QUESTION FOR OWNERS OF FULL KEEL, "BARN DOOR" RUDDER VESSELS

[VChild]

For those of you with a full keel and large “barn door” rudder, I was wondering what your maximum angle of rudder turn is with the helm hard over. Mine seems to be no more than 30 degrees. It looks like the limiting factor is the hydraulic ram of the autopilot on the steering quadrant. The hard stops on the quadrant are not quite reached. When spinning the boat using the “back and fill” technique, it seems that if I could get the rudder farther over, I could kick the stern sideways with more force. The autopilot was installed by a previous owner and I am considering relocating the attachment point of the ram on the quadrant. I could even move the hard stops on the quadrant quite easily. But, I would like to get an idea of what a “normal” maximum rudder angle is on this type of boat. Thanks.

[slug]

35 degrees sounds about correct

Auto pilot stops before you reach the rudder stop

Greater angles overload the rudder and are dangerous

[Paul L]

The autopilot should not be used as the rudder stop. The actual rudder stops should be adjusted so they take the load when the rudder is at max range. Your AP is not going to live long acting as a rudder stop when not engaged.
The raymarine linear drives are good for +/-35* with no load.

[billknny]

Just to be clear on the whys and wherefores...

A rudder turned more than about 30 to 35 degrees stalls and becomes LESS effective as it then becomes more a brake than a turning tool. That (among other reasons!) is why the stops are there, about the point the rudder exerts maximum turning force.

The relationship between hard stops, and the end of travel for the autopilot can be a bit confusing.

With the autopilot in standby, turning the rudder by wheel (or tiller), the hard stops MUST be what stop the rudder travel. Anything else will damage the autopilot drive. This geometry is set during the hardware installation of the AP drive. If it is wrong it must be fixed.

When the autopilot is running, it should NEVER hit the stops. Hitting the stops in this case will also damage the autopilot drive and over stress lots of steering system components as the AP tries to drive it further. This should be handled by the autopilot rudder positioning sensor and software that is configured as part of the setup routine when the autopilot is first turned on or reset.

[VChild]

Yeah I was thinking mine was a little restricted (less than 30). I know the dangers of going astern without full control of the helm to prevent it from going hard over. Just didn’t know if there was an agreed upon standard for max rudder angle on large rudders. Trying to get a feel for what other full keel double enders have as far as limits.
Bllknny: Understand completely, thanks.
I believe my problem can be explained better by these pictures (sizes and angles not to scale). Turning hard to port (or starboard), my autopilot swings critically close to the rudder post due to angle of attachment. It is digitally programmed to stop just before it would collide. On further inspection, it appears that my hard stops would also hit in standby mode just before collision and that, in autopilot mode, the programmed stop is just before the hard stop. So, all should be ok in that regard.
But regarding maximum rudder angle of 30-35 degrees, do your safe and effective numbers refer to forward motion of the boat only. In other words, when the boat is at a standstill in a marina and I just want to kick the stern sideways without significant forward movement, would I not get a little more sideways thrust with some extra rudder angle? Or would greater than 35 degrees give no better sideways thrust component when the boat is stationary? Obviously I’m not worried about the “braking” effect in this situation.
I could probably squeeze a few more degrees if I mounted the ram further outboard on the support beam and then readjusted my digital stop and hard stop accordingly. Of course I would need to be extra cautious controlling the helm when making significant way while going astern.

[VChild]

This picture may also help. Notice the window between the rudder and the aft end of the keel where the prop sits. Because of the closeness of the prop to the rudder, the rudder "feels" a dramatic effect from the prop wash, unlike boats where the prop is much farther from the rudder.

[Paul L]

VChild,
In my experience (Alberg 35) backing up a barn door from a stop or slow, the rudder does little. Controlling the prop wash is far more effective in getting the boat to go where you want. Pretty much everyone who has owned a barn door cruiser has wanted more control in reverse.

[Bill O]

Originally Posted by VChild

This picture may also help. Notice the window between the rudder and the aft end of the keel where the prop sits. Because of the closeness of the prop to the rudder, the rudder "feels" a dramatic effect from the prop wash, unlike boats where the prop is much farther from the rudder.

the "window" is an aperture.

We have a large double ender w/a modified full keel. Our full rudder range is 70 degrees (35 degrees each side). We have set the soft stop on the AP (electronic) at 30 so it doesn't spike the hydraulic motor. Never has hit the soft stop.

Unless you are trying to turn in a tight circle, doubt you'll ever need to apply more than the 30 degree of rudder, so I'm not really sure why you want to move/adjust the attachment point on the quadrant.

