Weather helm/mast rake

[Scott21120]

On our recent delivery, we noticed that our new to us Oday 34 has quite a bit of weather helm. The 150 has pretty much served its useful life, so the previous owners had been sailing with the working jib, which is in very good condition, and which we used for the entire trip. We have a fairly small aspect main which is in reasonable condition, so I am not sure if the issue is related primarily to an imbalance in sail size, or other factors? Would the working jib be more appropriate with a reef in the main? I tried easing the traveler to leeward, and spillling off wind from the main, which made a slight improvement, but not what I was looking for. I am wondering if giving the mast a little forward rake might help, but am not sure how to actually determine the mast rake? I have read about using the halyard as a plumb bob to determine mast rake, but how do you determine if the boat is level in the water as opposed to bow or stern heavy? It seems without a fixed point of reference, anything the plumb bob test reveals is meaningless. We do not have an adjustable backstay, and the Isomat spars don't seem to be set up for a lot of bending as a means of sail trim. Any advice or suggestions?

 

[Dave]

Rake

I sail O'Day 25 and recently attending a "Check and Tune Rigging" at Crowley's Yard in Chicago. Rake should be about width of mast or about 1% of "P" as starting point. Reduce rake to reduce weather helm but never forward rake. These are per my notes. Also, Selden products has a website with instructions for tuning. Hope this helps a little.

 

[Tom Hoppin]

center of effort and center of resistance

My response in full detail would take up too much space and time - so here is a "balance your boat" 101 quick explanation that may be some help. I hope so.First of all, in theory all the many forces being generated by your sails (above the waterline) can be condensed to a single imaginery 'point' at any moment in time. For example, if you have a 200 pound force at the aft end of your main and a 200 pound force at the leading edge of your jib, there is a "point" about half way from bow to stern that "represents" the combination of the two forces.If you were to draw a "force diagram" as you sail, the "imaginery" point changes on your particular boat with the angle of wind, amount of wind, set of your sails, and size-and-shape of sails. Got this part?OK, there is a corresponding imaginery point under the water that represents the collective forces on the hull keeping the hull from sliding sideways by the forces on the sails. This point is called the "point of resistance". So, a boat under sail has one point "pushing" it to leeward by the wind, and another point below the waterline stopping the boat from slipping.When these two "points" are far apart bow to stern you feel the boat turning and you counter that turn by corrective steering - and there is a windward or leeward helm.Since keel boats can't change where the center of resistance is, corrections to the helm typically come through changing the size or set of the sails . . . but a centerboard boat can change the location of the center of resistance by lowering or raising the centerboard incrementally . . . or "balancing" the boat's steering.Both keel and centerboard boats can change the location of the center of effort forward or aft by shifting the set of the sails, by the rake of the mast, by "dumping" some power of the main by tightening the "cunningham", by easing the jib sheet slightly, etc. Of these, how you set your sails is the easiest and offers incremental changes with wind conditions. Since you have a fixed backstay, rake is static once you tune your mast.If, after a lot of tweaking and testing, you find you have severe pressures on your steering, you might consider changing your rudder for underwater balance, or get a qualified sailmaker to look at your sails with an eye for rig size and balance.I hope this might help your thinking and that you have some fun testing.

 

[Moody Buccaneer]

Weather helm or high rudder angle?

