Dear All,
A couple of weeks ago we had a interesting related experience. Gua decided to reverse the rudders to make them easier to raise. One of those ideas that seems good at the time. So we spent a couple of days sailing with the long part of the rudder facing the direction of travel.
The consequence of course was that the rudders were very unstable and would suddenly flip from one side to the other causing dramatic stearing unless the tillers were held very firmly at all times.
It was just funny, but in high winds he instability could have been disastrous. It has made me very clear that rudders must either center or not move if unattended. With unconnected rudders the aft rudder will behave as you shunt, but what happens if you forget the fore rudder? Will it shunt on its own or become unstable?
For linked balanced rudders what will happen? If they can be stopped from being unstable it might be safer than unlinked rudders.
Any experience or views?
Best regards
Herb
--- In harryproa@yahoogroups.com.au, "tsstproa" <bitme1234@...> wrote:
>
> If you collide with something at 15 knots and happen to clear both bows and only hit front steering board it should be by design allowed to kick up in either direction mine do. I still want to refine the two arms connecting the backer plate for steering bopards. I think I will raise the lower one piggy back with upper and move linkage either up or down making it one brace higher form waterline for each board.
>
> I don't follow Speer foils I here alot about them. What shape was the foil you used? Was it bidirectional? Was it symmetrical fore to aft? was it symmetrical windward leeward? Or?
>
> Were both boards down steering with linked counter rotatating or steering with aft board only and front locked down in a fixed position?
>
> Todd
>
>
> --- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@> wrote:
> >
> > It is not about it tracking straight, or working when linked. The problem
> > for my boats, what happens when the front one kicks up in a collision or
> > grounding at 15 knots. I also had problems with the Speer foil as a rudder
> > because it stalled sooner in one direction than the other.
> >
> > rob
> >
> > On Tue, Oct 25, 2011 at 12:20 PM, tsstproa <bitme1234@> wrote:
> >
> > > **
> > >
> > >
> > > I don't see why it wouldn't track straight. Planes flight level
> > >
> > > Two linked counter rotating rudders down will always be better than one aft
> > > rudder down on a shunting craft. Look at my shunts in videos with linked vs
> > > unlinked . Its simpler faster and more effective over raising ,lowering ,and
> > > rotating, two boards that are unlinked.
> > >
> > > My speed on current boat has been limited by sail area and design of sail
> > > Its A junk rig made of poly tarp and has sinse stretched out really bad top
> > > speed 12mph in about 15mph winds. I have a 120 sqft mylar full batten custom
> > > Hansen sail. But still need all the rigging.
> > >
> > > Better yet would be to place a hobie 14 rig on my current boat and test.
> > >
> > > That said I see no reason the foils can't be refined further for higher
> > > speeds still being connected to maintain effect.
> > >
> > > Simple aero dynamics a slant/ or angle is less efficient than a striaght
> > > non angled leading edge. Same with a tappered chord vs a non taper one.
> > >
> > > So why would you want to angle boards back for balance of boat sails center
> > > of effect and other factors. If balance is taken into consideration to begin
> > > with there is a buffer zone so to speak in lining up these force instead of
> > > angling boards aft which is inefficient!
> > >
> > > Todd
> > >
> > > --- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@> wrote:
> > > >
> > > > I don't believe a single unattended foil with the rotation axis at 50% of
> > > > the chord will point straight ahead at 15 knots. Until I see one, and the
> > > > physics that explains why, I cannot agree that it is a good thing to have
> > > on
> > > > a boat.
> > > >
> > > > Linked rudders solve a lot of problems, but unless they work when one is
> > > > raised, are no use. Rotating them aft is a solution, but is an extra
> > > layer
> > > > of complexity. As the rudders have to turn for steering, turning them
> > > > through 180 on a shunt is no big deal, unless they are mounted on the
> > > hull
> > > > or utilise wheel steering, but even here, there are simpler methods.
> > > >
> > > > regards,
> > > >
> > > > Rob
> > > >
> > >
> > >
> > >
> >
>