Lock Crowther designed and constructed 1962 Kraken 25 "C" Class trimaran restoration/rebuild project updated 1/9/2015

This interesting project is well underway.  The trimaran is a hand me down from my parents who sailed the boat at Blairgowrie in the late 60's and early 70's.  Initially I thought much of the original cold molded structure would be salvageable but careful examination revealed that all of the hulls were beyond saving except as an interesting decoration.  I've taken on the task of building new hulls using the cold molded/epoxy method detailed in the Gougeon Brothers on Boat Construction.  The new hulls are being constructed out of paulownia/kiri a lightweight timber with similar mechanical properties to western red cedar they are being skinned internally and externally with a lightweight triaxial glass reinforcement/epoxy lamination.

Some photos of the boat from the 60's

First task with a build of this type is to construct a mold in the case of a cold molded structure it needs to have vertical (mold frames) and horizontal elements (battens).  The molds set the hull shape and the battens provide a surface over which the diagonal elements can be curved and stapled. On this mold the stem lamination was made from epoxy laminated Tasmanian Oak and the keelson laminated merbau the mold segments were made from masonite floor underlay.

Also of interest is the strongback which is made of chipboard/melamine formed into a box the edges are glued and screwed and the box has two bulkheads in its length to help keep it true.  It also has castors which is handy for moving it around when necessary.  When I built the box/strongback I trued it with a laser level and it's stayed in shape well.

After you have your mold segments set you need to batten the mold.  In my case I used 18mm mdf sheet ripped into 18mm x 18mm strips and attached to the masonit mold sections with right angle brackets and screws.  It came up well but in future I would use a dimensional lumber for the gunwhale batten as I found the pressure of the lamination tended to make the gunwhale a bit wavy down the molds length it's nothing too serious but will mean extra fairing before the hull is finished and painted.

The stem lamination and keelson requires fairing into the hullshape shown above it's actually quite easy to do I used a hand plane and surform to translate the shape of the battens onto the stem.  Since I'm not going to use the timber keelson and am taking the approach of a poured epoxy keelson I've not installed the daggerboard case but have left reference marks in the lamination and keelson to place the daggerboard housing when the main hull lamination is removed.

8/6/2011 Main hull lamination blog entry 1)

I've faired off the mould and stem/keelson laminations and am moving on now. The original floats and crossbeams appear to be salvageable and have been stored under cover but the main hull rotted and was broken up when I was a kid I suspect the bronze beaching skids (which were just screwed into the keelson) were the hulls demise as it delaminated from the keelson out.

I've decided at this stage I wont lift the keelson stem and transom which were built to the original specification with the boat and substitute lighter and stronger alternatives in each case. I've just managed to lay up the first layer of veneer in the triple diagonal construction I'm using a paulownia veneer (sometimes called kiri) which has proved very light, stiff and easy to work with. Feels like I'm making some progress now.

6/8/2011 Main hull lamination blog entry 2)
I've fitted the first layer of veneers to both sides of the main hull now. I've also restored the rudder and daggerboard from the original boat. Most likely I'll use twin tiller extensions on the restored boat and shockcord them to the shrouds or a deck fitting (undecided there).

18/8/2012 Main hull lamination blog entry 3)

I'm onto the second diagonal lamination and have nearly completed one side of the hull the lamination has a tendency to spring away from the mold at the rear of the boat so I'm holding it on with clamps where necessary.

When the lamination is completed I'll insert a proper stringer along the gunwhale to hold the shape. I have the other side of the hull to complete then onto the final layer to complete the triple diagonal construction.  The hull is getting fairer as the laminations go on which stands to reason as each veneer is straight grained and basically a fairing batten in itself.

At this stage of the build I was using full length veneers and trimming to length.  I later decided that I'd cut and test fit the veneers in advance before preparing the glue and stapling less waste of glue and less loading on the gunwhale mold batten.