"quite a bit of weather helm" is hard to evaluate.If the rudder is near centre and it takes considerable effort "weather helm" to hold it there, the boat is fine, the design of the rudder and steering system causes high effort.If the rudder has more than 5-7 degrees deflection (usually accompanied by high effort) the boat probably has too much weather helm.What heel angle were you sailing at? What point of sail?Almost all boats develop too much weather helm when they heel too much.Almost all boats have high steering effort when reaching, even with the rudder on centre.As far as rake goes, all you are trying to do is change the relationship between the sail effort and the hull effort. Hull trim moves the centre of the hull effort, mast rake moves the centre of the sail effort.Trimming the hull also moves the sail centre of effort. If the hull has bow down trim it will have more weather helm even though it has less rake. If the hull has bow up trim it will have less weather helm even though it has more rake.Most of the boats we sail have a bit of lee helm at low heel angles, so moving the crew forward and to leeward induces enough weather helm to make the boat sail to weather properly. As the wind picks up, move the crew to weather and aft do reduce weather helm.It is all tied together, every adjustment effects the other adjustments.Start with trimming the boat to the water line, then check the rake of the mast. If you find that the halyard plumb bob shows 10-15" of rake, you have found your problem. (Don't laugh, I've seen new boats horribly miss-tuned with 15-20" of rake).If you find the rake that far off, you probably will not be able to adjust it out. Look for an extra toggle (or two or three) in the forestay. A typical case is the installation of a new furler and someone not adjusting the forestay length when they add a toggle.Don't even consider raking the mast forward, something would have to be horribly wrong to require forward rake on a production boat!

 

[Alan]

Lots of good info here...

...most all the points are valid. I would first look to your main. As heel and helm increase the main needs to get really flat, outhaul, cunningham, vang, halyard all need to be tensioned. At this point the main should be practically flat as a board. This will reduce weather helm. The next step is to lower the traveler. A small amount of traveler will have a dramatic affect on helm. The next step is to reef.

 

[RichH]

STOP !!!---- FIRST properly shape the mainsail to

properly locate the position of maximum draft. The position of maximum draft should occur about 40% of the distance from the luff of the sail going towards the leech. The position of maximum draft will have MORE influence on 'weather helm' than probably any other 'control'. You control the position of where you want the maximum draft by the HALYARD tension. Most folks simply 'raise' a sail and never properly shape or set the sail by halyard/outhaul, etc. tensionYou dont state the current age of the mainsail and its construction. If the sail is old and has a three strand dacron 'boltrope' (rope in a 'sleeve' at the luff (and foot) of the sail) then there are TWO distinct possibilities OTHER than mast rake that can severely affect 'weather helm'. 1. if the sail has the three strand 'boltrope' it must be raised, then the luff must be additionally *stretched* (to remove the 'preload' of the boltrope by applying MORE halyard tension. Typically on a NEW boltroped sail one typically has to after 'raising', additiionally STRETCH the boltrope by approximately 1 inch for every 10 ft. of luff length .... if you dont do this the draft will be very aft and very full. Setting the halyard to overcome the 'luff preload' (as above) will 'set' the sail for good 'shape' at approx 15-18 kts. of wind strength. 2. Constant raising and lowering a sail with a boltrope will cause the thrree strand dacron rope in the sleeve to eventually 'shorten' - just like your three strand dock lines get fatter and shorter over time. Either you have to add additional halyard tension OR take the sail to a sailmaker to have the boltrope 'eased'. Symptoms of a boltroped sail that is improperly raised or one that has a shrunken boltrope: WEATHER HELM, max. draft position is aft of the 40% of cord length, the leech will be be 'hooking to windward', the sail will look 'baggy' ...... and when 'just raised' (no additiional halyard tension) the **boom end (aft) will be LOWER than the gooseneck/tack** !!!!!!! The angle that the sail makes with the mast at the boom (dont have my sail dimension book handy) shoule be LESS than 90 degrees. With the sail raised with proper halyard intitial tension (additional 1 inch fore every 10 ft. of luff length) take a sheet of 8-1/2" by 11" paper, stand a far distance away from the boat and use the sheet of paper as a 'visual' gauge. Sight so that the paper is 'sighted' along the mast and the 'corner of the paper' is at the gooseneck .... if the aft end of the boom is lower, then you have either not enough halyad tension OR the bolt rope has shruken. Temporary solution: bar tight halyard. If you experience weather helm, keep adding halyard tension (brings the draft forward) until you get the 'helm pressure' / balance you desire --- if you cant get enough halyard tension, then take to a sailmaker to get the boltrope 'eased'.Mast Rake to correct weather helm is the VERY LAST thing you should do to affect helm balance correction ... as weather helm is 'usually' caused by a badly shaped mainsail with not enough halyard tension (and usually due to a shrunken 'boltrope'). Hope this helps.

