fore and aft rudders on a cat...... no keel or dagger

Discussion in 'Boat Design' started by Owly, May 19, 2018.

  1. Owly
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    Owly Junior Member

    I've been looking at some of Rob Denney's innovative design features on his Harry Proa designs, and am quite impressed with is outside the box thinking........ I'm a sucker for unconventional thinkers. Bucky Fuller was my hero growing up.

    From putting the accommodations on the main hull, and mast on the ama to his fore and aft rudders that can both be deployed, in lieu of having a keel, centerboard, or daggers, to his "intelligent infusion" concept, and various other ideas. Rob sets himself apart from convention.

    I'm planning a 30' catamaran project, loosely based on two designs, which will use a single central free standing mast and a cambered split junk rig, a rig that many people seem to go to great lengths to talk me out of, though not from actual current knowledge. This is a purely voyaging boat, where low human stress and effort are a priority.

    I'm gradually being persuaded that foam core is the rational way to construct it, and in the end, probably the easiest though not the cheapest way. The real deciding factor here is payload. A 25% reduction in empty weight as compared to plywood is not beyond the realm of possibility. Every pound I can eliminate from the structure is a pound of payload, and half a ton is nothing to sneeze at. It enables a 30' cat to do the job of a much larger cat, which ultimately means lower initial and ongoing costs.

    One of the most compelling ideas to me is Rob's fore and aft rudders. They are necessary for a proa, but also perhaps address some catamaran issues. Break away forward rudder(s) on the inboard sides of the hull(s), offer some interesting possibilities. They would seem to eliminate the need for dagger boards, which are a nuisance, or fixed keels that increase draft, or centerboards, etc. Good airfoil sections can provide positive resistance to leeway, probably better than fixed keels or daggers, and they could be retractable like daggerboards.
    The most compelling idea is that of being able to steer both rudders in opposition, which should very rapidly pivot the boat, with the stern moving one way, and the bow moving the other for tacking. With both fore and aft rudders inclined to windward, the boat would tend to resist leeway quite effectively.

    I've been delayed in my current small multihull project, a sailing "canoemaran", but that may be a blessing, as it will give me an opportunity to test this concept, as well as to build my amas using foam core and infusion. Rob's process involves making a very simple female mold for each half hull, and infusing both surfaces. There are no compound curves, nor do I have any intention of using compound curves.

    Anybody have any experience with fore and aft rudders?

    H.W.
     
  2. rwatson
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    rwatson Senior Member

    Just for the sake of historical accuracy, the "Harryproa" layout was promoted by the late Joseph Norwood, that ended up as a publication "21st century Multihulls"

    In correspondence with Joseph, he expressed his keenness to me for someone to actually build the design. As far as I can tell, Rob is the only person to take up the challenge.
    Rob also was clever enough to consult with Derek Kelsall, whose ideas have heavily informed the "intelligent infusion" processes that are used.

    But acknowledgements aside, if you think daggerboards are a nuisance, wait till you try rudder to replace them.

    There are heaps of stories about people trying to have just forward rudders, and then finding how much they muck up your maneuverability.
    For boats that have to tack, forward rudders are just a interesting idea.

    You do actually have compound curves in foam - you have to carve out the bows. And unlike the Proa designs, if you don't taper your sterns on the catamaran, you are going to lose performance.
    I suspect that the same is true of the Proa hulls, but obviously they have to function differently.
     
