Started on a 1m catamaran on the weekend as another design as you go project. It will be modelled roughly on the 18' Ron Given (NZ) designed 'Hustler MK2' 'A class' catamaran I restored in 1979, (pics) and so far it's progressing ok. Hull is from three 25mm strips of polystyrene laminated using foam safe contact spray. Laid the 2 blanks on a flat board with 2 4" nails through each to stop them moving, and weighted them down for a day to set.

While waiting, I cut the decks from 5mm ply and shaped the bow sections. When the blanks were dry, I glued the decks on with lots of PVA glue, (which sticks foam well to wood,) and weighted them down with clamps sideways to stop them from moving. Left them for 2 days to set in my warm shed then gave the bows a rough shaping. Next was the fun part, shaping the hulls using a Surform file which creates a major mess with lots of vacuuming needed. The beauty of it is, is that the basic hulls were shaped and tapered (bow to stern) in about an hour. The laminating seams are used as a guide when shaping, plus eyeballing and straightedges.

Today, while the deck sides were still parallel, I set the hulls up in the work table and routed out preliminary spaces through the deck for winch, rudder servo and radio. Tomorrow, I'll hopefully be routering a side taper to the decks, (hulls will taper bow to stern on bottom and sides) The hulls will then have to be refiled to the new shape.

Shaping is done 90% with the Surform, then longboard sanded and hand sanded to the final shape, later to be completely sealed and glassed.

Crossbeams are 12mm ally tube with orange conduit bored to a tight fit and epoxied to the ends, then steel saddles epoxied over them. The whole tube/saddle assemblies will also be drilled and screwed together to prevent any tendency to turn. Center beam will probably be a double like the 100% cat, (yet to be worked out). Would be nice if they could be made like the originals, but welding thin ally tube might not be feasible.

JB

Almost finished fairing/filling the foam before sealing it prior to glassing, (stops the resin seeping through the cloth to fill the foam texture rather than the cloth- needing more resin)

I'm using a very easy sanding spackle filler, as if you use a harder setting filler you end up removing foam rather than filler. Ideally you want a filler which has the consistency of soft balsa wood. With this filler, you can't apply it too thickly, as it takes days to set, so I've done it in thin layers, and used a straight edge to check as I sanded. Takes a few days but worth getting as near as possible before glassing, but after glassing you can use epoxy with fillers (eg micro balloons) to get a good finish and be a bit more heavy handed with sanding.

Thought I'd show the few tools etc required for these foam hulls. Belt sander was only for touching up the ply deck and transom shape, Surforms for basic shaping, long board sanders and sanding blocks, saw for initially cutting the 'blanks' to length, and my Emcostar multi machine for cutting to size, band sawing and shaping the ply decks with the disc, (this can be done with most tools,- jigsaws, planes etc) Deck cutouts done with the router, but can be done any way before gluing the decks onto the foam.

Next steps will be to paint the hulls with a water based Zinsser sealer, then acrylic paint, To make doubly sure nothing will attack the foam,) then glassing, then sealer, then acrylic lacquer. I bought a litre of epoxy resin yesterday to be ready to do the eventual glassing, (almost doubled in price from 7 yrs ago!) Paid $100 for 4L to do my sailing dinghy resto, now $45/L (just the resin,)- luckily I bought 1L of hardener last year, or that would have been another $45/L (don't need 1L as it's 4:1 mix, but always handy.)

Hopefully sealing the hulls in a day or so, depending on the weather.

JB

Have now made the center beam, but need to make a few width adjustments to the mounts on all 3, now I know what the width between hull centers is going to be, with the hull tapers. I always seem to build 3 steps in advance, then go back 2,- happens when you design and build on the fly. Hulls now have 2 coats of Zinsser water based sealer, and are ready for sanding and a few coats of acrylic paint before glassing.

I want to get everything tested for fit and ready to screw together once the hulls are finished.

JB

All of the beams have been adjusted to the correct width, holes drilled for the front and rear beams, and the holes reinforced and waterproofed with epoxy forced into them and spread with a wooden skewer. I have also epoxied in reinforcing plates for chainplates if I decide to go with a fully stayed mast. Haven't decided yet, but they will be there if I need them.

Been experimenting with various epoxies and their effect on polystyrene foam. The resin from the local f/glass shop is fine, (pic 3) also a brand of Chinese resin which is marketed by an Australian company, and sold here by a Korean $2 shop. I found that another Chinese brand of epoxy resin eats foam, so I'm assuming it's more like a polyester, --smells nasty as well. Still have a couple more to test,- another variety of the Aust one, and a US marine resin, made by PC products, Allentown PA (never seen it before looked interesting so bought one to try. ) apparently can set under water, has anyone used it ?

Goes to show, you need to test these Chinese glues before using them on anything. I find them generally ok for most things, but foam and plastics (like ABS) are another thing.