28/8/2012 Main Hull lamination Blog entry 4)

I've completed the second lamination on one hull side now. I'll do the other side then fair it off in preperation for the final diagonal veneer. On the final veneer I'll use packing strap between the staple and the timber to reduce the crushing of the veneer. In this centre layer I've been using up all my short off cut veneers, on the interior and exterior veneers I use full veneers and trim this is in line with the recommendations from the Gougeon brothers on boatbuilding manual.

I find my block plane set to a shallow setting and a surform perfect for smoothing out the veneer surface and removing any blobs of thickened epoxy left over from the lamination, the surform particularly slides through it like a knife through hot butter and doesnt clog.

I've found the raised movable strongback a real help, its a huge back saver not having to drop down to floor level when stapling veneers and pulling staples. Its a simple mdf and chipboard box with two bulkheards in its length its filleted with thickened epoxy to help with its dimensional stability I trued it up with a laser when I built it.

I've trimmed the veneers using a fein multitool with the circular blade (makes it easy) I've also used a small saw for the same job and it works nearly as well just slower thats all.

When Lock designed this boat he was quite influenced by the Swedish square metre boats with thier long thin hulls and large overlapping genoa. The flat rear section of the hull was designed to promote planing when the float was depressed and the main hull unloaded.

30/9/2012 Main hull lamination blog entry 5)

More progress I've now done the second layer of veneer on both sides of the hull. I'm fairing the hull lightly but still leaving plenty of key on the veneer in preperation for the final layer of diagonal veneer. The hull is reasonably fair on boat sides now I've also faired the keelson and placed station marks from the station molds to the hull to help with daggerboard case placement I'll probably use the fein saw to cut the daggerboard slot once the hull is lifted and turned and will use the Gougeon brothers method of letting the case into the keelson area and tab it in with a fillet and double bias tape on the inside. This boat will have a slightly squared off stem like the original.

15/10/2011 Blog entry 6, main hull lamination and various jobs

I've managed to retrieve the rest of the boat from its storage location. I'd not been able to look at the floats in their storage racks due to junk being packed around them. I've also had to have a bees nest exterminated from the inside of the main crossbeam. The little critters have done a lot of damage to the structure the weight of the honeycomb has actually cracked the fairing near the centre I'll take some photos soon.

The float hulls are looking pretty sad the double diagonal construction has suffered considerable glue bonding failures along its length. Maybe this last year being wet after so many dry years has been too much for the old glue because I'm sure they were holding up ok until recently, the good news is it all looks salvageable. At first glance it looks like the wood Lock used is Meranti/Pacific Maple there is some rot evident around the stern on one float where the hull comes to a canoe style transom.

I'm going to have to decide whether I restore or make new floats I have no worries about the process and the relatively low volume and surface area of the floats makes their construction easy my dilemma is that I'd like to save as much of the fabric of the original boat as possible so I'll have to weigh carefully the pros and cons of repair versus building new.

The inner layer seems sound so I might remove the deck and stabilise/repair the inside of the boat then remove the outside layer and replace with a full lamination or rebond the existing timber if its in acceptable condition. The main positive I can see is the hulls are dry and dimensionally stable. At worst I may be able to repair the hulls sufficiently that I can use them for show and make a new set for when I'm racing. In my restoration I have attempted to be sensitive to the history of what is quite an interesting and innovative boat but I do want to be able to push the thing with confidence so it has to be light and structurally sound. I'm a huge fan of boats that can be used not just museum pieces.

The rear crossbeam is in acceptable condition and a good candidate for reuse just needs a clean up. I'll remove the top fairing glue and fillet the internal structure and close up the box again. The main crossbeam has been rebuilt at some stage it looks like non standard timber sizings have been used and its excessively heavy I think I'll build a new one. The worst addition is that they have used about two dozen bolts in the rear of the main ply web. This isnt the original plan spec and is an unnecessary weight penalty.

