New Rudder

[Guest]

Because of poor steering performance and on advice I am in the process of making a new rudder for my 9t Hillyard. The old rudder is a D shape and apparently inefficient. The new rudder is more like a spade. Total area is not very different. Hillyards changed rudder shapes in the 1960's from the D shape to the spade shape.

I am making the new rudder with two layers of one inch good quality marine ply but now find that having glued and cut out the shape the weight is substantially greater than that of the old rudder which is made of some sort of hardwood; probably mahogany.

My question: Is this extra weight (I would say 50-100 percent higher) going to cause problems and unacceptable stresses particularly on the lower strap? The rudder is attached to the boat by two straps and with three bolts per strap. The top strap hangs directly on the rudder stock and the bottom strap from a gudgeon on the keel face.

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[Sniper]

I would be surprised if you had a significant problem. AS the rudder is by definition immersed, its weight will be substantially less than it is out of the water. If you wanted belt and braces, you could always add another strap between the existing two.

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[Plum]

The highest stresses on the pintles are from water pressure, not the weight of the rudder, which being timber will be fairly weight neutral below the water.

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[Mirelle]

I would not expect a problem with the weight; the rudder will be inclined to float anyway. If she is tiller steered, you will probably find that the old rudder has a lead weight somewhere in the lower part of it; this is to stop the rudder floating and keep the rudder amidships.

Try to keep the cutout for the propeller out of the rudder as much as you possibly can. If you must have a cutout in the rudder, make it as small as possible. This is a cause of bad steering, but the spade shape rudder will certainly help.

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[Guest]

Thanks to everyone for your advice. I can go on with confidence. Incredible though how heavy decent marine ply is.

I am not making a cut-out for the prop. It just clears and I am looking forward to better steering particularly astern when the prop wash should hit the rudder now.

I converted in the summer from the old cable and pulley steering which, without even a quadrant, was heavy and inaccurate to a Vetus hydraulic steering system. After the initial panic (when without the usual strain and feedback I couldn't feel what I was doing) I got used to the steering and it was a great improvement. Hopefully the new rudder will make it perfect! Mind you she'll still go where she wants when she wants particularly when approaching a marina berth with lots of onlookers!

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[Peterduck]

The apsect Ratio of the rudder has a lot of bearing on its behaviour as well. My old "Swallow" has a "D" shaped rudder, too; solid Jarrah. As she was a fishing boat in the early years of her life, control at low [ie., drifting] speeds was important, so a low aspect [nearly as wide as it is high] rudder was fitted. Fast yachts have long, narrow rudders as these are more manageable at higher [3kts +] speeds. Francis Herreshoff advocated a groove running up [or down] the length of the trailing edge of rudders. He maintained that it made them more effective.
Peter.

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[clyst]

What do you call "good quality " marine ply ? Dont be tempted to use anything other than "top quality " ply even then I suggest you epoxy cloth the entire rudder . I once towed a "Folk song" into Falmouth who's transome hung plywood rudder had snapped like a carrot . Have to say though it looked as if it was made from laminates of far eastern stuff (blade was about 2'' thick )

Hope this helps

Terry

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[Guest]

In answer to Peterduck Aspect ratio about twice as long (deep) as wide.

In answer to clyst I use marine ply supplied by Robbins Timbers their super elite sapele. It comes with 17 ply per inch so in total 34 over two inches. They guarantee this stuff for 25 years. The only gripe I have with it is the weight and its pretty hard on tools. Broke a router bit and have to resharpen plane and chisels every few minutes. The good news is that bar a few little corrections it fits!

After the adjustments I shall seal it with 3 or 4 coats of G4 primer sealer then metaclor primerand antifoul.

Hopefully it will stay good for a coupleof decades.

I do appreciate all yr input. Thanks

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[armando]

it's a bit late for an answer but may it could help. I am owner of a Hillyard 12ton
sloop and I am in the same situation. I have planned to change the existing rudder into a new one with a NACA0012 foil. This symetrical foil should increase the
manoeuverability dramatically. On older boats, rudders looks often like a plane plank between two fittings. Water flow over such a shape will collaps as soon as you turn the steering wheel. NACA0012 is a symetrical foil which means that the highest thickness of the blade will be 12% of the witdh of the rudder blade, measured 30% from the front edge of the rudder blade. As example: width of rudder 65 cms (in my case), 12% = 7.8cms thickness, measured 19.5cms from the front edge. From this 30%, the foil will be decrease down to app. 2cms at the end of the rudder blade. This foil could be used up to a speed of 6-7kts so it's suitable for the most sailing yachts. The faster the boat, the thinner the foil. Hope you understand above message. My english is not the best....have good time.

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