Light weight big open deck catamaran

I'm looking for a relatively minimalistic ocean sailing capable catamaran in about 14 - 15 m size range. Since I ideally want payload capacity of around 2 - 3 tons and have good performance then I have to go for long waterline with about 12 to 1 length beam ratio. Short fat hulls just don't sail well. I don't need all the fancy expensive stuff modern factory production catamarans come overloaded with, just long slim hulls and reasonable sailing rig. At this scale hulls are big enough to comfortably live inside so no oversize deck cabin needed. Think Macgregor 36 cat scaled to larger size
https://sailboatdata.com/sailboat/macgregor-36/
This also good example although way out of budget with carbon everything SIG 45 - VPLP Design https://www.vplp.fr/en/cruising/sig-45/
Tiki 46 | James Wharram Designs https://www.wharram.com/gallery/tiki-designs/tiki46
This also potentially good example although I don't like hull shape, too much wet surface area.
I'm also open to building myself since budget is limited and it seems that there is almost nothing similar on second hand market in my area. 8 years ago I built small 9,5 m catamaran, similar to that Macgregor 36, just a bit shorter hulls and plywood deck between mast beam and rear beam. 15 m boat is a big and expensive job, but should be managable if boat kept as minimalistic as possible and I could get some help when needed. Plywood epoxy construction, design optimized for quick build, maybe only one hull fitted out for living, other simply for storage, second hand mast and sails, outboard motor, exterrior finished to work boat finish not yacht grade that takes forever of sanding an filling.
Finding and buying half way built and then abandoned project boat also may be an option if relatively nearby and in reasonable condition.

 

Why stop at 12 : 1 ?
18 : 1 at the waterline would be easily attainable given your initial SOR.

 

The Woods Mirage cat has a L/B ratio of approx 12 on the waterline - however she is 'only' 11 metres long.
Sailing Catamarans - Mirage - 11m hard chine open deck cruiser https://sailingcatamarans.com/index.php/designs-2/5-catamarans-over-40ft/179-mirage

But if you used something like this as a reference, you could maybe scale her up to 15 metres in length, and that might then give you your payload capacity of 2 - 3 tonnes?

 

Wouldn't that be too narrow causing increased wet surface area drag when loaded? I'm looking at Scioning Gforce 1500 and it lists hull length/beam ratio of 14.5 /1 and payload of 2600 kg
G-Force 1500 C Catamaran - Schionning Designs International https://schionningdesign.com/g-force-1500-c/ So at 15 m length it seems length/beam of 12/1 - 14/1 would be good compromise.

That's what I'm looking at. Having big enough cabin space and payload by going longer instead of fatter and taller like nearly every production cat. Unfortunately there are almost no second hand boats like that and I'm even struggling to find plans for a boat I would like. A boat optimized for simplicity and performance by sacrificing some luxury making it also much more DIY friendly. Closest thing are those Wharram catamarans, but their hull shape leave much to be desired. They also are built in large numbers so there is a demand for big and simple DIY boat. Seems strange no one is offering plans for similar plywood epoxy boat in 14 - 15 m size range like Tiki 46 or Pahi 52 , but with more performance oriented hull shape.
I designed my 9.5 m cat myself with help from another Latvian boat builder, I probably could do the same for this boat, but having professional level plans would make the build much easier like make parts to spec and put them together.

 

You could try contacting Richard Woods and asking him for his opinion about 'stretching' the Mirage design from 11 metres to 15 metres?
He posts occasionally on here - here is a link to his profile :
Richard Woods https://www.boatdesign.net/members/15041/

It might be possible to keep the overall hull depth the same, and simply increase the spacing between the transverse hull frames (?), although you might want to add some extra longitudinal stiffeners as the panel sizes between the frames will have increased by 35%.

 

Depends on your target speed and many, many other factors.

 

I will try, although I think in the end it would end up mostly another boat if you stretch it that much. Overall beam also would have to be increased requiring stronger crossbeams, beam to hull connections would have to be reinforced. At that point why not make hulls a bit wider too for more room at shoulder height.

