How to dimension a sailing catamaran?

[terhohalme]

Hi all,

Couldn't find this from literature or net, so I had to do it myself. I modified this excel table "catamaran parameters" to match the pdf-document "How to design sailing catamaran". There can be mistakes or misspellig, feedback is wellcome.

Boat Design Forums

Have fun

Terho

[Nordic cat]

Hi Terho,

You sure are a productive guy! Thanks for yet another handy toll when playing with catamaran design.

I wish I had such a paper before I started a couple of years ago, it would have made life a bit easier

I have made some comments in the PDF. Drop me a mail with your e-mail adress and I can send it to you. My mail is (alan(at)insatech.com)

Regards

Alan

[BigCat]

Hi, Terho

I've been having fun with your spreadsheet, inputing BigCat 65. It seems to me that some of your parameters diverge from what I have seen as typical for midsize cats-Narrower overall beam, higher sail area, and lower PCs. Materials costs-do those include equipment such as engines, winches, etc? Materials costs seem high for just the structure, unless the materials are the best rather than average.

Plus, a lot of water. 3800 liters = 950 gallons = 7600 pounds. Guess not everything scales exactly. Is the wetted surface for one hull or two?

I expect to reef at 23 knots, -my design is beamier than your paramaters and has less sail area and less air draft (unusual rig, lower CE than usual-biplane and not marconi rigged.)

[terhohalme]

Did I left the watertank in the spreadsheet? Just an idea how to estimate some supplies and fill the gap between lightship and fully loaded one. Yes I'l take them off until better ones appear.

Did you notice that you can use what ever beam or sail area you like. The spreadsheet just calculates what happens then. In biplane just set kJ to 0 (J=0) and double kE (E) to get both the sails in calculation. How wider? Your LBRC=2.31

Misspellings are under constuction...

Terho

[BigCat]

"How wider? Your LBRC=2.31"

Hi, Terho

If LBRC is total beam, my LOA is 64.66 ft. and my beam overall is 35.5', so 1.82 I would say most of the latest cruising 40' to 65' designs are a bit narrower than mine, typically about 1.95 beams over all per LOA, though a few are narrower or wider.

[Robertcateran]

Thanks Terho,
Makes me realise what a different beast a Harryproa is

[terhohalme]

Hi all,

Redefined catamaran parametric study. Now, there is included a calculation of design righting moment for rig design.

Terho

Boat Design Forums


ps. Redefining of document is on going...

[BigCat]

Hi, Terho

Your new spreadsheet thinks my boat displaces over one million kg. The old one predicted about 45,000 pounds.

[terhohalme]

Didn't change anything there.

[Italian Taitano]

That'll be a big help as I design my flying cat.

[BigCat]

Originally Posted by terhohalme

Didn't change anything there.

I put the PC in without a decimal, and the spreadsheet generated a huge displacement. I noticed this time that your beam stat is between hull centers. Mine is 27.5' between centers, or 2.35 in your spreadsheet. It thinks my boat is going to be pretty light, though, about 35,000 pounds loaded. I'm thinking more like 45,000, but loaded with about 450 gallons each of fuel and water.