Skeg hung rudders

[Jeff_H]

Its funny about sailing terminology. When I started sailing there seemed to be clear and very rigid definitions for the various sailing terms, and these terms were drummed into us and used nearly religiously. When I started sailing, sailing courses drilled the neophyte on terminology before they even got out on the water.

But in the past decade or two, sailing schools and even sailing primers seem to focus on learning how to operate a boat without as much of a focus on the precise use of terminology, or even much of a focus on the technology or physics of sailing.

Please understand that I'm not making a value judgement here, but it has lead to some big changes in how terms are used today relative to their historic useage. In the past, misusing terms labeled one as a land lubber and lubberly use of language was frowned up. For better or worse, that does not seem to be the case anymore.

With regards to the term 'balanced rudder', historically the term had been counter-balanced rudder, which refered to the fact that the portion of the rudder forward of the pivot axis counterbalanced the steering forces giving the helm a lighter feel. That said, it is pretty common to see the term counter-balanced has been short-handed to balanced rudder.

The only problem with that I see with that short-hand is that it can be confused with the terms 'balanced helm' or 'balanced rudder' which refers to a condition where sail trim is balanced with the hull dynamics so that the helm is neutral; lacking both weather and lee helm.

Respectfully,
Jeff

[Giulietta]

A little about rudder design (and now its the Aeronautical Engineer talking, not the sailor eheheh)

John, I don't know in English but if I translate to English from Portuguese, we refer to those rudders (such as mine) as couter Balanced rudders (leme contra balanceado) in Portuguese.

The "design" of the balanced control, comes from the Aeronautical industry, where to reduce the amount of effort required in the pilots controls, to move the controlling surfaces as speed increased, and air pressure over the control surface, created some resistence. This was also used to save weight and cost, for systems with hydraulics, to reduce the weight and size of the system, by requiring less effort form the hydraulic system.

To achieve this, the axix of the surface is further back from the leading edge, and when moved, some part of the leading edge of the control is allowed to move in the opposite direction of movement exposing the "opposite" side of the rudder to the air (water in this case), that helps "push2 the control in the desired direction, and thus help move the control surface. Off course not too much other wise it creates drag and slows the process...its calculated.

This system, allows, for example, an in my case a very very light rudder feel and control, but above all, it allows the rudder to be very responsive with small changes of the wheel.

It also allows the boat to turn more rapidly and in a smaller radius.

The draw back is its less stable, and requires a better "helm hand", to keep the boat straight, but for race boats, that inherent stability is a requirement, as manouverability is required for obvious reasons. Also causes excessive drag and reduced speed if "over turned".

To compensate for this inherent un-stability, and still allow the rudder to be neutral, in the design, the rudder is swept back, having more area of control after the axis, towards the rudder tip, which hellps the ruder self center if released.

The drawing bellow shows how having the axis behind the leading edge helps "balance" the effort in the rudder. The water that hits the part of the leading edge that is now exposed to the flow "pushes" the rudder in the opposite direction

[Plumper]

In my old Admiralty Manuals of Seamanship, mid 50's printing, the spade style rudders were called balanced. I have never seen the term counter balanced associated with rudders at all. The books go to great length describing the various styles of rudders on various types of ships and boats and their pros and cons.

[JohnRPollard]

Thanks Jeff, Giulietta, and Plumper for your comments. I found them all very interesting.

For anyone poking in here for a look, I just wanted to mention as an aside that some different standards from the other forums are used. Whereas in other forums it might be considered nitpicky or otherwise impolite to correct another's use of terminology, here in the "Design and Construction" forum such fine technical distinctions are invited and encouraged. Some of us enjoy learning about and debating these distinctions, and this is where we come to do it.

[sailaway21]

I'm glad that the question of terminology was raised. All references to follow are from Baker on Steel Shipbuilding, originally published in 1943.

What is being referred to here as the rudder post is more commonly known in ships as the rudder stock. the rudder stock is what turns the rudder and supports it's weight. The rudder post is that vertical section of what is being referred to as a skeg to which the gudgeons are attached.

There are unbalanced and semibalanced rudders. Both types can be mounted on the rudder post via gudgeons and pintles, with the latter's bottom portion protruding forward of the the rudder stock and also the rudder post. (Imagine a section of rudder on a full keel boat that extends deeper than the keel and extends forward of the rudder stock.) usually about 25% of the rudder is forward of the stock in a semibalanced rudder. A spade rudder is a semibalanced rudder without the presence of a rudder post or gudgeons and pintles, and takes it's name from the fact that it resembles a spade in it's shape.

""Quite often the expression "balanced rudder" is used for "semibalanced rudder". The term "semibalanced' is used in this text, for no rudder is "balanced" throughout the entire turning angle.""

