To see my blog about building this catamaran, click here: Home Building the BigCat 65 Blog
This design has been thoroughly inspected by the engineers of the United States Coast Guard's Marine Safety Office in Washington D.C., in an exhaustive 10 month review process, and they have approved the design, scantlings, construction, rig, and equipment to carry up to 149 passengers.
Dimensions: 64'6" LOD, 62'9" DWL, BOA 35'6" BWL of each hull 5'2", BMax per hull 7' 6", Draft in cruising trim, 3'9", Freeboard 7'6" in cruising trim, Cruising displacement, 45,000 pounds
Design statistics: Prismatic coefficient of .65. LCB 36.25, LCF 35.9, PPI per hull 1345# (multiply x 2 for the total PPI,) hull draft 1'2" at 45,000 displacement, Footprint weight 19.5 pounds per sq. ft. (This is the displacement divided by the footprint, or the overall length x the overall beam-The Gunboat 66 has a disp. / footprint of 21, and standard cruising catamarans are about 26,) DWL/BWL of hulls, 12.125. Bruce Number @ 45,000# 1.38, Air draft 70', Sail Area to Disp. ratio 30.35 (at 45,000 disp.,) Displacement to Length ratio 78.5 in cruising trim with full tanks, 61 lightship, and the Bill Roberts' K Factor of 3.3 which is governed by the DWL to BWL ratio, predicts a maximum speed of 26 to 26.5 knots. (Note: Where displacement is not specified, I am using the displacement in cruising trim for all calculations, with the vessel's very large tanks full. For lightship, subtract about 10,000 pounds, and for half-loaded, subtract 5,000 pounds. Unfortunately, most builders and designers don't tell the reader which displacement they are using. When in doubt, I assume lightship.)
Design Comparison: Compared to a Privilege 585, this design has about the same amount of cabin space. Restricting the interior to that of a smaller boat gives this the BigCat 65 a much greater speed potential. The Privilege 585 weighs about the same as a BigCat 65, but because it is shorter, it has a D/L of 117, if you add 5,000 pounds to its lightship displacement to give an idea of its cruising displacement. The BigCat 65 has a fully-loaded D/L ratio of 78, which is much lighter. The Privilege 585 looks to have a hull waterline beam of a little over 6', which gives it a L/B of 9 or so, compared to the BigCat 65's hull L/B of 12. The BigCat 65 has about 12% more sail area than the Privilege 585, even if you use the Privilege 585's gennoa when attributing its sail area. So clearly, the BigCat 65 is a much faster design, at perhaps 1/5 the cost. The Privilege 585 has expanses of varnished wood, which is very pretty, but then it costs about $1.5 million. If a boat is going to cost you 500% more, you should get something for your additional expense!
Design Features: The "V" section is carried right aft, insuring that the hulls will not slap even if anchored in an open roadstead. The transoms are well tucked up and the buttock lines exit at a very low angle, guaranteeing speed under sail. The bows are narrow at the waterline, have no bow overhang, and yet have a lot of reserve buoyancy to prevent burying the lee bow, because the deck is much wider at the bow than it is at the waterline. This feature is called flam, though it is often mis-called flare. Flam is a positive outward curve in a section, however, and flare is negative or reverse outward curvature in a section.
The BigCat 65 has many (10 in the hulls,) watertight compartments, greater privacy for the cabins, full engine rooms with shaft drives rather than saildrives, and no more weight for a given set of materials. Additional benefits are simpler construction and no berth "shelves" to make noise and slow the boat.
(Read Charles Kanter's critique of shelves at Elusive Cruising Catamaran Performance )
This boat should move right along, as it has a long waterline, narrow hulls, light displacement, and a large sail area. The rig is low and easily handled, so there is no struggle or anxiety involved in getting the best out of its performance potential. The vessel has a high bridge deck with over 3 1/2' clearance in cruising trim. Even overloaded to 70,000 pounds of displacement, there is a 3' bridge deck clearance.
The sterns are designed to have low resistance even if the vessel is drastically overloaded, and if overloaded, the hull beam and length keep the 12 to 1 ratio as the beam and waterline length increase proportionally. The low 1'2" hull draft (at 45,000 displacement) makes a shoal draft possible, while still giving good lateral resistance due to the ample keels and skegs. This low hull depth is possible because the high-tech materials and construction, long length, and the relatively modest accommodations for a vessel of this size add up to a very light boat which displaces little water for its length.