  3. Richard Woods
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    Richard Woods Woods Designs

    Check the Mull designed 12m USA61, the Everitt Backlash etc for forward rudders/canards. Consider how you will control 4 of them so they work properly when turning, as Akkerman linkage makes a big difference on a catamaran. Never mind potential damage to bow rudders when hitting flotsam or even big lumps of weed

    I have sailed 3 proas by different designers, and cruised one for some months and been on several more and talked to their builders/designers. I strongly suggest you sail one before committing to build one. Most people find they are not suitable for close quarters sailing in crowded waters (read Tom Follets' Cheers book for more comments)

    Richard Woods
     
  4. Owly
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    Owly Junior Member


    Richard:
    The proa itself is of no interest to me for my purposes, and never has been. Design of boats, aircraft, and other machinery are of great interest to me, particularly where designers come up with innovative and unconventional solutions. I am really only interested in catamarans in the 30' range for voyaging, and none of the existing designs obviously meets all of my criteria. Toying with the kinds of innovations Rob has incorporated into his proa designs is an interesting mental exercise, but a long stretch from actually using them in a full size boat. My 15' canoemaran project is a nearly ideal platform for playing with this sort of thing.
    Rob's rudders are not at the bow and stern, but mounted to the inside sides of the hulls, and are designed to trip when they strike something.
    Having designed and built a number of land vehicles (machinery), actually quite a few over the years, I am well acquainted with Akerman, as in some of my very early efforts, I ran afoul of this principle. Several wheel mounted loaders I built had 4 wheel steering, and a number had rear only steering, and I currently own and operate a 14 ton machine with 4 wheel steering on an almost daily basis. A factory built piece of equipment. It had issues with coordinating front and rear steering from the day I purchased it, and I've resolved those issues now to the point where it steers seamlessly in 3 different modes, as well as having a completely independent mode which can be quite exciting ;-). Fortunately it is large and slow.
    As you know, Akerman is a fairly simple principle, and is built into the steering based on fairly simple geometery, normally involving a connecting linkage which on a vehicle is called a tie rod. The points on the rotational arcs of the two arms that are joined by this tie rod govern their rotation relative to each other. This applies on either end on either a vehicle or boat. One side turns a larger circle than the other. Turning to port, the starboard hull will scribe a larger radius circle, and the tighter the turn, the greater the percentage of difference there is. Many things from the automotive and aviation world apply to boats.

    The discussion of Akerman really distracts from the real issue of how a system like this would be controlled effectively without being complex. It would be very simple to steer both ends in opposition to each other... a simple linkage would do that, mechanical or cable, etc. This would probably produce much quicker steering response than one really wants. There is a response rate that is ideal. Too quick would not be comfortable for manual steering, and probably wouldn't work well with wind vane or tiller pilot. Too slow requires moving the wheel or tiller too far, and would wear one out quickly. logically the stern rudder would do most of the steering, and the bow rudders would normally be mostly used to trim for leeway, and aside from that would be used fully deployed to one preset stop one way or the other for rapid change of course. They would have 3 positions in normal use "center", which would be trimmed as needed, and "full" port or starboard deployment. Ideally when fully deployed for a tack, the trim would be lost, and the rudders would return to center, rather than their offset trim position. You would then trim for leeway on the new tack.

    The challenge is how to do something like that without becoming complex. As you well know, complex systems cause endless trouble. Your own designs reflect an understanding of this born of experience.

    Toying with ideas is a long way from actually building a boat........... I've built 3 boats so far, and am in the early stages of a fourth, none of them on anywhere near the scale of what I would like to begin in the next couple of years. If there's one thing I've learned from building machinery and aircraft, it's that it's a mistake to incorporate too many untried ideas into a project........ Too many problems to resolve. People follow proven plans for good reason.

    H.W.
     
  5. Richard Woods
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    Richard Woods Woods Designs

    The tractors etc I have seen tend to have levers/cables/pipes etc on the outside. Good for maintenance, not good for aesthetics or for building an interior. You really need finger tip steering. Check this video of a 30ft Sagitta.

    Richard Woods
     
  6. Doug Lord
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    Doug Lord Flight Ready

    CBTF- This system has been used on quite a few monohulls-this is an excerpt from a description of the system:
    The steering system is equally well-designed. Since the six-foot tiller is behind the rudder, a crank arm and tie rod link it mechanically to the primary rudder. Low stretch synthetic lines connect the steering quadrants of the two rudder shafts so that they work in unison to steer the DynaFlyer. A solid linkage could be used, but it would interfere with use of the cabin, and the stretch-free lines have proven successful.