Final veneer/lamination on main hull

Float glue bonding failures/delamination

Main crossbeam damage from possums and bees

Original floats and crossbeams

21/10/2011 Blog entry 7, float work

I opened the main crossbeam fairing skin on the underside to get an idea of whether its worth reusing, it might if I remove the very heavy hardwood brace (and bolts) from the rear of the beam and use the correct thickness of ply on the underside it might solve the weight problem. I also removed the honeycomb that the bees had built inside the beam (might make myself some candles they should come in handy when I cant pay the power bill due to buying boat bits).

I've stripped the paint off both of the float hulls now. One is so far gone that its not worth considering the other might be able to be repaired but probably isnt worth it the inner layer on the worst float is riddled with dry rot over 50% of the veneers are gone too far to be worth repairing. What I've settled on doing is to take the worst of the two floats, strip the outside diagonal layer then build two new floats using the inner layer of veneers as the mould. The final floats will be 2.2 mm per hull skin larger than the old but it wont have a negative effect on the boats dynamics and I'll have two lightweight and strong float hulls.

I'll then use my spare cut off veneers to rebuild the original float hull that I've stripped the exterior veneer from and keep the two original floats as keepsake display hulls.

19/11/2011 Blog entry 8, More main hull lamination and decision making

Progress has slowed down a bit lately work gets much more busy this time of year which means less time to dedicate to the boatbuilding. I've managed to get about another quarter of the main hull done with the final layer of veneers. I've also managed to cover one side of one of the original float hulls covered with one layer of veneer.

I ended up stripping off the outer layer of original veneer on one of the floats and I'll build a double diagonal float hull using the inner layer and float as a mold. The gunnel strip will be a little narrower and the hull will be approximately 4.4mm wider overall at the waterline which should make no difference to performance.

I'm using packing strap to staple through which makes it easier to remove the staples without dinting or gouging the exterior surface excessively. As I get towards the front of the boat I'm able to wind back the amount of staples required and just staple down the veneer seams.

Blog entry 9, Main hull lamination, a beauty shot and float progress

I'm making reasonably rapid progress on the final veneer on the main hull completed slightly over 2/3rds of the hull now. Could not resist sanding back the blobs of epoxy and rough surface for a bit of a beauty shot (well I think she's attractive and curvaceous anyway ). I've also set the first master veneer on one side of the float mold a momentous moment when your cold molding. The paulownia is so nice to look at it seems a pity to cover it up with paint I'm sure I'll be thanking myself in the future though when maintenance chores come round.  The orange plastic on the float hull mold is there to prevent the new lamination from sticking to the mold underneath.

Blog Entry 10, 2/12/2011, main and float hull lamination progress

I've finished the final triple diagonal lamination on one side of the main hull. I'm getting faster as I go, now with experience I can look at a veneer and decide by eye whether it needs spiling and how much is required it really speeds things up. I've started on the second diagonal lamination of the float on one side, the floats are so quick and easy by comparison to the main hull I'm making very quick progress.

5/1/2012 Blog entry 11, Main and float hull lamination, cold molding tools

I've completed one side of one of the floats with a double diagonal lamination and am moving onto the second side now. I'm putting the final triple diagonal lamination on the main hull about 1/2 a hull to go. I'm looking forward to posting updates that dont relate to hull construction and talk about bulkhead and crossbeam work not too far away now. Also a photo of my favorite cold molding tools. From left to right surform, long pointy nose pliers, staple puller, short pointy nose pliers, air powered stapler.

21/2/2012 Blog entry 12, main hull lamination finished

Main hull triple diagonal cold molding is done, finished today and feel like having a party after that effort. I've decided I'll keep the transom the next step will be double bias on the exterior of the keelson area then I'll lift the hull off the strongback with mold sections still fitted turnover and place in a cradle on the strongback in preperation for the rest of the work.

