Review of Impala 28 (Thomas)

Basic specs.

The Impala 28 (Thomas) is a sailboat designed by the British maritime architect David Thomas in the late seventies. A few hundred boats have been produced.

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Hull

The hull is made of fibreglass. 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.

Rig

The Impala 28 (Thomas) 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

Fin keel

The Impala 28 (Thomas) is equipped with a fin keel. The fin keel is the most common keel and provides splendid manoeuvrability. The downside is that it has less directional stability than a long keel.

The boat can enter most marinas as the draft is just about 1.68 - 1.78 meter (5.51 - 5.81 ft) dependent on the load. See immersion rate below.

Engine

The boat may be equipped with an inboard Yanmar 1GM diesel engine at 9 hp (6 kW). Calculated max speed is about 5.2 knots

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 Impala 28 (Thomas) is 2.28, indicating that this boat would not 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 6.4 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.

Immersion rate

The immersion rate is defined as the weight required to sink the boat a certain level. The immersion rate for Impala 28 (Thomas) is about 133 kg/cm, alternatively 746 lbs/inch.
Meaning: if you load 133 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 746 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 Impala 28 (Thomas) is 13.8.

Comparing this ratio with similar sailboats show that it is more comfortable than 12% of all similar sailboat designs. This is a comfort value significantly below average.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Impala 28 (Thomas) is 3.02.

Compared with other similar sailboats it is more spacy than 54% of all other designs. It seems that the designer has chosen a slightly more spacy hull design.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Impala 28 (Thomas) is 154 which categorizes this boat among 'light racers'.

86% of all similar sailboat designs are categorized as heavier. A light displacement requires less sailarea and has higher accellerations.

SA/D (Sail Area Displacement ratio)

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

The SA/D for Impala 28 (Thomas) with ISO 8666 reference sail is 20.3, with a 135% genua the SA/D is 23.3.

The SA/D ratio indicates that it is faster than 92% 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 24m² (258 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	26.8 m	(87.9 feet)	8 mm	(5/16 inch)
Jib/genoa halyard	26.8 m	(87.9 feet)	8 mm	(5/16 inch)
Spinnaker halyard	26.8 m	(87.9 feet)	8 mm	(5/16 inch)
Jib sheet	8.5 m	(28.0 feet)	10 mm	(3/8 inch)
Genoa sheet	8.5 m	(28.0 feet)	10 mm	(3/8 inch)
Mainsheet	21.3 m	(70.0 feet)	10 mm	(3/8 inch)
Spinnaker sheet	18.8 m	(61.6 feet)	10 mm	(3/8 inch)
Cunningham	3.5 m	(11.5 feet)	8 mm	(5/16 inch)
Kickingstrap	7.0 m	(22.9 feet)	8 mm	(5/16 inch)
Clew-outhaul	7.0 m	(22.9 feet)	8 mm	(5/16 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 Impala 28 (Thomas) 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.