Veal Heel for Small Trimarans

Discussion in 'Multihulls' started by Doug Lord, Mar 30, 2011.

  1. Doug Lord
    Joined: May 2009
    Posts: 16,385
    Likes: 283, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    I've mentioned this before but it has too much potential to just leave alone. The concept is described in the quoted post below. I know a lot of people have no interest in numbers for various reasons but if you're interested in high performance small tri's you might want to take a look. I did this to see what was possible-see the "schematic" illustration below.
    -----
    16' singlehanded trimaran
    18' beam(cl of very small ama to cl of very small ama-beam is greater if very small foil span is considered)
    Sail Area-160 sq.ft @ 8' CE
    Max pressure before reefing/ depowering=1.8lb. per sq. ft.
    180 lb crew uses sliding seat to move 5' to weather max.
    Boat weight 220lb.
    ==========
    This is where it gets interesting:
    Max Heeling moment in 1.8lb/sq.ft. pressure=2304 ft. lb.
    Veal Heel-nominal 20 degrees
    Max Righting Moment(RM)= 2304ft.lb. as follows:
    ----1) RM due to Veal Heal= 440ft.lb. for boat ; 360ft.lb. for crew-TOTAL-800ft.lb.. Note: Veal Heel moves the boat CG and the crew cg 2' to weather
    ----2) RM due to crew @ 5' from CL= 900ft.lb.
    ----3) RM due to very small "power foils"= 604 ft. lb.( 2.5" X 20" hydrofoil developing 54.9lb of downforce @ 11' from Center of lift of main foil) Small foils are not used in light air)
    Conclusion : Veal Heal allows a 35% increase in RM over what would be possible without it with ZERO changes to the boat. ( Total RM= 2304 Ft. Lb. RM due to Veal Heal= 800ft. lb. or 35% / RM due to very small foils= 604 ft. lb. or 26%)
    ------
    It seems to me that 35% of Max RM for Veal Heel is an extremely significant number as is the 26% of Max RM from one very small hydrofoil. In my opinion this stuff should be looked at real carefully in considering the design of a high performance small trimaran. The percentage of overall RM is even greater due to Veal Heel in lighter wind when the very small "power foils" aren't being used...



    Rough sketch of the physics of Veal Heel in combination with two lifting foils on the main hull and a very small hydrofoil to weather for a trimaran(click on image):
     

    Attached Files:

  2. Munter
    Joined: Jul 2007
    Posts: 285
    Likes: 11, Points: 18, Legacy Rep: 125
    Location: Australia

    Munter Amateur

    Doug,
    Your calculations focus on righting moment and appear to assume the heeling moment generated by the rig does not change in the foiling case. Given that the centre of lateral resistance is now much lower I'd suggest that the lever arm between the sail force and the lateral resistance is even longer so the heeling moment is also greater. You can't just move the pivot point for righting moment and not heeling moment.

    If your assume the center of lateral resistance moves downward by 2' then based on your own figures you should also acknowledge an increase in heeling moment of 25% (ie 10/8) making for a net gain of what 35-25 = 10% (under ideal circumstances). Its also an unstable equilibrium whereby righting moment decreases with an increase in heel making for a real challenge to sail. Have you seen how moth sailors wear out mainsheets?

    Given the thread title why have you confused the topic with righting moment from retractable winglet hydrofoils?

     
  3. Gary Baigent
    Joined: Jul 2005
    Posts: 2,937
    Likes: 90, Points: 48, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    If I sail Flash Harry with Veal Heel in light winds, the boat is slow. Better to slide your weight to centre or to leeward a little and get the platform moving at decent speed again.
     
