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Polar diagrams

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Rubato View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rubato Quote  Post ReplyReply Direct Link To This Post Posted: 13 January 2009 at 21:25
So very true!
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christian View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote christian Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2009 at 16:04
TBS1 TWA1 TBS2 TWA2 TBS3 TWA3 TBS4 TWA4 TBS5 TWA5 TBS6 TWA6 TBS7 TWA7 TBS8 TWA8 TBS9 TWA9 TBS10 TWA10
6 3.10 45.50 4.89 52.00 5.26 60.00 5.62 75.00 6.04 90.00 5.84 110.00 5.48 120.00 4.77 135.00 3.98 150.00 3.44 142.70
8 3.78 43.80 5.92 52.00 6.37 60.00 6.77 75.00 7.09 90.00 6.91 110.00 6.65 120.00 5.94 135.00 5.07 150.00 4.39 148.60
10 4.33 44.50 6.63 52.00 6.98 60.00 7.47 75.00 7.75 90.00 7.60 110.00 7.36 120.00 6.84 135.00 6.07 150.00 5.25 149.10
12 4.64 42.40 7.02 52.00 7.44 60.00 7.78 75.00 8.10 90.00 8.05 110.00 7.89 120.00 7.47 135.00 6.84 150.00 6.04 160.70
14 4.82 40.10 7.24 52.00 7.66 60.00 8.05 75.00 8.27 90.00 8.45 110.00 8.28 120.00 7.93 135.00 7.43 150.00 6.68 168.50
16 4.94 40.50 7.39 52.00 7.77 60.00 8.24 75.00 8.41 90.00 8.84 110.00 8.72 120.00 8.29 135.00 7.88 150.00 7.22 170.50
20 5.03 40.40 7.51 52.00 7.88 60.00 8.41 75.00 8.83 90.00 9.30 110.00 9.61 120.00 9.14 135.00 8.60 150.00 8.03 175.40
Hanse 370e # 346
X Hanse 312 #247
1991 11:Metre One Design 2003 Stingray 5,2 RIB 90 Suzuki X First 25 X First Class 8 X Triss Norlin
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christian View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote christian Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2009 at 16:12
This is my polar for 110% jib and genakker on boom.
Works with my silva system.
Shows target boatspeed and target angels.
 
Hanse 370e # 346
X Hanse 312 #247
1991 11:Metre One Design 2003 Stingray 5,2 RIB 90 Suzuki X First 25 X First Class 8 X Triss Norlin
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Strand View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Strand Quote  Post ReplyReply Direct Link To This Post Posted: 21 January 2009 at 22:21
Hi Christian, thanks for sharing.
As far as I can see you have recalculated the basic IMS figures into speed. Do you reach targetspeed and angles when sailing?
Bjørn

H430 # 350 - "Diva"

Previously H370e #002 - "FUS"
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colincooper View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote colincooper Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2009 at 06:40
From Hanse Site TWA TWA TWA TWA TWA TWA TWA TWA
52 60 75 90 110 120 135 150
Wind TWA AWA BS VMG AWA BS VMG AWA BS VMG AWA BS AWA BS AWA BS AWA BS AWA BS AWA BS VMG TWA AWA BS VMG
6 45.5 30 3.1 2.2 29 4.89 3 32 5.26 2.6 39 5.62 45 6.04 56 5.84 64 5.48 83 4.77 112 3.98 3.4 143   110 3.44   2.7
8 43.8 30 3.78 2.7 30 5.92 3.6 34 6.37 3.2 41 6.77 48 7.09 61 6.91 69 6.65 87 5.94 115 5.07 4.4 149   120 4.39   3.7
10 44.5 31 4.33 3.1 32 6.63 4.1 36 6.98 3.5 44 7.47 52 7.75 66 7.6 75 7.36 92 6.84 117 6.07 5.3 149   123 5.25   4.5
12 42.4 31 4.64 3.4 33 7.02 4.3 38 7.44 3.7 47 7.78 56 8.1 71 8.05 80 7.89 97 7.47 121 6.84 5.9 161    143 6.04   5.7
14 40.1 30 4.82 3.7 35 7.24 4.5 40 7.66 3.8 49 8.05 59 8.27 74 8.45 84 8.28 101 7.93 124 7.43 6.4 169    158 6.68   6.5
16 40.5 31 4.94 3.8 36 7.39 4.5 41 7.77 3.9 51 8.24 62 8.41 77 8.84 87 8.72 105 8.29 127 7.88 6.8 171    163 7.2   7.1
20 40.4 33 5.03 3.8 38 7.51 4.6 44 7.88 3.9 55 8.41 66 8.83 83 9.3 91 9.61 109 9.14 131 8.6 7.4 175    172 8.03    8
 