This interior plan offers complete privacy, with 4 double cabins each of which has its own head and shower, and each of which is accessed from on deck rather than through a companionway. The engines are ensconced in their own spacious engine rooms, where their noise and fumes are isolated. There are 2 fore peaks with a single berth each, which could also have heads fitted for the use of a crew, bringing the sleeping accommodations up to 10 persons.
The use of beams to connect the hulls rather than bulkheads and cabin top gives the builder tremendous flexibility in customizing the bridge deck. In fact, if the builder wished, the cabin on the bridge deck may be omitted, and the helm station may be placed between the connector beams rather than above the aft connector beam. This would reduce the windage, improving windward performance. One option for the interior in this configuration would be to turn one cabin into a dinette and galley, or if a larger galley and dinette were desired, two cabins could be used for the galley and dining area. The bridge deck could then be covered with a tarp cover to provide shade for the 'tween beams area when in port. An open seating and dining area placed here would be quite nice in the tropics.
Flush Deck Version Another layout places two cabins with double berths on the bridge deck. In this configuration, you have 6 cabins with queen size berths and private heads with private showers. You still have two private single cabins with this layout, and so the boat sleeps 14 - 16, if you put bunk beds above the berths in the bridge deck cabins. In this layout, you also have a double dinette that seats 16 and a spacious galley, all on the bridgedeck. What a great layout for charter, sailing expeditions, or a sailing school! SOLAS exempts vessels that carry 12 passengers or less on international voyages, so this design escapes SOLAS requirements-leaving you with a crew of 4, that is, a skipper, two deck hands, and a cook, in addition to your 10 to 12 passengers.
8 Cabin Expedition / charter version There are 10 watertight compartments in the hulls, (5 per hull,) and full polyurethane foam floatation in the bridgedeck greatly exceeding the cruising displacement. The boat is designed to float high out of the water even if completely holed or upside down. The helm station can be either fully sheltered or very well ventilated, at the helmsman's preference of the moment. There is excellent all around visibility from the helm. Kobelt hydraulic steering is specified.
Rig: Easily reefed and furled fully-battened WingSail rig. Unstayed masts with no potential failures due to stainless stress or corrosion fatigue. Maximum and working sail area 2400 sq. ft. The biplane rig is completely self-tacking and requires no sheet winches, despite its large sail area, due to its balanced design and 7 to 1 sheet purchase. Because the sail can be made as separate panels, which may be attached to the battens rather than each other, and because it has no camber cut in it, the camber coming from the hinging battens, no sailmaker is needed. Yet another benefit of giving the rig its camber using batten hinges is that the sail draft is not affected by mast bend-which has been a problem in efforts to combine marconi style sails with unstayed masts.
Using this rig should save over $100,000 USD compared to a marconi rig, which isn't a lot compared to purchasing a large catamaran retail, but it is a huge amount of money to the home builder. This rig saves the builder 25% to 33% of the cost of building the boat.
The rig shown uses a wing sail, in which the sail camber is provided by a hinge at the point where the wing or fairing part of the batten assembly joins the straight portion. This version hides the mast inside the sail, so as to streamline the rig, creating an effect similar to a pivoting wing shaped mast. This is similar to the Swing-Wing rig, except that the fairing portion is an aerodynamic foil shape, which the Swing-Wing rig does not use. I have used the Clark Y foil, as that was recommended in an article by aerodynamic scientist and multihull sailor, Tom Speer. (See the links at the foot of the page for links to Tom's article, and to see PHA, with its now modified Swing-Wing tandem rig.) This rig is as weatherly as a fixed keel catamaran can take advantage of, and the use of the biplane layout means that the sails will not back wind each other when running downwind. On a beam reach, the windward sail is slacked more than a marconi mainsail, the lee sail is hardened in more than a marconi mainsail, and they form, in effect, a single airfoil when seen in overview. This rig is capable of tacking through at least 90 degrees, and cruising catamarans are rarely capable of that, with tacking through 100 degrees being more common.
