new hull form for catrigged boat

Hi Silver! I wish I were the guy at the cockpit. No, this jewel isn't mine Beyond the performance of Gil's boats, they are really good looking!

 

Right, that beautiful shot is on my pin board as well!

Thanks guys for all yr comments.
Well... the easiest way is to copy Gil's master piece!(or even with minimal changes)
There wouldn't be much wrong with that.
Adriano

 

For those having interest in Gil Smith work:

Daria Elizabeth Merwin: Gilbert Smith Master Boatbuilder
http://nautarch.tamu.edu/pdf-files/Merwin-MA2000.pdf

http://woodenboatworks.com/index.php/boats/custom

http://s90.photobucket.com/albums/k253/holzboat/Gil Smith sloop/

 

All Gilbert Smith's designs are works of art but Lorelei appeals more to me because not only is it beautiful but the fuller bow and more powerful after sections, has to make a fast boat without crankiness.
Whereas your extremist fine ends, hollow waterline entry, weak stern design would definitely provide that behaviour. Nice clean wake in light winds though.

 

Gil Smith

Thanks guys I appreciate.
Nice useful pictures!, D.E. Merwin's thesis was already in my files.
Am passionated sailer with some interest in the science of "how a sailboat moves through the water". Am simply exercising on that nice Delftship tool the best I can.
Any of Gil's catboats looks wonderful, I've never been sailing any of them
so I do not know about the sailing properties , but going by the lines
Lucile is the one which at most pleases my eyes, especially when looking at the sheerline!
I was wondering whether anybody knows any hydrostatic data like volume (Cp,LCB, CLR etc), water plane, midship, curve of areas referring to any of Gil's master pieces.
It would be interesting for the sake of my studying process about catboats.
Many thanks in advance
Adriano

 

Hi Paul,
As mentioned I try to get as close as possible to Gil's Lucile catboat
by changing the fore part to a finer entry, Mast would be of course in light weight!
I remodeled the my cat boat of 5 mt. LOA, LWL mt. 4.22,
0.15 mt. draft max beam 1.515 mt.
Cp 0.502 LCB -3.44%
I assume for beamy boat it would be difficlut to get a higher Cp.
I would be interested to hear yr comments at this stage
You should be able to open the attatched file.
Thanks
Adriano

 

Lucile

Now I have my own Gil Smith, a virtual one.
There's some lack of matching between the published linesplan's views. Main particulars don't fit with the published linesplan, also. Anyway this is what I got. Hydrostatic report attached.
http://www.boatdesign.net/gallery/showphoto.php/photo/21495
http://www.boatdesign.net/gallery/showphoto.php/photo/21496
http://www.boatdesign.net/gallery/showphoto.php/photo/21498
http://www.boatdesign.net/gallery/showphoto.php/photo/21497
http://www.boatdesign.net/gallery/showphoto.php/photo/21494

 

Thanks Que,
Very fast to reproduce the original lines! Definitely very expert on CAD!
I just try to better understand the dynamic of those nice catboats.
Now looking at the hydro report, the original one is supposed to have a Cp 0.576 (over the 0.56 acceptable range!) and the LCB of 2.28% which is far from the optiumum location of -3.5%!
I understand that those catboats originally were designed for working purpose, having more loading space and more stability through form rather than speed! Correct me if I am wrong.
My concept is not to copy the original lines but ruther bring some changes (improvements if ever with minor changes as possible on deck/sheer line !).
First Iwould build her in light weight Red Cedar veneer/cold molding to get the weight reduced to approx 0.300 tons by 5 mt.loa.0.15 mt. draft. The next attempt is to bring back the LCB to approx. -3.5% to reduce wheather helm which is big issue on those boats!
This is feasable but at same time is allost impossible to have a Cp somewhere between 0.54-and 0.56?!
I agree that my first attempt was too extreem but the second one shouldn't be too far away!?
It would be interesting to read some comments on those hydrostatic data concerning catbots, I would appreciate very much.
Adriano

 

You need a lot more study before attempting scrutiny of yacht lines Adriano. I mean no offense, but I've just completed a sailboat design with a .587 Cp and considered it a close to ideal for it's speed potential.

The are lots of cat boat designs to look at, each will be different, some dramatically so. The working craft are very different from the racing versions and many "freaks" where built, further stretching out the possibilities.

