• Content Count

  • Joined

  • Last visited

Community Reputation

24 Suckup

About neuronz

  • Rank

Profile Information

  • Location

Recent Profile Visitors

6,754 profile views
  1. Hi Ian. With the antenna on deck level you might just as well go with a handheld vhf since antenna height is the main driver for range. I do understand that avoiding wiring in the mast saves work and weight in a crucial area. However, I you consider your vhf a safety device I still think the antenna in the mast top is the way to go. I witnessed that the 5 or 7 miles of range you are left with with an antenna on deck level can be quite short when a boat close to us lost its mast and we could only hear the relay messages from a nearby ferry, but not the actual transmissions.
  2. neuronz

    Full batten main with swept spreaders?

    As some have suggested already, think about mixing 2-3 full battens at the top with half battens in the lower half of the sail. That should get you the best of both worlds. You should be able to open the top without flogging in strong winds and still have good shape in the bottom.
  3. neuronz

    Boats and foils comparison

    this is not correct. Assuming same angles of attack on each side of the foil the forces perpendicular to the strut compensate each other which means the total lift has to be aligned with the strut. Thus, the vertical and horizontal components are exactly the same for both types of foils. There are two possibilities to break the symmetry, independent flap angles and leeway.
  4. neuronz

    Boats and foils comparison

    Is there a rule that the foil has to fit in the box in any configuration? Anyway, even a 50% flap will not require 200mm of space as they will only run a few degrees of flap angle. Furthermore, I have included the additional lift due to the anhedral angle in the calculation (+6%), but it is cancelled by the increased aspect ratio. Last but not least anhedral has zero influence on the cant angle of the foil arm since the direction of the total lift does not change. There also is no magic angle. The best angle is where vertical and transverse forces are in equilibrium with the least amount of total drag.
  5. neuronz

    Boats and foils comparison

    I just tinkered around with some numbers based in the two extremes allowed in the rule, maximum anhedral and the planar foil. My calculations are based on a simplified, trapezoidal version of the dotted red boundary and I neglected the strut at the top which is the same for any foil. If you use the maximum possible anhedral the max span of the foil increases from 4m to 4.24m (+6%). Assuming constant area this increases the aspect ratio by 12.25%. The combined length of the leading edge which can be used to approximate wetted area decreases by almost 10%. To generate the same vertical force the total lift of the anhedral foil needs to be 6% higher. Taking into account that induced drag is proportional to lift squared divided by aspect ratio the induced drag is the same for both. This still leaves the wetted area advantage for the max anhedral foil which means it should have less drag. Furthermore, I can imagine additional benefits from less drag at the junction due to the larger angle between strut and foil. However, it will operate somewhat closer to the surface.
  6. neuronz

    Boats and foils comparison

    If I recall correctly the rules allowed a difference in angle of attack between the rudder elevators of three degrees. Thus you could use the windward rudder to create downforce and thus righting moment. The catamarans being very wide the windward rudder would get very close to the surface or even airborne at very small heel angles. If this happened the boat would instantly lose righting moment and pitch stability. Hence keeping the windward rudder submerged was very important and ensured by avoiding heel to leeward.
  7. neuronz

    Boats and foils comparison

    I think what we saw was bow down trim and instantaneous deviations to windward only from zero target heel. I suspect they wanted to avoid any heel to leeward because the windward rudder provided righting moment which would be lost with heel to leeward. Hence they decided to rather allow larger deviations to windward instead of symmetrically around the neutral position.
  8. neuronz

    Boats and foils comparison

    Lift to windward could also be generated by moving the foil arm upwards. I can imagine that windward heel will give slightly more righting moment since the total center of gravity will be quite high. Not as high as in a moth, but significantly higher than in a keelboat. However, the small gain in RM could easily be cancelled by the loss in aerodynamic efficiency. Aerodynamic drag is likely the biggest contributor to total resistance so losing a few percent of efficiency can have a big impact.
  9. neuronz

    Boats and foils comparison

    Maybe because they have been training in Pensacola over the winter?!
  10. neuronz

    Boats and foils comparison

    Yes it actually would be correct. What you want to do is increase the distance between the lift force and the total center of gravity. To achieve this you need to move the individual masses to windward. With the windward foil being vertical in the air the position of mass along the foil is irrelevant. The leeward foil however is almost horizontal so you need to move its weight to windward to achieve your overall goal.
  11. neuronz

    Boats and foils comparison

    To increase RM you would actually have to move the center of mass inboard since the leeward foil will be more horizontally aligned than the windward foil. Hence if you move the foil center of mass to the outside, you move the total center of gravity to leeward which is the opposite of what you want to do.
  12. neuronz

    Boats and foils comparison

    Interesting to see that all teams except ETNZ have significant dihedral in their foil design, giving a bit more span and better aspect ratio but less favorable force vectors.
  13. neuronz

    Dynema standing rigging howling in the wind

    Foam ist way overkill in my opinion. All you need to to is break the symmetry of the shroud cross section. A very small diameter line spiralling around the shrouds will do the job and most likely be cheaper and longer lasting than foam.
  14. neuronz

    Dynema standing rigging howling in the wind

    Go for the spiral. It is the default solution for such resonance problems.
  15. neuronz

    tuning a single spreader, fractional rig.

    Rigs are tuned from top to bottom. 1. Connect the wires and set mast rake with the forestay. Hand-tighten the shrouds and make sure the mast is centered/vertical. 2. Tension the backstay to induce some bend and start tightening the uppers symmetrically by counting turns on the turnbuckles. Release the backstay if you want to check tension with the Loos and re-tighten before working in the turnbuckles. The mast should have significant prebend after this step, because you are going to remove bend in the next step. 3. Release the backstay and tighten the lowers symmetrically (same number of turns on each side). Make sure the mast stays straight athwartships. Correct sideways bend if necessary by releasing one and tensioning the opposite side. Continue tensioning for desired prebend. If the mast inverts at the spreaders there is too much tension in the lowers relative to the upper shrouds. (4.) On your rig the shrouds control headstay tension since there is a long and bendy piece of mast between the headstay and the masthead. If you want more headstay tension you need to tighten your shrouds. Limiting the bend with the lowers is important to keep the mast from bending under compression from the headstay which will decrease your headstay tension.