Engines: John Deere 6068SFM50 engines are shown. If this engine were tuned to its lowest rpm rating for maximum longevity (M1,) it would produce 182 hp flat out, and burn 9.62 gph. The Deere 6 cylinder (M1) engines would give a top speed of 17.8 knots at 45,000 pounds of (cruising) displacement at the M1 rating, and 14.3 knots at 70,000 pounds of (overloaded) displacement. These engines would be suitable for either commercial use or for a 100% / 100% motorsailer designation.
Running just one engine, the boat could cruise at up to 12.5 knots at 45,000 pounds of displacement, while burning 9.62 gph. To take this to an extreme, one of these engines run at 1000 rpm would push the boat at 4+ knots, giving it a range of 1660 miles, if loaded to a displacement of 45,000 pounds. Running one engine at 1000 rpm while motorsailing to windward would make various difficult windward passages much easier, such as Hawaii to Tahiti, Florida to Puerto Rico, or Panama to Jamaica.
ZF 85a transmissions would be suitable. The engines drive 1 3/4" ss. shafts with traditional bronze stuffing boxes fitted with GFO packing, 24" diameter props located in front of balanced rudders which are fully protected by skegs and rudder mounting struts. Racor 500MA fuel filters with bronze seacocks and cooling water filters, and fiberglass lift mufflers situated so as to be unable to flood engines under any circumstances. There are 440 gallons of diesel tankage under the cabin soles. Extra tankage could be provided under the berths on either side of the midships bulkhead, if more fuel or water than the already generous tankage provided were desired.
Smaller engines may, of course, be fitted. Planning for large engines insures that the vessel will have room for smaller engines and smaller propellers and that the weights on board will balance well with smaller engines. 2-80 to 100 horsepower diesel engines (such as Yanmar 4JH3-HTE engines,) for example, would push the boat at a maximum of 9.3 knots, if run at 2/3 of their rated horsepower with the vessel loaded to a displacement of 45,000 pounds.
Deere 4045TFM-135 hp.(M3) 4 cylinder engines run at 2/3 of their rated speed (106 hp. each,) would push the boat at up to 10.8 knots, if the boat were overloaded to 68,000 pounds of displacement, and at up to 13.5 knots, at 45,000 of displacement. The Deere engines would between them use 5.2 gallons per hour at 1800 rpm, though they can use up to almost 8 GPH each run flat out. Running one Deere engine only at 1800 rpm. (a common practice on catamarans,) would push the vessel at up to 9.5 knots at 45,000 displacement, burn 2.55 GPH, and give a range of about 1500 miles.
These engines are said to be good for 20,000 hours, and were Steve Dashew's choice for his new powerboat, Wind Horse. I think the Deere 4 cylinder engines would be my personal choice. With these Deere engines, ZF 63A 2.05 to 1 transmissions would give the boat 23" diameter propellers. Luke feathering propellers would be a good choice for the props.
Design type: Radius chine design. A radius chine design is a hard chine design where the chine has been replaced with a semicircle to soften the turn of the bilge. This design has a 2' diameter at the turn of the bilges in all sections intersecting with the chine. Despite the large 2' radius, only 2% of the displacement has been removed from the chine version by softening the turn of the bilges. The diagonal measurement of this radiused area is about one foot.
The hull and deck scantlings were designed to ABS Offshore Yacht rules, and the crossbeams to Lloyd's. Hull plans available as DXF files, complete equipment list, electrical, and plumbing plans available, all plans and details compliant with CFR 46. Hulls designed for easy DIY construction.
Materials: Vacuum infused composites using Vectorply quadra-axial e-glass, Hexion flame-resistant vinylester, and 1-1/4" Baltek pre-coated balsa above the waterline, and 1" balsa in the decks. There is only solid laminate below 12" above cruising DWL, and 6" above an overloaded 70,000 pounds of displacement. Connector beams, masts, and battens are made with Vectorply carbon fiber, Vectorply bi-axial e-glass, and Hexion vinylester.
