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-   -   Weather-helm (http://www.sailnet.com/forums/seamanship-navigation/74198-weather-helm.html)

EJO 05-06-2011 12:28 PM

Weather-helm
 
I just need a theory confirmed. I have a lot of weather-helm due to an old full sail and possible mis-tuned mast.

Am I correct by reducing my weather-helm if leaning my mast forward and tightening up my outhaul clew and my cunningham to flatten my sail a little.

The main question is should a lean my mast forward a little (shorten the fore-stay)

RichH 05-06-2011 01:07 PM

Weather helm with respect to old woven dacron sails can be attributed to mainsail SHAPE ... ie.: the position along the horizontal chord of the sail where the maximum draft occurs.

Here's an article Ive written on how to 'properly' raise a woven dacron sail and the methods/suggestions to follow so if that this 'proper raising and stretch-out' doesnt correct weather helm then what to do about it. Once this methodology fails to correct so-called WEATHER HELM, then and only then, should the mast be 'raked'.

How to properly RAISE a woven dacron mainsail - SailboatOwners.com

EJO 05-09-2011 01:14 PM

Rich thanks for the article. This is what I was planning on doing this season using my cunningham (not used last season) and raking the mast slightly.
I'll report back sometime in June with the results.

RichH 05-09-2011 01:31 PM

Suggest you rake the mast only as 'last resort' to correct for 'helm balance' !!!!!!
Also suggest that you contact your mast manufacturer and adjust-in the proper amount of mast 'pre-bend'. Prebend is also usually considered/corrected for in sail design so if your mast isnt at the proper pre-bend configuration ... the sail will 'more full' than the 'design'; more full shape increases (slightly) 'helm balance'.
If you dont know the mfgr. then put in 3/4" forward pre-bend in a single spreader rig and 1/2" for each spreader on a multi-spreader rig.
an example of setting pre-bend from the 'net': A Mast Tuning Guide - The Light Version or do websearch for "prebend + mast". Seldén masts have a very good source of info on prebending - Seldén Mast AB

;-)

BubbleheadMd 05-09-2011 01:44 PM

Quote:

Originally Posted by EJO (Post 728594)
Rich thanks for the article. This is what I was planning on doing this season using my cunningham (not used last season) and raking the mast slightly.
I'll report back sometime in June with the results.

Dang, you haven't even applied any cunningham yet? Definitely try all of your sail shaping tools before moving your mast around.

Yes, check your pre-bend as Rich says. Luffs are cut slightly curved, and the pre-bend helps get the luff tight. When sailing upwind in a moderate breeze, put your outhaul and cunningham on to get the sail flat and move the draft forwards. Downwind, apply some vang.

If you don't have a draft stripe, you might purchase and apply one. It'll help you see if the belly is moving forwards or not.

Bottom line- Try to pull the belly out of the sail first. It may not be blown out. Hopefully this will lessen your weather helm.

One final thought- Recently followed a thread on another forum about a fellow who had horrendous weather helm. It turns out that his rudder had hit something and the rudder shaft was bent aft a few degrees. It's amazing the difference just a few degrees made. He carefully straightened it and weather helm disappeared.

If you've seen your boat out of the water, then disregard this last part.

EJO 05-09-2011 02:26 PM

OK Gentlemen (Rich/Bubblehead) it is great what you are saying, but be advised I'm working with a almost 40 year old deck-stepped mast and an not original added rollerfurling system that has 3 extra links on the bottom of the main-stay and I do not have a quick adjustable (double chained) back-stay. The only adjustment (turn-buckles) I have are on my 6 shrouds (4 lower & 2 upper with single spreader) and single back-stay. Pre-bending my 38ft tall old mast sounds iffy.
I don't know the exact age of my newest main sail but I expect 12-16 years old so yes it's lazy and blown out.
I'm not racing the boat I just want to get rid of some excessive weather-helm and thought flattening the sail (outhaul/cunningham) and leaning the mast slightly forward by taking out one of the snap-shackles would do that.
Hey when I windsurf I lean my mast forward to fall-off and pull it aft to go windward.

RichH 05-09-2011 03:27 PM

If you had any means to control the SHAPE of your windsurfer sail, you wouldnt need to 'lean it'.
Pre-bending a mast is STANDARD set-up and your mainsail was most probably cut expecting this prebend in the design.

Suggest also that you go to ArvelGentry.com ---> magazine articles and start at "Checking Trim on the Wind" (and the next sequence of 3 allied articles) ... as sail 'shaping' is equally as important as sail trim. Probably 95% of all non-racing sailors have no idea of 'sail shaping' .... and have 'problems' with 'weather helm', etc. etc. etc. etc.
;-)



;-)

EJO 05-09-2011 04:09 PM

Inexpensive solution
 
I do change the shape of the sail on my windsurfer by leaning forward, aft and/or lee or windward. The angle of attack is changed doing so therefore the wind over the sail is different each time and the board moves a certain way. My mast is always pre-bend and my sail is fully battened ensuring a certain foil shape.
Rich as a Fan Engineer I understand the principles of fluid dynamics and their effect on foil, airfoil, flat BI, cupped and other shapes. Air is a fluid although compressible compared to liquids and it's characteristics do change with temp and elevation.
If I were a rich man:rolleyes: I would own a brand new top of the line sailboat with mylar or matrix titanium, etc. sails. True foil shaped rotatable mast and boom, or maybe even solid adjustable foils etc. You get the drift, for optimum trimming and performance. :D
I have an old cruiser that needs to be relieved of excessive weather-helm without spending any money. i.e. I don't want to pay for a rigger to trim, pre-bend the mast, I can't measure shroud and stay tensions (tight is tight) I can flatten (change old sail shape) and hope for relieve and if I can do it with the sail I will otherwise I lean the mast forward. I or anybody else doesn't know the exact trim specs for my boat anyway.
Thanks for your referals and recommendations.:)

ccriders 05-09-2011 05:04 PM

How much wind do you have when the wather helm starts? What effect does reefing have when weather helm starts?
I have a Pearson 28 and put in a reef at about 15kts to relieve wheather helm, and increase boat speed. Before I bought new sails, I couldn't reduce weather helm to an acceptable degree regardless of adjustments made. I also went with a loose footed main on the new sails and I'll bet that also helps reduce weather helm.
Reefing is cheap.
John

EJO 05-10-2011 08:17 AM

John
WH starts at about 7-8 kts wind which is much to early to put in a reef. I probably should reef at 15 kts but never do until 20 kts:D
Like I said B-4 I'll try to flatten out the old main sail this season and if that doesn't work I'll pray to Santa Claus for a new(er) main.

Again thank you all for your feedback.
Let's go sailing another couple of weeks B-4 the boat is in.


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