2 metre catamaran build

In the spirit of Claudio, Dick, Siri et al I though I would start a thread to provide occasional updates on my 2metre catamaran build. The boat’ hulls are based on the lines for the centre hull of the Midnight Oil trimaran, I squeezed them horizontally and stretched them a little vertically.

THe hulls will be moulded over a male plug, which I have constructed from thick plywood - the lines in the ply are excellent for sighting along to check symmetry and fairness. The plug is split into two halves along a horizontal plane parallel to the waterline. As these are “Mk 2” versions I’m currently tidying up the plug - I’ve reduced the freeboard at the bow and have rounded the stern over. I’ve just rubbed down the whole plug down ready for finishing.

Another change I’m making is to mould in the recess for the crossbeam. On the previous version I moulded the hulls and then cut into them and glued in a recess but this added weight and wasn’t as strong as I expect moulded in recesses to be. If you look at the pictures of the plug you’ll see a curout in the top of the hull. I’ll show how I make the final recesses in a future post.

For now here are some pictures of the plug “as is”.


Having decided to mould-in the recesses for the crossbeam I introduced the need to build left and right-handed hulls (the crossbeam is ‘arched’). I decided to achieve this by having removable inserts for the recesses, i.e. an interchangable part to the plug.

The first thing I needed was a building board to keep everything true. I actually used a thick piece of kitchen worktop. I then set four pieces of studding into the building board, checked for sqareness and accuracy. The studds are positioned to be on the centre lines of the hulls.

The top half of the plug already had vertical holes drilled and this enabled the top part of the plug to slide down onto the studs. I then used soem aluminium section and carefully drilled holes to locate over the studding and also to align with the fixing bolt holes in the crossbeam. This enables me to horizintally align the crossbeam. The pictures should explain it better.

I then used some packaging tape to act as a release barrier on the plug and the bottom of the crossbeam (I used several layers on the crossbeam to build it up to the thickness of the laminate when it gets layed-up. I also used some PVA release agent over the tape. After aligning everything on the jig I filled the void between the hull plug and the bottom of the crossbeam with glassfibre/polyester resin paste.


Having filled the void with the paste it looks a bit of a mess at this stage. After the glassfibre paste has cured a liitle effort saw the crossbeam release. The resulting glassfibre insert had some voids but these should be fillable. Following some hardwork the insert is cut back fair with the plug and released from the plug. Not perfect but usable.

I reckon it took about an hour of effort to get the insert to this stage. Of course there’s another one to make.


Work is mainly progressing on finishing the plug and I should start waxing it prior to moulding over the weekend - not very exciting.

I’m still moving forward on other components though and have just about finished the riuders and fins. I build these using blue foam cores, cut with a hot wire by a guy who makes model plane wing cores.

To keep the fins/rudders the same, I start by vary carefully aligning and glueing in carbon tubes to accept the rudder stock or fin mounts to one of the cores. I then joining the foam cores together, again being careful to ensure alignment, before glueing the carbon tubes to the second core - I use this approach because everything is kept in alignment properly. After fairing in the carbon tubes I laminate over the core with a couple of layers of 200g carbon fibre. Once cured I seperate the two fins rudders.

Below is a picture of the fin cores, showing the carbon tubes prior to lamination. Second picture is an almost completed rudder, complete with ‘inverted wing’ across the bottom (this is actually a balsa core laminated with carbon).

Each rudder weighs 40g (about 1.5ozs) and each fin 50g.


Hi Ray

I realize it’s massive, but is a single cross-beam going to provide sufficient stiffness and resist twisting between the two hulls?

The old FREIGHT TRAIN design with single “wing” cross-beam suffered from torsional twist, and even my big cat with two beams still had issues.

Just wondering if the issue has been considered?

Looks good and I like your idea of using vertical ply for plug hull shape, and you were right about the under-beam filler photo. Looks like someone “sneezed” and it came out blue. :smiley:

Hi Dick, I don’t have the technology to prove that the cross beam will be stiff enough before building it so ultimately the proof will be in the pudding, however, I’ve done the right thngs; its curved, it has a fairly thick cross section, there’s a lot of unidirectional carbon along the beam but also cloth at 45deg and 90deg to provide torsional stiffness and the mating area where it bolts to the hulls is fairly large.

My mini40 tri has single swept back beams and they seem upto the job - it was built by Mike Dann who knows what he’s doing and I’ve also used him as a sounding board ideas on the big cat too.


OK - just curious. As I mentioned, my big cat was 5.5 meters long and not quite 3.5 meters wide. With two cross beams, I could lift the bow on port hull, but starboard hull stayed on the sand beach. Finally found a way clamp the cross beams to the hulls much tighter than the two SS straps, and it stiffened up a lot, so at least both bows would rise if only one lifted.

Hey, forgot to add - Love the idea of a master plug with variable inserts depending in idea and designs. Great idea to build the plug that way.

I have some old shelving removed and looking at the end section (looks like a ladder) am thinking it could make a great building board/surface/strong-back for a 2 meter. Darn it - now you have me thinking of a possible cat myself. !:mad: :smiley:

Thanks for the feedback Dick; I know you’re sold on the small multihulls that you and Siri and that is great but it would be interesting to see you buld a 2metre boat using your foam core approach. My personal preference is for larger boats on the basis that the meduiums in which we operate (water and air) don’t scale and have an increasing impact as you go smaller.