As Jeff and John state, terminology does change, usually causing nothing but confusion. Chemists do not deign talk with you until you know the periodic table. Boaters, on the other hand, are expected to deal with and make accomodation for all kinds of nuttiness like that wood thingy that turns the boat. Those being trained for service in the Merchant Marine are not alloted the latitude to make up their own terminology.

Even with commonly agreed upon terminology for the most part there will always be differences in terms in different parts of the world and between different portions of the maritime industry. For instance, I know of no one who refers to the ship's propeller as anything but that or, perhaps, the screw. Yet every shipyard, where the prop is pulled and replaced, refers to the job as pulling the wheel. The wheel is what shipyards refer to instead of the propeller. Both are technically correct but one seems more descriptive of the actual device than another.

[Plumper]

By way of comparison with Giu's balanced spade rudder, here are two other designs. One is a partial skeg, the other keel hung. It is very apparent the differences in rudder protection and ease of jury rigging steering. If the rudder jammed over on the keel hung boat you would be in real trouble.

I can't figure out how to attach a picture to this post.

Sorry.

[tdw]

Originally Posted by JohnRPollard

More comments below....




TDW,

I can't tell from your photos, but it looks like Raven may not have what I call a "balanced" spade rudder? Could it be that the rudder post on Raven runs down through the leading edge of the rudder (like in the photo of the Crealock 31 that I posted at the beginning of this thread)? Such that all or most of the rudder's surface are trails behind the rudder post? In which case, I would still call it a spade rudder, just not a balanced spade. If so, that might partially account for how well your boat tracks. Any more close up photos you could show us?

John,
attached is drawing from the Van de Stadt web site of the standard hull design for the VDS 34. Show it better than any photo I have. Raven is as illustrated with the deepest of the
(fixed) keel options.

[JohnRPollard]

TDW,

I still can't say for sure, but looking at the drawings my best guess is that your rudder "stock" extends straight down from the tiller head through the leading edge of your rudder. This would make it an unbalanced spade rudder, which is a favorable design for straight-line tracking, not unlike our skeg hung rudder but lacking the skeg. It lacks the "power steering" feel of the semi-balance rudder, but since your VDS 34 is fitted with a wheel you probably don't notice the extra effort necessary to turn the rudder.

Another advantage of this arrangement is that a small piece of material (either a bent piece of bronze or some kind of plastic/rubber flap arrangement) can be fitted to the bottom of the hull just slightly forward of the upper leading edge of the rudder, to prevent warps, grass, or other debris from wedging and snagging in the gap between the top of the rudder and the bottom of the hull. With a balanced rudder, the forward leading edge of the rudder pivots out to one side or the other, making that gap larger and more difficult to shield.

P.S. I like the lines of your boat and the sensible interior layout.

[Jeff_H]

This has been an interesting discussion for me. Like most who come on this discussion forum I come here to share ideas, to learn as well as to endeavor to provide where posible useful and accurate information. Sometimes a part of learning is when you discover that something you thought you knew really well, turns out to be a mistake. Such is the case on the term 'balanced' vs 'Counterbalanced' rudder. Time to eat crow here.

My recollection was that when I was growing up the correct term was 'Counter-balanced' rudder. A couple of the posts above quoted historic references to 'Balanced' rudders, and so I began to wonder about my recollection. So. I went back into my collection of old ship and yacht design books. I grabbed Skenes which I thought had a drawing of various rudder types and was surprised that the text referred to 'motor boat style balanced rudder'. Humm, that wasn't what I expected. So I started flipping through outher texts. Sure enough, virtually every one of them (Chappelle [1936], Skenes [1927, 1938, 1973], Manfred Curry [1928,1949], Gougeon-Knoy [1973], Gutelle [1979], Larsson-Eliasson [1994]) used the term 'Balanced Rudder' for rudders with a portion of the rudder forward of the rudder post.

Its not as if the term 'Counter-Balanced rudder' did not exist. I pulled up a couple 1960's era Cal brochures that refers to the benefits of their 'counter balanced' rudder [ http://www.bangorpunta.com/Cal/1967-...4sAreHere.html, http://www.bangorpunta.com/Cal/1967-...nspacRace.html ] but frankly, that doesn't make the term right.

So I wish to graciously thank those who corrected my eroneous post above, allowing me to stand very much corrected.

Respectfully,
Jeff

[bestfriend]

As far as protection is concerned, I cannot speak of first hand knowledge. But I think SimonV can attest to how much more work is involved in keeping a boat with a spade rudder on course. The difference between his boat and mine. He made a comment on how tender the steering was on my boat. I have no auto pilot or wind vane, and the wheel needed constant attention on the swells. You have taken yours out, haven't you, Simon? ....Simon?