Spade rudder — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/spade-rudder/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
Catalog version: 2026-10-20

Sizes: see table below
- 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.

parameter  value or range  source
Balance area  up to ~17%; ~15% on boats over 45 ft (Perry)  Good Old Boat
Max thickness position  30% chord  Good Old Boat
Thickness ratio  10-12% typical (Stewart); 10-18% (Wurmfeld)  Good Old Boat
Favoured foil  NACA 0012 (Perry)  Good Old Boat
Rudder area  ~1.4% of sail area (Tanton)  Good Old Boat
Max rudder angle  35-40 deg  Good Old Boat

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Good Old Boat: The rudiments of rudders — web — Publisher's page; dimensions are facts — https://goodoldboat.com/the-rudiments-of-rudders/

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/spade-rudder/index.json
API: https://xemstudio.com/api/geometry?object=spade-rudder