Technique: Upwind Problems

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Upwind Problems

Printed From: Yachts and Yachting Online
Category: Keelboat classes
Forum Name: Technique
Forum Discription: 'How to' section for keelboat questions and answers
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=7325
Printed Date: 08 Dec 19 at 1:03am
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Topic: Upwind Problems

Posted By: nmartin
Subject: Upwind Problems
Date Posted: 01 Nov 10 at 9:31am

Hi,

I'm currently skippering a First 27.7. Downwind and on reaching legs we easily keep with or are faster than the fleet. However upwind we loose lots of ground. We are always a minute or two behind the fleet even if we win the start.

I've noticed that on port tack we sail as much as ten degrees higher than on starboard and can usually average about a knot more boat speed!

Any ideas as to what this might be? I've ruled out some of the obvious issues like weight imbalance, jib sheet track position etc... could it be a rig problem?

All comments welcome!

Nick

Replies:

Posted By: JimC
Date Posted: 01 Nov 10 at 9:36am

Rig or keel: sure seems as if something's asymettrical...

Posted By: Martin - LSC
Date Posted: 01 Nov 10 at 11:13am

The Beneteau 27.7 tends to lose out upwind a little . However check the rig is central (side to side in the boat - tape/ dyneema halyard from mast head to toe-rail on each side)

If the sender for the log is not central in the boat, you'll get a slightly different reading tack to tack, likewise if the sender is not directly in line with (or parallel to) the centre line of the boat.

As already said, if the keel is assymetric (not faired and checked) then this also will cause a speed differential tack to tack.

You can also check by measuring from the bow that the cars are actually equa distant.

Jim at Maiden Marine (Lake Windemere) is a good guy for tips on getting all things Beneteau to race.

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FINN 57 LSC

Posted By: nmartin
Date Posted: 01 Nov 10 at 1:09pm

Thanks for the advice - I'll double check the cars and measure how central the rig is.

Posted By: rb_stretch
Date Posted: 01 Nov 10 at 5:06pm

Originally posted by nmartin

Thanks for the advice - I'll double check the cars and measure how central the rig is.

Have to say I've never had a keel boat where both tacks were identical, despite checking everything was central. It is very difficult to calibrate the wind to be spot on, often waves are not always directly in line with the wind and then you have tidal effects......almost impossible to account for it all.

Posted By: Isis
Date Posted: 03 Feb 12 at 11:48am

Im willing to bet your observed change in speed and TWA is an instrumentation setup or calibration issue. Remember that even when everything is central you have things like wind sheer which affect readings from tack to tack. On high end instrumentation its possible to dial all this out so that your numbers are identical, but many people prefer to leave it as it and calculate the shear offset in their heads as you go.

If you are sure its a boat speed issue then making sure the rig is central and in line with the keel is the first priority. If you cant get the boat out the water then measuring from the mast tip to the toe rail on each side as suggested above is a reasonable approach but never assume anything is truly symetrical. Its more important to have the mast in line with the keel than to have it perpendicular to the deck.

There are any number of other things it might be related too but the rig being out is the most common and easiest to sort out so its worth starting there.

Posted By: nathan
Date Posted: 03 Feb 12 at 1:40pm

All my money would be on dodgy instruments...

Posted By: bert
Date Posted: 03 Feb 12 at 2:43pm

"all my money" would be on the question being answered ----- last year

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Posted By: NickM
Date Posted: 03 Feb 12 at 6:51pm

I once sailed in a Sonata that had a slightly sideways bent mast and it behaved exactly as you desibe: much faster and higher on the tack towards which the mast was bent. Have you looked up your track to check it is straight?

Posted By: DFF
Date Posted: 13 Sep 12 at 11:49am

All my money would be on the IRC break this boat sails in: you are against 33 ft - 40ft all and sundry most likely and they will :

1) go faster upwind due to pure water line legnth- tweaks to rig get you quarter of a knot , 8 feet on the water line give you a knot!

2) give you masses of wind shadow and disturbed flow as they sail ahead of you due to 1: try sailing out to the right hand side of the course asap, even start behind the transom of a bigger boat at the committee boat end and tack away as soon as you can to the RHS.

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Crewing on a Melges 24, against my better judgement...

Posted By: G.R.F.
Date Posted: 13 Sep 12 at 1:17pm

It's probably tide. Are the instruments GPS based?

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Posted By: Peaky
Date Posted: 13 Sep 12 at 1:27pm

How many times do old threads need reviving? Seems to be a specialty of yours DFF?

One way or another, I hope the OP's problem has been sorted by now!

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Posted By: graeme_wilson
Date Posted: 20 Feb 13 at 1:56pm

Originally posted by G.R.F.

It's probably tide. Are the instruments GPS based?

Did you get a reply to this ? would like to know myself