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Antiguo 15-10-2010, 11:42
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Cedemont Cedemont esta desconectado
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Predeterminado Re: Veleros que aguantan el mal tiempo y los que nunca lo haran

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Originalmente publicado por guillermogefaell Ver mensaje
La hoja que tengo de Excel para hacer encajes es bastante complicada y solo yo me entiendo con ella, pero veré a ver si puedo hacer algo sencillo para subir aquí (cuando tenga tiempo).

De momento aquí tienes las fórmulas, por si quieres ir trabajándotelo tu.


DESIGN BASICS

http://www.johnsboatstuff.com/Articles/design.htm


ROLL PERIOD (T) = 2*PI*((disp^1.744/35.5)/(82.43*LWL*(.82*beam)^3))^.5

The roll period is based on the moment of inertia, waterline length, and beam. The moment of inertia, (disp^1.744/35.5), was developed by SNAME. Large values resist rolling forces. The moment of inertia is very sensitive to the distance items are from the CG. A heavy rig can greatly increase I, with little impact on displacement. This equation was developed to support the 1987 Fastnet race investigation. The term (.82*beam) has been substituted for the waterline beam due to lack of data. Using (.82) results in a close match for the few boats with measured periods. Simply stated, a sailboat’s roll period, in seconds, is inversely proportional to its stability. Tender boats have long periods, stiff boats have short periods. The roll period is very easy to determine, you simply grab a shroud and push / pull until the boat is rocking over a few degrees. Then measure the time it takes for ten full cycles , and divide by 10. The general rule of thumb is that boats with periods less than 4 seconds are stiff and periods greater than 8 seconds are tender. The roll period is related to LOA and strongly related to COMFORT FACTOR.


ROLL ACCELERATION = (2*PI/T)^2*RADIUS*(ROLL ANGLE*PI/180)/32.2 ( units of G's)

In Marchaj's book, SEAWORTHINESS, THE FORGOTTEN FACTOR, chapter 4, "Boat Motions in a Seaway". The author presents a graph of roll acceleration ( in G's ) Vs four physiological states; Imperceptible, Tolerable, Threshold of Malaise, and Intolerable. Malaise starts at .1 G, Intolerable begins at .18 G. Spending much time under these levels of acceleration reduces physical effectiveness and decision making ability through sleep deprivation. The radius term assumes an off center berth located 1.5 feet inboard from the maximum beam. The roll angle is 10 degrees. G levels above .06 are considered undesirable for offshore cruising conditions. Several light weight, beamy designs have G levels above .4, definitely "intolerable" for any length of time.

PI=3,1416
El Roll Angle se toma como 10º y el Radius se toma = (B/2)-5

Está todo en unidades Imperiales (pies, libras, etc), por lo que hay que hacer la oportuna conversión si los datos de que se dispone están en el sistema internacional (métrico)

En este enlace encontrarás también más información de utilidad:
http://dan.pfeiffer.net/boat/ratios.htm
Si, las formulas se que estan ahi, pero a ver si puedes hacer algo en excel, e introducimos a la cofradia conceptos de aceleracion de rolido y otros...

Gracias
__________________
Cedemont

El hilo del STIX,"Veleros que aguantan el mal tiempo y los que nunca lo harán"