Back a few years, I came up with the idea of an easy to build, less costly method of making a trimaran or catamaran.At the time I ran across an article of a big boat trimaran builder making day sailing trimarans in the 20 - 24 foot range, where he used shaped foam for bottom and tops of hulls, with glass fiber sides. I thought it might work for an r/c multihull and named the project “Economaran”. Basic effort was to use shaped foam for deck and hull bottom and balsa sheets for the sides. The actual hull building could be easily accomplished in a couple of weekends of work (mainly shaping the foam) and removing the labor to strip build any curved surfaces. The bigger Formula 48 and Mini 40 multihulls didn’t take off with any interest here in the US so the project wound up on a shelf - and I found it and decided to resurrect the project. Following I will try to show some photos as work moves forward, and perhaps those thinking of building a multihull (catamaran = 2 hulls or trimaran = 3 hulls) would find the process relatively inexpensive, with less labor and less time. Each hull consists of two pieces of sheet balsa, 1/8" x 4 inches wide x 48 inches long, and two pieces of 3/4" thick foam. The sheets of balsa are glued together at the vertical bow and two pieces of balsa are glued between the sheets at approximate cross beam locations. There is a small cross piece glued across and between the hull side forward to help keep a shape to the balsa. The hull is laid on top of the foam and a line is drawn (Sharpie pen) following the outside profile of the hull. this can then be cut using bandsaw or hacksaw blade to general shape. If in doubt, cut larger as it can always be sanded down. At the time I started this I was using the NACRA Inter 17 as a hull profile - and planned on tall very thin bows. Now the designs seem to favor reversed bows and I simply cut the bow in a reverse angle. It is straight to start, however I can always saw in a curved radius. (as drawn in green on a couple of the photos)

Dick Lemke
Minnesota USA

smPlanned approximate side profile.jpgsmHull-deck foam side view - exploded.jpgsmHull-deck foam profiles rough cut.jpgsmHull-deck foam profile marked.jpg

Additional work done - foam glued to bottom of the balsa sheet hull sides, and shaped. Profile cut and hard spots located inside the hull for fitting attachments. A taped mock-up of the hull with wing mast, and sails was set up to verify location fore/aft between hulls. Photos show original hull design (NACRA) and more current hull designs of A Class catamarans. The blue bottom trimaran is 24 foot in length and is built using glassed foam on bottom and on top. Vertical photo is side view of profile after cutting and hull foam bottom after shaping. Final photo is mock up of wing mast, and sails checking for fore/aft location - as well as length of sail (which I may shorten in the future).

FYI - this cat will NOT be built for foiling, although conversion would be easy.

Hi Dick,

I like the straight bows!
With a non-foiling catamaran you want to know when the bows start to submarine during a bear away or at a reaching.
These sharp straight bows will give you a nice spray when the top end of the bows meet the waterlevel.

So let it spray!!! :slight_smile:


Thanks Wolfgang

Always appreciate your comments, opinions and views. Getting ready for Thanksgiving Holiday here, so won’t be too much work done this week.


I’ll keep the foam/balsa method in mind!

Happy Thanksgiving to you and your family!


Thanks, and the same back to you and yours.


I managed to find a bit of time, and started the glue-up of the second hull. Only got the bulkheads in place and decided to lay the first hull with foam bottom next to the second hull. I then pulled out some old foam crossbeams originally cut to fit my trimaran, and just laid them in place. I think I will go with a plywood cross beam (plywood in vertical orientation) and then glue some foam on to shape and give it a bit of water shedding properties. Interesting in that a third hull (quickly made) could easily be slipped under the middle of these foam beams, and it might work fine as a trimaran.

Anyway, these beams are too wide for this cat, and tacking could become a nightmare. I will layout and cut a new set of beams with not quite so much arch coming off the hull. These beams are 46 inches wide, and I think I will make a new set keeping the to somewhere around 40 inches max. I will be giving up some platform stability but hope to reduce the tacking issues of a wide boat. Attached are two photos. One is the “Wide” version and the other a bit closer showing one hull and where a beam would be located.

Hey Dick, these sails are really good looking. they really look like real sails in scale really, Your conception too?

No - sorry… just about to get started on sails for this multi.

Those sails were sent to me by a good friend in the UK who was building a 2 meter, double mast multihull, but fell ill and couldn’t continue. The film is a little heavy for this boat’s size, unless I try them for heavy wind. The most recent sail design is a uni-rig (much like a “real” A Class catamaran) to start, and then expand - adding a jib (still within the sail area limits of .9 m2) I used to sail a uni-rig catamaran ( 18 Sq meter) and found the uni-rig almost always out-pointed a jib rigged boat upwind. Unfortunately, downwind was another story, and difficult to keep it in the “groove” and gave up some sail area in light wind. Anyway, it will be a challenge to see if I can sail and read the wind with only the mainsail standing on shore - instead of being on the boat. It will (as of now) have a sleeve luff and will see how that works out.

The current design is using the sail more as a trapezoid and is more rectangular than most are used to seeing. Only time will tell.