Hull Design

WOW!

Tad
I love your site and your work! That liberty is one fine machine. Your interior design is some of the best I have seen. The express cruisers are fine pieces of work too. Keep up the good…great work! 8Kts

 

Tad, I'd like to ask you, from what are these curves derived? I don't have the 1987 Stars & Stripes article in front of me, but from memory it seems to me the optimum curves for 12 meters in it look a bit different than your curves, even the low speed one, in that the 12 meter curves are more hollow in the region of section 8, making them more nearly symmetric about midships. Also, I think the LCB info in Larsson has the optimum moving forward a little as speed slows, but less than your curves suggest (again this is from memory - I don't have the book in front of me, and I've only seen the first edition). Is there some reason powerboat curves and sailboat curves would be different?

 

8knots;

Many thanks, I've been admiring your spline weight drawing. I have a bunch I bought from Waterlines almost 20 years ago. They are a handy shape with big indents in the sides for grip. About lost their paint.


Stephen;

The basis for these curves came to me as part of a handout when I was attending YDI (Yacht Design Instute) in Castine, Maine. I believe they had originally been published in a German book or magazine. I'm afraid I never had a reference. I also believe they were intended to relate strictly to powerboats. I revised them to aline with comments on LCB location by Bill Garden and Tom Fexas. I also re-faired them and converted the units to match modern S/L.

That said there is no reason powerboat and sailboat curves should be different, at least in the lower speed ranges. They were definitely created well before 1987, I may have a copy of the paper you mention but cannot lay hands on it at the moment. As for hollow in the curve aft, Bruce King did a great deal of tank testing with Pete De Saix in the sixtys and seventys, he was always adamant that the curve be straight aft. This was done with the "bustle", the idea was to reduce "separation " aft. But those were low speed hulls, which sailed through the water, they had no conception of the speeds achived by modern sailing yachts.

In use these curves have produced hulls that performed as expected. But they are only a guide, very handy for quick layouts and calculations. I will start with one of these curves and then revise lines as required and in light of what I'm trying to accomplish with a particular boat. For instance I would never put hollow aft in a section curve for a high speed powerboat. But I could see it in a slow speed full displacement hull. Say a tug where you are making room for huge sterngear. And modern hulls with prop pockets may in fact be hollow aft.

This business continues to be fascinating.

 

The Stars & Stripes '87 hull design paper, entitled ""Analysis of Wave Resistance in the Design of the 12-Meter Yacnt Stars & Stripes" by Carl A. Scragg, Britton Chance Jr., John C. Talcott and Donald C. Wyatt was published in the October 1987 issue of MARINE TECHNOLOGY, the journal of SNAME:
www.sname.org

In it the authors cite the formula below as defining the optimum curve of areas. They go on to explain that one must add a constraint mathmatically if one wishes to shift the resulting symmetrical curve of areas to a yield a non-midships LCB (it's not just a matter of skewing the curve). Unfortunately I don't know what all the variables are, and the formula for the constraint is not given. The resulting curves look a lot like Tad's.

Larsson discusses the fact that sailing yacht designers also often constrain the problem to preclude an immersed transom as a way of achieving a wider performance envelope (good at low speed and high).

 

I am the International Projects Director fro Concern fro Kids, Ltd. which is a humanitarian organization rebuilding the devastated Iraq for the past 12 years. I need to discuss how the villagers here may be able to build a four-car ferry boat with available iron and welders. This project is very important since terrorists are blocking the NGOs from travelling through Mosul and TelAfar and we need to ferry across the Mosul Lake Reservoir on the Tigris River. We have iron and welders and we need to ferry 20 tons across 4 kilometers of lake water. Olease help! Regards, Robert

 

I am the International Projects Director for Concern for Kids, Ltd. which is a humanitarian organization rebuilding the devastated Iraq for the past 12 years. I need to discuss how the villagers here may be able to build a four-car ferry boat with available iron and welders. This project is very important since terrorists are blocking the NGOs from travelling through Mosul and TelAfar and we need to ferry across the Mosul Lake Reservoir on the Tigris River. We have iron and welders and we need to ferry 20 tons across 4 kilometers of lake water. Please help! Regards, Robert

 

Ferry for Ninebeh in Iraq

I am the International Projects Director for Concern for Kids, Ltd. which is a humanitarian organization rebuilding the devastated Iraq for the past 12 years. I need to discuss how the villagers here may be able to build a four-car ferry boat with available iron and welders. This project is very important since terrorists are blocking the NGOs from travelling through Mosul and TelAfar and we need to ferry across the Mosul Lake Reservoir on the Tigris River. We have iron and welders and we need to ferry 20 tons across 4 kilometers of lake water. Please help! Regards, Robert

 

Ferry boat

Hi Robert,

Do you still need a design of ferry boat? If so, I can make it. Let me know if I can help you.

Igor Cherpak
romanoffinv@yahoo.com