9/3/2012 Blog Entry 13 Lamination float hull

I've moved onto laminating the second float side having completed the first diagonal veneer layup I'm laminating on the second and final veneer. I've also purchased a Barton snubbing winch to replace the original and very heavy bronze snubbing winch.

24/3/2012 Blog Entry 14 One float lamination finished

I've completed the double diagonal float lamination, pretty quick and straightforward versus the main hull I've nearly got a proa now,  one float hull left to laminate for it to become a trimaran a bit of glassing then onto the interesting fitout stuff and crossbeams.

2/4/2012 Blog Entry 15 Float decided to cut it in half down the centreline

The project is coming along although in many ways it would have been easier to make a new float mold rather than using the original float with a veneer removed as a mold. The advantage of building the mold is you can setup the position of internal bulkheads prior to lamination which gives you much better certainty of positioning.

The main problem is Lock moved a lot of things around on the boat relative to the plans while he was experimenting and nothing really lines up. The floats are also custom, shorter than the ones in the plans and came out of his head undocumented so it's a bit of a challenge getting everything right. I'm still half inclined to cut the deck off and have a look at his bulkheads for reference.

What I've settled on doing is laying up the float laminations and cutting them into two halves down the centreline then I'll glass the inside of both halves with 265gsm double bias glass refit them to the mold with screws and hold the gunwhale area with a deck jig I should then be able to take the original positioning of deck gear and crossbeam mounts as a reference. I'll then join the float halves down the centre with a tape of 400 gsm double bias pour an epoxy keelson on the inside and more 400gsm as a tape on the outside and glass the outside of the shells with 265gsm double bias fit internal bulkheads and finally join the deck onto the float.

If I was building in WRC I would not glass inside and out simply sheath the exterior with 200gsm boat cloth however the paulownia I've used for lamination is really soft and will need protection. I hope to prevent bruising when I hit anything the advantage though is if you choose to glass with double bias is it reduces print through from the lamination process and makes getting a fair exterior a much less onerous task it should also sandwich the internal lamination and make it less easy to puncture and significantly stiffer I will suffer some weight penalty though.

2/4/2012 Part 2

I've popped off one of the hull sides and sanded the inside of all the epoxy lumps and uneven sections in preperation for the first layer of glass. I'n going to drape plastic back over the float mold. Then I'll drop the hull section back into the lower edge and screw the top edge back into the keelson of the old float/mold to let the glass set off in the correct shape. The lamination is quite stiff it feels about the same as a 6mm sheet of gaboon ply as a reference. The advantage of the half hull approach is I can glass the inside easily with good access to the very fine bow and stern section.

18/4/2012 Blog Entry 16 Glassing inside of float halves

I've glassed the inside of one float side with double bias glass (265gsm) and refitted it to the mold. I have a thick plastic sheet seperating the glass from the mold underneath It's not strictly a mold release membrane but it's done the trick so far (no problems so far pulling bits off).

I've also sanded the inside of the second float half in preperation for the glass unfortunately no photos of the glass on the inside of the first float side too much of a rush to get everything wet out and positioned.


I've managed to spend a little time on this project I've remounted the hull sides on the old float I'm using as a mold and started joining the two float sides with 400gsm double bias glass.  The inside will be a thickened epoxy poured keelson with a layer of 400gsm joining the two sides over the poured section. 


I'm making a deck jig at the moment for the floats. The big problem I've found is that the floats I have don't agree with the plans these are prototype floats, custom and a different length and shape. I'll set the new float on the deck jig and it should help with positioning of bulkheads, deck gear and crossbeam mounts and help to keep the appropriate shape.

The deck jig consists of some cheap luan 3mm ply, I'll laminate two layers together for stiffness. My plan is cut the sheets in half lengthwise lay the two up together onto the curve of the float deck and glue together in situ to get the correct curve. I may laminate on another layer if I don't think it's stiff enough.


Lately I've been working on the rear crossbeam I was going to pull it apart but after a careful inspection I think it's fine to use again so I've just repainted it ready for reuse in international paints snow white Toplac brightsides.


