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

[VChild]

Originally Posted by Mike Banks

One might imagine the maximum angle of rudder would be 45 degrees, but in practice it is much less than this. I think what you have is about right. The idea of a rudder is to deflect the stern laterally, not to act as a brake. The bigger the rudder angle, the more it slows the vessel, and the slower the vessel, the less the effect of the rudder regardless of angle.

So--I would leave it alone, if it seems to be working OK. By a Barn Door rudder I take it to mean one hung abaft the keel itself with a cutaway in the keel heel--and maybe the rudder face too, to allow for a propeller.

I hear what you’re saying about braking effect and slowing of the boat while in forward motion but I’m actually talking about a situation where the boat is stationary in a tight channel in a marina. In this situation the goal is to “spin” the boat with no forward or backward movement like a spinning ballerina. I’m not an expert here but I don’t think braking action comes into play in this situation although stalling of the rudder would, hence the Schilling rudder with much higher stall angles.

[mowerandy]

irrelevant aside...my old Windrider 16 trimaran has rudder stops at 90 degrees both sides - those are the "brakes"
Only boat I have known to have brakes, and by golly they work very well too (mostly for chickening out off wave faces that require more guts than the operator possesses, but occasionally for collision avoidance in close quarters)!

[psk125]

Might be worth asking a naval architect, rather than us armchair admirals, if going from 30º to 35º will make any difference.

[fish53]

Originally Posted by psk125

Might be worth asking a naval architect, rather than us armchair admirals, if going from 30º to 35º will make any difference.

I have, it's well presented in Dave Gerr's book on marine systems along with my classes at the Maine Maritime academy and as I stated 30 will work but 35 is the max.

[Bill O]

Originally Posted by VChild

If that achievable angle happens to be greater than 35 degrees, I would be very interested in looking into getting a Schilling type rudder.

As a scientist, it would be interesting to see how the added 5 degrees of rudder movement to either side made any significant change. If I had to guess, it may not be that significant as you would hope to do the job.
If you want a Schilling rudder on your boat (or a modified version), you'll probably have to make it yourself. Making a new rudder isn't as hard as one would think and most likely you would just do modifications/add-ons to your current rudder to get better lift. Whenever you haul out your boat again, look at Xsection of your rudder, then compare it to what a Schilling rudder Xsection.

We made a new NACA 0010 semi-balanced rudder a couple of years ago and it made a huge difference. It was fairly straight forward and not too difficult. Making add-ons to your rudder should be much easier than making a whole new rudder.


Bill O.

[mvweebles]

I see your underbody is almost exactly same as my Wm Garden designed displacement/ballasted trawler (Willard 36). Several sister-ships have modified their rudder to a "Fishtail" or Schilling rudder. Results have been impressive, and I am in the process of having it done as part of a larger refit. I've never heard of them on a sailboat - perhaps there is a drag penalty. But would hopefully solve your close-quarter maneuvering issues.



https://www.researchgate.net/figure/...fig2_281097586


Video showing a single engine power boat spinning. Reliable reports indicate this is not out of the realm of possible, though this boat obviously has a lot of hp driving the prop.

https://www.youtube.com/watch?v=rhDopwxTCbg

Will try to remember to report back in a couple months when my refit is done. I carry a Perkins 4.236 @85hp, so probably similar to your Lord Nelson 41.

[VChild]

Originally Posted by mvweebles

I see your underbody is almost exactly same as my Wm Garden designed displacement/ballasted trawler (Willard 36). Several sister-ships have modified their rudder to a "Fishtail" or Schilling rudder. Results have been impressive, and I am in the process of having it done as part of a larger refit. I've never heard of them on a sailboat - perhaps there is a drag penalty. But would hopefully solve your close-quarter maneuvering issues.



https://www.researchgate.net/figure/...fig2_281097586


Video showing a single engine power boat spinning. Reliable reports indicate this is not out of the realm of possible, though this boat obviously has a lot of hp driving the prop.

Will try to remember to report back in a couple months when my refit is done. I carry a Perkins 4.236 @85hp, so probably similar to your Lord Nelson 41.

Very impressive video.
Lets us know how yours turns out.

[VChild]

Originally Posted by Bill O

As a scientist, it would be interesting to see how the added 5 degrees of rudder movement to either side made any significant change. If I had to guess, it may not be that significant as you would hope to do the job.
If you want a Schilling rudder on your boat (or a modified version), you'll probably have to make it yourself. Making a new rudder isn't as hard as one would think and most likely you would just do modifications/add-ons to your current rudder to get better lift. Whenever you haul out your boat again, look at Xsection of your rudder, then compare it to what a Schilling rudder Xsection.

We made a new NACA 0010 semi-balanced rudder a couple of years ago and it made a huge difference. It was fairly straight forward and not too difficult. Making add-ons to your rudder should be much easier than making a whole new rudder.


Bill O.

I'll report back after the autopilot modification. Appreciate all the info.
Thanks

[HC43T]

dealing with this very subject right now on my Hans Christian 43t.
discovered it doesn’t have any rudder stops😱. And when the 3 blade max prop goes through feathered when changing from forward to reverse and rudder hard over, the blades can hit the rudder! the max prop blades come back several inches in the feathered position. I’m guessing I was getting 45 degrees deflection and it must have been coming up against the cable and sprocket in the pedestal. I’ve now fashioned stops but need to figure out what deflection this leaves me with. for sailing 30-35 is plenty, the ability to really crank it over in a tight marina I might miss. Hope I don’t ram the dock when she first goes back in the water! anyway, if you have a max prop take into consideration where those blades go when feathered

[Cadence]

Originally Posted by HC43T

dealing with this very subject right now on my Hans Christian 43t.
discovered it doesn’t have any rudder stops😱. And when the 3 blade max prop goes through feathered when changing from forward to reverse and rudder hard over, the blades can hit the rudder! the max prop blades come back several inches in the feathered position. I’m guessing I was getting 45 degrees deflection and it must have been coming up against the cable and sprocket in the pedestal. I’ve now fashioned stops but need to figure out what deflection this leaves me with. for sailing 30-35 is plenty, the ability to really crank it over in a tight marina I might miss. Hope I don’t ram the dock when she first goes back in the water! anyway, if you have a max prop take into consideration where those blades go when feathered

It appears you have a little wiggle room to move the shaft forward? If your rudder has a decent amount of leading edge, what about scalloping out a section just enough for blade clearance. Just food for thought.

[VChild]

Originally Posted by Cadence

It appears you have a little wiggle room to move the shaft forward? If your rudder has a decent amount of leading edge, what about scalloping out a section just enough for blade clearance. Just food for thought.

Agree. I had to do a little scalloping myself when I went to a 24” diameter prop. But the modification was on the trailing edge of the keel, not the rudder. The recommendation was a prop clearance of 10% of the prop diameter. So I had to cut out and reshape about 1-1/2” on the back edge of the keel in a small area. Not noticeable on a full length keel.