If you have read our book you will know how we feel about spade (unsupported) rudders. We don’t like them and consider them a pretty bad idea for a voyaging boat. For those that haven’t read the book, a properly supported rudder is an essential facet of a voyaging boat. A spade rudder simply hangs down from the hull on a stainless steel shaft. This make them fantastically vulnerable to damage from collision with sea debris (floating logs, half submerged containers, dozing mermaids, etc.) and we go to great pains in our book to discourage all potential sea gypsies from buying this type of boat. (See picture).
Something we did not go into (and probably will in the next edition) is the added risk of “work hardening” on spade rudder shafts. We have all experienced work hardening in other areas of our lives. This is the process that allows us to break certain materials by repeated bending. Take a paper clip and straighten it out. Now bend it backwards and forwards. Pretty soon the paper clip will break at the point where you have been bending it. This is not because it has got softer, but because the point where all the “work” was being done actually got harder, and therefore more brittle and no longer able to bend as efficiently.
As is often the case in so many areas of life – that which cannot bend, breaks.
All rudders have to absorb large forces from the sea. That is a given. The problem the spade rudder has (being unsupported at the bottom) is that each time a wave rolls across it, the shaft flexes from one side to the other – just like the paper clip in the experiment – with the point doing the most work being where the shaft of the rudder exits the hull. Can you guess what happens?
You got it – work hardening at that point. Then failure. (The much higher forces on the shaft of a spade rudder often exacerbate any crevice or anodic corrosion that may pre-exist and often lead to a false diagnosis. Any type of rudder post can suffer crevice or anodic corrosion, but it is principally spade rudder posts that fail catastrophically as the added forces and lack of safety margin in construction tend to expose other faults more dramatically).
Funnily enough, I was just explaining this very process to a potential sea gypsy who contacted us after reading our book, when we heard that a boat had been towed into the local yard with rudder problems (we are currently in Fiji).
Being fantastically nosey about this kind of thing, I dashed over (all of 500 meters) to find out what had happened. I think the pictures tell the story (see below).
Spade Rudder sheared off.
As you can see in the first picture, the rudder has gone. The whole thing is now resting in the silt 5 kilometres under the surface of the Pacific Ocean and will cost several thousand dollars to replace.
In the next picture, you can see that the shaft has snapped at precisely the place the principal of work hardening would predict.
This poor sailor is also facing a bill of $7000 for the tow into Fiji, and a couple of thousand for the boatyard. Had he been further offshore, the tow could have cost several times that. If he had been offshore in bad weather, the cost may not have been calculable in dollars.
Spade rudders are cheap to produce and fit. Manufacturers tell us that they are also a good idea and produce all kinds of spurious figures and twisted logic to convince us that what they want to sell us is what we want to buy.
Regardless of what the salesmen and racing crowd say, there is no possible way a spade rudder is stronger than a supported rudder. The numbers simply don’t add up any better than the numbers for building a house without foundations. Find me a qualified engineer that will say any different in writing and I will show you someone who is working for the yachting industry.
But while uninformed sailors continue to buy spade-ruddered boats for their marble counter tops and en-suite bathrooms, this is what the manufacturers will continue to produce. And who can blame them? They have to sell boats in a very competitive environment and new sailors don’t give a hoot about the rudder.
It is up to us to demand sea-worthiness in yacht design by rejecting unsound practices – no matter how nice the cockpit cushions are or how large the aft cabin is.
Rejecting spade rudders is a good place to start.
Fair Winds,
Rick and Jasna
PS Has anyone else got any spade rudder horror stories? We would like to hear them -especially if you have photos.
English
Slovensko
Italiano
Scary…
http://www.jadralniklub-nm.si/si/prispevki/detajl/?id=678
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eh, ja…žal…
After reading your book I don’t like spade rudders. It had to be said….
Good man Phil! Glad to know even the land-lubbers are getting the message.
If it was not for your book and advice, me and my wife could have been in the same situation as the above boat.
Thanks.
No worries Gary. Glad to help!
Just finished reading your book which I simply could not force myself to put down.
My wife has actually been getting angry at me for reading which is most unusual.
Well written and so impelling.
I’m now dead-set on becoming a sea gypsy.. Only slight bit I can’t quite fathom: how to do it with a 2yr old boy and a 5month baby boy in tow??!