I've completed the deck jig for the float lamination.  This helps set the shape for the gunwhale strip and will also help with positioning deck hardware and beam bulkheads.


I've now glassed the mainhull together down the keelson.  First I filled all the irregularities along the seam with thickened epoxy the I joined the sides with 400 gsm double bias glass.  This time I used a squeegee to wet out the glass and peel ply which made the whole process painless.


I've lifted the main hull shell off the mold and am sanding the inner surface and getting ready to pour a keelson and glass on the inside.


I've set the gunnel strip on one side of the main hull with resin and thickened glue.  It consists of 19x19mm clear Oregon it is joined in situ on the side with a 8 to 1 scarph.


More progress during the week I removed the deck jig and fitted the starboard gunnel strip and cleaned up the ragged ends of veneers the weeks work also included removing the cured blobs of epoxy from the inner skin of the hull in preparation for poured keelson and glassing.

Over the weekend I've leveled the hull on sawhorses, fitted and tabbed in the transom, poured the epoxy keelson, wet out and fitted double bias glass over the poured epoxy and finished off with peel ply to get rid of excess resin.



Solid progress on the main hull of recent times.  Gunwale strip fitted and all the deck stiffeners are in place and gusseted and bulkheads fitted at forestay, main and rear beam positions and tabbed and glassed into position.


  1. i remember this boat pulling up on the beach at Rye. It would have been Easter in 1966. It was the blue colour seen in some of the photos.It was the first trimaran I'd ever seen and very impressive. I was 13 and an enthusiast for all things sailing and particularly multi hull. I sailed a quick cat and a mark 2 moth at the time and was a keen follower of the Cunninghams' attempt at the Little Americas cup but this beast was something else. Good luck with the project!

  2. Thanks Dai, Great to hear from you this boat sat on the beach with some pretty interesting off the beach multihulls over the years including the wingmast catamaran Miss Nylex when she was a challenger for the Little America's Cup and other racing cats. They ended up at Blairgowrie Yacht Club and had great fun sailing the boat out from the beach there. From their reports it was very fast particularly in light conditions and overtaking keelboats would give somewhat of a Doppler effect as the speed difference was so great.

    It subscribed to a lot of the early thinking on trimarans and small floats which were submersible my parents never used the trapeze but they added a turbo as you could reduce the float immersion and sail the boat somewhat like a superfine dinghy keeping it level on it's main hull. The floats by modern standards are not all that good as the mostly "v" shape gives considerably more wetted surface area than an equivalent "semicircular" shape. A positive side effect is that the floats are quite small and light which counters their less than optimal shape.

    It's a pretty interesting boat and should be better than ever in it's rebuilt form. Due to advances in cold molded epoxy construction we can get rid of a lot of the hardwood in the boats structure which weighed a lot and did not add much strength and replace them with ply ring frames. The other positive is the paulownia timber used for the lamination is impressively light and strong enough for the application.

    The biggest challenge I've found is that being the prototype the plan set I have doesn't agree with the floats at all I've read that Lock and his brother once crashed the boat into a large and very solid keelboat in the Gippsland Lakes and built new floats to replace the older and much smaller floats. I've not been posting much on this rebuild as I've been doing lots of rather boring work building deck jigs and making mock ups of bulkheads for the beam mounts and the captive bolts that hold the crossbeams on it's been quite tedious but I am making progress.

  3. Corey,

    That is beautiful work. I can tell you love what you do.


  4. For the book I am writing on Little Cup, I redraw a profile in color of the C-Class Kraken 25, if any body get some photos in color of 1962-3, I am interested.
    Francois Chevalier fracheval@free.fr

  5. Hi,
    What is the name of your tri, I don't see on the forward
    Francois Chevalier

  6. This was the class leader and prototype of the Kraken trimarans and was simply named "Kraken" by Lock Crowther