By Rich
Recently I’ve been lucky enough to steer a variety of sailboats nearly back-to-back, and I’ve been amazed at how different each helm felt. Most of the differences can be traced to the boats’ widely varied rudder designs, which caused me to ponder the challenges naval architects face in designing them.
It might seem that rudder designs should be pretty straightforward. After all, in the end a rudder is just a fiberglass board that gets dragged through the water at the back of a boat so it can be steered right? In reality, however, I’ve noticed that different yachts (even coming off of the drafting table of the same designer!) can ship to customers with completely different rudder designs – often for little discernible reason that I can identify. More interesting still, the designer’s success in creating a good rudder varies widely – at least in my own personal opinion! Before I dig into specific examples of ‘good’ and ‘bad’ steering traits, let’s take a look at the critical elements of rudder design and how they effect the helmsman’s experience.
Rudder “Balance”
It’s important to note that rudder balance is not at all the same thing as helm balance. People often confuse the two. Helm balance is a more commonly used term and is actually tuned by the crew of the boat while underway by easing or trimming the mainsail relative to the headsail. “Weather helm” is encountered when the boat wants to turn up into the wind if the helm is released, while “lee helm” is encountered when the boat wants to fall off if the helm is released.
A rudder’s “balance” describes a characteristic of the rudder foil itself and is baked in to the rudder design as soon as it’s made. A “balanced” rudder refers to a rudder constructed so that some portion of its surface area is upstream of the rudder’s pivot point. The pivot point is formed either by the rudder post or by the rudder gudgeons (in the case a transom-hung rudder). In practice rudder balance is not a “yes” or “no” binary where a rudder becomes “balanced” all at once, but rather a rudder is designed with more or less surface area upstream of the pivot point and therefore with more or less balance. A rudder is considered unbalanced if all of its surface area is aft of the pivot point.
This J/22 has a transom-hung rudder that is completely unbalanced, because all of its surface area is aft (downstream) of the gudgeons (hinges) on which it turns:
The same is true of this J/29:
By contrast, here is a photo of our Sabre 42’s rudder. Note that some of the rudder’s surface area is forward of the rudder post. This rudder offers a lot of balance.
The design tradeoff: an unbalanced rudder will give the helmsman better feedback (“feel”) at the expense of higher steering loads, while a balanced rudder will give up some feedback in exchange for lighter steering loads. As a broad generalization, an unbalanced rudder will be more appropriate for a near-shore buoy racer or daysailer, while a balanced rudder will be more appropriate for an offshore boat because helmsmen (or auto pilots!) will need to stand longer watches behind a helm that will tax them with less physical exertion – especially in heavy weather. Because of their ability to track so easily, an exception to this broad generalization may be made for full or very long chord length keel designs, but the generalization holds for more modern fin keel designs.
Aspect Ratio
As with any foil such as an airplane’s wing or a yacht’s keel or centerboard, rudders can be constructed to be high aspect ratio (long and thin) or low aspect ratio (short and wide).
Here is a very high aspect ratio J/70 rudder brand new from the factory and still in its protective bubble wrap as Hull 207 was being commissioned. Compare it to the image of the low aspect ratio Sabre 42 rudder above.
The design tradeoff: High aspect ratio rudders create less drag relative to the lift (effectiveness) they offer. However, they have two drawbacks: first, high aspect ratio rudders will be deep rudders, meaning they are only compatible with deep draft yachts. Second, high aspect ratio rudders will tend to stall more abruptly with less warning than low aspect ratio rudders. In practice aboard a sailboat that means a greater risk of broaching unexpectedly when sailing downwind under spinnaker. High aspect ratio rudders are therefore more often found on inshore racers than on ocean passage makers.
Size (It Matters!)
A larger rudder means more drag, a slower boat, and higher steering loads – especially if the rudder is unbalanced. A smaller rudder reverses those dynamics at the risk of introducing control problems – especially downwind in brisk conditions.
