Review of Luders 21

The hull is made of fibreglass while the deck is made of wood. Generally, a hull made of fibreglass requires only a minimum of maintenance during the sailing season. And outside the sailing season, just bottom cleaning and perhaps anti-fouling painting once a year - a few hours of work, that's all.

The boat 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 genaker or a spinnaker for optimal speed.

The boat can enter even shallow marinas as the draft is just about 0.91 - 1.01 meter (2.99 - 3.29 ft) dependent on the load. See immersion rate below.

What is Capsize Screening Formula (CSF)?

The capsize screening value for Luders 21 is 1.95, indicating that this boat could - if evaluated by this formula alone - be accepted to participate in ocean races.

What is Theoretical Maximum Hull Speed?

The theoretical maximal speed of a displacement boat of this length is 5.4 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.

The immersion rate is defined as the weight required to sink the boat a certain level. The immersion rate for Luders 21 is about 55 kg/cm, alternatively 311 lbs/inch.
Meaning: if you load 55 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 311 lbs cargo on the boat it will sink 1 inch.

What is Motion Comfort Ratio (MCR)?

The Motion Comfort Ratio for Luders 21 is 13.3.

Comparing this ratio with similar sailboats show that it is more comfortable than 46% of all similar sailboat designs. This comfort value is just below average.

What is L/B (Length Beam Ratio)?

The l/b ratio for Luders 21 is 3.81.

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'.

What is a Ballast Ratio?

The ballast ratio for Luders 21 is 29%.

This ballast ratio shows a righting moment that is higher than 18% of all similar sailboat designs. A righting moment (ability to resist heeling) significantly below average.

What is Displacement Length Ratio?

The DL-ratio for Luders 21 is 163 which categorizes this boat among 'light racers'.

66% of all similar sailboat designs are categorized as heavier. A light displacement requires less sailarea and has higher accellerations.

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

The SA/D for Luders 21 with ISO 8666 reference sail is 16.9, with a 135% genua the SA/D is 19.0.

The SA/D ratio indicates that it is faster than 38% of all similar sailboat designs in light wind.

The Luders 21 has more rig than 100% of all similar sailboats, which indicates that the boat is significantly overrigged.

When buying anti-fouling bottom paint, it's nice to know how much to buy. The surface of the wet bottom is about 10m² (107 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.

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.

This section shown boat owner's changes, improvements, etc. Here you might find inspiration for your boat.

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

We are always looking for new photos. If you can contribute with photos for Luders 21 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.

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