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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > Weather helm and Weight
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Topic Review (Newest First)
06-26-2014 03:47 PM
SHNOOL
Re: Weather helm and Weight

putting butts forward of the mast drives the bow down (which digs the boat in, usually a slowing effect)... if you have weather helm until that happens you likely have too much rake (again assuming every other trim setting is good)... As a side effect forestay sag as mentioned, it will shorten rake if you tighten the forestay (and eliminate sag). But as was said, lighter air some sag is good, or off wind trying to power up, so you might need to ease some backstay while tightening forestay. By the way it's odd that the boat heads towards leeward with weight foreward... usually weight forward causes steering to windward... that tells me you might have WAY to much weight aft.

A boat with all your weight neutral (centered over keel, forget the driver at this size), and less than 10 degrees of heel, you should have very mild weather helm...

As it pipes up, you get butts on the rail (amidships, because forward or aft affects weather or lee helm), note the mentioning of racers with butts hiking, they are always directed to the rail at widest section of beam (for more righting moment, but also to keep neutral balance fore/aft). If you started with 15+ degrees of heel, and the butts put you back down to 10 degrees or less, your helm should be neutral again... Hence why racers do it... you have the same power, less heel, so hopefully netural helm (meaning less drag) and therefore you are going faster.

This assumes that your angle of attack, your leech, your halyard, your sheet, draft, etc, are otherwise perfect (unlikely)... but it's a start. Others have you looking at trim (as should be)... but your rig tune might also be suspect (especially given that you have new[er] sails).

Its a balancing act of what provides the most VMG... generally sailing flatter is better (to a point), and extra ballast should be centered fore/aft, port/starboard (until you start to heel excessively... you only move weight (crew - pronounced rail meat) to the rail as your heel angles get excessive (which is also something that is boat specific).
06-26-2014 02:19 PM
theonecalledtom
Re: Weather helm and Weight

Returning here to add an extra piece of information I saw I'd missed Rich's above post - good information! Not sure about adding stitches to my favorite sail but I might tack on some glow in the dark tape at top, and middle so you can see the line when sighting up from the tack (and in the dark!!).

I have two new headsails and a reasonable condition #3. None of these other sails exhibit the same hook, or need to be tensioned so tightly to reduce it so in the end I think this sail is just blow out. Later this summer it'll go back to the sail loft to see if there's anything further they can do beyond the leech adjustment already done without busting the bank.

Trying to save my good #1 I still sail with this not so nice sail and recently have put some effort into getting it to point. Experiments showed that forestay tension is critical to reducing leeway and getting VMG up but left me feeling there was more to be done. This is what I learnt.

Normally I set up the lead position so that all the luff tell tales lift at the same time. With this sail this is very tricky and in doing so the lead is in a very forwards position pulling the leech closed and leaving a very deep shape low down.

Reading the North U trim book, which I love, they talk about running the bottom of the sail on the edge of a stall, and the top of the sail on the edge of a luff. Last night we tried this for the first time (in a race of course, when better to experiment?) and were able to point a couple of degrees higher.

Given we sail on the pacific ocean there's always some sort of wave action and this setup will also benefit from keeping the power steadier as the mast moves with the waves, one part of the sail might luff / stall while the rest keeps working.

Having said that last nights breeze was very light and shifty, but I think that the groove might be harder to helm with this setup, but suspect the sail is a bit more forgiving for leaving it as different parts are at different angles to the wind.

Now - overall there's less power in the sail with less depth so this adds and extra adjustment to our tacking maneuver. Post tack start with the leads forwards and the deep sail, trim the lead back and bring the sail in as speed increases and you move to pointing mode.

I'm excited to try this out with a better sail and see what angles we can get (and also with a bit more breeze!).
10-15-2013 01:05 PM
RichH
Re: Weather helm and Weight

Quote:
Originally Posted by theonecalledtom View Post
One thing that concerns me was knowing when to stop adding tension...
This may be more than you want to know, but here goes .....

