Subject: Re: [harryproa] Re: rudder frame desgn
From: "Rob Denney" <>
Date: 4/10/2008, 9:53 PM


I agree, it is fascinating.

Your analysis is correct, but what allows it to work is 2 sheer pins
which hold the rudder down. One above the height of the beam (visible
in the last picture in the Files) and one at the level of the bottom
of the beam. They are not actually sheer pins, but sheer plates, in
as much as they will only break in one direction, away from the beam.
When it is the bow rudder and it hits something, the top pin lets go
and the rudder with bearings attached, kicks up around the bottom
pin. When it is the stern rudder, the bottom pin lets go and the
rudder kicks up around the top pin. The flanges on the fea model have
been lengthened fore and aft to support the rudderand bearings all
the way to horizontal, in both directions.

The pins are strong enough to hold the rudder shaft, but it is the
extended flanges which keep it at right angles to the beam. The
bearings never leave the flanges, so there is no need to flare the
flanges for re entry.

This system is better than anything else we have tried so far. The
thing I like most about it is that it is all compression loads over
short distances, which are easy to resist. The rudder shaft sees
bending loads, but we have a pretty reliable technique for very strong
carbon shafts, so I am not worried about this.

Next is the details. The bearings (pvc drainpipe is not up to scratch
on Elementarry, suspect UMPWE would not do it either. Blind Date is
using a stronger, tougher plastic, rated for the loads. Worse case
scenario is we need ball or roller bearing shafts, but these are
easily made, or bought. Steering is also tricky. Tiller and
extension is not trouble, but wheel steering is a bit more of a
challenge. BD is using a rack and pinion, another boat a spur gear.
The charter boat will have conventional rope and quadrants, both
rudders linked to a single wheel.

Blind Date's rudders are vertically liftable reducing the draft to the
same as the ww hull.

John Wright,

Attachments to posts are a problem, please put them in the files or
photos section. Ta.



On Thu, Apr 10, 2008 at 11:18 PM, jhargrovewright2
<> wrote:
> Mr. Denney,
> I am fascinated.....with the finite element analysis image.
> Impressive and colorful.
> Can you elaborate a little for us laymen. This is the bracket that
> attaches to the beam that holds the rudder shaft which will fit in
> the channel, vertically? This assembly replaces the fabrication
> shown in the other pictures in that folder? Is there a picture of
> the pivot pin (point) that allow the rudder to swing up. And last,
> what holds the rudder down?
> Thanks,
> John
> --- In, "Rob Denney" <harryproa@...>
> wrote:
> >
> > G'day,
> >
> > I have just uploaded a finite element analysis (fea) of the beam
> > mounted rudder supports for Blind Date to the "Rough beam rudders &
> > fea of rudder supports" file in the Files section. The picture
> shows
> > the loads and exaggerated deflection of the rudder box with 7 tonnes
> > load on the rudder, which is what we ended up designing it for.
> This
> > is more than double the weight of the boat, so we are pretty
> confident
> > that this part won't break. The test rudder shaft took 15 tons so we
> > are pretty confident about that as well. Now just have to sort
> out
> > all the details.
> >
> > The other pictures in the file are the test version on my
> elementarry.
> > Rough, but so far nothing has broken.
> >
> > All engineering from now on will be done with fea. Costs more, but
> > gives a much better result, plus I like looking at the pretty
> > pictures. ;-)
> >
> > There will be some more pictures of Blind Dates rudders on the web
> > update, which unfortunately can't happen until I get a password from
> > the web host, which comes by surface mail, for some reason.
> >
> > regards,
> >
> > Rob
> >

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