Mama Cocha, the first Husky 6.2 Clubracer
Beachcat to Trimaran Conversion, the rebirth of an old idea
Photos with permission from Michael, http://husky6/blogspot.com.au
Graphics from the author
In spring 2013 Michael from Brisbane contacted me and asked if I could design him a Club Racer Trimaran for his local races. He wanted to use a beachcat as a base for the new tri, using the hulls as amas and the rig and as many parts as possible to save lots of cost and time.
I've been studying the principles of sharpie hull design for more than three years now and find the idea of a beachcat to tri conversion very interesting for even longer. I posted some related posts and concept studies in different threads on boatdesign.net and other platforms.
The Statement of Requirements
Michael called for a fast boat with two crew and just enough payload for the desired 2 hp outboard motor, a farrier style folding system and some additional sails. The tri should have a well sized cockpit for comfortable daysailing with his girlfriend and a small cabin house for a dryer ride and good access to the generous stores in the mainhull.
Very important too was a simple and fast construction, because Michael is skilled in woodworking being carpenter but has never built a boat before. This was a real success.
The boat was finished within 6 month after-work-building and at around half of the weekends.
Husky 6.2 Clubracer, Data:
LoA and LWL 6.2m, BoA 5.5m, SA 23m² (main 18m², jib 5m²), Weight unknown, but should be around 270 to 310kg. Displ. Max. 420kg.
|Husky 6.2 trimaran completed|
Building Method and Materials
The three plate Sharpie Hull is the easiest to build hull possible. Mama Cocha went together really fast. The mainhull is built upside down on a stable building jig or a flat concrete floor. It has 7 frames/bulkheads and one pairs of stringers in the middle between chine- and sheer stringer to stiffen shell and to develop a little three-dimensional shape to the plywood. The hull is all plywood with 6mm (¼'', 5 veneers) okume/gaboon in boatbuilding quality, all lumber is hoop pine.
Michael planked the hull sheet by sheet with butt joints along the way made directly onto the hull. I would prefer scarf-joining the sheets first and do the planking in one glueing session to save the weight of the doublers. The mainstrength bulkheads and have wooden coamings as a reinforcement and to give a bigger the glueing surface. Minor frames have a glass joint. All gluing and sheeting is done with Epoxy.
This building method sounds a little conventional, but I think in this kind of hull it is superior over the stitch and glue method in terms of building time and control of the shape. You simply cut the ply a little bigger as needed and glue it to the stringers and bulkheads. Then you plane it down to the stringers. This is much faster than the work with the fairing batten.
|The Base, all cutouts were made later because the design was not finished at this point|
We agreed that I was responsible for the design, balance and structure of the boat and Michael to work out the folding system and it's statics. The folding system was very important for Michael because he has to store the boat on the trailer after sailing and he wanted to be able doing this alone.
I gave Michael a list of high volume beach cats that could work as amas for his tri and just a few weeks later he found a Hobie 20 in good condition and for a reasonable price. He bought it and the design process started.
First step was that Michael measured the hull so that I could redraw it to locate the centers of flotation and lateral resistance, volume and so on. The big surprise was that the Hobie 20 has a volume of more than 750 litres, giving the later tri a lot of righting moment.
The shape of the mainhull were drawn, the centers set into the right positions in relation from mainhull to amas, bulkheads and frames located. I sent Michael the first drawings, allowing him to start with the frames and he immediately began the construction of his mainhull. It all went together very fast. To be honest, Michael built faster than I could produce plan sheets with all the details.
If you want to follow the building stages, have a look at Michael's building blog at ... http://husky6.blogspot.com.au/
The most expensive and time consuming detail was the folding system which required help from a pro-welder and a lot of thinking, but in the end the tri folded nice and easy.
The first test sail in december showed that the concept works better than expected, the boat is neutral on the helm, fast and safe and with only the minimum of equipment mounted and jib and main hoisted, the tri accelerated to over 12 knots in 12 – 14 knots of wind, more than 7 knots upwind and tacking within 90°. There is no noticeable transition from displacement to planing mode at the hullspeed mark around 7 knots. All in all, a very promising behavior without genoa, spinnaker and further development of the boat.
|the first sail|
The idea of a trimaran with beach cat hulls as amas is not new and it's is still the same as in the times when Dick Newick designed his original Tremolino with Hobie 16 hulls. In comparison to the open catamaran a trimaran offers comfortable and dry sitting in a cockpit versus sitting on a deck or hiking in the trapeze. A tri has dry stores in the mainhull for your cloth and camping gear or, in the bigger types sufficient space for bunks and seats.
Pain and Gain (minimizing financial pain and maximizing gain)
The idea is simple … have or buy a suitable beachcat, build one mainhull and two beams and you get a complete trimaran. Use nearly every part from the beach cat: hulls, mast, sails, boards, rudder(s), mainsheet and traveller. To say it short, everything what is really expensive in boatbuilding and what you would have to buy if you are building from scratch.
Ok, you will have to modify this or that to prepare the parts for there different use or increased forces, but in the end you will save a lot of money.
What to to Buy Extra
Beside the cost for the material to build the mainhull you will need round alloy tubes (or used mast sections) for the beams, new trampolines and some additional sails (sreecher or genoa). Bits n pieces, thats all.