 

Mulkari. You want fast, accommodation in hulls only, designed by Nigel Irens try this design.2008 CONSTELLATION YACHTS Gaff Rigged Schooner (64ft)-Sold Catamaran: -Vessel Summary https://www.catamarans.com/used-sail-catamaran-for-sale/2008-constellation-yachts-gaff-rigged-schooner/sandpiper/500070 Jpegs below.
Next suggestion but will be hard to find the plans of, is Malcolm Tennant designs. It will take a day or 2 and I will find some drawings of his 12 and 15 meter tube cats he designed which may be along the lines you want.
If you want 50 foot of tradition try this: Polynesian Vaka Twin hull traditional catermaran by Salthouse Boatbuilders - NZ Builders of Quality Custom Yachts and Launches https://www.salthouseboats.com/polynesian-vaka.html jpeg below

I am just making suggestions as I suspect the Malcom Tennant sailing cats will be more of what you want. just imagine a Turissmo 10 extended to 15 meters

 

Rob Denney swears that resin infusion can be made to be quicker than a plywood build, and gives you a longer lasting hull. See Intelligent Infusion — Harryproa https://www.harryproa.com/intelligent-infusion. He is very keen on radical simplification, and builds moulds out of single curvature MDF panels. If you were willing to design a hull with a deck that is the mirror image of the bottom, then you could use the same mould to make both the port and starboard half of each hull, and that one mould could build four hull halves. That would cut down on building effort.

Rob Denney did once design and build a catamaran with the accommodation in the starboard hull, rig and storage in the port hull, a single beam, and an articulating connection:

Actually, that video shows no accommodation anywhere, but I am fairly sure I saw a drawing of that same boat with an accommodation pod on the starboard hull.

Possibly Rob's proa designs would meet your requirements, especially the cargo proa.

 

Yeah, that Turissmo 10 scaled to 15 m and redesigned to be built in plywood epoxy to keep costs down would be ideal. I have built a cat that's basically similar to Turissmo 10 and it is great. Light, sails well, draft 30 cm with boards up, only drawbacks if you load it with stuff there is noticeable performance loss and hull interior is cramped especially with multiple people onboard. Scaling to 15 m would solve these two issues.

Infusion benefits should also translate to plywood build and plywood is cheaper than foam and require less fiberglass covering that means less epoxy too although yeah plywood boats require more care to last long term.
Looked up those harryproas, interesting boats and very light although I would definitely want to see one in real life and preferably sail one too to get a feel how everything works before committing building such "weird" boat. It also seems to require highly custom rig not something you can get cheap on second hand market, those free standing carbon masts are big $$$
For example my current 9.5 m catamaran has 13 m aluminum mast I bought for 150 Euro, mainsail was 500 , genoa 150 jib, 100 on second hand market. Dyneema rope was 700 Euro, some other bits and pieces like winches, blocks. rope stoppers, mainsail track together around 500 second hand. Whole boat cost me around 12 k Euro to build. 5 years later I upgraded to brand new sails for around 8 k Euro. They improved upwind performance around 20 - 25 % If I had ordered everything brand new it would be easily over 20 - 25k just for rig and sails.
There are huge savings to be made by using second hand sails and hardware and it is easy to upgrade later if desired.

 

There are stalled projects/dreams out there…

Here’s one interesting example.

I realize it doesn’t check all the boxes, but it is an interesting design.

I’m always looking, but haven’t seen much in the 50’ range, but quite a few interesting Cats in the 40-45’ range that had good hulls with accommodation with flat bridge deck or a minimal Pod cabin.

Of course location and shipping logistics can hinder finding the right project, especially at the length you want.

If you have the time and skill, building exactly what you want probably makes more sense anyways.

 

Hi. Try Woods design Ondina. The plans are older but Woods may sell a copy. Plywood 45 foot open bridge deck, probably could be extended to 49 foot. The link below just a sampler, go to woods direct. Page 163 Multihull Structure Thoughts thread. Ondina has a 10 mm ply skin with 37 x 25 mm stringers. The keels are multiple layers of 25 mm timber to the depth you require to provide a rounded shape. The secondary bulkheads a 9 mm plywood with 12 mm plywood crossbeam bulkheads. The decks are 8 mm plywood on 50 x 25 mm deck stringers and 75 x 25 mm deck beams. The interior is 6 mm and 8 mm plywood with 8 mm plywood floors and bunks. The cross beams are wooden box beams with a 15 mm plywood web 50 x 50 mm top bottom flange, 15 mm ply web with 75 x 50 mm top and bottom flange, 15 mm ply web with 50 x 50 mm top and bottom flanges then the final 15 mm ply web. The main mast cross beam has 100 x 50 mm centre flanges instead of the 75 x 50 mm top and bottom flanges. All exterior surfaces are covered with 300 gsm glass cloth and epoxy. The entire build should be epoxy saturated as per West system. The plywood is glued and screwed to stringers etc. How many screws? Try 5,000 countersunk brass screws. Oh, my sore wrist.
Ondina. V hull open deck cruiser https://boatplans.cc/woods-designs/ondina/

