[Rhodes22-list] STEERING QUESTION

Mon Aug 4 12:49:20 EDT 2003

Bob,

On Dynamic Equilibrium, as long as the rudder blade is fully down, the
tiller can be turned full lock without the rudder blade hitting the
outboard's lower unit.  If the rudder blade is even partially up; then,
there is interference.  It's easy to check.  With the outboard motor lowered
but not running, simply put the tiller over & see if there is interference
between the rudder blade & the motor's lower unit.

By the way, such extreme rudder angles do not cause the boat to turn faster.
Think of the rudder blade as a hydrofoil, an underwater wing.  Just as the
air flow over an airplane wing will stall out beyond some angle of attack,
the water flow over the rudder blade will stall out if the rudder is turned
too much.  Stalled out flow over an airfoil or a hydrofoil involves the
breakdown of smooth laminar flow, sudden loss of lift, & the generation of
lots of turbulence & drag.  Let's define a rudder angle of 0 deg when the
tiller is pointed straight ahead down the centerline of the boat.  Most
steering is done with rudder angles of  <= +/- 30 deg.  The water flow over
the rudder blade is certainly stalled out beyond angles = > +/- 45 deg.
Because of the sudden loss of lift & generation of turbulence & drag, once
the water flow over the rudder blade is stalled out, the rudder blade
behaves more like a water brake than a steering device, slowing the boat
down rather than causing it to turn!

You can exploit this water brake phenomenon when you want to stop the boat
quickly.  Putting the tiller all the way over to the mechanical stop
effectively puts a 3 sq foot drag device into the water behind the boat.
Because the deceleration force from this water brake is slightly offset from
the boat's centerline, the braking force generates a torque about the hull's
CLR that will cause the bow to yaw slightly in one direction or the other.
Putting the tiller hard over to starboard will cause the bow to turn
slightly to port & putting the tiller hard over to port will cause the bow
to turn slightly to starboard as the boat slows down.

Remember, there must be water flowing over the rudder blade in order for it
to have any steering or braking effect.  Once the boat stops, the rudder
blade can be turned any which way with no effect upon the boat.

So there, now you know how to use the rudder properly for steering, turn
quickly to port, & stop the boat quickly.

Go practice & enjoy - Good luck, Bob!

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Robert Dobson" <dobson777 at hotmail.com>
To: <rhodes22-list at rhodes22.org>
Sent: Sunday, August 03, 2003 11:14 PM
Subject: Re: [Rhodes22-list] STEERING QUESTION

>
> Roger, As usual you give me stuff to think about and to practice. You are
> right , I am mounted off-center on the transom to port on Gb's motor mount
> raising system. I am correct to leave the motor in the straight position
and
> do all  my steering with the tiller? It just looks like the rudder and the
> prop are going to intersect. What your telling me is that I do not need to
> be turning the rudder near as far as on a starboard turn. The rudder can
be
> fully down all the time without a problem. Thank you for your answer.
>
> >From: "Roger Pihlaja" <cen09402 at centurytel.net>
> >Reply-To: The Rhodes 22 mail list <rhodes22-list at rhodes22.org>
> >To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> >Subject: Re: [Rhodes22-list] STEERING QUESTION
> >Date: Sun, 3 Aug 2003 18:33:55 -0400
> >
> >Bob,
> >
> >I am assuming your Rhodes 22 has the outboard motor mounted off-center on
> >the transom to port of the rudder.  If your outboard is mounted to
> >starboard
> >of the rudder; then, everything I am about to tell you will need to be
> >reversed.  Actually, if your outboard is on the starboard side; then, I
> >don't understand why you are having a hard time turning to port!
> >
> >In forward gear, the port offset location of the thrust from the outboard
> >motor generates a turning force or torque about the hull's Center of
> >Lateral
> >Resistance (CLR) that tends to turn the bow to starboard.  This torque is
> >in
> >opposition to any forces that are trying to turn the bow to port.  Under
> >power in forward gear, it's as if the rudder were less effective turning
to
> >port & more effective turning to starboard.  If the outboard motor were
> >mounted on the centerline of the transom, this apparent difference in
> >port/starboard turning ability would disappear.
> >
> >Try this experiment in open water, because you are going to be very
> >surprised how fast the boat will turn to port.  With the boat moving
> >forward
> >at docking speed (1-2 knots), shift into neutral, & then push the
outboard
> >motor's tiller all the way over to port.  Now, hang onto something, warn
> >your passengers, put the tiller over for a port turn, shift into reverse
> >gear, & apply a burst of power!  Was that port turn fast enough for you?
> >What happened was that both the rudder force & the thrust from the motor
> >were directed to push the stern to starboard, which makes the bow turn to
> >port.  Now, that you know what the boat is capable of in terms of deg/sec
> >yaw rate to port under power, practice this technique until you develop
> >control.  Just imagine the capability this kind of port turning ability
> >will
> >give you in a crowded marina &/or cross wind situation?!!
> >
> >You mentioned your outboard is a little hard to get at when it's in the
> >down
> >position.  Even if you leave the motor in the straight-ahead position,
> >apply
> >a little power in reverse gear, & steer with the tiller.  The reverse
> >thrust
> >from the port offset motor will still assist the port turn.  Again,
> >practice
> >this maneuver in open water until you develop control.
> >
> >Good Luck, Bob!
> >
> >Roger Pihlaja
> >S/V Dynamic Equilibrium
> >
> >
> >----- Original Message -----
> >From: "Robert Dobson" <dobson777 at hotmail.com>
> >To: <rhodes22-list at rhodes22.org>
> >Sent: Sunday, August 03, 2003 3:35 PM
> >Subject: [Rhodes22-list] STEERING QUESTION
> >
> >
> > > I have a question of appropriate procedure on steering in harbor areas
> >when
> > > using sail and motor. My concern is turning to port with engine
engaged,
> >If
> > > the rudder is fully down the prop is going to be in contact if I am
not
> >very
> > > careful to limit my degree of turn. Obviously I am doing something
> > > improperly, Excuse my ignorance. I am assuming steering with the
rudder
> >and
> > > leaving the motor alone in the strait position. Any advise is
> >appreciated.
> >I
> > > can not find any mention of this in the support material I have found.
> >Is
> > > the answer to steer with the motor with rudder is tiller lock
position.
> >This
> > > inefficient and very tuff because the motor is very low over the
stern.
> > >
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> >
> >
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