The design tradeoff: To keep performance at its peak, yacht designers generally will want to make rudders as small as they can while still offering good control of the yacht. Interestingly, the hull form of the yacht creates a very important interplay with the sizing of the rudder. To illustrate the point, I’ll take two hull form extremes: a flat, performance-oriented underbody with a bolt-on keel, versus a deep “whale” underbody with a centerboard and internal ballast. Here is a flat underbody shown on a new production cruiser:
As you can see in the photo, the flat underbody offers a clear flow of water aft to the rudder. Now consider the opposite extreme, shown on a Ted Hood-designed Gulfstar 40:
Note that the underbody on this boat looks more like a pot belly, out of which the centerboard will drop. The formal definitions that translate to “pot belly” are “deadrise” (the “deep V” shape of the bottom as viewed from the bow or stern) and “rocker” (the curve in the underbody when viewed directly from abeam, as in the upper photo). This whale underbody has a lot of rocker and deadrise, both of which interrupt a clean flow of water to the rudder. Boats of this type will need a larger rudder to compensate for this interrupted flow, and the designer will need to expend some effort in smoothing the water flow and directing it toward the rudder to maintain good handling in the boat.
Although “whale” underbody’s such as Ted Hood’s have fallen out of favor in more contemporary designs, I include them here as being illustrative of the challenge shoal draft, offshore hull designs create for rudder design. Offshore hull forms often will have more deadrise and rocker than inshore race boat designs, and as such they create challenges for rudder design similar to (but not as extreme as!) those created by the whale underbody shown above. In general, an offshore hull form combined with a shoal draft creates the need for a short rudder that extends no deeper than the keel (to protect it from grounding loads). Consequently, such a rudder spends much of its life in waters without a smooth, direct flow of water over it. As such it will need to be larger and well designed to maintain good yacht control. As an amusing side note, Ted Hood created a novel, retracting rudder for this Little Harbor 52 to try to overcome this challenge!
To my own personal knowledge this is an unusual design that has not often been repeated, though I think it’s a very interesting solution to the problem.
With those rudder design fundamentals examined, let’s take a tour of some of the boats I’ve experienced and my reactions to their steering characteristics. Remember, these are only my own personal opinions which may or may not be shared by others. That being said, readers who are shopping for yachts may find them useful during sea trials as reference points for what to look for given their intended use of a boat.
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Yacht: Sea Sprite 34
Rudder: unbalanced, hung off of a full keel
Reflections: Comparatively high steering loads with excellent feel. A very pleasant boat to sail upwind. The full, long chord-length keel means the Sea Sprite tracks very well, which in part offsets the comparatively high steering loads introduced by the rudder’s lack of balance. Great for bay / near shore cruising and day sailing. May be a bit more taxing than preferred on long open water passages for either helmsman or auto pilot.
My Verdict: A perfectly acceptable design choice given the boat’s intended uses. A joy to sail.
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Yacht: J/105
Rudder: Large, almost totally unbalanced spade type
Reflections: With the tiller steering, the J/105 exhibits some of the highest helm loads I’ve personally ever encountered. The boat was offered with a wheel or a tiller, so I would speculate that Rod Johnstone kept this rudder almost totally unbalanced to preserve feel when the wheel option was chosen. It’s also likely that the rudder was designed to be so large out of fears that the J/105 – one of the first sprit boats of this size with a factory asymmetrical spinnaker – might be difficult to control otherwise. The consequence, in my opinion, is much higher loads and more sluggish response when equipped with the tiller than I would prefer.
I’ve personally spent many hours steering one of Johnstone’s own earlier designs, the J/35 and have not had anything like a similar experience. A look at the J/35 rudder shows why: the rudder stock is much further aft on the foil, putting more surface area forward of the pivot point and introducing just the right amount of balance. The J/35 rudder is in my opinion just about perfectly weighted for racing or short passages, and is far superior to the J/105 rudder.
My verdict: The J/105’s steering is far too heavy for my taste. The rudder is too big and needs much more balance to provide a satisfying steering experience. I hate to say it, because I have many close friends that own these boats, but the J/105 is one of the least satisfying boats to steer that I have encountered.