For sail shape and optimium performance -
Follow the advice on how to match jib luff sag with wire tension as found here as a basic set up for 'optimization' of jib shape via a starting point of optimization of the backstay/forestay tension relationship: http://www.ftp.tognews.com/GoogleFil...f%20Hollow.pdf

This will get you 'close' to optimum boat output and will help lessen the boat from 'skidding to leewards' ... felt in the helm as 'weather helm', but isnt'. If youre just starting out serious racing you can have a single 'line' of stitching (or 'pin stripe' adhesive-backed tape) applied to just behind the leading edge of the luff section with the sail on a flat floor and that section TOTALLY FLAT (see article) so that you have a visual clue of the exact sag (luff hollow) that was cut into the sail by the sailmaker. When laid out correctly on a flat floor so that the luff section can be totally flat to the floor, there will be a curve to the luff when that stitched indicator line is 'dead straight'.

When having doubts about backstay/forestay tension just go forward and look across the boats centerline to the row of straight stitches to see if theyre all in a straight line, and make adjustments in backstay tension to get to the 'starting point' (straight line of stitching) of final adjustments via the speedo and your VMG (and helm pressure).
That stated, if the boat is a planing hull or close to a planing hull, overtensioning of the backstay will cause the overtensioned forestay to help get a bit of extra 'roundness' in the luff section (so will slight overtension of the jib halyard but with relocating the position the sails maximum draft going forward too). That extra roundness or wee bit of curl in the luff entry due to over-tensioning is especially fast for 'planing hull' boats. For a full displacement boat, flat luff entry shape is usually/probably better, especially in the lower windranges. But if youre into optimization, youd better be laboriously trying/testing and writing down all these numbers and results on the speedo and VMG vs. rig tensions, etc. If youre into serious racing/sailing, dont guess about tension, sail shape, etc. etc. look at the numbers you developed earlier during your earlier optimization/trial program .... then make your 'guesses' for the days wind/wave conditions and based on the numbers in addition to that pre-recorded data. :-)

Rigging service life considerations -
For just futzing around sailing you can monitor the 'active' headstay/backstay tension with a tension gage temporaliy attached to the backstay and simply record or remember later at what angle of heel the backstay tension goes over ~30% of wire tension. Repeatedly going well beyond ~30% wire tension during 'actual sailing' will lead to quite short rigging/wire service life via 'fatigue'.
If racing, just dont bust the rig, but do plan on complete rigging turnover/replacment every few years.

hope this opinion helps. ;-)
10-15-2013 12:54 PM
ctl411
Re: Weather helm and Weight

I had a similar problem with out new to us boat (weather helm). Too much weight (junk) stored in aft locker and anchor and chain not on the bow. This is a several hundred pound shift in balance on a 34000 pound boat. I moved what I could for now and it made a difference like the OP noted. Keep extra stuff off the back of the boat.
10-15-2013 12:05 PM
theonecalledtom
Re: Weather helm and Weight

With a few more miles on the boat it seems that increasing the headsail halyard tension significantly removes most of the curl, you need to relax the tension when dropping off the wind or you get vertical wrinkles.

Still haven't worked out how to tension the headstay beyond application of backstay, shortening it seems to do just that without hugely noticeable increase in tension. Rest of my rig seems to be at the North sails 16knot setting, which should be over-tensioned for the conditions we typically see.

One thing that concerns me was knowing when to stop adding tension...
04-25-2013 11:18 AM
RichH
Re: Weather helm and Weight

Quote:
Originally Posted by theonecalledtom View Post
Thanks for looking! Now I want to record video with the balance aft and forward to see what difference it makes.

Totally agree that the leech hooks up too much - suspect that the leech line was too tight - is the requirement for a tight leech line to prevent flapping caused by the tension on the headstay?

I feel like the early shot of the boat as the kite is being launched makes the sag look more extreme than it actually is, the shot at the end is more representative (still a fair amount). Perhaps as much as 6" but possibly less, will have to tray and measure this.

