design of a fast 27 catamaran

[SAILFASTtigre]

Hi everybody.

i am designing a 27 foot sail catamaran to sail steady trade winds, long ocean swells.

I have completed preliminary hull lines, and the hydrostatics for one hull are:

Displacement 1 tonne
Volume 34.44 ft^3
Draft to Baseline 1ft 4.99in ft
Immersed depth 1ft 1.05in ft
Lwl 26ft 11.92in ft
Beam wl 2ft 10.01in ft
WSA 78.41 ft^2
Max cross sect area 2.01 ft^2
Waterplane area 58.25 ft^2
Cp 0.634
Cb 0.414
Cm 0.696
Cwp 0.761
LCB from zero pt -8.67in ft
LCF from zero pt -1ft 11.3in ft
KB 1ft 0.57in ft
KG 1ft 4.99in ft
BMt 10.15in ft
BMl 75ft 2.45in ft
GMt 5.74in ft
GMl 74ft 10.03in ft
KMt 1ft 10.72in ft
KMl 76ft 3.01in ft
Immersion (TPi) 0.141 tonne/in
MTi 0.221 tonne.ft
RM at 1deg = GMt.Disp.sin(1) 0.01 tonne.ft


Can somebody comment on these? I will be glad to share the computer file design with anybody willing to collaborate,

best regards to all,

david

[oldsailor]

I see your hull L/B ratio is 9.5 :1, which is a good fineness ratio for a cruising mulltihull, but what is your beam overall. For the waters you are considering sailing in it should be 15' wide, or approx 12' wide on hull centrelines.

Cheers. Oldsailor. :cool: :) :D

[SAILFASTtigre]

right.

i was looking for a commentary on the hull hydrostatics. what about the LCB and LCF?

would you like to check a 3d cad image?

regards,

david

[oldsailor]

SORRY DAVID.

I am not "UP" on hydrostatics, but if your are able to post a 3 view of your design I would be happy to see it.

Cheers. Oldsailor. :cool: :) :p

[sharpii2]

Hi S.F.tigre.

Being a graduate of THE LANDING SCHOOL I am embarassed to admit I know what only half those numbers mean.

What I think would be helpful is a list of design objectives. Such as:

a.) intended use. Is it a huge daysailer? A weekend cruiser? or is it expected to cross an ocean?
b.) payload expectations. How much do you want it to be able to safely carry?
c.) performance expectations. From your handle, I'll asume you want it to be as fast as possible. But there is always a price for speed.
d.) budget limitations. Even the richest man in the world has to live on some kind of budget. (maybe by successfully doing so in the past is why he is so rich.)

And these are only the ones I can think of off hand.

As you can see, they all relate to one another.

During my final months at the school, we were to do our 'final project'. With in certain limits, of course, we were allowed to design to our heart's content.

One other conditon was that we were to write a brief summery on what the design was to be about along with a freehand sketch. I handed in a bunch of numbers that were mostly about the dimensions of my new boat. It was to be based on a famous American workboat called a 'cowhorn'. It was to be over 42ft long.

A day later, my summery was returned with what in effect said 'unacceptable' written on it. I couldn't figure what the old guy wanted, so I asked him.

My next summery was over three pages long. It started out with a simple purpose, to cross a great ocean. Then the 'conditions' multiplied like rabbits. The new boat I sketched was almost eight feet shorter than the original and slightly less than 60% its displacement. And it handily met all of my objectives.

That summery got a quick green light, along with a wink, from the old guy.

Let me suggest that you make up such a list. Make it as short as you can but as long as you have to. And put the things you care about the most at the top of the list. In the design process a lot of things on the list are often going to end up being abandoned, so its a good idea make sure those things are not the things you really want.

Just for the fun of it, why don't you post this list so everybody can compare it with the numbers you have already posted.

Good luck on your project.

Bob

[SAILFASTtigre]

Right Bob, thanks for your reply, there you go:

Island hoper, dismountable –avoid marina and insurance expenses, hurricanes-, fun –I mean fast-, but able to deal with 6-8 long swells –not steep-, 20-30 knots.

