Overhangs

Recently I've been working on the racing yacht hull. And I got to the problem. What overhangs should I propose?

I've noticed, that many racers have as long LWL as can be - I mean the overhangs are close to 0 - vertical bow and no stern overhang. I've also found, that there are many yachts with vertical bow, but their stern overhang is quite large.

For example the Opens racing in Around Alone have vertical bows and, I think, immersed stern.

On the opposition lie the AC yachts, which have huge overhangs both on the bow and stern.

And Maxi Yachts starting in the Volvo Ocean Race have almost vertical bows, but they have some stern overhang.

Had anyone worked on this problem? Or maybe there are some conclusions from VPP/CFD studies?

I'll be greatful for any comment.

 

Hi Ibi

I'm not an expert on this, but I would imagine it is driven by the measurements of the race rules/handicap system that you are designing for. For a very simple example, waterline that is only immersed under way (either heeling or surfing for example) is "free" if the race rules measure the waterline at rest .

Since the open 60 rule for the around alone consists of " thy boat shalt not be longer than 60ft overall" they want all of that as waterline for light airs. - Also of course they spend most of their time planing on that fat, flat transom.

http://www.vendee-globe.tm.fr/Vendeeglobe2000/reglenglish.html#Anchor-44306

Here is an article on exactly this subject by one of my favourite designers (for general interest)
http://www.boatus.com/goodoldboat/ratingrules.htm

Also this on the Overhang Ratio :
http://my.en.com/~danp/boat/ratios.htm#OR

Hope that helps

Paul