Hi Jonathon,
Sorry for the tardy reply – been away from the online world for a while! Thanks a lot for your positive feedback on the book, it is greatly appreciated even if it gets you into marital difficulties.
Don’t let a couple of ankle biters put you off the sea gypsy life! There are hundreds of couples with young families bringing up glowing neurosis free kids on board. Have a look at this and get yourselves out here!
Thanks again and let us know if you need any help or kicking towards taking the plunge
Cheers,
Rick and Jasna
Endurance, fault tolerance, and redundancy are key elements for a voyaging yacht. Spade rudders offer none of these. They are superior for racing yachts. We have a racing yacht with one and have no complaints… for the purposes of coastal racing. We also don’t cross oceans in it. (Aphrodite 101, Averisera)
No argument from me there Norman! The problem is that many manufacturers are marketing their fin keel/spade rudder boats as “bluewater” cruisers….
Being a pilot and physicist I see nothing inherently wrong with a properly designed spade rudder. Look at the 747. Two giant spade rudders sticking off the sides, but we usaully call them wings. A narrow skeg hung rudder could be significantly weaker than a beefy spade shaft. What if that shaft were made of large diameter carbon fiber tube? No metal fatigue. Much stronger and more durable than steel. Only downside I can see is possible extra drag from the larger diameter shaft. You would of course also need very strong bearings and support for the shaft.
Does anyone make such a rudder? Probably not. Too expensive for the tiny market that would understand and care. Until then I will stick with the skeg hung rudder. Thanks for an excellent book!
Hi Kelley,
Thanks for the comment and your kind words about our book. Most appreciated. It is a very important subject which I think is a bit of a scandal waiting to happen
There are a couple of assumptions about spade rudders that you have made that are not entirely correct.
Firstly, the wings of an aircraft are not analogous to the rudder of a boat. The wings of a plane provide lift, so in your metaphor, are comparable to the keel and the mast (with the sails up) as these are what provide lift on a sailboat – kind of like an airplane on its side. The argument you are presenting is one that is often used to promote unstayed masts and is undeniably a good argument, but not a relevant comparison to rudders. If you want to use an airplane metaphor, it would be more accurate to compare the rudder on the aircraft’s tail plane to the rudder of a boat – and all airplanes I know have a tail rudder that is supported in several places on a skeg (called a stabilizer) rather than simply sticking up out of the fuselage on a bar. This is for very good reasons. Not only does the aircraft’s skeg provide directional stability in flight (as it does for a boat in water), it also prevents flexing (and therefore work hardening) as well as protection from collision and all the other advantages it does for a boat as listed in the article. (See photos below).
You also say that a well-engineered spade rudder could work but it may be,
“too expensive for the tiny market that would understand and care”.
You have a good point here. The yachting industry does not try and sell us spade rudders because they confer an overall advantage to a cruising boat. They sell spade rudders (and removable keels) because it seriously reduces the costs of manufacturing and shipping (the keel and rudder can be removed and the whole boat can fit in a single shipping container). Therefore, a spade rudder that cost a fortune is, as you so rightly say, something that rather defeats the object.
However, I would go even further. An unsupported, unprotected rudder is nothing but a giant lever. The fact that they are generally pretty badly made by the big boat builders is currently something of a blessing because when they slam into something, they break, leaving the hapless sailor with no steering but still afloat. If a stronger spade rudder is made, then it simply becomes a stronger lever transferring all that energy into the hull of the boat itself (possibly via a beefed up bearing, but it will still transfer that energy).
Sweden Yachts who make very well built boats, decided to take that path. A very good friend of ours bought one and that is precisely what happened to him. The very well made, but still unprotected, spade rudder collided with some ocean debris. The Sweden Yachts spade rudder, being quite massively built acted like a giant lever and opened a hole in the boat, which sunk very quickly. Fortunately, as they were crossing the Atlantic as part of the Atlantic Rally for Cruisers, help was quickly there. One of the rescuers filmed it and you can see it here. https://www.youtube.com/watch?v=jIZvq9sRKvo
And they are far from alone. Following the path of stronger spade rudders will only increase the amount of similar incidents. Spade rudders are fine for racing around the harbour, but we should resist any attempts to persuade us they are a good idea for blue water by boat builders who have such an obvious conflict of interests.
Thanks again for your comment and don’t hesitate to get in touch if we can help you in any way.
Cheers,
R n J
another one… this time showing several attachment points