Sails load rating

The sails load rating is a dimensionless number for sailing ships , which puts the sail area in relation to the displacement . It is often stated as one of many criteria when assessing ships, as certain characteristics of a sailing ship can be read off from it. A high sails load rating suggests a more sporty design of the ship, a lower value suggests a more safety-oriented design of the ship.

Some sail load ratings in comparison:

Tall ship : ≈ 3.5 to 4
Modern sailing yachts : ≈ 4.3 to 5
America's Cup IACC yachts : 6.2
Skiffs : ≈ 8 to 15

Calculation (metric)

The load rating of the sail is defined in Europe as the ratio between the square root of the sail area divided by the cube root of the displacement:

{\ displaystyle sail load rating = {\ frac {\ sqrt [{2}] {x}} {\ sqrt [{3}] {y}}}}

where the sail area is in square meters and the displacement in cubic meters of water (tons). The sails load rating is dimensionless (the square root of square meters and the cube root of cubic meters result in both units in the meter; in short, the result therefore no longer has a unit). It is not clearly defined which sail area should be used as the basis for the calculation. Of course, it makes a difference whether the calculated close-hauled sail area or the actual one - for example with a large genoa - is included in the calculation. ${\ displaystyle x}$ ${\ displaystyle y}$

Calculation (imperial units of measure)

In the Anglican system of measurement also another definition is common, also known as Sail area / displacement ratio is known:

{\ displaystyle ratio = {\ frac {SA} {D}}}

.

First, the displacement per cubic foot is determined:

{\ displaystyle DCF = {\ frac {displacement} {64}}.}

This is measured in pounds (lbs) and divided by the weight of water per cubic foot (64 for salt water, 62.4 for fresh water). ${\ displaystyle displacement}$

Last is with

{\ displaystyle D = DCF ^ {({\ frac {2} {3}})}}

Calculate the displacement per cubic foot to the power of 2/3 and divide the sail area in square feet by the result. It should be noted that the results according to the American and metric systems are not comparable and the number range is not identical. In the imperial system, the number range is roughly between 16 and 22.

example

The Hanse 388 is a 11.4 meter long sailing boat. She has 71.91 m ² upwind sail area and weighs 8.090 kg empty. This results in a load rating of . So this is more of a cruising boat than a racing yacht. ${\ displaystyle {\ frac {\ sqrt [{2}] {71 {,} 91}} {\ sqrt [{3}] {8 {,} 090}}} = 4.22}$

For the same ship in imperial units of measurement: 71.91 m ² is 774 ft ² , 8,090 kg is 17.835 lb. → → . ${\ displaystyle DCF = {\ frac {17835} {64}} = 278 {,} 6}$ ${\ displaystyle D = DCF ^ {({\ frac {2} {3}})} = 42 {,} 66}$ ${\ displaystyle {\ frac {774} {42 {,} 66}} = 18 {,} 1}$

Individual evidence

↑ ^a ^b CRUNCHING NUMBERS: Sail-Area / Displacement Ratio . Retrieved January 20, 2019.
↑ Hanse 388 . Sailboatdata.com. Retrieved January 20, 2019.

literature

Schult, Joachim; Sailors lexicon ; Keyword sails load rating, 13th edition 2008; ISBN 978-3-7688-1041-8

[numbers-1] CRUNCHING NUMBERS: Sail-Area / Displacement Ratio . Retrieved January 20, 2019.

[2] Hanse 388 . Sailboatdata.com. Retrieved January 20, 2019.