About 90% of the boat's structure is cored, and the cored panel layup weighs about 2.1 pounds per square foot for the decks and 2.6 pounds per square foot for the topsides. The solid bottom laminate weighs 4.5 pounds per square foot, only 20% more than its cored equivalent. The bulkheads weigh about 1.6 pounds per square foot, and the furniture weighs about 1.4 pounds per square foot. The wall thickness of the connector beams is about 1" of solid fiberglass, mostly unidirectional laid lengthwise, and it weighs a whopping 8.25 pounds per square foot.
The beams are rather heavy, but there is a huge benefit to the home builder in using beams for constructing the boat. Since you don't assemble the boat until you reach the launch site, you don't need a huge shop to build it, and it is easy to transport the pieces of the boat separately. No piece to be transported needs to be wider than 7.5' wide, whereas boats built using the deck house for the connection of the hulls have to assemble the boat at the shop and move it as a whole. Just imagine trying to truck a boat 35.5 feet wide from your back yard to the launch site!
The use of vinylester resin makes the hulls blister-proof, while giving almost the strength of epoxy resin without epoxy's high cost and working toxicity. There is no glass mat in the construction. Gregor Tarjan, author of "Catamarans, Every Sailor's Guide," rates epoxy at a 10 for strength, and vinylester at 9.7 (97% as strong.) With a tensile strength of 12,000 psi and an elongation of 4%, the vinylester resin specified, Hexion 755-8590, is actually stronger than epoxy resins usually used in boat building, and almost as elastic. This resin develops full strength at room temperature (no heated post-cure required,) fits the USCG criteria for fire retardancy, and can be thinned with 5% styrene to give it a very low viscosity (150Cps) for resin infusion. CoRezyn 8440 is a similar resin from another vendor that could also be used.
The use of balsa instead of foam prevents sun softening of the decks in the tropics, makes a stronger and lighter hull, and is less costly and more fire resistant than foam. The balsa is kept well above the waterline and well away from the deck edges, insuring that there will be few places where the builders need to protect the balsa core from penetrations. Lifeline bases and sampson posts, for example, are located in areas with no coring.
Construction method: Flat vacuum-bag infused panels are made on a melamine-surfaced laminating table. All panels except for the narrow hull bottom panels are made with balsa core. Hull panels are assembled on cradle with no mold required. No fairing or filling required except a minor amount at the chine radii, and at panel joins. All panels are made full-length, and so have a natural tendency to be very fair, as well as requiring few joins.
Detail of panel joints of hullsSince the hulls get their shape from the cradle, the cradle is essentially a negative of the chine shape, with cradle members at each section, so there are 10 cradle frames. There is no mold, however, except a small radiused area about 6" above and 6" below the chine. It is easy to make the cradle / mold, as each section is defined by only 3 points-the deck - topsides intersection, the chine, and the keel bottom. Once you have marked these three points, you simply draw 2 straight lines connecting them, and cut two pieces of plywood simultaneously. You flip one piece of plywood over, and you have a full section marked in plywood. Screw in some 2 x 4 stiffeners, and you have a section. When you have the sections cut out and attached together, you position them plumb, square, and level, attach them to each other with 2 x 4s, and you have a form fitting cradle / mold. No lofting is required.
Easy method for making radius at chines: Radii at the chines made by attaching sheet material to the cradle at the chines, filling the chine area with Bondo, plaster with glass fibers, or similar, and scraping out the excess filler with a section of a 2' diameter circle cut in plywood while the Bondo or other filler is still wet. This forms an easily made mold for the radius, and makes the hulls easy for amateurs or professionals to make. The radii of joins between the topside and hull bottom panels are the only place where anything resembling a mold is used during the hulls' construction. The same method is used at the join of the deck and hull topsides, to provide a 3" radius. Note that the chine-radius filler is part of the cradle, not part of the boat, so it doesn't add to the weight of the boat.
Easy method for making composite masts: This simple mold-forming technique can also be used at the deck edge, and at any corner or edge to be given a radius. It can even be used to make a form for the masts, by making a mast-length plywood or OSB box and filling the box with reinforced plaster, Bondo, etc., and scraping out the excess while still wet. One may make an accurate taper by placing "bulkheads" at intervals in the box with the desired semi-circle at each point being cut in the bulkheads. Attach strips to form an overlap on one mast half per mast, and bond the halves with Plexus cyanoacrylate structural adhesive. This will give a circular mast section when finished.
