Weather helm on half tonner

Discussion in 'Sailboats' started by nemo, Oct 12, 2009.

  1. nemo
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    nemo Naval Architect

    Hello, I have a Farr 31 half tonner, and it suffers heavy weather helm, of course increasing with the wind speed. The rig is fractional 7/8 (even less), and I surprisingly found that the mast have been shifted forward by the previous owner, so one would expect that the boat should have lost the weather helm.
    At first, I thought that the reduction of the forward triangle, following the shift of the mast, lead to the movement of the centre of effort aft, but after some calculations I found out that this was unlikely.
    I am now concentrated on the rudder: like other IOR boats, it has a big bustle in front of it, and I am thinking of removing it, as the boat is now out of the water, and maybe re-designing and balancing it.
    Any consideration/advice?
     
  2. Gary Baigent
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    Gary Baigent Senior Member

    Your bustle will be helping to keep the centre of lateral resistance aft, which is what you want - removing bustle, you'll have to increase the rudder size to compensate (or put in a balancing daggerboard in the cockpit to take some of the weather helm load off the rudder). Maybe having the mast weight further forward where there is less buoyancy, the boat is heeling more and digging in the bow ... which will make the boat hard helmed. Are you carrying extra weight forward below deck? That won't help your helm balance either. This is iust guessing on my part, could be completely wrong.
     
  3. PAR
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    PAR Yacht Designer/Builder

    There are a number of things that could be called "weather helm". What is the actual angle of incidence of the rudder, close hauled in 10 knots? What is the condition of the sails? What is the current mast rake and how far forward has the mast been moved? Have you talked with other Farr 31 owners?
     
  4. waikikin
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    waikikin Senior Member

    Hi Nemo, before I started changing the boat I'd try some diferent trimming techniques paticularily in regards to the main, the boat I used to sail on in the eighties- a Swarbrick the main trimmer would realy drive the boat in harmony with the helmsman, pretty much playing the traveller to the helm b est from Jef. All the
     
  5. daiquiri
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    daiquiri Engineering and Design

    My two cents worth:
    In a main-jib (or genoa) combination, the jib carries the biggest part of the aerodynamic load. By moving the mast forward (and therefore decreasing the jib area) the contribution of the jib to the total load decreases, while the main's increases... This could move the total aerodynamic center of the rig aft, contrary to the first-thought logic and contrary to the initial intention behind the modification.
    In addition, by having the main sail working more (and has the main's area been increased too, to compensate the decrease of jib's?), the aerodynamic center travels up, increasing the heel lever. The heel is the fundamental origin of the weather helm. More heel, more weather helm.
    It is a general consideration, don't take it for granted. Too many things could play a role there, maybe you have some other issues which still need to be reckoned.
    As Waikikin correctly pointed out - before spending tons of bucks on modifying the rig, you should play a lot with trims and try to resolve it in that way. Your goals should be: lower the aerodynamic center of the mainsail and increase the load of the jib/genoa (or decrease the load of the main).
     
  6. Garry Hartshorn
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    Garry Hartshorn Junior Member

    In the old IOR boat's it was typical when going to windward that the main was feathered for the most part. As mentioned in an earlier post it is how the class was sailed. This is due to the IOR measurement formula, and in my belief one of the many reasons why in the end the system was left behind.
     
  7. Omeron
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    Omeron Senior Member

    Moving the mast from its original position is not something you can do easily and quickly, as it would require several other modifications. If the previous owner went into that much trouble, it is also likely that, the mast itself may have been lengthened to compansate loss of fore triangle area. This would definately increase the mainsail area and destroy the balance. It is worth checking.
     
  8. gonzo
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    gonzo Senior Member

    How much rail meat do you carry? Those boats were designed with a fairly large crew in mind. They always get weather helm when they heel. It was one of the reasons the formula died. They also tend to nose dive and pitchpole in heavy weather because of the pinched ends.
     
