Sailing catamaran parameters

[terhohalme]

Hi all catamaran designers,

I added a spreadsheet of catamaran parameters. It is a collection of simple equations from physics, design books and ISO standards to "solve" a sailing catamaran. Just input some dimensions and ratios and you have all other main dimensions on one simple sheet. There are two other sheets in workbook to estimate Texel and Multi2000 ratings.

Yes, I know there is no formula for a perfect sailig catamaran, but this leads you closer at the first shot. I tested it with many catamarans from Heavenly Twins and Wharrams to modern cruisers and to Med Club and Playstation and found decent results.

Try, test and enjoy. Comments are wellcome (just study first...)

Terho

http://www.boatdesign.net/forums/dow...?do=file&id=42

[Nordic Cat]

Hello Terhohalme,

an impressive piece of work!

I seem to have a problem changing the figures? Only the yellow fields are variable it seems. Am I doing something wrong?

Some explanations, or even better, a sketch showing where to take the measurements would be very helpfu, as some of the designations are not clear for me, not being a proffesional designer.

Regards

Alan

[terhohalme]

Yes, you are right, only change the yellow fields, they are input. Others are calculated values. If you like to see the equations, turn off the sheet protection. The protection is on to prevent the user to distroy the sheet accidentally.

There are some hints in shells with a red corner. Use google or books to find the terms (something to do yourself, too).

[lazeyjack]

yar jar Mr Finn man
nice, have some rep points

[masalai]

Thanks terhohalme, downloaded for future reference

[terhohalme]

Updated Sailing catamaran parameters.

http://www.boatdesign.net/forums/dow...?do=file&id=43

Corrected some equations and added new comments.

[Nordic Cat]

Hi Terho,

I tried inputting my design data, this is for a bi-rig cat, there seems to be some issues. Will you have a look please, and tell me what I did wrong??

Thanks

Alan

[terhohalme]

Input Bas again, it was text, not a number.

[terhohalme]

For bi-rig, double your J and E, not the height. If you have no jib, input foretriangle ratio to 0 %.
Did you noticed that Length/beam ratio is (lenght of hull)/(beam between center lines)?

[Nordic Cat]

Thanks.

Can't input J and E,so I played around with the Rigging size ratio and boom length to include wing mast areas, and get the right total square meters in sail area.

I must say I'm impressed! Alot of the numbers add up quite well, compared to the actual figures we are using.

I have used the formulæ that Multihull Dynamics use to give an idea of performance relative to other designs. They calculate "performance index" and some other figures. These show a performance index of a bit more than 1,0. Your predictor is a bit lower at around but as you say, it is not the best possible speed you use. It shows 8,9 knots average in 10 knots wind.

Are your daggerboard sizes for one or 2 boards? They seem big for only one.

I think this is a nice tool, to get you started when designing a cat, you dial in some numbers and get an idea of where you will be.

Thanks alot Terho.

Regards

Alan

[terhohalme]

The daggerboard area is assumed to 1.5% of nominal sail area. Perhaps 1.0 % was enough? It is corrected though by term (10/LWL)^0.5 to decrease proportional area at faster (longer) boats. Mayby this is not necessary. Any thoughts?

[Nordic Cat]

Originally Posted by terhohalme

The daggerboard area is assumed to 1.5% of nominal sail area. Perhaps 1.0 % was enough? It is corrected though by term (10/LWL)^0.5 to decrease proportional area at faster (longer) boats. Mayby this is not necessary. Any thoughts?

I just redid my area calculations, yoor sheet suggests 4,4 m2 daggerboard area, and mine are 3,8 m2. My chord is 0,9 and you suggest 1,18m.
My sailarea is quite high at 160m2 with no jib, so that may be the reason.

I have a big deviation in rudder area because i have input the rig ratio very high to get the correct sail area. When I input actual rig height, I get comparable figures to yours.

I have seen suggestions that rudder and daggerboard area should be around 2,5% of wetted area seen in profile. How did you get to your parameters?

Regards

Alan

[terhohalme]

If you take off the sheet protection, you can see the formula in shell.

[mallia.s]

Hi,

Could the parameters be adapted for a single hull vessel? I am currently studying a fishing boat hull (about LOA: 6-7m) and how its characteristics be altered for improved seakeeping.

Any help would be GREATLY appreciated.

Steve

[terhohalme]

Sorry, these are only for catamarans.