Subject: Re: [harryproa] Re: Design your proa
From: Rick Willoughby
Date: 5/15/2011, 7:03 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Todd

I gather you agree with me that the flat sided hull is better at generating lift than V section for any given lateral area.  I agree the lateral area will be a function of beam, displacement and hull section shape.

It seems your flat bottom models sail well.  

The speeds that your models are capable of will not show any issue with ventilation.  It is one of the many factors that do not scale well when taking observations from models.  Your model would need to be moving much faster to observe effects of ventilation.  So be wary of making conclusions on performance about the best rudder placement from your models.

Rick
On 16/05/2011, at 4:55 AM, tsstproa wrote:

 



Rick, So your talking about the natural bite of the square bottom hard chine hull. On My simple hull prog that I use. It will show in degrees of heel that you choose how the hull sits in the water. Heeling square bottom hulls all ways sit deeper the more they heel. The hull program also shows the waterplane shape of hull. Have you noticed the differences in under water plane shapes. The V lifts by and inch or so at 15 degrees of heel were as the square bottom digs in to a depth of 2 or more inches. The interesting part though is the difference in under water plane shape between the two hull types. Do you see it?

The V skidding not producing lift. Maybe so for lateral area vs lateral area of each hull form. But how could you get same lateral hull area from two differently shaped hulls of same length for same displacment. Talk about putting the cuffs on. Either way which ever hull you start with to compare for given underwater plane one will have to much weight or the other will have to little. So I disagree with you on the V hull skidding and not producing lift for a given lateral area.

3-4 years back I built this final 24''model 1/12 scale using a hull program to design varying types of leeward hulls. As a test to see how big or small leeward hull needed to be for a well balanced weight to windward proa. I called it Square Harry but it didn't sit well. So switched it to Slam Tacker as it evolved.

The hulls I designed for this model are 24' and 16' long having 15'' bottoms 36 '' height keel to sheer and are 30'' wide at center sheer. Draft is at an 8'' with a displacement from memory of around 800-1100 lbs. Model sits and sails on scaled water line mark. Notice all my models have there steering boards on beams most Logical and easiest place to mount.

http://www.youtube.com/watch?v=jgCSYi5pwS8

Todd



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