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Spade rudder

What is a spade rudder and why do racing boats use it? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: balanced rudder, rudder balance, rc yacht rudder, spade vs skeg rudder, rudder foil, NACA 0012 rudder, rudder area, rudder stall

Exact dimensions. True size, with no printing tolerance added.

sizes
6 in table

Notes

  • A spade rudder hangs free of the keel with no skeg, so it acts as a pure foil and can be balanced with area ahead of the stock (Good Old Boat). Its stock must resist bending as well as twisting.
  • Balance cuts helm load but too much makes steering hard to control: old practice capped it near 10%, modern rudders reach 17% (Good Old Boat, quoting designers).
  • Spades run fat, round leading edges to resist stall; typical thickness 10-12% (Stewart).
  • The file is a reference example built by Xem Studio from the numbers above (NACA 0012 per Perry; size illustrative.). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

Spade rudder size chart

parametervalue or rangesource
Balance areaup to ~17%; ~15% on boats over 45 ft (Perry)Good Old Boat
Max thickness position30% chordGood Old Boat
Thickness ratio10-12% typical (Stewart); 10-18% (Wurmfeld)Good Old Boat
Favoured foilNACA 0012 (Perry)Good Old Boat
Rudder area~1.4% of sail area (Tanton)Good Old Boat
Max rudder angle35-40 degGood Old Boat

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Good Old BoatThe rudiments of rudderswebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

spade-rudder-appendagerudder spade: 300 mm deep, 60 mm chord, NACA 00-series foilSTEP · STL
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Plain text: sheet.txt · JSON: /api/geometry?object=spade-rudder

Spade rudder, isometric render of a generated part
Render of spade-rudder-appendage from the free STEP; not to scale.

Fits with

Fin keel with ballast bulb, isometric render of a generated part
Fin keel with ballast bulb5 sizes★ 1 file
Skeg-hung rudder, isometric render of a generated part
Skeg-hung rudder2 sizes★ 1 file
Daggerboard, isometric render of a generated part
Daggerboard2 sizes★ 1 file
Centreboard, isometric render of a generated part
Centreboard1 sizes★ 1 file
Canting keel, isometric render of a generated part
Canting keel3 sizes★ 1 file
Rigid wing sail1 sizes★ sheet

Questions

How much balance?

Around 15%, rarely above 17% (Good Old Boat).