The Robert's K factor of 4.3 or so gives this boat a theoretical maximum speed of about 35 knots! How skinny is a 16:1 hull DWL/BWL ratio? It is the same ratio as 'Stars and Stripes,' the catamaran used to beat the Kiwi monster in the America's Cup a few years ago. The 'Stars and Stripes' was basically a giant high-priced beach cat. That's skinny.
The wing fairing is mounted on a fixed unstayed round mast inside the fairing. (This rig can also be used on the original BigCat 65 without alteration, as its location, sail area, mast height and diameter, and location of the center of the sails is all the same as in the wingsail rig.)One caveat about solid wing fairings-They need to be able to freely align with the wind for safety, in storms or when moored. My plan is to cut the fairing into two portions, which can be detached from each other-one above the furled sail bundle, and one onto which the sail bundle stacks, and to which the boom is attached. These are to be uncoupled from each other when moored or when running in storms, so that the boat isn't overpressed by lift from the wing fairing. The lower portion would then be aligned fore and aft, with the boom and sail bundle safely secured, and the majority of the fairing would be free to align with the wind.
Or, for those seeking something a little more traditional that still offers 4 private cabins, easy construction, and easy handling--
This monohull has 4 double berth private cabins, a dinette that seats 8, 2 heads, one with a shower, inside steering, a chart table, a "garage" for a single and a double sit-on-top kayaks, and the pilot house has excellent visibility for the cook, the helmsman, all 8 people sitting at the dinette, and the navigator. The compromises are that the navigator has to stand if he is using the navigation station, and the cockpit is only 6' long.
It has a junk schooner rig of the modern, weatherly, cambered sail type and a long 64' waterline. This long waterline gives it a hull speed of 10.8 knots, if it is calculated at 1.35 x the square root of the waterline. The DWL is only 15' wide, so it has an easily driven hull with a beam to width ratio at the waterline of over 4. It is very stiff, however, as it picks up bearing rapidly as it heels, due to the immersion of the chine. Despite the fine bow and stern, it has a shallow buttock exit line (an easy run, it is sometimes called,) for a good turn of speed and minimal fuss in the wake.
The design statistics for this monohull design are: LOD 64', DWL, 64', Beam Max 16 1/2', Disp. 61,000 lbs., Draft 6' 1.5", Ballast 24,000 lbs, Ballast/Disp ratio 39%, Square root of DWL 8, SA/Disp 21.79, (if you use 80% of the sail area to figure this, as this is the maximum possible sail area, the SA/Disp ratio is 17.44,) LCB 53%, LCF 54.5%, PC .57, CE Height 33.75', VCG 2" below the DWL, Hull form righting moment at 30 degrees of heel (does NOT include ballast effect,) 211,553 lbs.
This boat would be great for high-latitude expeditions or for sail training. Alternatively, you could put a sizable family on board, with privacy for a couple and 3 kids. It could easily be adapted for radius chine construction if a "yachtier" look were desired. If desired, some of the cabins could be configured for other purposes, such as use as an office, or as a full bath with bath tub.
To purchase plans or kits, E-Mail Tim Dunn at:
dunnanddunn@gmail.com
Resin infusion links: See Tim's resin infusion links on the Yahoo resin infusion group Tim started.
Tom Speer's aerodynamic paper on wing masts and sails
Junk rig skeptics should know that this rig is not just a theoretical concept for me, as I sailed a 34' junk schooner whose rig was designed by Blondie Hasler, Batwing, from Seattle to: the Marquesas Islands, the Society Islands, Samoa, Tonga, New Zealand, Fiji, Tuvalu, Kiribati, Guam, the Caroline Islands, Papua New Guinea, Palau, the Philippines, and Hong Kong. Skeptics should also know that Batwing, displacing 18,000 pounds and having 770 sq. ft. of sail area, normally operated under sail rather than under its small 20 hp. motor and 2 bladed propeller, and that she tacked through many a strait and channel against headwinds.
Arne Kverneland's article on putting camber in the junk rig to make it more weatherly. He is a pioneer in this area.