Trailerable, meaning after dismounting three cross beams –standard aluminum extrusions-. Three people needed. Can be shipped in specially purposed built crate and or 40’ container –perhaps mast has to be spliced.-

Fast, so light, -wood composite or foam but vinylester to keep it cheap- round sections at the sterns with lightly swept up buttocks, fine bow sections. Prindle, f-18, … shape but a little more conservative-for weight carrying, without creating under wing wave resistance. – weight/performance compromise - High cross beams, meaning not necessarily in the same plane as the deck, bit higher. Cutter rig with furlers –only profurl-, full batten main with lazy jacks and reefing system –harken style-, for easy single handling. Water proof vhf and chart plotter, for Safe Island hopping. Able to fly a hull upwind or reaching for performance, but only enough to clear the water, no risking it here, mainsheet in hand… meaning also one hull supports full displacement.

No living quarters. Only storage. Maybe a bunk without standing headroom and a small copkit with swept up deck for boat handling in bad weather. Open deck, trampoline, maybe a small deck part in center, between the two cross beams. At anchorage boom can be used as a support for tent or sun cover. Electric Autopilot –piston-, simple steering, beach cat style.

No crossing oceans here people…

No engine –maybe a small long leg outboard -, small battery bank for lights and instruments charged with solar panel or air marine wind generator.

Small flexible 2 water tanks –maybe connected, hand pump transfer for water ballast. Barbecue on stern, fishing poles racks and a small bikini in aluminum tube.

Dagger boards for upwind performance and kick up rudder for beach landing or unseen reefs, uppssssss.

Surfboard or windsurf rack somewhere.

$40,000 total construction cost max, loaded. That is a guess.

Payload, about half ton.

[oldsailor]

SORRY DAVID.

I don't want to rain on your parade, but you have just described the

Malcolm Tennant "Great Barrier Express". It's a bit like re-inventing the wheel.

Go to Google and enter Great Barrier Express and you will see what I mean.

I have the plans, patterns and photos of this design but have never got around to building it, and now AGE has got in the way.

Over the last twenty years it has proved to be the ideal Cat for fast cruising, racing and inter-island hopping.

Cheers. Oldsailor. :cool: :) :D

[SAILFASTtigre]

nice boat, I have seen before in multihulls magazine. There are many boats of this type, check the list at the end, cats 26-29. Includes the barrier reef. i personally like more the corneel 26 -see fotos in:

http://www.multisailing.com/imag/2387bCorneel%2026%20Love%20Sirenien/page_01.htm

or perhaps the firefly http://www.firebirdcat.com/


I would centarly like to have a look at those plans.


