design of a fast 27 catamaran

Discussion in 'Multihulls' started by SAILFASTtigre, Apr 18, 2005.

  1. SAILFASTtigre
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    SAILFASTtigre Junior Member

    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,

    Last edited: Apr 21, 2005
  2. oldsailor
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    oldsailor Junior Member

    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
  3. SAILFASTtigre
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    SAILFASTtigre Junior Member


    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?


  4. oldsailor
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    oldsailor Junior Member


    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
  5. sharpii2
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    sharpii2 Senior Member

    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.

  6. SAILFASTtigre
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    SAILFASTtigre Junior Member

    design objectives 27' cat

    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.
  7. oldsailor
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    oldsailor Junior Member


    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
  8. SAILFASTtigre
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    SAILFASTtigre Junior Member

    great barrier express

    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:

    or perhaps the firefly

    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
  9. DaveB
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    DaveB Senior Member

    cad file


    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'?


  10. Peter Renew
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    Peter Renew New Member

    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?
  11. SAILFASTtigre
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    SAILFASTtigre Junior Member

    lcb and lcf

    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.
  12. SAILFASTtigre
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    SAILFASTtigre Junior Member

    cat corneel 26

    check this jpg.

    Attached Files:

  13. SAILFASTtigre
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    SAILFASTtigre Junior Member

    jpg and igs files cat 27

    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,


    Attached Files:

  14. oldsailor
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    oldsailor Junior Member


    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

  15. SAILFASTtigre
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    SAILFASTtigre Junior Member

    new hydrostatics cat 27 -for one hull-

    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
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