    Remember that the forward rudder is ahead of the canting ballast strut (which is the pivot point for turning), so the bow rudder turns in the opposite direction as the aft rudder. Having two rudders not only provides lateral resistance, but it also improves the handling of the DynaFlyer considerably, allowing it literally to spin almost within it's own length.

    The twin foil concept also allows other sophisticated adjustments. One unique control has been dubbed the "collective", a helicopter term for the ability to pivot both foils in the same direction. By setting both rudders to angle slightly to windward, the DynaFlyer can achieve 0° of leeway when sailing upwind and, when compared to conventionally keeled yachts, the Red Hornet seems to almost be pulled to windward.
    ==============
    Implementing the system on a cat may push your limits of complexity but with your experience there seems to be an equally good chance that you could solve any issues that come up. One of the originators of the system is Bill Burns-it might help if you talked with him. I dealt with him when I was working on a production version of a CBTF RC model. He is first class and easy to talk to. If you're interested I'll find his current contact info.
    Found it: https://www.linkedin.com/in/billburns3

     
  7. Owly
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    Owly Junior Member

    BINGO..... exactly what I was fishing for. Actually doing it on a cat, with the forward rudders, or all 4, mounted to the inboard sides of the hulls as on some of the Harry Proas might not present all that much of a challenge as far as the linkages are concerned. Achieving both steering functions seamlessly is another matter. The handling characteristics described are exactly what I was envisioning. Bolger played with forward only rudders briefly, and made brief mention of fore and aft rudders that I found after a bit of searching, though he apparently never tried it.
    I'm really rather amazed that it has taken so long for designers to start getting away from the crude "barn door" rudders of the past and move toward efficient foil shaped partially balanced rudders. It's interesting that the Viking ships used a rudder that resembled an oar, and was clearly designed for balance area, which projected down the side of the boat, the helmsman using a fore and aft motion, on a tiller that was attached to the top of this rudder and projected laterally into the boat. A thousand years ahead of the times..... almost literally.
    Another thing to consider is steering while surfing in extreme conditions. The aft rudder will often be out of or nearly out of the water, leaving some sort of drag device as about the only reliable way to avoid a broach. With fore and aft rudders, one would have at least some rudder control from the forward rudder about the hull's "natural" center of lateral resistance.

    H.W.
     

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  8. Richard Woods
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    Richard Woods Woods Designs

    video here

    Of course only two rudders, not 4. I have steered a boat with a Viking style rudder/tiller. Designers of fast boats haven't used "barn door rudders" since WW2 and before

    Very rare for a catamaran to broach at speed, I have never done it.

    RW
     
  9. Owly
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    Owly Junior Member


    Thanks Richard:

    I hadn't see that one before. In speaking of 4 rudders, I was thinking of your daggerboards and dual rudders. Forward rudders instead of daggerboards, though the location obviously is completely different. Note that on the Harryproa, the rudders are both retractable like a daggerboard, and trip aft if they strike anything. "Fast boats"........... but many solid blue water cruisers use very unsophisticated rudders. Obviously the most efficient rudders are not hinged to a keel or skeg, are airfoil shaped, and are well forward of the transom, under the hull where they stay submerged. This is not a combination that makes for a bullet proof rudder. Rudder loss and dismasting, both seem to be fairly common occurrences. An unprotected rudder that can't trip seems like a poor choice for serious voyaging, fine for racing where help is near at hand.

    John Pederson's blog Journey on a Woods Sagitta catamaran: Crossing the Atlantic, again http://sagittacatamaran.blogspot.com/2015/05/crossing-atlantic-again.html describes using the Abbott drogue during his crossing of the Atlantic in Scrumpy to reduce the danger of broaching.......an interesting and useful read. I was not suggesting that broaching was a big problem with multihulls, but they do surf very readily in large waves making a drag device something one would not want to be without, and any boat with a transom mounted rudder would seem to have situations where rudder control was lost for a brief, but potentially critical period of time.