The costs for such a trimaran are as minimal as possible. For for a cat in good condition with a good set of sails (very important!) you will pay around $2000 to $4000 AUD, USD or EURO). If you have a good cat already, good for you. Expect to pay around $2500 to $4000 for a 20 to 21 foot camp cruiser or club racer. Much less if you want a smaller, more simple boat. A little more for a Cruiser Racer and much more if you want to have a folding system.
Actual Racing Cats are changing there hullforms in the moment towards the wavepiercer concept, so the last generation of "fat volume cats“ will be offered quite cheap in the near future. They are working good as amas. First generation wavepiercers Hobie Fox and FXone are interesting too, but this application has to be confirmed through measurements first.
Type of Boats
There are a lot of possible boats with different approaches, using different cat hulls chosen for their special task.
From a very basic 16 - 18 foot trimaran, possibly with one small bunk for a single hander up to a full cabin tri with sitting headroom for two. Daysailor, Club Racer, Camp Cruiser and even a small Cruiser Racer is possible if you have the right ama.
As said before the Sharpie Hull is fast, cheap and easy to build, that it makes it ideal for the task. Sharpies look simple but they are very sensible to design. The shape and the ratios have to be right to get a fast running- low resistance hull. Therefore this designs have to be around one foot longer than other boats in the same class. My hulls take advantage from a small three dimensional “soft stressforming” in the plywood to stiffen up the shell.
Design and Styling
Not every cat hull is possible for every kind of trimaran and so I just have a small group of cats types for a specific trimaran design or type. The volume of the ama has to support the weight of the boat and payload to give the boat a fast and safe ride. And of course the bulkheads must be located individually according to the positions of the cat's main bulkheads.
Most of my designs show a “modern” reverse bow, but they are no wavepiercers. This bow is just supporting the needs of the flat bottom that makes the sharpie hullform so succesfull in performance and sailing behavior. The “cutout” saves weight and makes it looking good. To match the style it is easily possible to modify the bow of the amas with some foam and glass.
I tried to give my designs a good and modern look with flaring sideplanks and angled bow and transom. But the flat bottom and the hard chines are a fact, fortunately you can't see them when the boat is in the water . Within limits, I allow a builder to modify some details to his taste.
Mama Cocha reached easily 12 knot at her first sail just with main and jib and no trimming equipment. In a 20 to 21 footer expect to get the best overall performance in medium winds above 8 knots windspeed. In stronger winds a max. boatspeed will be around 18 - 20 knots, hitting the16 regularly. In light winds under 6 knots you have to counter a little higher resistance of the hull with a genoa or screacher (code zero).
The simple chined hull has surprisingly only a little disadvantage in resistance compared to a full round one, mainly in very light winds. In winds over 8 knots it changes to some sort of “planning mode” and from there the hull runs fast and very stable.
Beams and Folding
I favor the old and proven “tube and wire” system. It is light, cheap and easy to construct. If you look around it may be that you find some mastsections from broken or abandoned masts that could fit the bill. A good chance to save some money.
Modern features as dyneema seastays and quick release shackles makes mounting/demounting fast. Have a look how it works (without seastays) at this modern production tri.
Farrier Folding System
I know that its like magic when a Farrier Tri folds together, in Germany we nicknamed them “garden chairs”. This is the same effect when the tv shows us the retraction of the wheels in a new developed airplane. Must be placed in men's brain somewhere.
But please be aware that this system is very cost intensive and has a lot of additional weight. The hullshape has to be adapted to the folding geometrics to make the system work properly. You will need a lot of custom made fittings and these will be very expensive if you are no metal worker able to weld alloy.
If you have to store your boat on the trailer or in a Marina Box or you travel regularly every second week you may think about a folder. But if you don't, try to resist the magic. Michael spend more time and money on the folding system than on the bare mainhull.
Outlook into the Future
The Husky 6.2 Club Racer / Daysailer Design with Hobie 20 Hulls is finished now and ready to be built again for builders experienced in boatbuilding or woodworking. Full building plans for the first time builder will be available around June 2014.
Other possible cat hulls for the Husky 6.2 are Mystere 6 and 5.5 (lengthened), Nacra 6 and 5.8, Hobie Fox and other fat cats. These have to be measured (by you) and adapted to the mainhull. This will take a little time.
on the drawing board for a second Client from Down Under is the
Husky 6.5 Camp Cruiser. This one is big enough for a lot of camping
gear and 350kg payload. The 6.5 works together with the same cats
mentioned above, smaller ones with simple modifications to fit some
|Husky 6.2 Club Racer|
Design is on the way, perhaps I can fit a simple interior to make a basic two person cruiser/racer with the same hull.
|Husky 6.5, first lines, preliminary design view 2|
In the concept stage is a 6.8 to 7.1m Cruiser/Racer with cabin and full sitting headroom Cruiser Racer with 400 kg payload, enough for weekend and holiday cruising as well as club racing. Amas will be from lengthened Hobie 20 Miracle or Mystere 6 cats (or other fat cats I have not discovered yet). I think this is the maximum possible if you are using the cat to tri conversion.
|The big one, concept stage|
In the pipeline
Smaller, more daysailer oriented boats are possible using smaller cat's.
I think a cat to tri conversion is a good way to get on the water with a multihull, if you have a proper concept and design. It may not be the fastest boat possible, but it is cheap and fast and you get a fair boat with a good overall performance.
In every way it is better than dreaming about a production trimaran you cannot afford.
Feel free to contact me . Send e-mail to firstname.lastname@example.org and we can chat about your ideas and possibilities.