  9. nemo
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    nemo Naval Architect

    Thank you for your replies!
    First of all, the rudder angle in close haul at 10 knots is about 5 degrees. The crew onboard can vary from 4 to 7 people.
    The mast has been moved forward by 0,2 metres. I have the original sail plan, so I will make some calculations comparing the actual centre of effort with the one marked on the plan, but I have the feeling that the overall centre of effort hasn't changed much. What is difficult to calculate is the effective power reduction of the foresail, due to the different shape.
    Unfortunately, I don't know any other owner of the Farr 31..
     
  10. gonzo
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    gonzo Senior Member

    5 degrees is good. That means the rudder is providing lift
     
  11. Charly Setter
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    Charly Setter Junior Member

    Hello Nemo

    Is it really Weather Helm (strong forces) or is the boat simply loosing stearing due to the fact that the rudder is lifted out of the water with increasing heel.

    I experience similar problems with my own 1/2ton. Not a Farr design, but "homebrewed"(red cedar strip planked, 1,9t overall weight, 1t lead keel). Due to formula changes resulting from Fastnet 79 during build time we had to cut sail area as a result of penalties for light displacement designs

    We increased boom length by roughly 30% on our boat 15 years ago (increasing mainsail from 21m² to the original planned 28m²) and were surprised to find no change in boat handling / weather helm, but only huge increase in downwind and reaching performance.

    Based on this experience I doubt that moving the rig has any significant influence on boat handling. The changes made on the boat by the previous owner are more and less fruitless efforts to reduce the "weather helm problem".

    Our measures to handle the problem are as follows:
    - We increased the rudder length (high aspect rudder, only 10cm shorter than the keel, 1,6m length, 0,35m cord length). Optimum solution would be a twin rudder design ;-)
    - place crew weight as far aft as possible on the rail (sometimes a bit difficult, when sailing double handed on a boat planned for crew weight nearly 50% of boat weight... ;-) )
    - reduce heel as far as possible by mainsail trim (traveller)
    - if ruder forces are too strong, balance the rudder, but don´t over balance....
    - tight reaching: Move the sheeting point of the jib forward/out and depower the main ( tight vang / loose main sheet
     
  12. Paul B

    Paul B Previous Member

    When you are sailing upwind you should have 3 to 5 degrees of helm. Your situations is not excessive.

    Have you had your sailmaker out to have a look at your sails and setup?


    What Design Number is your boat? I have sailed on an early production Farr Half Tonner. I sailed on it with the stock rig and after the rig height was increased by about 10%. It sailed fine both ways.

    I have sailed on many old IOR boats where the rigs have been changed a bit, adding up to 20% to the boom length in some instances. All the boats were easy to balance after the mods. Moving the mast on a Farr HT forward by 200mm would not be a significant change, and would definitely not increase weather helm.
     
  13. Paul B

    Paul B Previous Member

    Why would you post nonsense like this? It does no one any good to have things that are not true posted on the internet. If you don't know what you are talking about you should not say anything.
     
  14. Garry Hartshorn
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    Garry Hartshorn Junior Member

    That all depends one ones experiance. In my experiance most IOR boats carried bucket loads of weatherhelm when sailed to windward with the main sheeted in and driving. The mainsheet trimmer would be working in tandem with the helmsman and be continously feathering. It was also common practice on deliveries and when cruising to reef the main even in very light conditions to balance the boat. That was my experiance and observation and thats a FACT. In the latter years of IOR many boats were designed to take advantage of the rule not primarily designed to be seakindly and fast boats, that is my opinion. There are many that have the same opinion and many that don't, it's not nonsense.
     

  15. Paul B

    Paul B Previous Member

    Then please, tell us of all your experience with top level IOR racing.



    What designs were these? Who set up the boats, who was sailing them, and in what regattas?



    Because you don't know how to sail does not make something FACT. I have raced on IOR boats of every era at the top level and I have never seen one that needed to be reefed in light air to make it balance.



    Uh, no. As the years went on IOR designers pushed the limits of the rule MORE, not less. Please list these successful IOR designs that were designed to be seakindly and not push the limits of the rule.

    Your opinion is worth nothing. It is clear you don't know what you are talking about. I guess it makes you feel special to post nonsense "in your opinion".
     
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