JB

Trying the land yacht sail to get an idea of some proportions, and work out where the center of effort will be. The cat sail might end up being taller and narrower in the foot. The mast on my 18ft cat was 25ft, so I thought I might try following those dimensions, scaled for the model. Might be able to make both sails multi purpose for both models. I have to put another chain plate pad just behind the center beam, (for possible backstays) but need to find where the beam will need to end up first. Designing as you go is interesting🤔😐💥

I've also made a dolphin striker for the mast load (not that there will be much-if any) but it will be also be used to locate the mast with a pin. Normally the mast doesn't go through the beam, but sits above a short compression post, (see in pic) but in this case anything goes. This should enable the boat to use an unstayed mast as well.

JB

Been busy lately with yard work, fitting roof racks to the car for my new kayak (rescue vessel) etc, but finally got round to the exciting part ! Hulls are all faired now with a few coats of epoxy using West fairing/filler powder and mahogany dust to make it easier to sand, (the dust is to give it some colour so I could see where to sand to. Hulls are screwed to pieces of 100x50 timber with cross pieces screwed to them, so they can be screwed to the table to keep the hulls straight while glassing.
This was necessary, as the ply decks had twisted slightly over the length (about 2mm) in the 30c heat lately. Once glassed they will stay straight, (the cross beams will help as well.)

Used an orbital sander and long boards with 60 grit paper to knock the filler back. Cloth will go on in one 1200x300 piece for each hull.

JB

Hulls glassed last evening, and re-coated today . Centerboard boxes were previously filled with balsa plugs in their exits, which were sanded back flush when fairing the hulls. Now glassed over and will be cut out when the glassing is complete.

Decks will be glassed next, then gunwales will be taped to join the deck and hull surfaces so as to completely waterproof everything.

Centerboard blanks have been made from 2 x 2mm pieces of ply ea, cross grain laminated to prevent warping. They will be sealed with thin resin once shaped

JB

A bit more progress,- decks glassed, gunwales taped and faired, center beam attached (trial position) filler pieces under front and rear beam mounts to make up for the edge tape. I used cotton sewing tape as it was easier to tape round 90deg and stayed bent better than glass which always tends to want to straighten out.

Still had to keep working the tape till the resin had cured enough for it to stay put. Dynel cloth is better than glass for edges as well, but the tape made it easier to get a neater edge. Centerboards are glassed each side with very fine finishing cloth. The boards are wider than would be normal, as I will need to experiment with the CE for balance between the mast, sail and centerboards to get a slight bit of weather helm which cats need. I can cut them down if necessary and adjust the centerboard case to suit once sorted.

Sail in pic is from my land yacht, but I'll use it for a test. I plan to temporarily attach fixed straight rudders and lash the boom in the center for a water test to check if the current position is anywhere near correct for balance.

JB

Almost ready for a basic test. Rudders, tillers, gudgeon and pintle sets made, rudder blades made and glassed, link bar made, mainsheet pulley system worked out, rudder blades and centerboards painted, and centerboard tops and tillers varnished. Also made a rudder servo link which took a bit of experimenting with. Winch and servo/batt/RX compartments will eventually have waterproof lids, once I figure out where everything will fit.

Addition, --the pulleys are made from 16mm nylon bungee/shock cord buttons (for tonneau covers, boat covers etc) turned down on the lathe, with a brass tube sleeve and 3mm screw into a 3mm tapped hole. I was looking for small pulleys in the hardware store and spotted them. Almost exactly what I needed.

Was hoping to test it sooner and test the winch layout at the same time, but the winch did not arrive from Ali Exp, as the seller mucked me about, (think he was doing something dodgy) so ended up getting a refund from Ali Exp after waiting 15 days for the guy to ship it.

Have now ordered one locally which was supposed to come today, but the courier failed to make an adequate effort with the delivery. I stayed home specially all day so I didn't miss him, but he never knocked on the door, and just left me a card to collect from the base. Now I can't pick it up till Monday, and have to drive 12km to pick it up from the branch which is only a few kms from where I bought it, so I paid $15 for shipping for nothing. Couriers and the mail service here are becoming 3rd world ! Quite often they will knock once, and if you don't get to the door in 5 seconds they are off. So basically held up for 17 days because of shipping problems !

Vid of mainsheet system working, (substituting rubber bands for winch) Took a bit of thought, as it has to work across the boat. Basically a sideways version of the continuous loop system.

JB

Almost ready to give it a try. Winch, rudders, etc all sorted, just doing a few wiring mods to make things fit better, plus on/off switch and charging point (want to leave it closed up, to save undoing screws every outing) Mainsheet was fun to work out and set up, but a lot of choice words helped get it done 😎

Winch sits in the port hull, servo, RX and 4 cell NiCad square pack sit in the stbd hull. The lead for the winch comes through the aft beam to protect it. Compartment covers have sponge seals, but still some proper waterproofing to be done round the winch and rudder cable . I have to completely disassemble the boat to paint it once it's all finished, and make a proper sail (using the land yacht sail to test it with)

JB