 

[Scott]

Some clarifications to weather helm/mast rake

Thanks for the thoughtful replies - I should offer a few clarifications. I am not thinking of raking the mast forward, but I would like to determine if it is actually raked backward substantially - and I'm still not sure how to determine when the boat is level enough to use the halyard plumb bob test. When the weather helm was most apparent, we were sailing from close hauled to beam reach, heeled between 12 and 15 degrees, and the rudder was not just heavy, it was deflected beyond 5 - 7 degrees - you could hear a distint disturbance in the wake when it went from being balanced to overpowered. That being said, I will experiment some more with mainsail trim - the main is old, but it still has a fair amount of crispness - not like the original genoa, which is obviously blown. The main has sail slugs on the luff, and boltrope on the foot. The 34 is obviously quite a bit different than our 25, where we could raise and tension the main by hand, and I was hesitant to use the winch too aggressively when raising the main - perhaps I did not get the draft far enough forward - I will pay more attention to that the next time out. I am embarrassed to say there is not a cunningham rigged - there is a ring in the sail for it - but I am not sure if it is to be hooked on a reef hook, or be tensioned with a line to the winch?

 

[tom]

Mac 26 Mast Rake

I was having a lot of trouble controling my old Mac 26 when there was much wind. The weather helm would make it round up. I adjusted the mast's rake too much on the first attempt and the boat had a much scarier lee helm. After the next adjustment it was just right some weather helm but no uncontrolled rounding up.  On my Pearson 323 I noticed that the forestay was too loose but if I tightened it using the back stay I bent the mast. So using a Loos Gauge and a lot of time I loosened all of the lowers and retightend pulling the mast in column and fianlly tightening everything to the same tension. The boat sails much better now and the mast is not bent. I agree with everyone saying check your sail trim/boat trim first. But if after checking you still have pronounced weather helm you might want to play with the mast's rake. With the Mac less than an inch change in rake changed the weather helm dramatically. So go slow. A loos gauge is required to get the tension right. Before I got a Loos gauge I had adjusted my shrouds by feel and when checked with the loos they were off by 20% or more. Center of effort changing with mast rake is very familiar to me as I wind surfed for years. To steer a windsurfer you change the rake of the mast. Basically you pull in the boom to catch the air and adjust the rake to the desired course without falling into the water. At low wind speeds balance with your feet is most important. But at higher wind speeds you hang from the sail and your feet just keep the board pointed in the right direction.

 

[Bill]

More thought...

Hi Scott,Just a couple of other thoughts here:When your boat is in calm water with everyone off buy you (and you close to the centerline)- the boat is balanced. Try the plumb bob.Don't worry about the cunningham too much, just luff up a little and tighten the main halyard.Adding twist in your sail trim will help balance you in heavier air. This will make a big difference.Also, some boats just have more weather helm than you'd think. Ours does and you just sail accordingly... (and dump the traveler in big puffs)BB

 

[Bill]

oops...

sorry, that should be "everyone off BUT you"B

 

[tom]

Plum bob

Plum bob depends upon the boat being level. Just the amount of water in your tanks or beer in your cooler will affect trim. A better way is to use your halyard and compare side to side. The real test will always be how does the boat sail in the real world. Lakes and especially oceans are very rarely level. Going downwind tends to bury the bow upwind tends to raise the bow. All this ignores the obvious effects of people and pets moving around. You need to measure relative to the boat not the water or the surface of the earth. Mark your backstay or measure the amount of thread showing on the turnbuckle. Run a tape measure whatever but use the measurements of one part of the boat relative to another part of the boat. That is all that matters and all that is constant on a moving boat on a moving surface. I've notice that a modest wind can affect my angle of heel while tied to the dock without any sails. But unless something is seriously loose the distance between your masthead and stern or bow should be fairly constant under any circumstance.