TWA = true wind angle
AWA = apparent wind angle
BS = boat speed
VMG = velocity made good (either upwind or downwind).
Wind = wind
 
Here are the calculated figures from those given by Christian.  I did this to see the apparent wind angles he gets and the resulting speeds.  The columns are in blocks for the true wind angles given at the top of the table.  For the first and last block (max up and down wind) the TWA differs for each row.  In all blocks each row is a different wind strength.  For each TWA read off the AWA, BS and VMG for the different wind strengths.  I just did VMG for the upwind and downwind angles - with VMG being to either straight upwind or straight downwind.
 
Looks like 30 degrees apparent is the limiting factor going upwind.  I'm going to have to do some more trimming.  My normal best is more like 35 degrees apparent upwind.  What do others find?  
 
Also, it is interesting that the apparent wind angle varies little for a wide range of true wind angles when beating upwind.  When we cruise on autopilot I dial in the apparent wind angle and the autopilot steers to that.  However, that gives a wide range of true angles for very similar apparent angles.  It would seem likely that autopilot steering like that would not be the best policy - better to steer to a true wind angle.  I'm going to have to experiment a little on the water.  Note that this will not interest racers - just cruisers on a long beat.
 
Christian's figures seem about 0.2kts off the official polars.  Pretty good if you get that.  I'm not a racer - just a cruiser - and I'd say my norms are about 10% below Christian.
 


Edited by colincooper - 22 January 2009 at 07:15
Colin (owner of Hilde - a 370)
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Johan Hackman View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Johan Hackman Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2009 at 10:24
Colin et all, I think I just learnt something about sailing from your table that I didn't realise before. The apparent wind angle increases in spite of the boat going faster when the wind is stronger. I actually thought that it would be the same or decrease.

In medium winds I try to sail between 25 and 30 degrees to the apparent wind. I shall try to sail a little lower in strong winds next time.

Johan

Edited by Johan Hackman - 22 January 2009 at 10:59
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colincooper View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote colincooper Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2009 at 11:02
Johan,
 
Yes - the table is instructive in several respects.  It explained to me why various sailing rules-of-thumb actually work.  For example, I've always thought that the sail seems sheeted in quite hard when sailing at 90 to the wind.  The table shows that the apparent is still quite low.
 
It also strikes me that one could benefit from a much better wind/boat speed indicator that you currently get.  Have racers experimented along these lines?
 
Finally - what is the secret to sailing at 25-30 degrees apparent?  On a Hanse the jib is easy - sheet in block-to-block.   Where do you place the boom?  Presumably your traveller is a long way upwind.
 
 
 
 
 
Colin (owner of Hilde - a 370)
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Johan Hackman View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Johan Hackman Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2009 at 11:16
I talk to much. Now I seem to have said that I know anything about sailing. I don't, I'm just guessing.

However, Stampe says that the boom is parallell to the centerline and that he thinks that the "25-30 statement" only applies to ideal conditions - flat water and a steady medium wind.

Johan
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Johan Hackman Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2009 at 12:26
Colin, what do you mean by "wind/boat speed indicator"?

Johan
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Par Johansson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Par Johansson Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2009 at 13:10
The polars are useful in many situations. There are situations where they can mislead you though. Someone mentioned to sail a bit lower in stronger winds. Anyone that has done a lot sailing knows this won´t increase your VMG, you have to retrim the sails avoiding the boat gets knocked down and end up sailing a course to low. In stronger winds with flatwater you need to even "stall" a bit in the gusts and be very active with the main. In stronger winds with high seas, i buy the argument of sailing a few degrees lower going up the waves (also depending on the direction of the waves). This requires alot of work from trimmers to change gear all the time. I believe the polars are even more useful going downwind where it is not as easy to "feel" the right TWA, especially if you don´t have any boats around you. The polars gives you good guidance sailing downwind. With light planing boats like a Mumm 30 or similars, the opposite theory applies. The more wind you get sailing downwind the lesser TWA will give you the optimum VMG. Hanse and other displacements yachts you increase the VMG sailing downwind by sailing with a greater TWA when the wind increases.

Pär


Edited by Par Johansson - 22 January 2009 at 13:12
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