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- Sailboat Guide
Rainbow 42 is a 41 ′ 11 ″ / 12.8 m monohull sailboat designed by Frans Harter and built by Farsø Glasfiber (DEN) starting in 1986.
Rig and Sails
Auxilary power, accomodations, calculations.
The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.
Classic hull speed formula:
Hull Speed = 1.34 x √LWL
Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio .311 Hull Speed = Max Speed/Length ratio x √LWL
Sail Area / Displacement Ratio
A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.
SA/D = SA ÷ (D ÷ 64) 2/3
- SA : Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay).
- D : Displacement in pounds.
Ballast / Displacement Ratio
A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.
Ballast / Displacement * 100
Displacement / Length Ratio
A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.
D/L = (D ÷ 2240) ÷ (0.01 x LWL)³
- D: Displacement of the boat in pounds.
- LWL: Waterline length in feet
Comfort Ratio
This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.
Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam 1.33 )
- D: Displacement of the boat in pounds
- LOA: Length overall in feet
- Beam: Width of boat at the widest point in feet
Capsize Screening Formula
This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.
CSV = Beam ÷ ³√(D / 64)
Shallow draft: 2.05m/6.73’
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- About Sailboat Guide
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Review of Rainbow 42
Basic specs..
The hull is made of fibreglass. Generally, a hull made of fibreglass requires only a minimum of maintenance during the sailing season.
The Rainbow 42 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.
The Rainbow 42 is equipped with a fin keel. A boat with a fin keel is more manoeuvrable but has less directional stability than a similar boat with a full keel.
The boat can only enter major marinas as the draft is about 2.33 - 2.43 meter (7.64 - 7.94 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.
What is Capsize Screening Formula (CSF)?
The capsize screening value for Rainbow 42 is 2.42, indicating that this boat would not 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 8.1 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 Rainbow 42 is about 278 kg/cm, alternatively 1561 lbs/inch. Meaning: if you load 278 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1561 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.
What is Motion Comfort Ratio (MCR)?
What is L/B (Length Beam Ratio)?
What is a Ballast Ratio?
What is Displacement Length Ratio?
What is SA/D (Sail Area Displacement ratio)?
What is Relative Speed Performance?
Maintenance
When buying anti-fouling bottom paint, it's nice to know how much to buy. The surface of the wet bottom is about 51m 2 (548 ft 2 ). Based on this, your favourite maritime shop can tell you the quantity you need.
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.
| Usage | Length | Diameter | ||
| Mainsail halyard | 40.7 m | (133.4 feet) | 12 mm | (1/2 inch) |
| Jib/genoa halyard | 40.7 m | (133.4 feet) | 12 mm | (1/2 inch) |
| Spinnaker halyard | 40.7 m | (133.4 feet) | 12 mm | (1/2 inch) |
| Jib sheet | 12.7 m | (41.7 feet) | 14 mm | (0.55 inch) |
| Genoa sheet | 12.7 m | (41.7 feet) | 14 mm | (0.55 inch) |
| Mainsheet | 31.8 m | (104.2 feet) | 14 mm | (0.55 inch) |
| Spinnaker sheet | 27.9 m | (91.7 feet) | 14 mm | (0.55 inch) |
| Cunningham | 5.5 m | (18.1 feet) | 12 mm | (1/2 inch) |
| Kickingstrap | 11.0 m | (36.2 feet) | 12 mm | (1/2 inch) |
| Clew-outhaul | 11.0 m | (36.2 feet) | 12 mm | (1/2 inch) |
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.
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If you have any comments to the review, improvement suggestions, or the like, feel free to contact us . Criticism helps us to improve.
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