Boat LOA BOA SA Displ Design/Mfg
Heavenly Twins 26'00 13'09 340.00 6000.00 Heavenly Cruising
Jet 26 26'00 15'05 300.00 992.00 Halacre, Douglas
Leocat 26 26'00 19'00 420.00 1700.00 Kelsall, Derek
Max 26 Micro 26'00 16'00 430.00 1128.00 Spruit Performance
My-Cat 26'00 16'03 477.00 1322.00 Oudrup/Havkat/Micro-Boats,
Pahi 26TR 26'00 12'09 300.00 1200.00 Wharram, James
Scamper 26 26'00 14'03 300.00 1984.00 Prout Catamarans
Tiki 26TR 26'00 15'01 285.00 1400.00 Wharram, James
Tikiroa (Pahi 26)TR 26'00 12'09 300.00 1500.00 Wharram, James
Trail 26TR 26'00 n/a n/a n/a Kelsall, Derek
Tri-Star Cat 26 26'00 14'00 375.00 2800.00 Horstman, Edward
Week End 8 26'00 14'03 n/a n/a Multi Difusion
Week End 27 26'00 14'03 n/a n/a Bord'Ocean
X-Kat 26 26'00 16'04 409.00 3400.00 Kelsall Catamarans
Jeffcat 26 26'01 15'09 409.00 1322.00 Lerouge, Erik
Nova Cat 26 26'01 16'05 377.00 1323.00 Nova Cat
Zoum 80R Trailer Cat 26'01 14'09 334.00 2866.00 Novation Marine
Aquilon 800 26'02 14'09 n/a 1875.00 Staneck Marine
Campacat Sport 8 26'02 13'02 360.00 1800.00 Peter Brady & Assoc.
Clyde Cats Micro 26'02 20'03 470.00 3600.00 Shuttleworth, John
Dimanche 26'02 16'03 484.00 1545.00 Langevin, Sylvestre
Edel Cat 26TR 26'02 13'01 323.00 1102.00 Langevin/Edel Cat
Kat 26 26'02 12'00 363.00 3200.00 Kelsall, Derek
Andarin 26'03 16'05 388.00 1543.00 Vollmer, Alfred
Brady 08.0 26'03 14'00 322.00 3236.00 Peter Brady & Assoc.
Catman 26 26'03 17'00 506.00 1102.00 Lerouge, Erik
Catman 27 Micro 26'03 16'05 506.00 1323.00 Lerouge/Catman SA
Cheetah 26'03 20'00 470.00 1984.00 Clyde Cats
Clyde Cats Lynx 26'03 17'03 453.00 1764.00 Shuttleworth/Clyde Cats
Corneel 26 26'03 14'09 382.00 1543.00 Joubert-Nivelt/Fount. Pajot
Falcon Supercat 26 26'03 19'05 n/a 1060.00 Southwell, Phil
Firebird 26'03 17'03 338.00 1540.00 Smith, Martyn/Modular Moulding
Format 26 26'03 16'05 431.00 2000.00 Peter, J.
Format 26 t 26'03 16'05 431.00 2400.00 Peter, J.
Lavranos 26 Micro Cat 26'03 n/a 527.00 1433.00 Lavranos, Angelo
Micro 26'03 18'05 610.00 1400.00 Lerouge, Erik
Micro Class Daysailer 26'03 16'05 463.00 1213.00 Simonis, Alexander
Micro-Multihull 8m 26'03 19'06 515.00 1653.00 Shuttleworth, John
Multi Mar 26 26'03 17'00 411.00 2400.00 Callahan, Stephen
NixeTR 26'03 17'03 480.00 1800.00 Lerouge, Erik
Pair of Twins 26'03 16'05 452.00 1875.00 Veenema, Harm
Resonance 80 26'03 15'09 465.00 1102.00 Sass, Heinz-Jürgen
Shttlewrth 8m Cr.TR 26'03 n/a n/a n/a Shuttleworth, John
Shttlewrth 8m Rac.TR 26'03 n/a n/a n/a Shuttleworth, John
Shttlewrth 8m R/CTR 26'03 n/a n/a n/a Shuttleworth, John
Sirius 26 26'03 21'02 452.00 1720.00 Chantier Naval Force 3
Spyder Mk2 26'03 18'00 446.00 1100.00 Tennant, Malcolm
Spyder 26'08 16'05 199.00 946.00 Tennant, Malcolm
Backslash 26'09 15'09 499.00 2424.00 Simpson, Roger
Stiletto 27TR 26'10 13'10 336.00 1150.00 Higgins, Bill
Stiletto GTTR 26'10 13'10 352.00 1650.00 Wormwood, Peter
Black Cat 27'00 15'00 350.00 5500.00 Manners, E.
Catalac 8m 27'00 13'06 275.00 6283.00 Lack, Tom
Get 27 27'00 n/a n/a n/a La Griffe Marine
Heavenly Twins 27 27'00 13'09 390.00 6000.00 Heavenly Cruising
Sun Burner 27 27'00 13'06 385.00 3500.00 Harris, Robert
Tini 27TR 27'00 n/a n/a n/a Kelsall, Derek
Tri-Star 27CT 27'00 21'00 552.00 1500.00 Horstman, Edward
Tri-Star 27 PC 27'00 21'00 672.00 1900.00 Horstman, Edward