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Yacht: J/88
Rudder: moderately sized, unbalanced, high aspect ratio, transom hung
Reflections: My experience was limited to a brief test sail in 20+ knots of breeze, but this rudder felt really good to me. Upwind the rudder is large enough to scull the J/88 through waves like the J/29 and offers very good feel. Downwind, it’s large enough to offer very good control while planing the boat up into the upper teens in boat speed.
My Verdict: Ding! Ding! Ding! A winner.
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Yacht: J/70
Rudder: small, unbalanced, very high aspect ratio, transom hung
Reflections: only moderate feel with a weak bite upwind and highly prone to stalling without warning when sailing downwind in big air, causing broaches. This boat requires a high degree of skill on the part of both trimmers and helmsman to attain those mid to upper-teen planing boat speeds so popular in photos and YouTube videos without frequent broaches. Experienced sailors can do it, but it’s white-knuckle for rookies.
My Verdict: this rudder is too small and aggressively high aspect in my opinion. It’s a bit baffling to me because the J/88 is a scaled up version of the identical design, and the J/88 rudder is awesome. I’m scratching my head.
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Yacht: J/29
Rudder: large, unbalanced, moderate/high aspect ratio, transom hung
Reflections: a study in contrasts. Large enough upwind to offer great sculling through waves and excellent feel, but the lack of balance means very high tiller loads on broad reaches in a breeze. Exhausting on a windy reach of any duration.
My Verdict: for the boat’s use case, the J/29 is pretty close to right. I’d add just a bit of balance to make it perfect.
Yacht: Hylas 56
Rudder: balanced and hung on a half-length skeg
Reflections: the Hylas 56 offers excellent feel with reasonable helm loads when sailing to weather. And the rudder has enough bite to allow good sculling through waves even with the Hylas’ moderately long keel chord length. Off the wind, in all wind strengths, the helm offers less feel and “bite” than I prefer when sailing deep angles.
My Verdict: Frers nailed the amount of balance on this rudder. It’s an ideal tradeoff between helm load and feel upwind, and it’s great down to and just below beam reaches. However, the rudder probably needs to be bigger. Looking at the hull form, I suspect that this Frers design has a deep enough underbody to create turbulent flow over the rudder when sailing deeper than 120-130 degrees or so, and I suspect this disturbed flow explains the change in behavior sailing the deeper angles. My vote: keep the same basic design and just make it bigger to compensate for the underbody’s turbulence.
Yacht: Sabre 42
Rudder: moderately sized, low aspect ratio, balanced spade type
Reflections: very light effort and low on feel upwind. Plenty of rudder size for good control and low steering effort on a windy, wavy reach. Sidenote: on the Sabre 42 there is rudder to spare even in waves large enough to break into the cockpit, as we experienced broad reaching off of the south Florida coast!
My Verdict: the Sabre 42’s rudder balance was probably a great choice for a passage maker, but this boat’s use case was more in the performance cruising / racer-cruiser mold. I’d be willing to trade more steering effort for more feel by removing some balance from this rudder.
Yacht: Jeanneau Sun Odyssey 409 (Sunsail 41)
Rudder: moderately sized unbalanced spade
Reflections: decent upwind, high efforts on a reach in quartering seas
My Verdict: Good feel for coastal cruising but buyers with passage making ambitions would want more rudder balance to reduce the steering effort.
Yacht: Pearson 40
Rudder: unbalanced, hung off of a half skeg
Reflections: very high steering loads and poor enough rudder bite that hitting the steering lock is common – even when sailing close to the wind! An absolute bear to steer on broad reaches or off of the wind.
The Verdict: the factory rudder on the Pearson 40 was so ill formed and spent its life in such poor hydrodynamic flows (from the whale underbody of this Bill Shaw design, which is similar to the Ted Hood designs shown above) that a private owner’s association paid a naval architect to design a revised rudder that was larger and partially balanced. The Pearson 40 is a novel design that has a lot going for it, but there is no escaping the fact that its factory rudder was pretty close to a disaster.
Winners: J/88, Sea Sprite 34
Losers: Pearson 40, J/105
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