Model Boat Mayhem

The Shipyard ( Dry Dock ): Builds & Questions => Yachts and Sail => Topic started by: bigbloke on February 12, 2013, 11:14:43 pm

Title: mathematics of B and C rigs for 1m yacht [not actual iom]
Post by: bigbloke on February 12, 2013, 11:14:43 pm

hi all,

ive recently acquired a joysway focus 1m yacht . As far as im aware, its not IOM class
compliant and in all honesty, I've no interest in racing , sailing is my brain chill time.

nevertheless, id like to make up some smaller sails that would be the equivalent of B and C rigs for
higher wind sailing. as a kite and power kite maker of many years, sewing ripstop and icarex hold no fear !  :-)

i gather from an earlier post of mine that a B rig is 70% of the A rig area (thanks mrpenguin!) but what
percentage is a C rig please?

my distant memories of geometry recall that the area of a triangle is "1/2 base x height"

but a quick calculation suggests the scale factor [i'll call it x %] is not as simple as "x% (base) times x% height

can anyone clarify the correct scaling formula involved please ?

Many thanks in advance

Regards

BB

Title: Re: mathematics of B and C rigs for 1m yacht [not actual iom]
Post by: dreadnought72 on February 13, 2013, 12:26:56 am

~84% of the base and height distances that you have for the A-rig will give you a rig with 70% of the area.

83.667 = SQRT(0.7)

Andy

Title: Re: mathematics of B and C rigs for 1m yacht [not actual iom]
Post by: mrpenguin on February 13, 2013, 12:54:08 pm

@BigBloke:
The attached file shows nominal measurements for the three rigs for an IOM - I have used this as the basis for the smaller rigs I have made.
These plans are for an IOM (one metre boat) - to scale this to a smaller boat, reduce all measurements by the relevant amount - for example if you have a 600mm boat multiply all measurements by 0.6
 

Title: Re: mathematics of B and C rigs for 1m yacht [not actual iom]
Post by: bigbloke on February 14, 2013, 08:36:23 pm

thanks a load for your help folks

I should have thought that if areas was "squared" that the "square root" would be involved ...DOH :embarrassed:

I can use the chart to work out the scaling ratios then apply the formula to determine my own sail dimension

Many thanks again

regards

BB

Title: Re: mathematics of B and C rigs for 1m yacht [not actual iom]
Post by: tigertiger on February 27, 2013, 01:45:29 am

Perhaps the question needs to be,


Is it n% of the area of the sail, or n% of the lengths of the sides of the sail?


You will probably find information for different rig areas on the relevant class pages of the racing associations. I know that in the US it is the AMYA, but I am not sure for UK.

Title: Re: mathematics of B and C rigs for 1m yacht [not actual iom]
Post by: mrpenguin on March 03, 2013, 09:54:42 pm

I would assume it to be area as some side lengths change very little between rigs.

Please refer to the PDF I posted a couple of pages back (in response to BigBloke) for guidance..That is what I have used for sails I have made... the foot length changes very little, height is reduced to lower the COE