Subject: Re: [harryproa] Re: harryproa rudder fastening stiffness issue?
From: "J. Michael Crawford" <>
Date: 1/14/2006, 7:46 PM

  I think the stiffness of a thicker section in the rudder supports is a good idea -- extended beating in a heavy seaway could put a lot of repeated bending moment, shear, and torsion on a brace that doesn't have much area over which to distribute it.

  I'm uneasy about an angled foil section, though, for the same reasons Rob mentioned.  Most of the time a rear scoop would not be an issue, but there are times it could be dangerous, and those are the times that worry me.  I also like the idea of simpler forces in perpendicular planes.  An angled foil taking wave action could put a lot of stress on a structure that doesn't extend symmetrically to the leeward side of the hull.  Of course, a flat brace could also do that.

  I'd keep the basic idea of a thicker attachment and vary it a bit (apologies if I'm repeating):

  a)  Fair the top of each top support and the bottom of each bottom support into a shallow cone shape with the apex right on the hull, maybe five or ten cm high at the thickest point in the center.  This will spread the load way out, help with the bending moment due to slamming, and also shed a bit of water at the same time.  With a foam center and carbon skin this would not be very heavy.  The downside is that it might make it more difficult to get in between the brackets, but since they're already fixed, I'm not sure this is an issue.

  b)  Create hollow box with a rounded triangular shape to connect the inside top support to the inside bottom support.  It wouldn't be as sleek as the current empty space between the supports, but then there's normally nothing hitting that space, and if water were slamming into the hull there, the system would be better off with the box support.  The benefit would be uniting the top and bottom brackets into a single system that turns most forces into shear, tension, or compression.  This should be a lot easier to resist than the bending moment.  Even if this were only to extend halfway out to the edge of the supports, they should be able to resist a lot more bending moment, and the system would be a bit sleeker.

  c)  a + b.  Fair the top and bottom outside brackets, connect the inside brackets with a smoothed box structure.  Really strong, kind of clunky.

  d)  a * b.  Another combo.  Make short conical fairings on the top and bottom outer supports, and much taller conical fairings in between the inner supports.  That's stiffer than a and much sleeker than b.  Waves pass through and forces are greatly reduced.

  Any of the above mean that the foil, kick-up, or pintles will need to give before the brackets do, but that probably goes without saying..


  Also, kudos to Rob for having the guts to debate this all out in the open, even inviting additional debate from detractors on the proa_file group, and yet still answer design critiques patiently.  Most people would either hide the ups and downs, get grumpy when anyone doubts them, or both.

  It's also great to see a patient, iterative approach.  There's no way you'll ever think of everything ahead of time, and it's not always wise to try.  It's more valuable to create a good solution, try it in the real world, see what works and what doesn't, and then make a much more informed design choice based upon experience.  More is usually learned from failure than from success.