Catamaran 27 27'01 18'00 313.00 1100.00 Kurt Hughes Sailing Designs
Hughes 27 27'01 18'00 365.00 1100.00 Kurt Hughes Sailing Designs
Tri-Star Cat 27 27'01 14'08 375.00 2800.00 Horstman, Edward
Surfsong 27'02 17'01 377.00 3500.00 Woods Designs
Havkat 27 C/R 27'03 14'10 360.00 2600.00 Oudrup, Lars
Havkat 27 Racer 27'03 16'06 430.00 1540.00 Oudrup, Lars
Simpson 8.3m 27'03 16'02 336.00 5225.00 Simpson, Roger
Catlife 825 27'06 14'05 146.00 1433.00 Rifflart, Marc Louis
RC-27TR 27'06 16'00 450.00 800.00 Roberts, Bill
Mariposa 27'07 11'05 323.00 2425.00 Henriks-Catanautica
Kat 28 27'08 16'08 484.00 1432.00 KL Composites
Seawind 850 27'08 18'06 479.00 4800.00 Jutson, Scott/Seawind Catamarans
Seawind 850 Resort 27'08 18'06 479.00 4800.00 Seawind Catamarans
Viva 27 27'08 15'10 600.00 1750.00 Westerly/Houghtonob
Catfly 850 27'09 14'05 460.00 4189.00 Rifflart, Marc Louis
Great Barrier Expr. 27'09 16'05 410.00 2370.00 Tennant, Malcolm
Catman F-28 27'10 17'05 387.00 1499.00 Lerouge/Catman SA
Great Barr. Exp. MkIII 27'10 17'05 n/a 2374.00 Tennant/Pilkington
Kata 28 27'10 16'06 484.00 1389.00 Lucas, Paul
Diabolo 27'11 17'04 n/a n/a CN Force 3
Kat 28 Tonic 27'11 17'04 n/a n/a KL Composites
KL 28 Standard 27'11 16'07 411.00 1500.00 KL Nautique
Wildfire 27'11 n/a n/a n/a Tennant, Malcolm
Baron Noir F-28 28'00 n/a n/a n/a Lerouge, Erik
Cat 28 28'00 16'00 420.00 3500.00 Chris White Designs
Catfisher 28 28'00 13'06 380.00 7600.00 American Catamaranob
Crocodile F-28TR 28'00 17'07 689.00 1433.00 Nielsen, Niels
Crowther 28 #228 28'00 18'00 412.00 4500.00 Crowther, Lock†
Davey-y-Joan’s 28'00 14'00 400.00 4727.00 Crowther†/Calvert
Firefly 850 28'00 18'02 489.00 2756.00 Pescott, Mark
Fisher Cat 28 28'00 n/a n/a n/a JC Plaisance
Formula 28TR 28'00 19'08 750.00 1300.00 Lerouge, Erik
Formula 28 28'00 33'00 700.00 1350.00 Shuttleworth, John
IMD 28 Folding CatTR 28'00 14'00 593.00 2700.00 Int'l Marine Dev./Morrelli & Melvin
Myers Racer 28 28'00 16'00 400.00 1300.00 Myers, Hugo†
Myers Sprint 28 28'00 14'00 400.00 1200.00 Myers, Hugo†
Nimble 28.2 28'00 15'07 443.00 4299.00 M&M Boatbuilders
Shttle. Speed Mach.TR 28'00 n/a n/a n/a Shuttleworth, John
Sophisticat 28'00 15'00 360.00 8600.00 Cope, A.N.H.
Tiki 28 Coastal 28'00 16'03 330.00 3000.00 Wharram, James
Falke 8m 28'03 14'05 366.00 3527.00 Falke Katamarane
Lagoon 28'03 21'04 n/a n/a Certa
Resonance 86 28'03 16'09 538.00 n/a Sass, Heinz-Jürgen
Tanenui 28'03 12'06 310.00 2000.00 Wharram, James
Punch 8.50 28'04 16'00 n/a n/a Chantier Naval Force 3
Format 28 28'06 18'04 484.00 3200.00 Peter, J.
Design #127 28'10 17'00 380.00 3500.00 Chris White Designs
Shockwave 29 28'10 17'00 348.00 2500.00 Crowther, Lock†
Coral Coast 29'00 15'06 420.00 2646.00 Turner, Ross/Jarcat
Harrier 29'00 19'00 484.00 3500.00 Crowther†/Harrier
Harrier 8.8m 29'00 19'00 484.00 2500.00 Bosun Boats
Imp 29 29'00 n/a n/a n/a Bimini Catamarans
Warrior 29 29'00 16'00 456.00 2000.00 Bartolone/Conser
Windspeed 29 29'00 20'00 500.00 3500.00 Crowther, Lock†
Catalac 9m 29'03 13'09 420.00 8000.00 Lack, Tom
Stiletto 30 29'04 17'10 460.00 2100.00 Wormwood, Peter
Suncat 30 29'04 18'00 510.00 5300.00 Kelsall, Derek
Suncat Sport 30TR 29'04 18'00 510.00 4000.00 Kelsall, Derek
Akka 29'06 16'00 418.00 4000.00 Woods Designs

