Personal Offshore Catamaran Design

Hello all:

I'm new and just wanted to share or receive info for a personal offshore catamaran design. Currently I am almost finished with her and I have the former chief designer for Crowther Multihulls and current licensee holder, giving it a once over to make sure everything is okay. So far so good with my calculations etc, but I think it would be a good idea to run the design through the forum to get varied opinions from an enormous pool of knowledge.

I have spent about 2 years on and off on R&D and have experienced a very steep vertical learning curve in order to get to where it is. I think I studied everyone that is anyone in the nautical design field, whether NE or NA, and have to say that they deserve their props...I bow my sails to them.

I am currently putting all the specifics, calculations, equations etc, in some kind of understandable format so that I can maybe write a construction manual and publish the works...hopefully my autocadlite program won't blow-up by then. The design is a complete build it yourself, (everything on the boat from tang to sail is designed for self construction) with complete alternate recommendations for those that wish to purchase those items.

I will try to post some of that data and, if I figure out how to post the cad drawings, I will do that also. If not, I will paste onto a document and post it that way. Any help is appreciated.

Here is the fun part...all criticism is welcome as long as you can justify your argument, not just because "it doesn't look right" or "I don't like it". I will allow the plans for free use to anyone in the group that can make a significant contribution to the design. Significant to ME since I have almost completed the design, have spent time and money on it (shoot, I still am), and am almost ready to publish it for sale. The details on this drawing is unbelievable as you will see...even the heads on the bolts are to scale...what can I say, I'm a fanatic. I haven't had a comparable done on the plans, but from my own observations, they should be in the high thousand range. I'm a fair guy, and may be willing to redraw something significant, but would be more willing to make small alterations or addittions.

This was/is to be my retirement gift to myself...but, I'll be willing to license it for 1 free build for a significant contribution. At my pace, I would say I have another 6 months before I publish it. Only those interested in the thread or in contributing should participate...I don't want to get involved in other thread agendas.

Hopefully, collaboration may lead to a build...in which I would be happy to consult.
There it is. Questions? Comments?

Thank's

 

Please make a few renderings and post them in the multihull sailboat gallery. Thank you.

When do you plan on building your cat? Where is Coney?

 

What nero said......

 

Ahoy there Nero...

Happy 4th of July to all!
I will do my best to post what I can for everyone to view...how else can I get opinions? I would gladly welcome the procedure for doing so if you would care to enumerate it for me.

I'm not sure when I plan to build her yet. Did some looking around and space is charged at a premium rate around here...ahem which by the way is Coney Island NY...sorry...I'm used to just saying Coney. I think it will take me approximately 3 to 4 years because of a persistent nerve injury in my arm that acts up now and then, but to be realistic, it should take the average person about the same amount of time...part time, and squeezing out insane hours over the weekend religiously. Shoot for about 4000 hours and divide it up into your yearly work hours and you should produce a bristol yacht that you plan to retire into...or about 3000 hours for a very nice vessel you will end-up selling in 10 years. Please do not be fooled by some time estimates out there...I have personally witnessed a 3500 hour build turn into the victim of a chainsaw attack after 6000 hours of grief. Keep it real and know your limitations.

Where is the multihull sailing gallery? Not that I'm trying to skirt away from the learning curve here...It's just that I would like to look around.

In the meantime, I am cutting and pasting some of the specific information so that the "numbers group" can begin their analysis. I have an unbelievable amount of data that would make it almost impossible to cut and paste all in here so I will have to do it by sections until we exhaust each piece. In the meantime and in between, I will try to put it all together and will try to figure out how to put the drawings and spreadsheets etc...in here for perusal and analysis. I hope that everythings cuts and pastes okay.

CAT 2 Specifics

Loa 30'
Lwl 29.41'
Disp. 4K# Race Minimum/ 6K# Cruise Maximum
Draft 1.11' / 3' Board down
Hull Bm 5.5'
Hull Ht. 6.5'
Overall Bm 19.5
Bm/Loa .65
Ctr. to Ctr. Bm 14'
Lwl Bm 2.31'
Lwl/Bm Ratio 12.73 @4K#'s (Very easily driven).
11.36 @6K#'s (Good turn of speed).

Ctr LA X- 13.81' (Daggerboard Cord = 1.5625' - Naca 12)
Ctr LA Y- -1.17' (Daggerboard Lat Area = 5.01Sq.' = 20.5% of Lat Area.