So what is the right amount of sag to have? My understanding is too little and I'm just wasting power!
Of course, looking at your video are all 'long distance' views, so my answers are subjective.
To be sure of the amount of correct forestay sag via backstay tension, you really have to lay the sail on the ground as explained in http://www.ftp.tognews.com/GoogleFil...f%20Hollow.pdf. and acutaly measure the 'luff hollow' that was cut into the sail. Thats the only way you can MATCH the hollow shape that the sailmaker designed into the sail's luff and match with the correct stay tension. You really cant 'guess' about forestay tension ... and be the consistent leader of a racing fleet.
For 'precision' shaping have a sailmaker run a row of visible/contrasting stitching adjacent to the luff so you can monitor the shape/profile .... With a too loose forestay tension is very easy to have a gorilla on the jib sheet winch cause extreme sag in the forestay and luff entry shape ... and which results in a 'cupped up' or too light leech .... and which is easily monitored by the use of tell tales ON the leech and your eyballs watching that luff 'hollow' shape.

Also take a good look at the pic below on another 367 Bendy boat ... take a good look at the foot curve of that mainsail - the draft is waaaay aft due to insufficient mainsail halyard/luff tension, which causes the leech to hook to weather - 'weather helm'. This boat needs some drastic cunningham / halyard pressure. When you see such, you KNOW he's got weather helm (dragging his rudder!) and youre going roll right over top of him, and you dont want to get into a tacking duel but simply 'stretch him out' on long tacks for a big advantage as you know he cant match your speed. FIRST 36.7 (BENETEAU) sailboat specifications and details on sailboatdata.com
04-25-2013 12:44 AM
theonecalledtom
Re: Weather helm and Weight

Thanks for looking! Now I want to record video with the balance aft and forward to see what difference it makes.

Totally agree that the leech hooks up too much - suspect that the leech line was too tight - is the requirement for a tight leech line to prevent flapping caused by the tension on the headstay?

I feel like the early shot of the boat as the kite is being launched makes the sag look more extreme than it actually is, the shot at the end is more representative (still a fair amount). Perhaps as much as 6" but possibly less, will have to tray and measure this.

So what is the right amount of sag to have? My understanding is too little and I'm just wasting power!

Thanks for the complements - love the boat
04-25-2013 12:34 AM
paulk
Re: Weather helm and Weight

As others have said, the Beneteau 36.7 is weight-sensitive. It is also quite narrow at the bow, and quite... portly at the stern (e.g.: master double berth aft). If you send two crew forward, it's going to dig the bow in quite a ways. This lifts the rudder, at the other end of the boat, OUT of the water, while causing the bow, with it's v'd section, to dig in and keep the boat headed in a straight line. With all the crew weight aft, the rudder is definitively ALL in the water, and any dampening of helm that the lateral resistance of the bow section might have supplied will not happen: the BOW is now out of the water, and the directional stability it added is now gone. All of this is going to be affected by the sails you have up and their CE, as it relates to the Center of Lateral Resisitance of the immersed hull (which varies according to where the weight is.) There's a lot going on. That's why racers concentrate their weight 'midships and keep people OFF the bow and OUT of the cockpit.
04-24-2013 10:53 PM
RichH
Re: Weather helm and Weight

Quote:
Originally Posted by theonecalledtom View Post
Interesting point on stern wake RichH - in the video here we're sailing unbalanced as it was shot just before realizing the influence - can you tell if we're skidding?
Your stern wake somewhat shows that youre skidding but that is best viewed from the cockpit looking back.
The large slack sag in your forestay from what I can see in your video is definitely excessive ... probably the prime reason for the skid and the 'heavy helm'. The very first frame in the video shows absolutely NO jib luff except the very bottom of the tack section ... all the rest has greatly sagged behind the view of the mast.
What your probably feeling as weather helm is the skid's side pressure on the rudder.
At the end of the video the leech of the jib seem VERY tight (probably hooked up to weather) which kind of also suggests and supports the too loose headstay.

I'll try to find some geometric sketch / sail plan of the 36.7 and calc for you what the backstay tension should be to arrive at a 12-15% forestay tension. Is that one or twin backstays?

Nice boat !!!! good video. ;-)
04-24-2013 05:32 PM
ajoliver
Re: Weather helm and Weight

Don't know about Bendy-Toes, but for some boats weather helm can be greatly reduced (and pointing much improved) by raking the mast farther aft. I know this seems counter-intuitive (shouldn't more rake move the center of effort aft - thus causing even more weather helm?), but it works. And again, I cannot testify about any boat but mine.
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