G'day,
I assume by braces, you mean the horizontal
rudder supports? If so, I would keep them horizontal. a) they have
now been moved clear of the water, b) the aft one would act as a scoop and
c) they put the rudder pintles in bending rather than shear, which is much
easier to resist.
regards,
rob ----- Original Message -----
Sent: Tuesday, January 10, 2006 10:20
AM
Subject: [harryproa] Re: harryproa rudder
fastening stiffness issue?
Thanks Mark and Rob for detailed replies.
I was
considering making the braces in a foil cross section set about
15-20
degrees attack for the forward facing rudder. This would
provide
stiffenning as well as a bit of lift. Possibly vetilate them
in case of
severeely depressing the bows. makes sense to put the big
quadrant under
the floor. When I look at just about any other foil
arrangement in other
boats they are all vulnerable. Breking waves
from behind can put enormous
strains on the rudders of most boats.
overall your present design looks
pretty good and they obvoiously
work.
Robert
--- In
harryproa@yahoogroups.com.au, "Mark Stephens" <stephens@o...>
wrote:
>
> I really wouldn't be concerned about the rudder
brackets and
quadrants from a vulnerability to waves point of view.
However the
loads they see from leeway prevention are huge. For the last
few
months, prior to the first sail, I had been concerned about their
ability to withstand these loads and was tempted to take them off and
beef them up. I decided to leave them for a number of reasons: Better
to test them gently and see where the cracks develop, we may need to
adjust the rake angle which would also requires a rebuild, there was
plenty of other things to get on with. As it happened a shear pin
broke which put enormous twisting loads into the case causing
breakage. I fixed this quickly to get us sailing again. You can see
the repairs in the photos and video.
>
> On return from the
second sail we noticed some hairline cracks on
the unrepaired rudder case
which I have since repaired, again just
strengthening it enough to go
sailing again. Rather than completely
rebuilding the rudder cases I am
interested in keeping the variables
to a minimum.
>
> The
triangular brackets that attach the rudders to the hulls are
remarkably
strong. They may look a bit flimsy but there are 4 per
rudder with plenty
of carbon and glass and are well triangulated.
There are more upwards
loads than expected so a 45 deg brace will be
put in from the bottom pivot
bearing to the hull. When the first
rudder broke from the shear pin
shearing it caused the top bracket to
bend up about 120 degs. When I
detached the broken case and quadrant
it sprang back into position without
damage. I just had to replace
the composite pivot bearings.
>
> The rudders were always going to be the major challenge for us.
Consider that they have to rotate 240 degs., raise up and down 2
metres, break away if hit (but not under enormous sailing loads) and
be balanced under all points of sail. Also keep in mind they are
dagger boards, resisting all the sail loads, as well as rudders which
have to operate in two directions. The bottom bracket probably is too
close to the water. I have raised this by 100mm for Blind Date and
subsequent boats.
>
> Considering the above I think we have a
pretty good rudder design
once it has been strengthened. We are
considering other approaches,
such as beam hung rudders, but so far this
is the most workable. I am
considering replacing the large quadrant wheel
with a small one and
getting the 'gearing' from a large quadrant under the
cockpit floor.
>
> The slow progress must be frustrating for all
of you who are
watching this from afar. Now the boat is sailing, repairs
or
improvements and indeed sailing have to be done in 'play time' of
which there is little at this time of year. Harryproa has just landed
a very nice contract for 100 carbon fibre masts for GPS aerials on
container terminal forklifts. These have to be completed by the end
of
January so we will be very busy next month.
>
> A big thank you
to Luke for the pictures, video and report.
>
> Merry Christmas
to everyone,
> Mark
>
>
> Mark Stephens
>
www.harryproa.com
> 0431 486814
> ----- Original
Message -----
> From: Robert
> To:
harryproa@yahoogroups.com.au
> Sent: Saturday, December 24,
2005 10:03 AM
> Subject: [harryproa] Re: harryproa rudder
fastening stiffness
issue?
>
>
> Must
admit those forward rudders seemed vulnerable. Don't know
>
exactly how vulnerable as strong composites can be deceiving.
> Probably the loads on the rudder blades under sailing are
greater
> than the loads exerted by waves hitting the
supports. Don't see
mast
> stiffness as an especial
issues. The boat was travelling pretty
well
> for the
wind strength. Make it too stiff and the shock loads on
the
> bearings would be greater. Running stays would need a
reddesign
of
> the rig in terms of loading and sail
shape. Possibly the flex
allows
> the boat a little
movement without effecting the velocity of the
top
>
section of the mastas much?
>
>
Certainly impressive the motion and the speed and lots of nooks
and
> crannies for the kids to explore.
>
> Loved it
> Robert
>
> --- In harryproa@yahoogroups.com.au, "dominiquebovey"
> <dominiquebovey@y...> wrote:
>
>
> > Hi all,
> > after seeing
the video I have the feeling of two potential
stiffness
> > issues on the visionarry and HP in
general, the second is
rudder
> fixture:
> > I sailed in the irish sea lay May on a 28' monohull,
we got got
> pretty
> > rough sees and
wether, like Bf 8, wind against current, 15-
20'waves
>
(I
> > am translating from metric for you anglo-saxon
people ;-) where
the
> > boat fell hardly
because the front of the waves was almost
>
vertical.
> > I wonder how the rudders would bear such
shocks, especially the
> front
> > one
which takes the brint of the hit.
> > I am especially
worried about the horizontal wheel which could
be
> >
bent/broken by waves? Visionarry is a light boat which will
be
> > probably very fast with bare mast in 40-50kn of
wind and
> correspnding
> > sea
(european category A), so it'd better be TOUGH!
> > And
sorry, also the fastening to the hull looks fragile to me,
maybe
> > it isn't but it looks so.
> > I would think of an arrangement similar to the
catamarans: two
> tillers
> > with a
rod joining them, and sticks. But I agree that with this
>
you'd
> > have problems fitting an autopilot... HAAA
compromise, the
basis of
> >
engineering!
> > But maybe this is a solution for an
emergency steering system,
when
> > the cable-based
system breaks.
> >
>
>
>
>
>
>
>
> Yahoo!
Groups Links
>
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>
>
>
>
>
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