posted February 07, 2008 05:59 PM            

Eric
Member posted October 23, 2004 09:37 AM               
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I was looking at the picture of [the interesting shape of] Superpiper’s rudder blade, and wondered about the stock blade and it's orientation.

The blade on my rudder slightly cants aft. If you remove the blade, and install the other way around, it cants slightly forward. I did this when I refinished my rudder last spring. I did reinstall it the way it was before the refinish job.

Has anyone explored this? Is there any performance to be gained by having the blade cant forward?

Eric

IP: 130.63.85.93

SuperPiper
Member posted October 24, 2004 01:58 PM            
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Hey Eric:

I modified the rudder in 3 ways.

I found that the tiller got very heavy as the keel shared the load with the rudder. I rationalized that this was a little different than weather helm because the rudder was indeed midships. I was not forced to pull the tiller beyond centre to keep the boat straight. So I reduced the effort on the tiller by improving the balance of the rudder. I moved the centre of resistance forward - closer to the pivot axis. I did this by re-cutting the top of the rudder blade so that it rotated to leading-edge-vertical when it butted against the rudder stock.

The second modification was to change the plan view (actually the view from the side - confusing, eh?) to be elliptical. Apparently there is some high-level calculus that proves that an airplane wing or a sail or a keel/rudder is more efficient if it is elliptical. I didn't have the castors to cut the entire blade to an elliptical shape so I started half way down instead.

The 3rd modification was to change the leading edge and trailing edge sections to approximate a NACA foil shape. Again, I cheated by leaving a great deal of flat section between the leading and trailing sections.

So what was the change in performance? Damned if I could tell the difference. But it was fun to work on. I am like a kid with a tricked-out Honda Civic: great add-ons, but you can get better performance from an '86 Chevy pick-up.

IP: 69.156.58.30

Eric
Member posted October 24, 2004 03:59 PM               
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That's very interesting.
You touched on the balance issue. That's sort of where I was going with my initial comments. Turning the blade around so the rudder angles forward doesn't quite "balance" the rudder, but I wondered if it would make the tiller a little lighter, one of the benefits of a balanced rudder I've read.
All the new hi tech racing boats have the eliptical rudder shape, so I don't think you have caused any harm in your modification
Eric

IP: 130.63.85.93

Shortstay
Member posted October 24, 2004 08:03 PM               
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Supe, we're going to have to disqualify you from any competitions at the Rendezvous because you've altered the 'Piper design!

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Kevin
Shortstay III, #901

IP: 198.115.167.222

Darcy
Member posted October 25, 2004 12:47 AM               
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I'm not sure that moving the rudder forward is a great idea. Any boat I ever sailed on was always trying to move them back. Some of the 14s had the rudder hung on an extended frame back beyond the stern. A forward rudder might help you a bit going upwind but in a good breeze downwind you might start to broach all over the lake.

Our old 14 had a fairly square shape (like a Sandpiper) but deeper. It also had the NACA foil shape. This shape combination meant it worked like a second centreboard which seemed to really help upwind performance. I've only sailed Shortwave for a season but I get the feeling the rudder can work that way as well. So maybe the square shape is better. The boat might perform better with a little more lateral resistance.

The other issue is weight. Our 14 rudder, built by an aeronautical engineer at Boeing with an airex core weighed about 2 pounds. No weight in the stern stops hobbyhorsing. A small boat loses much more speed by rocking or hobbyhorsing than any well shaped foil could get back in speed. There's so much turbulence in the stern anyways that I think the well shaped rudder will not always be performing as designed.

I think if we have Superpiper race with my 8 hp motor clamped on the stern and my twin gas tanks in the lazerete that it would be even. In all seriousness, the rendezvous would be a great way to compare modifications and see how the work under the rigours of hard course racing.

D'Arcy

IP: 70.48.7.101

SuperPiper
Member posted October 31, 2004 06:22 PM            
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Apparently a team of researchers with some grant money from the US Navy has tested a theory about knobby fins on whales. The ideas are now patented (and probably classified by the military).

[This message has been edited by SuperPiper (edited October 31, 2004).]

IP: 199.243.115.165

Darcy
Member posted November 01, 2004 08:14 AM               
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Boy! Those whales are smart to patent such an amazing concept.

On the more serious side: Our pintles are a bit loose in the gugeons so the rudder jiggles a bit. any suggestions on how to get a tighter fit?

