Reshaping the barn door

[numbknots]

Guys ,

I just gotta ask, what is with this barn door rudder on these ck's? How inefficient can it be to use one of these off the back of a sail boat? Its like dragging a rudder sideways through the water. The best I can describe it is sailing a boat with a rudder that has kicked up. Has anyone heard of anyone removing some of the trailing edge to get better shape going through the water? Lets say 10 degrees from bottom to top off back edge. That would releive the pressure some what wouldn't it?
I find the excessive "weather helm feeling" just takes the fun out of sailing this boat anywhere except dead down wind. I suppose you can tie off the helm but I always felt sailing was most enjoyable going into the teeth of the wind as efficiently as possible, that is really sailing to me. Letting the design and balance of the boat do the sailing not the rudder. Just a thought. Numbknots

[Michel]

Well, if you want to get rid of the barndoor and the weather helm, you gotta buy a different hull first. Letting out the mizzen and reefing it early also helps a bit. And no heel beyond 20*.

[numbknots]

Michel,

You dont think reshaping the rudder would help? I ask that because its just not weather helm involved here because there is a load of drag on the rudder even when you steer back into the wind. Numbknots

[Michel]

You might do something on the rudder; we discussed earlier that there are a few modifications. The best is adding a balancing part in front of the pivot point. The trailing edge can then be reduced with about the same area you add. But this might get problematic if you have a folding propeller. With a fixed prop it might be possible. What you propose, sawing off the trailing edge will reduce steerage, I fear. A rudder is an object where a lot of thought goes into, no matter how awkward it may look. If you reduce the trailing edge, you need to compensate for this lost area, e.g. further down at the bottom of the rudder. Based on the water pressure at that depth, you might need less area than you remove as compensation. The physics law is that the deeper the rudder, the fewer area you need to steer the boat effectively because of the higher water pressure down there. Here in the NL's is a company specializing in modifying (improving) rudders. You might try to find a similar company in the USA. Or ask a naval architect to review the design of the rudder and see what can be done to improve it.

[numbknots]

Michel,

Well one thing for sure Im not about to start hacking on my existing rudder. If I found a scraped out Freedom it might be an interesting project though.
I "google earth" your lat lon the other day, that is quite a nice port to sail out of. Hope the weather breaks for you soon. Numbknots

[Michel]

Yes, the weather has been fine now for two says. Spring is out! After the weekend I'm moving the boat to the new location and slip. Enkhuizen is indeed a nice little 16th century port where the East India merchant ships came in. It's a picturesque town.

[Peter]

Numbknots,

I had a UK built F35 CB (same hull as the US F33) cat ketch in the nineties. I bought the boat in the Caribbean to where the PO had sailed from Europe. As he experienced quite some high forces in the steering of the boat during the Atlantic crossing, he cut at least 20% off the trailing edge of the rudder and laminated the new trailing edge over with some layers of fiber glass. Actually it looked more like a quick and dirty job to me, but as the price was right I did not bother and bought the boat after a test sail.

After the first season in the Caribbean I converted the boat to tiller steering as there was excessive play in the wheel steering gear. I did this mainly cause I installed a Windpilot pendulum self steering device for the intended crossing back to Europe. This way I expected a more direct drive of the rudder by the Windpilot and it worked quite well.

After one more season of four month I left the Caribbean and crossed the pond by way of Bermuda to the Azores. On this last leg which took us two weeks we touched the tiller for less than half a day and let the Windpilot do the steering for the rest of the time. Even during a gale of force 8 with gusts to force 10 the boat behaved like on rails despite the CB being in the UP position. We were surfing down the big following seas at an angle of about 20-25 degrees and once I saw a speed of 16 knots on the GPS!

IMHO the large chord of the barn door rudder is causing lots of drag and consequently high forces in the steering gear and makes no hydrodynamic sense. Steering by hand the boat behaved quite normal and was manageable all the time without any problems. But I have to confess that I have no comparison as I never sailed the boat with the original rudder.

Greetings
Peter

[numbknots]

Peter,

That is encouraging news. I have my feelers out searching for rudder design and chord placement. The trailing edge on my rudder is sharp to slightly rounded. I see many of the faster boats with squared off trailing edges on their keels and rudders. Do you know if that facilitates a better release of water flow after leaving the foil? Thanks Numbknots

[Capitan Sardina]

Hi,

Another option may be to add a trimtab to the rudder to controll the wheather helm.
That is a small hinged "mini rudder" at the edge of the rudder. Exactly the same as in airplane elevators, etc.
I recall an old magazine article about the Freedom 35 where Don Street proposed to remove the wheel and installing a tiller with that solution. In addition it makes for a very simple to implement autopilot.

I only tried my F-40 with a tiller once. Inside the marina to the pumpout and back when I was working on the tramsom repair. The difference in feeling and control of the boat was fantastic! It was a different boat. Almost... agile. I fantasize about removing the clunky hydraulics and installing such system, but I am not going to cut into a perfectly good rudder to try such experiment. Maybe one day...

cheers,

alex

[Michel]

Alex,

Another option to improve rudder feel is changing from hydraulics to cable or better still, a rod system like the Withlock/Lewmar Mamba that is often used on racers. You can fine-tune the balance between purchase/leverage and rudder feel exactly to your needs with such a system. I'm very happy with the simple Withlock cable system on the F44. The only thing I have to do to keep it going smooth is lubricating the rudder stock with liquid soap now end then.