       - Mike

Robert wrote:
You're right I do mean the rudder supports, but I can't agree with
your arguments in dismissing the idea
(a) They could be left where they are and keep that extra lever arm
(b)Not necessarily a bad thing but it would probably remain out of
the water according to my  reading your pics. It wouldnt necessarily
make a rooster tail
(c) don't see that necessarily follows. The supports would have a
thicker cross section and allow the top surface where the pintle
emerges to be near horizontal
--- In, "Rob Denney" <proa@i...> wrote:
> 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
> regards,
> rob ----- Original Message -----
>   From: Robert
>   To:
>   Sent: Tuesday, January 10, 2006 10:20 AM
>   Subject: [harryproa] Re: harryproa rudder fastening stiffness
>   Thanks Mark and Rob for detailed replies.
>   I was considering making the braces in a foil cross section set
>   15-20 degrees attack for the forward facing rudder. This would
>   provide stiffenning as well as a bit of lift. Possibly vetilate
>   in case of severeely depressing the bows. makes sense to put the
>   quadrant under the floor. When I look at just about any other
>   arrangement in other boats they are all vulnerable. Breking waves
>   from behind can put enormous strains on the rudders of most
>   overall your present design looks pretty good and they obvoiously
>   work.
>   Robert
>   --- In, "Mark Stephens"
>   wrote:
>   >
>   > I really wouldn't be concerned about the rudder brackets and
>   quadrants from a vulnerability to waves point of view. However
>   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
>   beef them up. I decided to leave them for a number of reasons:
>   to test them gently and see where the cracks develop, we may need
>   adjust the rake angle which would also requires a rebuild, there
>   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
>   the repairs in the photos and video.
>   >
>   > On return from the second sail we noticed some hairline cracks
>   the unrepaired rudder case which I have since repaired, again
>   strengthening it enough to go sailing again. Rather than
>   rebuilding the rudder cases I am interested in keeping the
>   to a minimum.
>   >
>   > The triangular brackets that attach the rudders to the hulls
>   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
>   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
>   it sprang back into position without damage. I just had to
>   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)
>   be balanced under all points of sail. Also keep in mind they are
>   dagger boards, resisting all the sail loads, as well as rudders
>   have to operate in two directions. The bottom bracket probably is
>   close to the water. I have raised this by 100mm for Blind Date
>   subsequent boats.
>   >
>   > Considering the above I think we have a pretty good rudder
>   once it has been strengthened. We are considering other
>   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
>   getting the 'gearing' from a large quadrant under the cockpit
>   >
>   > 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
>   a very nice contract for 100 carbon fibre masts for GPS aerials
>   container terminal forklifts. These have to be completed by the
>   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
>   >
>   > 0431 486814
>   >   ----- Original Message -----
>   >   From: Robert
>   >   To:
>   >   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
>   >   exactly how vulnerable as strong composites can be deceiving.
>   >   Probably the loads on the rudder blades under sailing are
>   >   than the loads exerted by waves hitting the supports. Don't
>   mast
>   >   stiffness as an especial issues. The boat was travelling
>   well
>   >   for the wind strength. Make it too stiff and the shock loads
>   the
>   >   bearings would be greater. Running stays would need a
>   of
>   >   the rig in terms of loading and sail shape. Possibly the flex
>   allows
>   >   the boat a little movement without effecting the velocity of
>   top
>   >   section of the mastas much?
>   >
>   >     Certainly impressive the motion and the speed and lots of
>   and
>   >   crannies for the kids to explore.
>   >
>   >   Loved it
>   >   Robert
>   >
>   >   --- In, "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
>   >   pretty
>   >   > rough sees and wether, like Bf 8, wind against current, 15-
>   20'waves
>   >   (I
>   >   > am translating from metric for you anglo-saxon people ;-)
>   the
>   >   > boat  fell hardly because the front of the waves was almost
>   >   vertical.
>   >   > I wonder how the rudders would bear such shocks, especially
>   >   front
>   >   > one which takes the brint of the hit.
>   >   > I am especially worried about the horizontal wheel which
>   be
>   >   > bent/broken by waves? Visionarry is a light boat which will
>   >   > 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
>   maybe
>   >   > it isn't but it looks so.
>   >   > I would think of an arrangement similar to the catamarans:
>   >   tillers
>   >   > with a rod joining them, and sticks. But I agree that with
>   >   you'd
>   >   > have problems fitting an autopilot... HAAA compromise, the
>   basis of
>   >   > engineering!
>   >   > But maybe this is a solution for an emergency steering
>   when
>   >   > the cable-based system breaks.
>   >   >
>   >
>   >
>   >
>   >
>   >
>   >
>   >   
>   >   Yahoo! Groups Links
>   >
>   >
>   >
>   >   
>   >
>   >
>   >
>   >
>   >
>   >   --
>   >   Internal Virus Database is out-of-date.
>   >   Checked by AVG Anti-Virus.
>   >   Version: 7.0.344 / Virus Database: 267.14.1/206 - Release
>   16/12/2005
>   >
> --------------------------------------------------------------------
>   Yahoo! Groups Links
>     a.. To visit your group on the web, go to:
>     b.. To unsubscribe from this group, send an email to:
>     c.. Your use of Yahoo! Groups is subject to the Yahoo! Terms of

Yahoo! Groups Links