Rob Rassy
--- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@...> wrote:
>
> Leeboards have the same efficiency pluses and minuses as side hung
rudders.
> No end plate effect from the hull, but no turbulent boundary layer
either.
> Pretty similar to daggerboards.
>
> Tracks on the lee side of the lee hull are going to be draggy, but
> otherwise no reason not to, apart from your comments and mine on
ensuring
> all possible degrees of freedom are accounted for and shunting in the
> previous post.
>
> Have a go, see how they work.
>
> regards,
>
> rob
>
> On Wed, Nov 14, 2012 at 8:02 PM, rob_rassy techsmart@...wrote:
>
> > **
> >
> >
> >
> >
> > Are leeboards inherently inefficient or was that just the experience
> > with "U"? If they were the same foil I would think they would simply
be
> > the same as a dagger board that was surface piercing!
> >
> > My thinking was to have two boards each pivoting from the top and
pinned
> > to the hull just above DWL by a curved track that would allow one
board
> > to lift/pivot clear and the other to lower when shunting. The setup
> > would require 4 boards instead of 2 (more weight / complexity / cost
&
> > in the way for mooring) but on the up side the leeboards are against
the
> > hull so less load handling and complication issues with the mounts.
The
> > rudders could be smaller with smaller loads on the hinges and
steering.
> > The drag on the leeboards would help counter weather helm.
> >
> > Rob Rassy
> >
> > --- In harryproa@yahoogroups.com.au, Rob Denney harryproa@ wrote:
> > >
> > > The deeper the hull and the wider the blade behind the pivot
point,
> > the
> > > more of a consideration it is. Steering with the aft rudder on
Vis, I
> > > would not like it any closer than it is.
> > >
> > > I tried leeboards on U, with out much success. They see loads
> > (rotating
> > > forward, floating to leeward) which are not what you expect, so
need a
> > lot
> > > of lines to hold them in place. The lower the boat performance,
the
> > > better they work. Any foil fixed fore and aft is going to make
> > shunting
> > > harder.
> > >
> > > rob
> > >
> > > On Tue, Nov 13, 2012 at 9:02 AM, rob_rassy techsmart@...:
> > >
> > > > **
> > > >
> > > >
> > > >
> > > > How close can the rudder be to the hull? Is wave action between
the
> > > > rudder and hull a consideration or does the rudder only need to
have
> > > > enough clearance to operate with out hitting the hull?
> > > >
> > > > I've also been thinking about lee boards on the actual lee side
of
> > the
> > > > lee hull and was wondering if they have been tested on a
harryproa?
> > > >
> > > > --- In harryproa@yahoogroups.com.au, Rob Denney harryproa@
wrote:
> > > > >
> > > > > On Fri, Nov 9, 2012 at 8:08 AM, rob_rassy techsmart@ wrote:
> > > > >
> > > > > > **
> > > > > >
> > > > > >
> > > > > > Rob I do have more questions, but don't encourage me too
much
> > > > > >
> > > > >
> > > > > The more the merrier!
> > > > >
> > > > > > ****
> > > > > >
> > > > > > I'm still confused how the foils can be liftable. When you
say
> > > > "centre of
> > > > > > rotation is mid chord" do you mean the actual pivot point is
mid
> > > > foil
> > > > > > thickness as well? (ie: The hinges will be recessed into the
> > foil)
> > > > or
> > > > > > are the pivots mid distance along the chord and mounted
outside
> > the
> > > > foil. I
> > > > > > realise the foil will have less camber on the lee/hinge
side,
> > but
> > > > unless it
> > > > > > is negative the chord will lie inside the foil (won't it -
> > correct
> > > > me if
> > > > > > I'm wrong).
> > > > > >
> > > > >
> > > > > The foil slides in a case. On the hull side of the case is a
> > > > > gudgeon/pintle arrangement. Means increasing steering loads as
the
> > > > > rudders are turned, exacerbated if the blades are not swept
back
> > > > and/or
> > > > > connected. If the loads are too high, the rudders will kick
up.
> > The
> > > > > gudgeons/pintles are mounted on a substantial shaft to allow
this
> > to
> > > > > happen.
> > > > >
> > > > > > ****
> > > > > >
> > > > > > My thought was to cant the rudder (tilt the bottom towards
> > "under"
> > > > the lee
> > > > > > hull) to put the offset pivot point mid way on the
longitudinal
> > (Top
> > > > to
> > > > > > Bottom) of the rudder, the cant angle would be quite small
to
> > > > achieve this
> > > > > >
> > > > >
> > > > > True. Definitely worth a try if the current setup doesn't
work.
> > > > although
> > > > > the top will have to be firther away from the hull so that the
> > blade
> > > > can
> > > > > rotate through 30 degrees each way without hitting the hull.
> > > > >
> > > > > > ****
> > > > > >
> > > > > > I reckon you might be right about the Blind Date crew
wrestling
> > with
> > > > the
> > > > > > rudders, if the direction of travel hadn't changed and the
> > rudders
> > > > turned
> > > > > > it would be difficult if not impossible to force them round.
> > > > > >
> > > > > One of those things that comes with practice. BD crew in the
> > videos
> > > > are
> > > > > first timers and apart from the helmsman and photographer, non
> > > > sailors.
> > > > > Interesting to compare them with first timers tacking or
gybing a
> > 15m
> > > > cat
> > > > > or mono, particularly one with an overlapping headsail.
> > > > >
> > > > > rob
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > >
> >
> >
> >
>