[DaveB]

Hi,

Neat problem... Looks like you're using Maxsurf... can you post the cad file so that we can see the shape of what you're describin'?

Cheers,

Dave

[Peter Renew]

Hi Sail Fast t

I'm confused about your LCB and LCF. I am taking these to mean lateral centre of Bouyancy & Floatation in which case -8.67in ft & -1ft 11.3in ft don't make much sense. Please could you clarify?

For a speedster without accomodation I would have thought a length to breadth ratio of 12 plus would be more desirable.

Also are you choosing vinylester over polyester for the longer curing and therefore laminating time?

[SAILFASTtigre]

being longitudinal, distance fron the center of the profile aftwards.

never heard of lateral centers of bouyancy, I guess if the hull is simetrical centers of bouyancy would be in the centerline. Only distance to calculate is longitudinal.

[SAILFASTtigre]

check this jpg.

[SAILFASTtigre]

I attached a couple of 3d renders and a iges file

Designers agree that the semicircular section -in the stern hafl side- is the best comprmise between volume displaced and wetted area, meaning buoyancy and speed.

To design a semicircular section using hull design software, you need to specify a three point surface, align at 90 and evenly spaced, with the weights set to one except the corner one, set to 0.7071. that would take care od the underwater semicircular section. Adding more points for the freeboard, hafly towards the deck, above waterline sections, would inflect a change in the semicircular underwater section, so my question goes, is there any other way to set the points so that you would need only one surface for the hull, or do we need to split into two surfaces and then bond them, to maintain semicircular section under water and flat or convex half way in the higher freeboard?

On the other hand, small cats are very wet, and, spcecially reaching and surfing waves, they tend to pithpole, -if you ever sailed a hobbie 16 you know what i mean, -the banana shape did not help-. I wanted to introduce certain convexity and the upper sections of the bow freeboard, to reflect water when sailing and to gain bouyancy when things start getting ugly.

My catana does this very well, with its bolbous bows ans convex upper bow sections. i have surfed -reaching to get speed, down the next wave to take advantage of the negative slope and the inertia- reaching 20.4 knots -gps- and the bow goes to the limit, but not beyond. Could this feature be incorporated into a smaller symetrical design? --catanas' are asymetric-.

best regards to all,

david

[oldsailor]

NICE LINES DAVID.

I think for the nasty short wave formations which I remember in sailing around the West Indies the forward sections look too fine. To prevent a very wet boat, and to reduce the possibility of pitchpoling you need more flare in the bow, or a bulb at the bottom of the stem-----or both.

Just my opinion from sailing lots of Cats in the 23' to 52' sizes.

Cheers. Oldsailor. :cool: :) :D

[SAILFASTtigre]

That is why I was wondering about the LONGITUDINAL CENTER OF BOUYANCY, my first question, widening the bow sections will move the cente of bouyancy forward, and the center of gravity has to be aligned with this LCB for the boat to sit trim.

LCG longitudinal center of gravity is calculated by measuring distances from a center point and weights of every component to find the center of the weight of the whole thing, including the hull and deck, and in these case crew, since it is big percentage of its displacement. that is why more time is spent in front of the spreadsheet calculating numbers than in front of the modeling software giving a shape to this numbers. You design around numeric parameters.

Does anybody know an average for LCG in cats these type 26-28 -in % of LWL-? What about waterplane numbers?

here are the hydrostatics of the above lines -one hull-, which are modified from the first ones:

Displacement 1.13 tonne
Volume 38.82 ft^3
Draft to Baseline 1ft 4.99in ft
Immersed depth 1ft 5.85in ft
Lwl 27ft ft
Beam wl 2ft 6.23in ft
WSA 85.84 ft^2
Max cross sect area 2.27 ft^2
Waterplane area 50 ft^2
Cp 0.633
Cb 0.384
Cm 0.705
Cwp 0.735
LCB from zero pt -2.16in ft
LCF from zero pt -2ft 0.12in ft
Immersion (TPi) 0.121 tonne/in

[oldsailor]

Quote:- That is why I was wondering about the LONGITUDINAL CENTER OF BOUYANCY, my first question, widening the bow sections will move the cente of bouyancy forward, and the center of gravity has to be aligned with this LCB for the boat to sit trim. Quote.

