johan Hackman View Drop Down
Admiral of the Fleet
Admiral of the Fleet
Avatar

Joined: 24 August 2005
Location: Sweden
Status: Offline
Points: 3753
Post Options Post Options   Thanks (0) Thanks(0)   Quote Johan Hackman Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 17:44
If the water and the air both are moving at the same speed and in the same direction there will be no wind. You will not be able to sail.

You could motor and then create an apparent wind that is the same speed as your boat speed through the water, but in the exact opposite direction.

If you are out there with no wind you could still see flags on the shore fluttering. There will be wind on the shore but not where you are.

If you are walking at the speed of 10 knots on the pavement your velocity in reference to the ground will be 10 knots. If you are holding your girlfriend's hand and she is walking at the same speed and direction you will not loose her. The velocity away from her is zero.

Johan
Back to Top
High Time View Drop Down
Rear Admiral
Rear Admiral


Joined: 04 September 2012
Location: Portsmouth UK
Status: Offline
Points: 628
Post Options Post Options   Thanks (0) Thanks(0)   Quote High Time Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 20:54
Johan

Everything you say is correct. However, it doesn't alter the fact that the TWS in your example is always 10 kts whether you are sailing, motoring or walking your girlfriend..

The apparent wind changes dependent on the motion of the boat (relative to the ground) and it is really only the apparent wind that is of any use to the skipper when sailing. However, knowing the true wind can be useful when entering a marina, lock or other slow speed manoeuvre, or maybe planning ahead for a sail change.
Roger

High Time (415 #038)
Back to Top
High Time View Drop Down
Rear Admiral
Rear Admiral


Joined: 04 September 2012
Location: Portsmouth UK
Status: Offline
Points: 628
Post Options Post Options   Thanks (0) Thanks(0)   Quote High Time Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2017 at 21:13
Hi Johan

I've just found an interesting paper that explains (more clearly than I could), the maths behind the calculation of true wind on a moving boat.


Just to bring us back to the original subject of this thread, the last paragraph of the paper above suggests a simple way to check if your speedo is accurate on both tacks.





Edited by High Time - 07 July 2017 at 21:22
Roger

High Time (415 #038)
Back to Top
 Post Reply Post Reply Page  <12345>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 11.04
Copyright ©2001-2015 Web Wiz Ltd.

This page was generated in 0.046 seconds.

Links : www.hanseyachts.co.uk www.hanseyachts.com www.fjordboats.co.uk www.dehler.co.uk www.varianta.co.uk