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Help, how do you calculate BRUCE NUMBER ?
- Thread starter mcm
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Richard Woods
Woods Designs
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Before you get too carried away with Br No you might like to read this article (extract below)
http://sailingcatamarans.com/index.php/articles/12-to-be-published-mainly-technical/51-hull-shapes
"People try to simplify hull design and performance predictions, formulae like the Bruce Number and KSP spring to mind. These coefficients rely only on basic sail area, displacement and length dimensions yet purport to give an accurate indicator of performance. It's easy to show that these formulae cannot be relied on if you consider that a Tornado would have the same rating whether it was sailing forwards or backwards! I suspect the latter is slower! Its probably as accurate as predicting car speed from the kerbside weight and engine horsepower."
And in fact since the BrNo has no length factor the answers are especially meaningless. For example, try a boat with length 1ft, sailarea 1sqft and weight 1lb. How fast will it really be?
A better simple multihull performance indicator is the Texel rating
http://www.texelrating.org/pub/Pagina.php
Other articles you might find of interest
http://sailingcatamarans.com/index....-articles-technical/40-multihull-rating-rules
http://sailingcatamarans.com/index....ormance-questions/107-performance-predictions
Richard Woods of Woods Designs
www.sailingcatamarans.com
http://sailingcatamarans.com/index.php/articles/12-to-be-published-mainly-technical/51-hull-shapes
"People try to simplify hull design and performance predictions, formulae like the Bruce Number and KSP spring to mind. These coefficients rely only on basic sail area, displacement and length dimensions yet purport to give an accurate indicator of performance. It's easy to show that these formulae cannot be relied on if you consider that a Tornado would have the same rating whether it was sailing forwards or backwards! I suspect the latter is slower! Its probably as accurate as predicting car speed from the kerbside weight and engine horsepower."
And in fact since the BrNo has no length factor the answers are especially meaningless. For example, try a boat with length 1ft, sailarea 1sqft and weight 1lb. How fast will it really be?
A better simple multihull performance indicator is the Texel rating
http://www.texelrating.org/pub/Pagina.php
Other articles you might find of interest
http://sailingcatamarans.com/index....-articles-technical/40-multihull-rating-rules
http://sailingcatamarans.com/index....ormance-questions/107-performance-predictions
Richard Woods of Woods Designs
www.sailingcatamarans.com
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When making any potentially dangerous or financial decision, always employ and consult appropriate professionals. Your circumstances or experience may be different.
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