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Rudder Design


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If the tip of the blade is too far behind the boat, it makes it hard to steer. The amount of force at the tiller extension can be so great that it's heard to keep the boat from rounding up in strong winds while on a reach.

Ah! You may think; so there's too much weather helm? But we're talking the amount of force on the tiller handle, rather than the boat's tendency to go in one direction or the other.

Bringing the tips forwards, under the boat, reduces the amount of force on the handle, by bringing the centre of pressure on the blade in line with the steering axis; neutralising the rotation force.

Curiously this does also affect weather helm, and does allow more mast rake.

Going too far and bringing the tips in front of the steering axis is a problem. The boat pulls it self into turns. If you let the tiler go it gets pull hard over to one side. If that happens at any speed the blades are pulled right angles to the boat and snap off. At least mine did.

It's difficult to find the right angle, and some people prefer different things. I like a bit of rearwards rake so can feel what's going on down there.

A guide is to set the boat up off the ground with the rudders on and in the down position.

Adjust the angle of the hull so that it the normal waterline is horizontal.

Use a spirit level to then adjust he rudder blade so the front edge is vertical.

Another related issue is the angle of the pivot axis. With the boat set up with the waterline horizontal, is the line through the rudder pins vertical?

On old Paper Tigers they are mounted flat to the transom, so the top one is 35mm in front of the bottom one, so the axis is forwards at the top.

This affects pitching; when you bear off the bows go down, and when you round up the bows rise up.

I thought this was good as I could control the height of the nose when going over waves, but then realised it limited my top speeed, as correcting weather helm brought the bows down when sailing a straight line in strong winds.

After sailing a boat with the steering axis vertical (Tigerdelic), I got back on the old boat with the sloping axis (Pelikinetic) and less than 1 minute after leaving the beach bore off in a gust for a fast reach and was flung in the air as the boat cartwheeled.

Definitely go the vertical steering axis.

Hope that helped, good luck with it

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Maricats, Hobies (14 and 16) have the rudders tucked under so that the bottom leading edge is about 30mm in front of the imaginary projected line of the pin, this gives neutral helm at max mast rake. the measurement is the same for S/Sloop and Cat rig. Most beach rudders have about 25% of the blade in front of the pin.

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