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glmark 06-10-2011 10:58 AM

weather helm?
 
I was out in our Hunter 25 last night. 20kt breeze. Used only the 110 genoa. I had considerable weathe helm. Why would that be? A headsail alone should give me lee helm correct?

DwayneSpeer 06-10-2011 11:15 AM

main sail
 
Weather helm is an artifact of the balance of the forces and yes a large genoa can generate weather helm. You were sheeted too tight for the conditions.

jackdale 06-10-2011 11:16 AM

Quote:

Originally Posted by glmark (Post 739243)
I was out in our Hunter 25 last night. 20kt breeze. Used only the 110 genoa. I had considerable weathe helm. Why would that be? A headsail alone should give me lee helm correct?

In theory, yes.

Heel will also generate weather helm.

RichH 06-10-2011 11:44 AM

Weather helm is a much much more complex issue than the simple relationship between The combined geometry of the sails (CE) and the geometry of the hull (CLR).

The 'dynamics' (aero & hydro) as developed by the sails shape and hulls shape are equally important .... and there are conditions that 'mimic' so called weather helm --- eg. the boat skidding sideways and giving undue 'side pressure' to the rudder.

The first aspect to sort this all out to be sure that the wake is coming off the boat's stern in a more or less straight line (no more than about 5 degrees difference than the centerline of the boat. If more than about 5 then the boat is skidding and developing undue side forces on the rudder which may feel like and may 'mask' weather helm. Chief causes of 'skidding' is the keel or centerboard held at a large heeling angle which reduces the lateral resistance (via trigonometry). Next major cause of skidding is a too loose rigging tension which allows the rigging/rig (chiefly the forestay) to sag drastically to the leeward side of the boat ... making the 'lines of force' as generated by the sails to be not parallel to the centerline of the boat.

Sail SHAPE has a strong influence on 'weather helm' as the 'balance' is determined by the 'actual' or 'adjusted' position of where the maximum draft occurs in the sail ... adjusted primarily by halyard (and/or 'cunningham') tension. This effect of correcting weather helm by adjust where this 'position of maximum draft' (POMD) occurs is quite important when using 'stretchy' sails such as those made from woven dacron - ie. the tighter the luff/halyard the further forward the POMD, and vice versa.

So, sail shape, how precisely one 'raises' and 'sets' the sails, how well the rig is tensioned, how fast the hull is moving through the water also determine 'helm balance'.

For the specific case of sailing (on a sloop rig) with just a 'small' jib up, in all probability you had the jibs clew trimmed in too tight towards the boats centerline and the boat was 'skidding' off to leeward. Most probably if you would have 'opened' the jib a bit you would have developed better 'dynamics' for less helm pressure. Next time you sail with just a jib (or any other combo) when you 'think' you have 'weather helm' the first thing you should do is LOOK AT THE WAKE COMING OFF OF THE STERN ... if the wake is coming off the stern in an almost dead straight (not greater than 5 angle) then you have 'weather helm', if more than about 5 then you are 'skidding' off to leeward. Once you are skidding the keel or centerboard will not be operating in a correct hydrodynamic flow and will be developing 'strange' patterns of turbulence and most certainly the keel/centerboard will not be 'lifting' or 'resisting' correctly - destroying or greatly altering the effect of static 'center of lateral resistance' CLR Just like the sails, you also must 'fly' the keel/centerboard (and the rudder) correctly !!!!!

Rx Its NOT weather helm if the wake isnt coming nearly straight off the stern. If the wake is not coming straight off (greater than about 5) AND there is a lot of 'helm pressure' then the boat is probably 'skidding'.
If youre flying just a small jib on a sloop you have to keep the clew quite far from the boats centerline ... or skid !!!

hope this helps

chef2sail 06-10-2011 12:14 PM

Good explaination Rich

jackdale 06-10-2011 12:15 PM

Rich

Great response - :thewave:

Can we quote you?

RichH 06-10-2011 12:33 PM

Quote:

Originally Posted by jackdale (Post 739283)
Rich

Great response - :thewave:

Can we quote you?

Sure ... but I ask for only in venues or written articles that are 'broadcast' free of charge and in which you dont receive 'compensation', please.

glmark 06-10-2011 12:59 PM

Great responses! Thanks! I can't wait to go out and apply this new knowledge! My boat has been in the lake for 5 weeks and I've only been out 4 times! The weather here has not been cooperating, so I've decided that I better learn to like it rough or I'll never get out.


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