Review of RNSA Twenty Four

Basic specs.

The RNSA Twenty Four is a sailboat designed by the British maritime architect bureau Laurent Giles & Partners Ltd. in the late forties. Only a few boats have been produced.

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Rig

The RNSA Twenty Four is equipped with a fractional rig. A fractional rig has smaller headsails which make tacking easier, which is an advantage for cruisers and racers, of course. The downside is that having the wind from behind often requires a gennaker or a spinnaker for optimal speed.

Keel

Full keel

The RNSA Twenty Four is equipped with a long keel. A full keel provide a better directional stability than a similar boat with a fin keel; on the other hand, better directional stability means also that the boat is more difficult to handle in a harbour with less space.

The boat can enter most marinas as the draft is just about 1.62 - 1.72 meter (5.31 - 5.61 ft) dependent on the load. See immersion rate below.

Sailing characteristics

This section covers widely used rules of thumb to describe the sailing characteristics. Please note that even though the calculations are correct, the interpretation of the results might not be valid for extreme boats.

Stability and Safety

What is Capsize Screening Formula (CSF)?

The capsize screening value for RNSA Twenty Four is 1.41, indicating that this boat could - if evaluated by this formula alone - be accepted to participate in ocean races.

Theoretical Maximum Hull Speed

What is Theoretical Maximum Hull Speed?

The theoretical maximal speed of a displacement boat of this length is 6.6 knots. The term "Theoretical Maximum Hull Speed" is widely used even though a boat can sail faster. The term shall be interpreted as above the theoretical speed a great additional power is necessary for a small gain in speed.

Immersion rate

The immersion rate is defined as the weight required to sink the boat a certain level. The immersion rate for RNSA Twenty Four is about 112 kg/cm, alternatively 628 lbs/inch.
Meaning: if you load 112 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 628 lbs cargo on the boat it will sink 1 inch.

Sailing statistics

This section is statistical comparison with similar boats of the same category. The basis of the following statistical computations is our unique database with more than 26,000 different boat types and 350,000 data points.

Motion Comfort Ratio

What is Motion Comfort Ratio (MCR)?

The Motion Comfort Ratio for RNSA Twenty Four is 38.3.

Comparing this ratio with similar sailboats show that it is more comfortable than 98% of all similar sailboat designs. This is a comfort value significantly above average.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for RNSA Twenty Four is 4.26.

Compared with other similar sailboats it is slimmer than 100% of all other designs. It seems that the designer has chosen a significantly more speedy hull design. This type of design is also referred to as 'needle'.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for RNSA Twenty Four is 311 which categorizes this boat among 'medium weight cruisers'.

24% of all similar sailboat designs are categorized as heavier. A heavy displacement combined with smaller water plane area has lower acceleration and is more comfortable.

SA/D (Sail Area Displacement ratio)

What is SA/D (Sail Area Displacement ratio)?

The SA/D for RNSA Twenty Four with ISO 8666 reference sail is 13.9, with a 135% genua the SA/D is 16.2.

The SA/D ratio indicates that it is faster than 18% of all similar sailboat designs in light wind.

Maintenance

Bottom Paint

When buying anti-fouling bottom paint, it's nice to know how much to buy. The surface of the wet bottom is about 21m² (226 ft²).
Based on this, your favourite maritime shop can tell you the quantity you need.

Note: If you use a paint roller you will need more paint than if you use a paintbrush.

Rig

Dimensions of sail for fractional rig.

Are your sails worn out? You might find your next sail here: Sails for Sale

If you need to renew parts of your running rig and is not quite sure of the dimensions, you may find the estimates computed below useful.

**Guiding dimensions of running rig**
Usage	Length		Diameter
Mainsail halyard	27.3 m	(89.5 feet)	10 mm	(3/8 inch)
Jib/genoa halyard	27.3 m	(89.5 feet)	10 mm	(3/8 inch)
Spinnaker halyard	27.3 m	(89.5 feet)	10 mm	(3/8 inch)
Jib sheet	9.8 m	(32.0 feet)	12 mm	(1/2 inch)
Genoa sheet	9.8 m	(32.0 feet)	12 mm	(1/2 inch)
Mainsheet	24.4 m	(80.0 feet)	12 mm	(1/2 inch)
Spinnaker sheet	21.5 m	(70.4 feet)	12 mm	(1/2 inch)
Cunningham	3.8 m	(12.3 feet)	10 mm	(3/8 inch)
Kickingstrap	7.5 m	(24.6 feet)	10 mm	(3/8 inch)
Clew-outhaul	7.5 m	(24.6 feet)	10 mm	(3/8 inch)

Boat owner's ideas

This section is reserved boat owner's modifications, improvements, etc. Here you might find (or contribute with) inspiration for your boat.

Do you have changes/improvements you would like to share? Upload a photo and describe what you have done.

Finally

We are always looking for new photos. If you can contribute with photos for RNSA Twenty Four it would be a great help.

If you have any comments to the review, improvement suggestions, or the like, feel free to contact us. Criticism helps us to improve.

References

[Ref 1]: ISO 8666 Small craft — Principal data.
[Ref 3]: ISO 12215-5 Small craft — Hull construction and scantlings.