Now heres an exchange on the fastidious question of how to navigate a plastic ship, 2.4 metres long under sail by using something to turn with. Enjoy. It's an exchange taken from the Canoe Sailing eList and I thank all the contributors for their generous assistance.I have been rigging my 'paddleski' for sailing and after a lot of experiment have ended up with a rig like this (pictured below)
I'm very happy with what I've engineered so far by trail and error.
The craft has superb manoevrebility -- it's like steering a Volkswagon -- but in a bit of wind I need a hand on both tillers at the same time.
But one thing confuses me: While I prefer a shallow draught on my rudders as I have to negotiate a lot of shoals ( to 40 cm/15 inches for instance) I am surprized how stressed they are as so much force seem to bear down on them. I was out in 14 knots the other day and one rudder -- the windward -- broke from
its arm..
I think my tiller arm is OK -- re-used crutch stems, joined together, curved to tuck along the hull -- but I'm wondering about my rudder shape. Assuming an arm that drops no more than 30- 40 degrees under water is it best, do you think, to run a blade vertically down, or to splay out a narrower blade lengthways like the
blade on a row boat oar?
Similarly is it preferably, do you think, to only run the blade down rather than also run the blade above the rudder arm.
I'm thinking that if I parred down my blades I'd still get steering without the massive forces working on stress points. The confusing engineering element is, of course, the fact that my rudder isn't in the centre of the craft but to the side of the rear like the back wheels on a 4x4 car.
A Gondola, for instance, runs outback an adapted oar as its rudder and 'propeller'. But a fish will deploy a fan on its tail....Traditional flat boats -- like the Kon Tiki -- and viking ships used a modified steering oar (pictured above left) .
how 'bout one rudder mounted on gudgeons on one side of the boat? the asymmetry wont matter much. maybe 8 screw holes in the plastic boat for gudgeons.
I've experimented with single sided ruddering and it works fine to windward until the wind comes up and the weakness in the rudder begins to come into effect.
The advantage with dual 'steering' is that there is much less play in a craft that is so short and so beamy. It is easier with two rudders to stay on course. With one the steering wheel is touchy.
The other advantage with dual rudders is that because you run the shaft close to the sides of the hull, what you lose on one side in way of leeway swing, is compensated by the swing arc available on the other. So to turn quickly and sharply is much easier and faster with two rudders rather than one if they are to be located on the side , rather than in the centre , of the hull.
After writing the original post I think my main problem is the way I have designed the rudder. If you check out the traditional 'steering oar' (as I'm now doing) it is very different from a rudder. The classic Viking ship steering oar was a design aesthetic although other ships of the period deployed what seem to be an over sized bat. And dual 'steering oars' -- one either side of the hull -- were often used. However, maybe if I redesigned the shaft so that it was 'sterring oar' shape I'd have more control using just one single rudder?
But single long shaft 'rudders' I find get complicated if you want to swap sides as unhooking them and then swinging them over the deck as you change tack or come about leads to immediate loss of control. I didn't expect these complications . Half the fun I guess. I had experimented with shorter shafts by using some extendable canoe paddles but the distance out back is almost a regulatory tail end with the dynamics improved by the fact that the curve in the arm more or less runs the steering blade in line with the hull. When I go short , under sail, the boat keeps wanting to come about. Although a leeboard may address these issues I'm thinking that adding more stuff over board will only slow down the forward motion while I'd need to keep fiddling with the leeboards to get them in place when needed.
Alternate: mount a 'false transom' leaving a space at the bottom for drainage . mount gudgeons in the middle of the transom board for a 'standard' retractable rudder. 4 screw holes in the plastic boat. seal all with silicone caulk.
For now, my 'design brief' is not to add holes to the plastic. The rig is tied/lashed onto the hull to what inserted bolts came with delivery. I've used 3 bamboo thwarts which I can unclip from the hull to convert the craft back into a simple paddling boat minus sail rig. My lashings are high quality cable ties and despite the windy conditions no thwart has been harmed or has pulled away from the hull. The strut supporting the mast at 45 degrees rests has its feet in little webbing socks that sit on the front thwart.And the mast 'step' is framed and held into place by crutch rods either side of the front carry handle. The mast is currently held in place at the strut by stretch cord.
To rig for sailing all I need do is raise the mast off the deck, thread the strut over a steel rod through the mast and crutch shafts, lash it with bungey cord and pull away from shore. Surprisingly this rig doesn't move about. and the only drawback I can complain about is that because I dropped the boom close to the deck I miss out on 360 degree views of the coastline. I'm nonetheless wondering if I can raise the latina sail to a sort of crab claw height so that I have more viewing space below the boom. But I suspect that I'd lose some of the force of the winds close to the water surface.
There was a lot more to the Viking steering oar than meets the eye.When W. Hodding Carter,had a replica knorr built.He retraced leif errikson's voyage.Altho he used a genuine replica rudder,they found that, as it was not designed for that particular type of boat(was from a dragon ship)It did not work.There is a lot more than sticking a flat board over the side.I'm looking at similar side rudder for my sailing canoe.I'll be interested in how you go.Good luck with your project...Looking good.
I gather there is the same deign issues for steering oars on Hawaiin canoe outriggers so I may explore the design principles discussed by Gary Dierking .