    Again, talk is cheap........ I'm a ways off from building or buying a cat, and rather enjoy examining the design features of various boats, and toying with ideas. Payload, safety, low upkeep, ease of sailing, comfort..... all come before speed on my list of priorities. I drive a Subaru for the same reasons.... I know it will do what I want it to, no matter the conditions, and stay right side up, and has more than enough performance for my purposes. I of course run tires that make a huge difference. A "Subaru Cat" is what I'm really looking for ;-)

    H.W.
     
  10. rob denney
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    rob denney Senior Member

    Owly,
    Thanks for the compliments. You need to be careful! Unstayed masts, infused foam, sensible rudders......... Only a couple more steps:

    1) a 40' x 20' proa is faster, safer, cheaper, shallower, more comfortable and easier to sail than a 30' x 16' cat
    2) shunting is less stress and strain than tacking and gybing

    and you will be moving to the dark side!

    Intelligent Infusion does allow compound curves. Kicked up sterns are not a problem, nor are flared bows but neither makes sense on a proa.
    If there is a theoretical loss of speed from harryproa hulls (rockerless, flat bottom), it is more than compensated by the reduced weight, lower freeboard and vastly easier building they provide.

    Daggerboards and fixed rudders are as absurd/unseaworthy/dangerous on a cruising boat as deck sweeping headsails and helm positions where you do not have 360 degree vision.

    From the beginning, harryproa rudders have been liftable for balance, shallow water, drying out and weathering a gale. And to kick up in both directions in the event of a collision or grounding. The originals were pretty clunky and there have been many ideas considered and tested since then. The latest ones are lighter than any similar size cat, require no additional beefing up of the boat and can be fitted/removed in seconds.

    Harryproa rudders steer far better than cat or tri rudders. If other proas do not steer as well, I suggest it is because their rudders are too small (usually the case with proas with daggerboards), they are not able to be used together or the hull shapes or rigs are are wrong.
    From an observer who wrote this on Mhml:
    "I watched Rob shunt his 25' proa upwind up the narrow (35m for most of it) boat filled channel in front of his house so fast and easy I thought he must've had an electric motor hidden in the leeward hull. I would've had a very difficult time doing it in a beach cat without stalling, hitting somebody's boat and/or breaking out a canoe paddle. With the exception of a wind surfer, I had never seen a sailboat with a reverse gear before. He could head right for something, then throw it in reverse, back away and bolt off in a new direction under perfect control.”

    From one of the first people to sail the original harry: "We were motoring home at about 6 knots and almost ran over a log. I was standing on the tramp, the helmsman swerved both rudders and the boat turned so sharply I was thrown off my feet. Far more abrupt than my 35' tri or 50' cat."

    From the owner of Kleen Breeze (20m harryproa just launched in Portugal) “Kleen Breeze” – PORTUGAL – Harryproa http://harryproa.com/?p=562:
    "Bidirectional rudders work well and are definitely keepers. I have found myself able to run for over 20 minutes without having to adjust the tiller."

    From me after my first sail on Blind Date: "The wind was quite fresh (15-20) and blowing us directly onto the jetty. A cat or a mono would have required springs, lots of yelling, rapid gear changes and high revs to get clear. We angled both rudders to windward, gathered the mooring lines, put the single engine in gear and the boat moved away at 45 degrees to the jetty. The fenders rotated about 90 degrees before they lost contact with the jetty. "

    You can get the same effect under sail to squeeze round an obstruction or to get out from another boat's bad air. However, unless you are in tune with what is happening, you are unlikely to improve your vmg. I think the CBTF folks discovered this as well.

    On harrys, it is usual to lock the aft one and use the front one for sailing upwind as it is so light and responsive, and the reverse the rest of the time. If tacking was an issue, you could lock the front one and steer with the rear one to simulate the usual cat arrangement.