Cruising World Article
Steel Silhouettes A webstore selling cut metal art, crafts, gifts, and lighting fixtures with Pacific Northwest Indian and wildlife designs by Tim Dunn
(A Footnote on Catamaran Stability:) The theoretical stability of a catamaran is given in the formula, displacement in pounds x the distance between the centerline of the two hulls in feet x .5 = righting moment in foot pounds.
To use my BigCat 65 design as an example, 45,000 x 28 x .5 =630,000 foot pounds (that is, a lever of an amount of feet times an amount of force in pounds.)
If considering a capsize from wind force, the theoretical heeling force is the wind pressure x the sail area x the CE (the height from the waterline to the center of your sail area.)
Wind pressure can be calculated from Martin's formula, which is windspeed in miles per hour squared x .004= pounds per square foot.
So, the heeling (capsize) force for BigCat 65 that generates a theoretical force sufficient to capsize it is: 9.21 pounds x 2400 sq. ft. of sail area x 41 feet (center of sail area above waterline) =630,000 foot pounds. This wind pressure is found at 48 miles per hour, which = 41.7 knots.
(One knot equals 1.15155 miles per hour, so divide the mph by 1.15155 to get the knot equivalent to the result of Martin's formula.)
So, in flat water, theory predicts the BigCat 65 will capsize at 41.7 knots in calm water if the sails are up and unreefed. This theory applies rather poorly to a biplane rig, which the BigCat 65 design has, because you can't get the full effect of the wind abeam if both sails are up, but it works pretty well for a typical catamaran with a single mast.
Obviously, this is all very theoretical, because a capsize is unlikely to occur in calm water, sails are rarely strapped hard amidships in high winds, etc., but it does give one a starting point for considering the forces at work. It does help explain how charter catamarans have capsized by coming out from the lee of islands in strong trade winds with the full mainsail sheeted amidships while under motor, when you consider that gusts are often equal to half again the average wind speed, and that winds will often increase as they funnel through channels between islands, or through gaps in cliffs to windward.
_) _) _) _) _) _) _) _) _) _) _) _) _) _) _) _) _) _)
Ma kela 'ao'ao moana holomoku awiwi,
Ho'omaika'i e Kanaloa a me Kane!
-A prayer to the God of the Sea, and the God of Canoe makers; "Sail swiftly across the sea, blessed by Kanaloa and Kane!
I support the Tibetan people in their struggle for religious freedom and human rights
Unstayed Masts Links
NA Sponberg on unstayed masts, wing masts, and the elliptical planform sail profile
Tandem (Bi-plane) rigged catamaran links
http://marine.bdg.com.au/
http://www.schionningdesigns.com.au/www/page.cfm?pageID=271
http://www.sailcoolchange.co.nz/
http://www.parlier.org/hydraplaneur/actualites/superbreve.php?lang=fr&id=16
http://www.cat2fold.com/
www.flyingcarpet.co.nz/about.html/
www.jasmine.org.uk/~simon/boats/slippery/slippery_0_4.html
www.scrumble.com.au/a-different-sailing-rig-for-scrumble/
outside.away.com/outside/magazine/200011/200011sailing7.html
Windmek wingsail
Omer wingsail
Wingsails.com
Windjet wingsails
Wingsailor.com
rcsailing.net wingsails
Wingsails
Boatdesign.net wingsails
A go fast machine with a rigid wingsail in Oz
Discussion on BoatDesign.Net
http://www.duckworksmagazine.com/04/s/vintage/multihulls/index.cfm
http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=54225
Bertrand Fercot's catamaran PHA, with his new modifications to the rig. Bertrand and I have been corresponding. He has recently modified his Swing Wing rig to make the sleeve portion of the sail more efficient. 
The junk rig user's group on Yahoo. This group has an archive of almost 11,000 posts.
Gary Hoyt has invented a rig remarkably like the junk rig, yet he acknowledges no debt to it. His rig has the advantage of a more aerodynamic design than the junk rig, and the disadvantage of a permanent yard aloft, which would be quite a problem in a serious storm.
Another Kanter Article
Dave Gerr on Stability
Shuttleworth Articles
Elusive Cruising Catamaran Performance
Seaworthiness and Safety by Derek Kelsall
Offshore Sailing Performance by Derek Kelsall