I wouldn't worry to much about the exactness of the CG, as it moves around by quite a considerable amount on a boat as small as this.

More important is the Centre of Bouyancy. You should design this so that from the lightest displacement to the displacement of the boat loaded to its max designed waterline, ---the Centre of bouyancy varies very little. If it does vary a bit it's not too important so long as the varience is more forward. This is paticularly important in a Catamaran since it relies on the lee bow for stability in gusty or knockdown conditions.

Cheers. Oldsailor. :cool: :) :D

[SAILFASTtigre]

I don't thing the lbc would vary from light to full displacement.

it does vary in monohulls as they heel, due to their shape.

regards

[fhrussell]

Any forward motion on your project? I am gearing up for a build of a 30' cat of my own design and have been reading this thread with interest.
Thanks,
Frank

[oldsailor]

All THE BEST FOR THE NEW YEAR to all who are reading this thread.

I had a Crowther International 23 catamaran. It had four single berths, a toilet and galley. Thats all. It was a very fast cat and a delight to sail. I only had it for a year and sold it when I moved interstate. It was called "Silent Runner" and now resides at the Hindmarsh Yacht Club in SA. Australia. It was fully trailerable with the hulls sliding inwards on the oval section crossbeams.
This limited it's overall beam.

Once I moved to Sydney I sailed on a Seawind 24, which was of greater beam and de-mounted by removing the crossbeams for trailering. It carried the rounded hull sections right up into the bows for greater driving power and was(and probably still is) the fastest small cruising Cat I have ever sailed on. One character even sailed one around Australia. No mean feat.

I still like the Great Barrier Express 28 best of all though. I recently saw one on the beach near my home, owned by a young man who is living aboard and cruising the East coast of Australia.

Cheers. Patrick. :cool: :) :D

[Zoro]

Living on a GBE... WOW! Thats minimalist!

I would like to build a Tennant Wildfire (GBE for the 21st Century!) but alas I have to work on the budget first.

[oldsailor]

GENERAL opinion among the worlds best multihull designers is that the Tornado hull design is to this day still the best one for any fast lightweight catamaran.

Therefore ---I suggest you get hold if a set of Tornado lines, blow them up 140%, increase the Boa to 16" and add a sailplan to suit the sort of sailing you envision.

Cheers. Patrick. :cool: :) :D

[Figgy]

I know this an old thread but I have a few questions.
1.Wont blowing up the lines give you a funny hull shape(beyond increasing the boa)?
2. Shouldnt the sail plan increase 140% also? If not why?
I've been considering designing a 30 catamaran, just for speed. Something between an a-class and the cat Afterburner.
Also, I'm trying to do this in Freeship. How do you get two hulls into the program? I'm still new to it, thanks for the help!

[oldsailor]

As you increase the dimensions of a design the stability increases dramatically. You can use a bigger rig as the righting moment increases faster than the increase in the overturning moment.

I suggest that you take a look at Malcolm Tennants web site and see what sort of sail areas he uses for his cruising VS racing rigs. http://www.tennantdesign.co.nz

Cheers. Oldsailor. :cool: :) :D

[Figgy]

Allright, I really think that idea might work. I have the Tornado plans, I just need a place to build it. (I'm moving to Maine soon) Would I be taken seriously tho' if I showed up at the marina with a 30' Tornado? I'm thinking between an Extreme 40 and an A-class. Right in the middle. No frills, and fast as hell!

[oldsailor]

SOUNDs Good Figgy.


Cheers. Oldsailor. :cool: :) :D

[fhrussell]

Figgy,
Blowing up the lines of the Tornado hulls shouldn't be an issue, but you should study the rig dimensions carefully. Depending on your displacement, your sail area should be considered.
The 40' CSK catamaran, Machete, borrowed heavily from the Tornado design and was even built with tortured-ply. I believe she's in a yard in Laguna if you have a chance to see her.
If you are looking for more info on a 30' cat and design scantlings, you can contact me at fhrussell@yahoo.com. When are you moving to Maine?
Best,
Frank

[Pilgrim]

...then it should work well for you!

The all-conquering 'Formula TAG' (later, ENZA, etc, etc) was allegedly described by the eminent Mr Irens as being an 'enlarged' Tornado, conceptually. Stretched later on, too.

