[Public-List] america cup

Jim Mennucci via Public-List public-list at lists.alberg30.org
Wed May 31 07:11:05 PDT 2017


Can anyone add to my understanding of how the hydraulically driven
hydrofoils work on the Americas cup 42 footers now racing in Bemuda--
here's what I think i'm seeing:

- In a way its kind a cool--going 30+ knots up and down wind doesn't
require much sail trim...hydrofoil trim is another matter.  Talk about
changing sail boat racing as we all understand it.  Trophy goes to team
that is best at hydrofoil control, in fact hydrofoil control is the only
area of boat design the is somewhat left to the syndicates to control on
their own. .  Optimizing hydrofoil control maximizes speed.

- unlike the 72 footers, the 40 footers will use hand controls i.e., no
closed-loop feed-back controls for the hydrofoils--this is what I wonder
about?  The hydraulic directional control valves used to pivot the foils
use some sort of electrically controlled linear actuator to open and close
flow to the hydraulic actuators,  It would be easy to add some feed back
control to the electrical part of the valve and if they don't that's good
because of the additional skill needed to manually maintain stability

- article I read says stored energy (accumulators) are not allowed and the
hydraulics must be provided by hand pump--hence they're always pumping
(like maniacs) to have fluid under pressure (must be a relief valve to
regulate pressure)

- the article talks about 3 hydrofoil controls: Cant, lift and pitch are
the 3 names used.in the article.
       - It sounds like cant angle corresponds to roll which is used to
add/control righting moment. Canting the wing off vertical tilts the
horizontal part of the wing which should result in some loss in lift making
an adjustment to the angle of attack to rebalance the lift--this is where
feedback control would be nice but making the helmsmen do the adjustments
in a manner that maintains foil stability adds old-fashioned skill to the
mix.  Thoughts?   pivoting the hydrofoil outboard adds righting moment
       -  lift control would pivot the hydrofoil in the pitch plane to
change angle of attack
       - pitch control to me is the same as lift except its listed as a
separate function.  So I wonder if the dagger board and the rudder foils
work in concert to change the pitch of the boat--much like bow and stern
planes on a submarine
- looks like linear hydraulic actuators are used to control 2 rotational
degrees of freedom on the dagger board foils and a single actuator to pitch
the rudder foils.
- the foil controls are built into the helm wheel and its looks like they
run the system open circuit i.e., no feedback control.  They hit buttons
built into the helm to open the directional control valves.  So the
helmsmen is also the foil trimmer.

any insight, thoughts appreciated

Jim Mennucci


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