D'Arcy

IP: 70.48.7.181

elmet3
Member posted November 15, 2004 10:26 AM               
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I hope to fit a home-built steering vane to my Sandpiper. In order to keep the vane and the linkages small and light it is necessary to reduce the tiller forces. I believe this can be done by "balancing" the rudder, or putting as much (nearly as much) rudder area ahead of the pivot axis as behind the pivot axis. The water flow over the front part of the rudder, ahead of the pivot axis, tends to push the rudder off to the side. The water flow over the back half of the rudder tends to push the rudder back to the center position. When well balanced, the rudder can be set to most any angle and held there with minimal force. This is ideal for a wind vane steering system that might exert only small forces.
Other than the very slight change in rudder location - the leading edge will be moved 6 inches forward, and this will reduce rudder torque on the boat - does anybody know of any reason NOT to adopt a balanced rudder? It seems like such a sensible thing to do that I don't understand why all rudders are not designed that way.
It must certainly reduce the "feel" of the tiller, but I don't know that i would miss that much.

SuperPiper - your photo shows the idea on a rudder with some area ahead of the pivot axis. Is this rudder on your boat? You said you can't tell any difference, I could interpret this as meaning you don't detect any deterioration in handling. Did you notice a reduction in tiller force?

IP: 67.107.33.106

2short S565
Member posted November 15, 2004 06:42 PM            
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Hey I don't even own a boat at the present time but I think I can answer this question;

Buy new ones!

Thats what I ended up doing this spring. Made a difference for me.

The only thing I could think of otherwise was to build them up (with weld) and re-reem holes or machine pins. Too much trouble vs the price of new ones.

Fred

IP: 67.70.4.55

Eric
Member posted November 15, 2004 07:39 PM               
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A friend of mine built a windvane auto pilot for his Kelt 7.6. This guy is my Sandpiper's PO! He was going to build it for the 'piper, but then bought the Kelt.
Long story short, he made a small rudder from stainless, and attached it to the trailing edge of his stock rudder. He incorporated a small tiller for this rudder, which is VERY light! Seems he always sails with the windvane rudder, either by hand or in "auto". He has a positive tiller lock for his stock tille/rudder, which is engaged when running the 'vane. Personally, I haven't gotten used to the vane tiller/rudder yet. I guess I haven't sailed his boat much. The whole idea of self steering by the wind is intrigueing(sp). It's quite an elaborate system, which seems to require a little tweaking to get just right. Once set, the boat sails herself!
I tip my hat to you Elmet3. Good luck with this project .

Eric

IP: 216.209.15.3

elmet3
Member posted November 16, 2004 10:41 AM               
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Thanks Eric. That sounds very similar to what I have in mind. I have worked through the conceptual details and simplified the design so I don't have a jungle gym on the stern of the boat, also found sources of some components, (nylon bearings, etc) but the actual build will take a lot of work. I'd like a little more assurance that it will work when done.
Did your PO use a balanced rudder?

IP: 67.107.33.106

Eric
Member posted November 17, 2004 03:45 PM               
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Hi Elmet.
No he made a small rudder and attached it to his original stock rudder. The Kelt rudder is a transom hung rudder, that is not balanced. The little rudder he made for the self steering, is just a piece of stainless plate, a fraction of the size of his stock rudder. I'll see him briefly tonight(we work together) and I'll ask him the size. It's very light. The windvane, through the links and levers controls the small rudder. The large stock rudder is locked in position with the tiller. So he drags the large stock rudder, and steers with his self steering rudder. I suppose that was easier for him to build the little attached rudder rather than rebuilding the boats stock rudder. The rudder on the Kelt 7.6, is of a fair size and weight. It's also glassed over wood(I presume).
The Sandpiper's rudder is smaller, and probably easier to build a new one that is balanced. On the other hand, building a separate "add on" rudder could be a simpler solution. Should you need to override the self steering while underway, the full size unbalanced rudder is still available to use. This may be needed if evasive action is required,(MOB or collision avoidence) or when beating to windward requires a strong grip on the tiller. The self steering isn't ideal in some situations.
Hope this helps. There are some internet sites devoted to self steering. I can look them up and post if you want.
Eric

IP: 130.63.85.93

elmet3
Member posted November 17, 2004 05:48 PM               
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I don't think a balanced rudder can get you away from using the small auxilary rudder, which is needed in any case.
But now that you describe it, my intention is a bit different than your friends. I intend to use the auxilary rudder to "steer" the main rudder. This produces a "power gain" that allows the small, weak, windvane to efectively control the boat. My interest in a balanced rudder was simply to further reduce the size of windvane and auxillary rudder needed. Among other things, this reduces drag.
I would be interested in hearing if your friend thinks he gets good control. If he has no means of achieving power gain, the system is probably sensitive to setup and will not control well if the wind speed increases or decreases, which I hear is typical of unassisted windvanes.