I find it disconcerting but challenging that a paddle blade plunged into the water alongside a boat will pivot direction very differently from blade turned underwater further back.
I've no sailing or paddling background to speak of but it's these little things that seem to matter a lot . I faced a similar challenge in regard to how far I'd locate and lash the steering arm away from the gunnels along my rear thwart.
I assumed I was creating a sort of rear outrigger but when you throw the blade too far away from the hull the forces on the blade increase sharply and while you get more room to steer the arm ( so that you can settle with just one rudder), you are up against much more resistance doing it.
Of course each hull shape is going to have its own design issues but the logic of the centrally located rudder on the aft end may be self evident when you have a straight butt end -- but like a make believe fish's tail I'm thinking that behind me where I aint got boat, I still have a phantom presence.
The problem with central rudders is, of course, where do you run the arm so that you can work it. Its' an issue of ergonomics.On some canoes you can sit to the side but on kayaks and the like you don;t have that option. Similarly steering a single oar/rudder on one side only forces you to turn toward the arm for the
distance of your sailing journey.
In a word:Ouch!
A canoe will allow you to alternate sides and throw the paddle over the deck -- and thats' where boat length is going to matter as there seems to be a sweet spot from which you can turn the craft when sailing something that tracks well (as mine does not).
Nonetheless, having not sailed a n bona fide canoe I wonder at how muhc force steering with a paddle -- or with a rudder -- is usually up against.
At over 12 knots in my little craft I'm working real hard on the tiller(s). But then I can still turn on a dime if I need to..
.. when you throw the blade too far away from the hull the forces on the blade increase sharply and while you get more room to steer the arm ( so that you can settle with just one rudder), you are up against much more resistance doing it.It should then be just a matter of reducing blade area to get same resistance.
I adapted Bill Mantis' design to create my sail rig and I know of the "Rudder-Like-Butter" -- so maybe thats' an option as you suggest.
(Bill's sail design works so well for my setup. It gave me a concrete design I could work from while also suggesting how I could begin to solve the problem of fixing a mast to a plastic boat. That I ran the mast at 45 degrees pushed the centre of effort further back so that I have no major nose issues. All other
vertical mast approaches fostered stability drawbacks.
Once I imported crutches into the mix I was master of my ship build.
I don't know if he is on this list, but elsewhere another canoe sailer pointed out that he too used crutches on his rig build such that he called his craft,"The Flying Crutchman".
But the fun is in negotiating these challenges, of course, and for now I'm working from the template that I can dismantle any rigging and strip the craft back to its pristine state for normal paddling.
I paddle steered my outrigger canoe for a while. I very quickly learned what you have noticed: a surprisingly light touch is required to get good steering response at low speeds. But as speed increases the leverage exerted by a blade trailing aft climbs rapidly: fatigue, breakage, poor control, even injury can
result.
I must say that from my experience I can;t see how you canoeist do it under a lot of sail without an independent rudder mechanism. It must be hard work steering with one paddle overboard, and the body turned to one side. I guess thats' why leeboards are so important in the mix?
A more vertical blade, even better if balanced with some area forward of the pivot, is much easier to control, even at higher speed. In your case shoal water would require this to be some kind of kick-up design, it may well also be relatively low aspect: to keep loads low and reduce the need to kick-up / push
down.
I'm in a bit of a bind as to my best course. That I have such a short craft encourages me to trail something behind as I get much better control. The drawback is that the longer the tiller and the deeper the blade, the potential for increased forces to be transferred up the arm. Nonetheless, traditional 'steering oars' may be worth studying to see what gives in way of options. All I have to do is find the right materials to create this or maybe adapt a row boat oar as a transitional step.
What I did not say was that rear rudders like this also offer a scoop means to propel the boat left and right by pulling laterally and medially in the water -- as on a sampan and gondolier. Makes parking so much easier.
I think I have confused two things and tried to force them together: a steering oar and a traditional rudder. A rudder I guess has depth to it while an oar has a shaft effect. I'm finding that because I can be in such shallow water so quickly my control isn't sabotaged because the blade simply bounces off the bottom and besides it probably runs usually 30 degrees from the back of the craft. Even at 10 or 20 degrees I still have navigational control. So drag is important.
Thats' a real plus as the water depth lessens.
How about something like the 'radio flyer' if you can adapt it to the stern of your boat. Could have a tiller, or could have a line running down each side of the boat, terminating in a short length of bungy, or a continuous line, could even rig up both tiller and line for steering? Another variation could be to
make the twin skegs short, drill a hole through the centre of each and bolt a deeper board so you have a twin kick-up rudder? May need lines to be able to re-set rudders when kicked up?
Re-setting rudders on a kayak type boat is going to be difficult because you are sentenced to the one seat with a limited turning circle behind. Kayak design -- sit on top kayak design too -- presumes the paddler is rooted to the one location. I think it is a major drawback for sailing (and why my next boat will
I was talking to a mate who paddles a 17 foot sea kayak and he is always complaining that grabbing anything from behind his seat is unbearably inconvenient and difficult. I find that my rear reach is a very limited arc. At its limit I have a spring clip to attach the rope that holds the sail boom. But reaching completely to the rear of the boat -- even on a wee short thing like mine -- isn't on.
Open canoes make a lot of sailing sense as you can -- to a degree -- move around and shift your weight carefully.
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