Next is a cat in NZ Carino. Page 55 of Multihull Structure Thoughts thread. Don't know if the designer is still in business. This is a story of what can happen to a reasonable design when business is the driver. Carino started life as a 40 x 23.6 foot cat designed by John Morgan. It weighs 8800 lbs and was designed to be a charter boat in NZ for day trips in the Bay of Islands and could carry 40 passengers which means its displacement was about 17000 lbs. The mast was about 200 x 150 mm carrying about 700 square foot fractional sloop rig could carry full sail in 30 knots of wind to meet charter regulations. The cat was basically two 6 foot wide hulls at gunnel level and an open bridge deck with seating for passengers. When I sailed on the boat it performed quite well doing about 7 knots upwind in 10 knots of breeze with a max of 12 knots reaching in 15 knots of wind. The day I sailed it only had 12 people on board.
The original construction was ply timber with 9 mm Gaboon ply hulls and hull decks with stringers at about 1 foot centre lines and ring frames every 3.5 foot. The bridge deck is 12 mm ply on top, 18 mm honeycomb core and 6 mm ply on the water side (remember this has to take up to 7000 lbs of passengers). The crossbeams are 2 layers of 12 mm ply either side of a timber top and bottom flange and uprights. The fore beam is an aluminium section. The bridge deck had a lightly framed canvas spay hood for guest comfort. A nice boat that could be turned into a minimalist cruiser for fun. But the charter business is not so kind. Carino was extended 10 foot to 50 foot long (cut here and insert and additional piece in each hull and bridgedeck).

Last Suggestion John Marples used to sell Constant Chamber Searunner catamaran plans in plywood up to 44 foot, the 40 foot and 42 foot were virtually open wing designs. His web site only vaguely mentions them but they were simple to build. Google pictures you will see what I mean.

 

Hi. Finally Malcolm Tennant designed several open tube cats with fatter hulls. But the ones to research are the Tehenga 12.4 which wsas 40 x 23 foot displacing 8000 lbs and carrying 863 square foot of sail. There was at least one built which went up for sale a few years ago. Round bilge double diagonal ply and tube cross beams. The final one is the Tennant Khan. Only one ever built. 49 x 26.2 foot 17,000 lbs displacement with 1215 square foot of sail. Tube cat but built in an early version of foam glass hull skin, the rest is plywood. These plans will be hard to find as Tennant business was done by another guy after Tennants death and that guy shut the plan business down 2 years ago.

 

Yes, that's one option, although transporting that size catamaran especially if it is in one piece over the roads would be cost prohibitive, it would have to be seperate hulls that fit on normal flatbed trailer like for example those Wharram catamarans.

If I build myself my most likely build site also demands demountable boat that can be built as separate hulls, beams and then assembled at water. I'm not in great hurry, my ultimate goal for this boat would be world cruise, but that's somewhere 10 - 15 years down the line, initially it would be sailed in Baltic sea and North Atlantic. If I decide to build myself I would probably start next year so I have some time to look around second hand market if something shows up nearby.

Thanks for the input. Considering moulds, not sure if it is faster than conventional bulkheads and stringers method for one off boat. It kind of is building the mould vs building and assambling bulkheads and stringer frame that itself becomes permanent mould for hull panels. My 9.5 m cat was made in foam fiberglass and I remember placing accurately particle board templates, putting foam strips over them, laminating fiberglass then carefully disassembling templates and setting them up for another hull was quite tedious and slow. I would like to build as little non boat stuff as possible.

 

https://www.mikewalleryachts.com/waller-1480-catamaran

Displacement 10,000 Kg

Hull Length / Beam 10.6:1

Sail Area 143.5 Squ Mtrs

Payload (Ave) 2000 Kg

Payload (Max) 4000 Kg

can not speek.