Subject: Re: [harryproa] Schooner v. Unarig |

From: "Rob Denney" <proa@iinet.net.au> |

Date: 11/29/2006, 12:35 AM |

To: |

Reply-to: harryproa@yahoogroups.com.au |

G'day,

Rob I don't mind the schooner rig, in fact on a big boat where a mainsheet winch is required, and if the fore boom of an Easy rig is too high to easily reach, they have a lot going for them. Horses for courses.

Herb The angle of deflection of a circular thin wall beam is proportional

to the square of the length

( http://en.wikipedia.org/wiki/ )Deflection

and the square of the radius

( http://en.wikipedia.org/wiki/ ).List_of_moments_ of_inertia R

The formula for cantilever deflection is

(Load*length cubed)/8*E*I Therefore it is a cube function of length, not a square. Halve the length, one eight the deflection.

E is the material properties, I is the 2nd moment of area about the neutral axis. I= pi*radius cubed *wall thickness. The radius is also a cube function, so half the radius, 8 times the deflection.

HHowever, each mast now has only 1/2 as much sail area, so the force on

each mast is 1/2 of what it would be for the single mast.

R

Yes and no. Each mast has to be strong enough to capsize the boat, as it is possible that only one sail would be fully powered up in a capsize scenario. This does not make each mast as heavy as a single one as to be stiff enough they are already stronger than required. However, depending on bury and other variables, it does make each mast much more than half the weight of a single one. On a harry, the bury will be very similar, although although a higher percentage of the overall length, which reduces the sheer loads somewhat.

HSo I am confused. Is a schooner rig really about 2/3 the weight and

cost of a unarig (ignoring sails), or have I misunderstood something?R

I would say 3/2 is closer to reality for the weight and cost.

regards,

Rob

Best regards

Herb

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