[VChild]

Thanks Paul L. Yeah, I understand what you’re saying and I agree completely. I’m not really talking about how to steer a full keel boat in reverse though. The only reason I mentioned reverse is that if you are not careful when water is flowing backward across your rudder (whether that’s from going in reverse or from sliding backwards down the face of a huge wave, the helm could accidentally whip hard to port or starboard with such force it could cause catastrophic damage to the rudder system. But what I am actually talking about is prop “wash” effect on the rudder with a quick short burst of thrust in forward gear while the boat is not moving, for example, while spinning the boat within its own boat length in a tight marina. That is, the “back and fill” technique, alternating short bursts of forward and reverse with the helm hard over. In that situation, prop “walk” helps during the reverse burst and prop “wash” over the turned rudder helps during the forward burst by kicking the stern sideways. So, the question is, can I increase the kick or effect of the prop “wash” on the rudder during the forward burst if I am able to modify my setup to get a greater maximum rudder angle. Seems like 45 degrees would be ideal in a marina when the goal is just spinning the boat. However, it could be dangerous in other situations. That’s why I was wondering what other double enders have. Mine is less than 30 degrees. There must be a reasonable happy medium somewhere.

[VChild]

Thanks Bill O. So you have 35 degrees. That is helpful. I think I can modify mine to get 35 degrees. The problem is I’m in a tight marina with the distance between docks being not more than a couple of feet more than my boat length. On a calm day I can carefully spin my boat within its own boat length to position it for entering or upon exiting my slip. But with any wind, it complicates things. When I spin the boat on its own axis using prop walk, the alternating forward and backward bursts do as they should and mostly spin the boat. However, there is always some component of forward and backward movement of the boat, and I essentially have no room to spare, no room for safety buffer when the wind is disrupting my maneuver. That is why I desire more lateral thrust with the helm hard over. That is, more of the thrust kicking the stern sideways and less of the thrust actually moving the boat forward since I have so little room in front of me.

[psk125]

Maybe time for a bow thruster or a different slip. As others have tried to explain, putting the rudder over further will cause the flow on that side to stop and turn into turbulence, rather than project it off to the side to help more with turning the boat. The turbulence will be dissipated trying to go around all three sides of the 90º-turned rudder - the outboard, inboard, and bottom, instead of being only directed to the side desired. At the same time, flow on the other, unobstructed side, instead of helping to turn the boat because its flow has stayed attached to the rudder, will become unattached, and work to push the boat forward instead. You come to a point of diminishing returns in putting the rudder over too far.

[mlydon]

I’ve owned a cape dory 28 and an allied sea wind 32, both with barn door aperature rigs. Neither one was controllable in reverse at all, unless you got up some speed. Then they seemed more effective when you backed down the throttle then when you were at high revs. Without the room to back up a bit, you’re doomed in a crosswind. Used to tell people for a turn on Tuesday, start on Monday.....

Propwash kick is the only reliable thing to use

Matt

[Bill O]

+1 on a different slip. Seems like a lot of work to change the quadrant attachment for little or no gain to help maneuver in your tight quarters.

Bow thruster would work, but again a lot of work and expense just to get in/out of your slip. A new slip would be an easier solution.


Bill O.

[Benz]

I used to back-and-fill an 80-foot steel schooner with rudder stops at relatively low angles--I never measured, but 35 degrees seems about right. Our propwalk in reverse pulled the stern to starboard, so we always back-and-filled to port, if possible. The propwalk was so pronounced that you could keep the wheel pegged to starboard, with the reverse bursts not really generating any sternway, just pulling the stern sideways, and the fwd bursts carrying on the turning momentum. Obviously the wind speed and direction played a role, but it was neat to be able to do.
My own boat has an outboard that articulates, so I can steer in reverse pretty reliably, as long as I keep the rudder amidships. Once it's lost to one side or the other, I'm pretty much turning that way.

[VChild]

Thanks psk125. I do understand the physics and the forces involved. But as you state, there is a point of diminishing returns and that is what I am seeking. What is the ideal rudder angle beyond which it is hurting more than helping. That is all I am asking. So far I’ve heard another double ender has 35 degrees. Mine has less than 30 degrees and that is most likely due to an arbitrary placement of the hydraulic ram by a previous owner. I’m just trying to find that magic number. It seems like it would be more than 30 degrees. If I can at least get mine up to the ideal angle, I could potentially avoid more expensive options and more distant marinas. Moving the ram attachment farther out on the support beam would be quite easy but I wouldn't want to go beyond the ideal angle. I would like to hear from more double ender owners to see if they have 35 degrees or even more. I have a balanced rudder with the axis of the rudder post well behind the leading edge of the rudder. So, when I turn the rudder hard to port, for instance, the leading edge of the rudder actually crosses midline of the boat well onto the starboard side which, in theory, would help capture even more prop wash and direct it to the port side. I’m not sure how much effect that has due to the blunt taper of the leading edge.