  4. Doug Lord
    Joined: May 2009
    Posts: 16,385
    Likes: 283, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    =============
    If I understand Flash Harry correctly you can't sail with Veal Heel in light winds! Veal Heel only works for a boat that is 100% supported by two foils on the main hull. It is not just heeling to weather-it is a technique that moves the CG of the hull to weather substantially-2' in the case of the boat in the first post. The distance of a vertical line drawn thru the center of lift of the main foil from the hull CG is the additional RA(righting arm) unique to Veel Heel and not possible with any other type of windward heel.(see sketch in first post)
     
  5. Doug Lord
    Joined: May 2009
    Posts: 16,385
    Likes: 283, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    =======
    1) My calculations focus 100% on Max RM-there is no discussion of the non- foiling, non Veal Heal case.

    2) "unstable equilibrium"-that's funny. Not applicable to this system in any way whatsoever. It's either unstable OR its in equilibrium.
    Wrong. With Veal Heel, RM(Righting Moment) increases with heel. see 3 below.

    3) As I said in 1) above my calculations were based on MAX RM. With a trimaran(not a bi-foiler monohull) the retractable, very small, "power foils" are necessary at Max RM and useful otherwise. The boat is wider than it is long specifically to be able to carry more sail than a monohull could while significantly reducing the size of the very small "power foils" that are required for Max RM for this type of boat. The "power foils", which are controlled by a wand, increase the stability of the boat as it is sailed with Veal Heel: they prevent your "unstable equilibrium" by maintaining the boat at a set angle of heel-pulling up or pulling down(normally pulling down) as necessary. Far simpler than having to do that manually as in a Moth. Also, with Veal Heel, the effect of the power foils on stability is increased by the greater distance from the center of lift of the main foil to the center of lift of the power foil.
    -------
     
  6. Munter
    Joined: Jul 2007
    Posts: 285
    Likes: 11, Points: 18, Legacy Rep: 125
    Location: Australia

    Munter Amateur

    OK Doug, - if the baseline is the foiling case then don't you think you should acknowledge that both the foiling cases the heeling moment for the same amount of power has been increased by 25% and that windward heel is simply recovering that? Never mind - I'm sure you'll see it differently.

    Unstable equilibrium. Your attempt at dismissing this issue without consideration merely shows the shallowness of your understanding. At the very least, type the term in to google and think about what it could mean for your design.

    Perhaps I could have worded it differently, heeling depends on your frame of reference. My point is that when a gust hits and the boat reacts by "heeling" (but in this case returning to the upright position), there are a number of forces that make it unstable. As you point out, righting moment reduces as the boat returns upright (now down by 35%!), heeling moment increases because the sail is now perpendicular to the wind and so the sailor needs to make a significant change to the sheeting of the sail in order for the boat not to fall over. I suspect that you significantly underestimate the size of this task.

    From the ideas you've presented on this forum it appears that your consideration of design stops once you have determined a single static case that balances and other circumstances are ignored for simplicity. A real boat in the real world won't allow you the same luxury.
     

  7. Doug Lord
    Joined: May 2009
    Posts: 16,385
    Likes: 283, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    Veel Heel for small trimarans

    =============
    That is an uniformed , baseless comment.
    -----
    The boat in the first post was selected to show what would happen in the Max RM case-usually the toughest case for any boat design. Any HM(heeling moment) requiring less than max RM(righting moment) is a simple case that can be handled by crew movement, Veal Heel, power foils or any combination thereof. For all practical purposes a boat like this is designed to foil in a 5-6 mph wind and from there on up to a wind pressure of 1.8lb. sq. ft. before reefing, depowering or both. Veal Heel can be infinitely varied w/o "power foils" though it is possible(and probably advantageous from an ease of sailing perspective) to sail with the power foils from the inception of foiling. In racing the "power foils" probably wouldn't be used until they were required.
    The fact that Veal Heal provides up to 35% of the RM is extremely significant since it is a technique and requires no changes to the boat whatsoever.The boat can be sailed with Veal Heel in more wind than it can be sailed with the crew in the max outboard position and upright. And in more wind still with "power foils" in combination with Veal Heel.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.