Simply put, there aren't any "acceptable range" figures, particularly with this type of boat, that saw so much unregulated development.

Cat boats can be lovely to look at, but most of the racers are cantankerous witches to sail, in anything but a light breeze. Most lack positive steering control, have nasty helm balance and become hard mouthed wenches when the wind pipes up. In short, be careful what you wish for. A half model is much easier to admire, then being short handed at 15 knots and building, aboard a real one.

 

catboat

Thanks Paul, I appreciate yr comments.

I am "trying" to design as far as possible that boat ruther due to my passion for sailing, than anything else, definitely I wouldn't build her that simply but would ask a guy like you to provide executive drawings!
This is eventually meant for back- calm waters not for open sea to form a sailing school fleet based on catboats and try to attract passioned (new) sailers and form a kind of "Catboat club". You know a little bit about my intentions.
Adriano

 

Cat boats of some note (speed) are best sailed with several well fed friends, that can act as rail meat. If you decrease the sail area enough to make them lovely daysailors, they're about as boring as it gets. If you keep the sail plan, you need huge amounts of live ballast just to wring her out in a moderate breeze.

 

Adriano, as a friend says: you can't have a Ferrari carrying 3 files of chairs. You must take some initial decitions. If not enought practice with ratios, then define what kind of boat you need (or like). An old fashion catboat with the ratios of a Melges 24 will certainly be impossible
If you are looking for a small and light school-yacht, IMO, make it unsinkable and open-stern to allow for a simple and fast uprighting. Safety first. Boats like Lucile will not return from a capsize.

 

Hi Paul, Que,
For sure I am not looking for a Ferrari nor for something impossible but simply try to understand how far it can be compromized and learn out of it. Obviousely this has to be clarified.
On the other hand it's allmost impossible to explain the whole background on a forum thread, pls understand.
Unforunately I do not have a teacher and try to learn on my own from the books as hobby and not at all as profession. At most when looking at somebody's else drawings I would prefere to know what we are talking about!
Said this, I strong believe that I'll not put somebody's life in danger just exercising on cad! This type of sailboat would have to be sailed on shallow back waters, they would be unsinkable and crew will have to wear a lifevest!
I'm not looking for a modern racing machine at all but what I am trying to model is to adapt those beautiful classic lines to new construction methods and materials I do believe I am not the first one thinking like that!?, Talking about pleaasure sail boats
also for me safty followed by classic design and maintenace issue are priority. Classic design will survive forever while modern design has short lifefor obvious reasons!
Of course I do not have anything against new technology in every direction!
That's a pity, there would be a lot to comment at each and every curve of those classic boats, same feeling when looking at the curve of a nice woman, am I right?. Actually I was expecting more detailed technical comments rather than
"Life insurance" kind of suggestions.....
Before getting into more sofisticated cad extentions I wish to learn more from experienced guys like you!
Anyhow thanks for yr time and kind efforts
Adriano

 

I completely agree with the classic lines need, but you have to establish a solid SOR and work with that. I would go with the "in the spirit of" approach. The boat could has exceptional looks and styling clues for what ever era you like, but incorporate a modern hull and appendages. You can still have a sweet counter and some bow over hangs, but also the sailing attributes of a modern preformance oriented craft.

Find a boat about the length needed and with the preformance envelop you desire, then make the styling changes you want and have fun. Designing one from scratch is a very difficult thing with limited expertise, so for a better success percentage once the boat does hit the water, you'd be best advised to modify an existing design with all the things you want; preformance envelop, sailing qualities, styling, etc.

 

Thanks Paul,
I also believe that's the most pratical way to go with, even though in this case, by using different construction materials/weight, some changes in the immerged body will be needed. Further the challenging part to reduce (sofar it's technically possible) "wheather helm" is still interesting me, somebody else has already done it, pls look at the pictures I posted right at the begining of this thread.
On the other hand, today for those who have such sofisticated softwares these issues are no longer representing "tedious jobs", I suppose tank tests today are of very limited use. Unfortunately in my case these expensive softwares will be not justified!
That's why also I was hoping to get some kind of input from the forum. Anyhow I'll search on the web try to find some literature explaining about hydrostatic on catboats if any available?!.
Maybe you are ware of any?
Thanks
Adriano