Regarding the crossbeam, as you indicate with your comments about your 5.5metre cat the way cross beams mate with the hulls is important and I observe pictures of model multihulls using small round cross section crossbeams mating with small round recesses on the hulls and this can allow relative movement between the beam and the hull, as I think you found, Also these small cross section beams can themselves be subject to torsional flex, which makes the situation worse.

I’m confident that my crossbeam will not be prone to movement between it and the hulls. I would like to demonstrate the beams strength (I’ve though about standing on it for example) but its a lot of work to make another one if it turns into ‘testing to destruction’ so I’ll do the testing on the boat.

Of course, the crossbeam is only part of the issue and even if you get that perfect it’ll still be let down if the hulls are too flexible. I’ve got some ideas on that score that time may reveal.


The plug is progressing well. I’ve finished shaping and have applied a couple of coats of finishing epoxy, applied with a foam roller, and I’ll start waxing as soon as that has cured. The epoxy really shows the lines from the plywood that I used for the plug and that are so useful for checking fairness and symmetry.

I’ve also laid up an experimental piece using Claudio’s cotton fabric decorative technique. I’ll update tomorrow when it has cured.


Incidentally, on the half of the plug for the bottom of the hull you might notice two black marks on the centreline, one near the stern and one about midships. These are in fact holes through the plug; when building the plug I glued in tubes at the locations of the fin and rudder and again the lines in the plywood are excellent for checking alignment. When I mould over the plug the holes will be plugged with some dowel and plasticene but after moulding the plugs will be removed and, whilst the moulding is still on the plug, the tubes in the plug will be used as a jig for drilling and aligning the rudder and fin mounting tubes. I have used the same approach on the top of the plug for locating the mountings for the crossbeam mounting bolts. I find this approach easier than trying to locate and align the tubes on a finished moulding that may not have any simple reference points.


I had another think about the moulded inserts for the plug that I mentioned in post #3 - the problem I had then was voids in the insert because I couldn’t consolidate the fibreglass paste well enough. The answer was obvious really and I’ve now made a Mk 2 inser using casting resin. The result is much better, the only problem being some small areas to fill as a result of the release tape crinkling a little from the heat of the resin curing. The affected tape was a thick PVC tape, the parcel tape that I used as the actual release layer was fine. Incidentally, I applied multiple layers of the PVC tape to the underneath of the cross beam to pack it out to the thickness of the laminate that I will subsequently lay-up over the plug, i.e. allowing for the thickness of the laminate.


I poured the other insert today, as per my previous post, and was reminded of that old adage 'check and check again. You see, casting resin is good stuff, providing there isn’t a hole in the bottom of the mould into which you’re pouring it - to seal the opening between the crossbeam and hull at the ‘bottom’ of the ‘mould’ I used liberal amounts of parcel tape, which worked perfectly on the first insert, but the resin found a small hole where I hadn’t sealed the tape well enough. I had to push a rag onto the area and hold it tight until the resin gel’d (and casting resin is relativley slow to gel!) Still, I kept the resin topped up and no harm was done other than an aching hand and arm.

I now have two finished mould inserts.

I’m away on holiday for the rest of the week but will be looking to start laying up the hulls shortly after I return.


Well, a bit of elbow grease later I’m ready to start producing the hulls. Pictures below are of the plug with the crossbeam insert taped in place, liberally wax polished and treated with PVA release agent.

I’ll be laying up the top half of each hull first, the bottoms come a bit later.

I’ll be laying up with the following laminations; 1 * 200g twill carbon, 1 * 180g harness weave kevlar and finallly some 120g patterned cotton material, as per Claudio. I’ll be vacuum bagging the lay-up.

I won’t have the camera to record the lay-up, time is too precious to stop and I’d probably end up with epoxy on the camera anyway so next post will be after that stage.


Well, its fingers-crossed time; this morning I laminated the top of the first hull.

Because of using the patterned cotton as the finishing layer I’m trying a new (to me) epoxy resin that is very clear but, while I’ll persist with it, its medium viscosity made it harder to work with than my normal low-viscosity resin, plus I had some trouble getting the laminate around the complex curves at the stern and around the crossbeam mount. I found myself fretting about gel times etc. Good job I had a cooler morning.

Anyway, I finished the laminating and its now sitting snugly in the vacuum bag. I’ll keep the cacuum on for about 12hrs and check it out in 24hrs so next update tomorrow.



This morning I removed the vacuum bag and peeled away the breather fabric and outer peel-ply from my new catamaran hull moulding. Whilst its not perfect - I have a couple of small wrinkles in the cotton fabric around the complex shapes - I’m pretty pleased with it.

The images below show it on the plug having been rough trimmed. Weight at this point is 500g (just over 1lb) but I haven’t removed the inner peel-ply yet and final trimming will remove about another 20% of the material so I’m confident it will come down by at least another 100g. That said, later on I’ll add some additional carbon internally around the crossbeam mount area and apply a finishing resin coat so I’ll surrender some of the weight reduction.

