Does moving the rudder so much farther aft in the LC style rudder have any affect on CE/CLR balance? Does that effect your steering, or is improvement in steering mostly due to the rudder balance and improved foil? 

The long underwater rudder strut from the keel to rudder in the ZBDB sketch bothers my impression a little, but I don't have a good reason. That's like 7ft/2m? Wetted area or drag a concern?

Alan,

Now I made a quick sketch, showing a new, balanced rudder, similar to the one Paul fitted to La Chica. I think that should improve your boat for the same reasons that it did to LC.

I bet Paul is able to knock up a building plan for you in next to no time.

Cheers, Arne

Alan B Martienssen wrote:

There is quite a lot of weather helm. Indeed, I have a piece of string that breaks  before the aries does. One night , recently, the string broke 20 times. The string breaks at about 50kg( maybe more) so  there is quite a load on the tiller, which is more than 2m long to make the pressure  manageable. And I have broken the tiller. Often Zebedee will not tack, occasionally, esp before having cambered panels, I couldn't wear round either. Most alarming with a lee shore! I am at least 6 inches deeper than the plan. With the aries I have to change the  chain link according to the wind strength, and it can be at the last link to give sufficient weather helm to get the optimum speed, anyspeed. The tiller is definitely not in lline in strong winds, maybe 20 degrees off.

Despite reefing, I still often had the rudder right over at 30 degs to keep LC sailing when on a beat and likewise sometimes struggled to come about. Ditto the rudder loads but fortunately my till is just a piece of 11/2 schd 40 SS pipe so it was not going to break (and the autopilot was doing the work).

Since the new rudder, rudder angles are typically 0 to 3 degs on the wind with an occasional foray into 5. Downwind, even being totally over canvassed (full sail in 27 odd kts on the way to Annie's birthday bash) I never saw more than 15 degs of helm applied.

I'm very aware of the rudder angles onboard LC as most of the steering to date has been by my autopilot and it displays the rudder angles.

Alan.

Here is a scanning of the shallow draught version of Benford 34'.  What other changes did you do than increasing draught with 6"? Does the rudder sit on the back end of the keel now? The barn-door size, unbalanced rudder you describe surely sounds like it need someone from the Armstrong family to handle it...

Arne

Arne, Your drawings are not current as I did not make any of the proposed keel changes. So no significant increase of draught took place and any that did was at the very end of the rudder supporting post. Certainly of no consequence with regards to improving windward ability.

Before building LC's new rudder I did a lot of research and spoke to several established naval architects. In the end my friend and also the naval architect that I served my apprenticeship with, Angelo Lavranos reminded me of a boat that I did while in his employ and that was the key that unlocked the magic for LC.

The take home point is that everything about boats is a compromise but it needs to be a compromise in the right direction. A small boat like LC (and also Zebedee) are strictly displacement hulls and move through the water a low speeds so you want a rudder optimised for what your typical boat speed is. In LC's case that is 3 to 6 kts. If you are a cruiser, you also want a rudder that does not stall easily and has a high stall angle. I also wanted a lot of lift as LC can be very demanding. Low speeds and lots of lift also point towards a large rudder, so I went for a balanced rudder to reduce the tiller loads.

The profile shape of LC's rudder is far from optimum but I wanted a rudder that I could fabricate accurately in steel and that would not take me a lifetime to make. Hence the simple rectangular shape. The large cutaway in front of the rudder ensures that it operates in relatively clean water. A NACA0015 (15% camber) section ensured good lift at low speeds and together with the modest aspect ratio (2.3) ensures that the stall angle (30 degs) is high.

In practise, the compromises have worked and in fact LC's controllability and upwind performance hive increased dramatic. Her response to the helm is quick and only small rudder angles are required. It was indeed a well worth the effort, time and expense involved.

For those interested the rudder section is NACA0015 (15% camber). 21% balance and 1 500mm long x 650mm wide. I suspect I could have gotten away with a width of 500mm but I was taking no chances. Photo of the rudder can be found here: LC's rudder photo's

Do be aware that getting as true a section to the correct NACA foil section is critical... every deviation from the correct section will rob you of lift and create unwanted drag.