Types of Keels.
Keels Explained
Keel design has been driven by the desire to go faster. Going faster in a racing context means actual speed through the water combined with racing rules and evolving competition standards which push designers to refine keel shapes for maximum efficiency. This has effectively meant that keels are longer, narrower, carrying more weight and lower centre of gravity. As a consequence, the attachment point of the keel to the boat has got progressively narrower. Add in the ability to “cant” a keel (move centre of gravity to windward) and new high tech materials and its no wonder we have problems with keel failure.
A more detailed historical journey can be found in Practical Boat Owner magazine “Keel Types and How they affect performance” by Peter Polland https://www.pbo.co.uk/boats/keel-types-and-how-they-affect-performance-76621
This article ties in the various ratings systems used in yacht racing and how it has affected yacht/keel design. It then goes onto rate the pro’s and cons of various keel designs for different types of use.
Eric Sponberg has produced two more technical articles for the technical peoples “Keel and Rudders- Engineering and Construction” and “Keel and Rudder Design” which takes a deeper dive into the world of keel design. Heavy reading, but perseverance through the technical bits will reward you with a good insight into the dark art of keel design. Both articles heavily reference various European build standards/codes which are not applicable in yacht construction in Australia.
When trying to understand more about why keels fail it is important to understand the terminology/jargon used, and how we got to the current keel designs. Going back to “101” for keels allows you to better understand the wide range of information that is out there, including social media “banter” (from the informed and uninformed), through to academic papers/books on keel and yacht design (which requires an advanced degree in mathematics to decipher !!!).
A good place to start is an understanding of how keel design has evolved. A comprehensive summary can be found in an article written by Ted Brewer – “Keel Design What’s Best” published on the Good Oldboat website https://goodoldboat.com/keel-design/ It provides an interesting historical perspective on how keels evolved then gets technical around aspect rations etc in modern keel design. It provides a good mix of advice for cruisers and racers and is written in easily understood language referencing popular yacht designs to illustrate the key points.
Types of Keels
| Keel Type | Description | Common Uses | Failure Risk | Notes |
| Bulb Keel | A fin keel with a torpedo-like bulb at the bottom | Performance cruisers, racers | Moderate to High | Adds righting moment; failure often linked to weld fatigue at bulb joint. |
| Canting Keel | High-performance keel that pivots laterally | Racing yachts (e.g., Imoca 60) | Very High | Mechanically complex; subject to structural and hydraulic failure if not rigorously maintained. |
| Bilge Keel | Two short keels allowing yacht to stand upright on tidal flats | Coastal cruisers | Low to Moderate | Lower stress, but hidden corrosion is possible if not inspected regularly. |
| Lifting Keel / Centreboard | Retractable keel design with variable draft | Trailer sailers, shoal cruisers | Moderate | Mechanical components can jam or corrode; poor maintenance may lead to jamming or leaks. |
| Wing Keel | Bulb with horizontal fins (e.g., Australia II design) | Racing / older cruisers | Moderate | Can snag debris or be damaged grounding; provides extra lift but adds risk in shoals. |
https://www.saltwaterjournal.life/blog/guide-to-buying-a-yacht#keel
Keel Yacht Terms Defined
1. Chord (Keel Chord or Foil Chord)
- The chord is the straight-line distance from the leading edge to the trailing edge of the keel (or any foil like a rudder or sail).
- It affects the hydrodynamic properties of the keel.
2. Draught (Draft)
- The draught is the vertical distance between the waterline and the bottom of the keel.
- It influences stability (deeper draught means more stability) and access to shallow waters.
3. Root (Keel Root or Root Chord)
- The root of the keel is the section where the keel joins the hull.
- Root chord refers to the chord length at this base area.
4. Tip (Keel Tip)
- The tip is the lowest point of the keel, farthest from the hull.
- Tip chord is the chord length at the bottom of the keel.
5. Aspect Ratio (Keel Aspect Ratio)
- The aspect ratio is the ratio of the keel’s span squared (depth squared) divided by its average chord length.
- High aspect ratio = long and narrow keel (efficient, less drag).
- Low aspect ratio = short and wide keel (more drag but more stability).
6. Leading Edge & Trailing Edge
- Leading edge: front part of the keel (faces forward).
- Trailing edge: rear part of the keel.
7. Bulb
- A bulb is a ballast-weighted extension at the bottom of the keel.
- It improves stability without significantly increasing draught.
References
keel-and-rudder-engineering.pdf
https://goodoldboat.com/keel-design/https://www.yachtingmonthly.com/gear/how-safe-is-your-yachts-keel-99116