Of course, it all depends on the intended use, but from what you say this might suit you well, just make sure that square-cube effects do not work against you as you scale up! Weight is the enemy, and for a one-off design a plywood composite is still one of the best approaches - wood is tough. An epoxy-glass skin saves the wood from water and weather, and is very low maintenance. Polyester or vinylester resin works OK if the budget is tight, but the gelcoat needs to be applied just right.

FWIW our cat is a Wharram Tiki 30, which is (almost) relevant to the thread since our WLL is 25 ft, and we displace around 2 Tons fully laden for cruising. Empty weight well under 1 ton, so the payload ratio is excellent - this is one of the benefits of a modern well-rounded deep Vee, with a knuckle above the waterline.

Other benefits include an excellent high speed ride - just gets better and better as you go past 15 knots - ask the offshore powerboats. When beaching, the vee takes the ground just fine - we have over a foot of structure between the sacrificial strip on the keel and the floor of the hull. So we have parked on reefs with impunity, so long as they are reasonably level. Berths for six, deep water cruising for three with a watermaker, since payload is the limitation when crossing oceans.

Vee-like hulls tend to triangular structural sections, which may explain why our home built 30 ft cruiser weighs almost the same as the (claimed) weight of a professionally built 'carbon composite' CoolCat at 26ft. Triangulation improves stiffness of a structure and that can allow the structure to be lighter.

The downside? Wetted surface is greater on a vee, this penalises you in light airs if you do not carry a reacher set flying.
We do.... and it's a *monster* on an 18 ft prod :D

Prod is also handy for lowering/raising the mast one-handed.

Lateral plane provision can be a pain.... Twin daggerboards do the job well, but a word of caution if you plan to spend time afloat - the daggerboards and cases seem to attract marine life, and I have seen a few stuck boards being prised out with ominous crunching sounds. One needed a power saw to cut it free. Big rebuild.

The JWD daggerboard case is perfect - it is a vee box, with only the bottom slot a tight fit on the board, and that usually has neoprene or similar flaps to improve the sealing. A light removable frame holds the top of the board so you can reach in and clean the slot when the board is out. You'll need to one day.

Central boards hung from the beam structure can ventilate air if great care is not taken to reduce the local lift coefficient near the surface, add fences, etc, etc. Hard to brace tidily too, but one board is lighter than two, and none is lightest:p

Round bilge hulls cannot be left on a drying mooring in some places, since the flat hull can sit on a sharp stone a day too long, and you can come back to find your boat awash. Seen a couple of Woods cats go that way on the Millbrook mud, very sad.

Rig?
For top performance to a price you cannot beat the Tiki Wingsail, imho.

The windsurfer style wraparound luff causes the mast to 'disappear' inside the aerodynamic envelope of the sail (like a 747 spar) so the mast can be cylindrical for strength (and cheapness). It can also be fatter for no drag penalty, since it is inside the sail. This means it can be stiff enough (especially with a foot or two of mast bury at the foot) to not need more than two shrouds and a forestay. Again, less drag. An aluminium flagpole supplier should be able to help you.... ;)

Our 34 ft mast is around 6" diameter and 1/10" thick marine aluminium.

Best if both ends of the mast are doubled in thickness for two or three feet - this is done by using some extra mast tube, slitting it lengthwise, closing the slit, reshaping and ramming the thing into the mast tube with some epoxy, then riveting it. 1965 monocoque F1 car technology....

The Tiki main is 4-sided, with a 'big batten' so that you can go square top (or even leave the top panel out for vortex lift like some of the windsurfers). OK, you might call the 'big batten' a gaff if you liked, but it surely works!

Result is a boomless rig that can be reefed going downwind (big sleeve luff and weight of big batten bring it down like trousers on a broomstick) and will point remarkably well, since it has a self-aligning wingmast, in effect.

We have put 90 degree tacks on the GPS plot when footing at 7 knots in a 10 knot breeze. Stunning for a deep vee cat that draws 2 feet and will carry a family around the world. Then bear away a bit and see 11 knots!

You may not want vee hulls for your needs, but you would love a Tiki rig, I am sure.

I'm ranting on again.....:rolleyes:

All the best, Ben

(Tiki 30 'Pilgrim' - Lanzarote de Canarias)