CE X- 16.05' ( Lead = 6.3% of Lwl @ 51.5% Aft @ Combined CE)
CE Y- 20.35' (@ Combined CE)

Clearance 41.33'
Main SA 231 Sq.Ft.
Genoa SA 170 Sq. Ft.
SDR 25.46 (Full Suit @4K#'s)

Brdgdeck Cl. (Bow) 2.31' (7.8% Lwl)
Brdgdeck Cl. (Stern) 1.8' (6.1% Lwl)
Windage 6.22' (20% Loa @4K#'s)
Mast Rake 3 Deg.
Mast Aspect (1.34 times Loa)

Ama (2K# Disp. calculation)
CB X- 15.84' Aft (53.85% Aft)
CB Y- .75'
CG X- 15.66' (53.23% Aft)
CG Y- 3.24'
Lat. Area 24.43 Sq. Ft. (Windage Area 147.5 Sq. Ft.)
CP .57
D/L Ratio 35
S/L Ratio 2.73
D/L Limited Spd 14.1 KNOTS
Hull Total Volume 562.5 Cu. Ft. (Approx.)

Ama Heeled
Heel Moment Arm Righting Force
1 Deg. .4” (67#)
5 Deg. = 2” (334#)
10 Deg. = 4” (663#)
20 Deg. = 7.7” (1282#)
40 Deg. = 17.8” (2953#) Max before declining

Performance
=8.58 Knots in 10 Knots Wind on Reach @ 4K#'s
= 7.67 Knots @ 5K#'s
= 7.00 Knots @ 6K#'s

Suggested Sail Inventory Relative Area SA
Mainsail 100% 231Sq. Ft.
Trisail (Storm Main) 45 102Sq. Ft.
Storm Jib 22 51Sq.Ft.
Working Jib 65
Genoa 85 196Sq. Ft. Design 170Sq. Ft./73%
Large Genoa 120
Spinnaker 300 693Sq. Ft.'

Angle to Lift windward hull:
4K = 8.12Deg./8.875” 5K = 9.13Deg./10” 6K = 10.08Deg./11”

(Rudder Cord =1.0625' - Naca 15)
(Rudder Lat Area = 2.43 Sq.' = 9.94% of Lat Area.)

There is the first part...enough here to belabor for quite a while I think. If, and only if it is really necessary, will I break out the calculations and formulas used to arrive at the design. It is a lot of math...remember most, but don't want to go through the pain again.

Oh yes...one more thing...I was trying to put together a Velocity Prediction spreadsheet but the algorythms and calculations for multihulls are insane so I gave up...does anyone have formulas or calculations that they would like to share...or perhaps a spreadsheet that is already written? I know...a lot to ask. Please...recommend something that is +/- 5 to 10% accurate.
Thank's

 

JCD,
I sent you an email. I'm here on Long Island with a number of catamaran projects in the works. Drop me a line....

 

Hello Russell:

Okay...First chance I get I will drop you a quick line. Feel free to jump in and comment on the above...could definitely use the advise for the construction manual.

Thank's

 

Some plans

Well...I hope this works. I'll start with these... let me know if the pictures look okay. Placing the background in grey makes it pop out and easier to see.

Please don't ask me to put it all out there at once.

 

Nothing is showing up...at least with my browser.

 

when attach files

You may need to wait a bit longer before clicking submit ... to allow the file time to upload.

Under the banner there is the Boat Design Gallery. Click it and scroll down. That is where the sailboat multihull gallery is.

You'll catch on once you see it.

 

Ahoy there...

Well...I found the gallery...thank's. Then I looked at the upload part and the band is half-red and half-green. I think I did something wrong because I can't find the file on the thread or even pull it off the upload page. Did it go to the gallery? Does anyone see it out there? How do I get rid of the red/green band and start over? I'll try again.

Thank's

 

Do not know. I posted a photo in a thread to see if I could find the red/green band. Remember seeing it somewhere.

Have not seen any photos from you. Your personal gallery is empty. So, I guess nothing worked. Perhaps the monitor has to approve your posts first? Keep trying you'll get it.

 

Hello:

Okay...cut and paste onto a text document...maybe this will fly. Had to cut out a lot of the drawings...but at least it got through. Please advise if you can see it or back to the drawing board.

Thank's

 

Lot's-O-Windage, JCD

Perhaps you are packing a huge amount of volume for a boat of that length? As long as your expectations aren't high for a boat that can have a good turn of speed, perhaps things will be OK. It could be very interesting to maneuver in a tight anchorage with the wind blowing.

I'm guessing that you've fully worked-out the appropriate submerged volume for the overall displacement, but it "looks" like there is just way too much boat for what you have in the water

I like the construction lines and how you have explored the potential for plywood construction in this design study.

 

How frustrating! I can download and open the document, but it's blank for me. Can it be emailed? Chris, are you able to send it my way?
Thanks!

fhrussell@yahoo.com

 

Not enough bridge deck clearance. Looks to narrow. But there is something about your design that I like. Have you looked at Dazcats?

Perhaps you could loose some or all of that rigging with a freestanding mast design.

Like your dual helms. I have gone to this in my design/build.

There are a lot of chines. Maybe use strip planking in the corners and below waterline. I like your hull crosssection.