Ray - now that is really neat. Ought to scare most of them off the water. Nice find on the cloth.


Progress has slowed a little as I am busy with work, however, I have trimmed the moulding to nearer its finished size and removed the inner peel-ply - weight is now down to 370g (about 13oz).

I’m hoping to get some more time on the project at the weekend.


Hello Ray - I finally received access to your pictures. It was a admin. problem. I am new to this, but catching up on the dialogue between you and Dick Limke. I have several questions:

  1. Why a catamaran vs the trimaran?
  2. Where do buy sails and rigging for these boats - Sailsetc.? Can you use
    Sword sails/rigging for Midnight Oil or your boat?
  3. I have never done any fiberglass or carbon fiber work. Please describe the
    process and materials for your fins/daggerboards and rudder/wing.
  4. After you make your molds, you will build two hull shells. How il you
    reinforce them internally - plywood or balsa bulkheads?
  5. We are entering an autonomus sailing competition and we are looking at
    the Midnight Oil. We want speed, but need stability. Is the trimaran a
    better choice that the cat, assuming no RC control?
  6. Any thoughts about building the hulls as follows:
    a) Balsa/lightply bulkheads, strip planking, carbon or fiberglass skin.
    b) Balsa/lightply bulkheads, foam filler, carbon or fiberglass skin.
    c) How many layers for skin and what type of material.

Lots of questions, but I appreciate your posts.



Well, thats a few questions, lets see…

  1. The majority of 2M multihulls are trimarans and maybe that tells you something, but I was actually inspired by Team Philips to go the Cat route - I didn’t overly analyse it. Team Philips was built only around 50miles from my home and I was fortunate in being able to visit her under construction. There’s more info here:


Sadly, Team Philips broke up in a storm when working up in the Atlantic. Have a look at the video clips, there’s one of her doing 32knots on her bare wingmasts.

Interestingly, for the next Americas cup multihulls are in; the challenger has gone Tri and the defender Cat so clearly designers have different views on the merits of each.

  1. You could use commercial fittings as you mention. Personally, I buy most of my stuff from Peter Wiles who I find very friendly and open to things outside of his catalogue and supportive of experimenting with multihulls.


That said, I use relatively few commercial fittings, especially as I’ve been using swing rigs.

My last sails are from Dragon sails but I’ve also got a suit from WindPower and used Peter Wiles sails before. They all work well. I can put you in touch with Dragon and Windpower.

  1. Rudders and fins are built the same way. I start by getting a guy who makes foam cores for model plane wings to hot-wire cut me some cores. I build them as a pair of mirror images in one go so insert carbon tubes into the foam cores and then laminate over the cores with carbon fibre, typically two laminations of 200g cloth. Whilst they cure I consolidate them using either heat shrink tubing or a vacuum bag. After curing and finishing I seperate them to get the two fins/rudders and the previously inserted tubes provide accurate locations for rudder stocks and fin tubes. Have a look at my earlier post on my fins/rudders and let me know if there any specific points that need clarifying.

  2. I don’t install bulkheads, the shells are strong enough without them. Additional reinforecement is laminated inside the shells where needed, such as where the beams connect to the hulls, at sheeting points, rudder pivot points etc.Internal platforms are installed across the shells to hold the winch, servo, battery etc…

  3. I wouldn’t want to sail a tri or a cat without radio control in anything other than a very gentle breeze - with any wind you have to watch and react quickly to keep them the right way up and sailing optimally. Are you looking to borrow from the free sailing fraternity and equip your boat with vane steering, self-tacking etc?

  4. Balsa should be fine but I would use it as the core of sandwich construction, plank the hulls and then laminate them with a light glass layer (I would guess 1 * 50g and 1 * 25g laminations should be about right) and when that’s cured remove the hull from the build board, turn it over, remove all the bulkhead shadows, lighly sand the inside and then laminate the inside as per the outside. Don’t go to thick with the balsa, I would estimate a core of maybe 3mm might be good but I must emphasis that I’ve not tried this approach. One benefit of this approach is that you’ll avoid the issues with the ingres of water because of pinholes in the hull laminations that have been discussed on the dual build thread by Claudio, K1w1 et al. BTW, if you build with a balsa core you’ll still need to add some local reinforcement.

Hope that helps and please come back with any more questions that will help you get started.


Thanks Ray - very helpful. If I understand this correctly, when you mold on a mail plug, you coat with resin, lay-up one ply, let dry, Lightly sand?, apply one more resin coat, lay-up the second ply, let dry, lightly sand?, and finish.

If you wanted to see the carbon fiber grain, can you sand and polish out the resin? If not, I would assume you would use microballoon type filler, primer and paint?When you apply a second coat, do you always need to sand inbetween coats, for better adhesion? When you join the two halves, I assume you apply some type of tape seam and more resin. How do you handle the thickness transition. Is it just fared back into the shell?

You are using the mail plug mold because it involves less time vs. making a female mold after that as well?? I guess the advantage of the female mold, you would be you have a perfect finish out of the mold?

I really appreciate your time and help.