    I see no reason not to use harry rudders on a cat, but 4 of them would be as pointless as 4 rigs (or 2 daggerboards). Mounting them on the hulls would not be easy on a cat, nor would arranging the steering for the front one, but if you think about it when you design the boat, it won't be hard. Another option (maybe not as good, but a lot more sensible than daggerboards and fixed rudders) is to put them in the middle under the bridgedeck and use the kick up mechanism to lift them rather than physically doing so.

    Be wary of comments from people who make generalisations based on all the boats they have sailed, if they do not mention the boats names and detail what the problems were. Doubly so if the only boat they do mention by name was designed over 50 years ago!

    Broaching on a cat is not uncommon in big waves/wind and is scary. I am not sure that front rudders would help much, but if you are going to sail in those conditions, it would be well worth experimenting to see.
     
  11. Owly
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    Owly Junior Member

    Rob:

    I have nothing against your Harry Proa designs, they just don't fill the bill for me.

    I agree that 4 rudders is probably a bit absurd. Cats virtually all have 2 rudders, and of course Richard's designs use two daggerboards. I was suggesting eliminating the daggerboards in lieu of forward rudders........ or rudder. There would seem to be no reason to have both. The transom is not the ideal location for a rudder. I've liked your rudders alongside the hulls (conceptually) from the first time I saw them. Reminds me of Bernd's "luffboard" design, a kind of airfoil shaped leeboard on the inboard face of the hulls of a cat. I don't think anybody has built them.... perhaps never will. He has since gone to a single pod mounted foil under the bridge deck to compensate for the failure of his AV panels to do the job.

    I'm not sure how mounting forward rudders on the hulls of a cat would differ from mounting them on the hull of a proa..... what am I missing....?

    H.W.
     
  12. David J Ritchie
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    David J Ritchie Junior Member

    GREAT youtube find Richard

    That articulating canting balast daggerboard is a great idea but personally i don't like the maintenance and future problems of a major hydraulic system onboard. I don't know much about sailing so i wonder how catastrophic it would be when that thing seizes up at full deflection? If you can limp home it's OK.

    I seem to remember the forward rudder idea being tested in early aircraft history without any success. Both air and water are described by the same fluid dynamics equations so i doubt that adding a forward rudder on boats will produce the super maneuverability that it seems to promise.

    I love unconventional ideas too!!!
     
  13. Doug Lord
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    Doug Lord Flight Ready

    It's important to understand that on a CBTF(canting ballast twin foil) boat that the twin foils, one forward and one aft, work together to steer the boat and together to provide all the lateral resistance for the boat. The keel is a fairly thick strut that is not designed to provide any lateral resistance as would a "normal" keel.
     
  14. rob denney
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    rob denney Senior Member

    Tongue in cheek icon on.
    From this:
    "My inclination is to go with plywood epoxy. With proper construction I don't believe that the weight will be anywhere near the 20% more that was quoted."
    to this:
    "it would be silly to build the one of the boats I was considering in plywood"

    indicates that you use logic in your boat building decisisions and are not afraid to change your mind based on evidence.

    "I'm a sucker for unconventional thinkers."
    indicates that you are not scared to think outside the box

    Therefore, I am hopeful that sometime between now and when you build, you will go from this:
    "I have nothing against your Harry Proa designs, they just don't fill the bill for me."
    to this:
    "I decided to build a harryproa as the ease of build, ease of sailing, layout, safety and general usability outweigh what can be achieved on a cat."
    Tongue in cheek icon off.

    I look forward to the conversation between now and then, regardless of whether you change your choice or not.

    Nothing, if you think about it at the design stage. Raising them will be a challenge if the bridgedeck or trampoline are in the way. They are high load items, so think about bulkhead locations. Running the control lines/tiller extensions also needs some thought.
     

  15. David J Ritchie
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    David J Ritchie Junior Member

    Stitch and glue plywood is faster, cheaper and easier to build than foam infusion and it can actually be pretty good weight wise. I must admit this even though I personally don't like plywood as a core material due to its poor impact resistance. No nice curvy shapes with plywood though, that is true. We should do a thread on modern material science as the boat industry is lagging behind.
     
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