Duo 480 Jigsaw by Bernd Kohler
TRAILERABLE BIPLANE RIG SAILING CATAMARAN
Built in Auckland New Zealand 2012 to 2014
August 2012
I start construction. This boat is built by joining 3 preshaped panels plus the bulkheads to form the main shape for each hull.
Stringers are added and faired, and then the 2 hulls are joined by a large
bridgedeck panel which becomes the cabin floor, as well as the cockpit sole.
The inner hull panels are then added, and the whole assembly is turned right
way up to allow the closing in of the cockpit and the construction of the
cabin. Using the methods described below I built a half sized model from cheap particle board to learn the process. I will not describe how to mark out the hull panels as it is covered very well in the building instructions.
First job is to cut
out the bulkhead pieces and the 3 main hull panels: outer side, deck, and keel.
All the bulkhead cuts are straight lines. As I do with all nearly straight
cutting I use a handheld circular saw with a home made guide (see photo) and I
can not see why anyone would want to use a jigsaw on anything but curved lines
(or very short cuts).
The bulkheads BHstem, BH1,BH2,BH3,BH4,BH5, and transom piece (10) are cut as per the plans exactly to the sizes shown, but with the top sections all at the same 508 mm above the cwl.
( BH2 and 3 have the upper shapes made up later to form the main cabin walls, as with the top of BH1 which helps form the curve of the cabin top. (see later photos) )
There are also "ghost" bulkheads shown on the plans which show the dimensions at that point but you don't actually use these.
Note re the BH and panel sizes: the first thing you notice is that the keel, deck and side panels dimensions are the same as the bulkhead sizes, which means that when they are all assembled there is a small gap at the outer edges , the thickness of the plywood. This is easily taken care of when the hulls are together by epoxy filler along the outer keel line , and the outer edge of the cockpit seat. Every where else will be taken up with the ply for the upper stages.
Further note re the panels:
1: deck panel: I made it extend slightly longer than the last bulkhead, (about 50 mm)to give me something to trim off and also temporarily attach things to when doing the transom.
2: keel panel: the plans show the length as 4.4 metres, which clearly is too short, although if you did by chance cut it to this size, you would still be able to assemble the hulls as 4.4 is past the last main BH and the tiny transom piece can attach onto the outer hull panel. What I did was make the keel panel using two lengths of ply scarfed in the centre and let it end a bit short at the transom end. Then after assembling the hull permanently I added the tiny extension , with a big overlapped butt joint. So the last little section of the keel panel is in effect 18 mm thick. I probably had to shape the curve of these small bits with the belt sander. You can see the join in later photos eg Oct 2012.
I installed the stem pieces, the upper and lower stringers onto the outer hull side panel before assembly, checking out the top and bottom of the bulkheads accordingly to receive them. I installed the angled hull stringers in the outer hull panels AFTER the hulls were together (note: a horizontal outer hull stringer is an option but harder to do so I chose the angled stringer method at Bernd's reccomendation.)
Alternatively, the outer hull panel could be made taller by the thickness of the ply top and bottom, but I found when I build my test half size hull in cheap fibre board it was MUCH easier to keep things aligned by doing it with the panels and bulkheads cut as per the plans. I strongly reccomend to never reduce the size of the bulkheads as it just makes the boat smaller and creates many possibilities for errors.
The only exception I made to the above was the inner hull panels which I scribed onto the boat, but this comes later when the hulls are joined by the bridgedeck panel.
I had to decide whether to make up the pieces for one hull or do both as I went. I decided to make up the panels for both hulls, but then to only to actually build one hull at a time, for space reasons. Also I had to decide on pre coating with epoxy resin all the sheets of plywood for the boat first, or to coat the panels as I made them. I did the latter but with hindsight it would have been quicker overall to pre coat the full sheets of ply in advance, at the expense of the wastage of the epoxy on the offcuts. One side benefit of coating the made up panels is that the CWL and centre lines , which are pencilled on the components are trapped under the epoxy coating and are unlikely to be obliterated during the building process. Marking all the bulkhead locations plus CL on BOTH sides of the deck panel is important too for the construction of the superstructure after the boat is turned.
Plywood on my boat is Gaboon marine ply, a combo of 6 and 9 mm thick as specified in the plans. I also precoated all my Macrocarpa stringer material. Mostly a 3 coat minimum for the internal coating. All the bulkhead panels have wood stringers around them to provide a big enough surface for the hull panels to be glued onto. From the halfway point of each hull the bulkheads towards the front of the hull have the stringers glued onto the front of the bulkhead, and those in the rear section must have the pieces glued to the rear of each BH. This allows for fairing off . The long stringers on the hull panels must also be faired off before the hull panels are assembled.
The bulkheads BHstem, BH1,BH2,BH3,BH4,BH5, and transom piece (10) are cut as per the plans exactly to the sizes shown, but with the top sections all at the same 508 mm above the cwl.
( BH2 and 3 have the upper shapes made up later to form the main cabin walls, as with the top of BH1 which helps form the curve of the cabin top. (see later photos) )
There are also "ghost" bulkheads shown on the plans which show the dimensions at that point but you don't actually use these.
Note re the BH and panel sizes: the first thing you notice is that the keel, deck and side panels dimensions are the same as the bulkhead sizes, which means that when they are all assembled there is a small gap at the outer edges , the thickness of the plywood. This is easily taken care of when the hulls are together by epoxy filler along the outer keel line , and the outer edge of the cockpit seat. Every where else will be taken up with the ply for the upper stages.
Further note re the panels:
1: deck panel: I made it extend slightly longer than the last bulkhead, (about 50 mm)to give me something to trim off and also temporarily attach things to when doing the transom.
2: keel panel: the plans show the length as 4.4 metres, which clearly is too short, although if you did by chance cut it to this size, you would still be able to assemble the hulls as 4.4 is past the last main BH and the tiny transom piece can attach onto the outer hull panel. What I did was make the keel panel using two lengths of ply scarfed in the centre and let it end a bit short at the transom end. Then after assembling the hull permanently I added the tiny extension , with a big overlapped butt joint. So the last little section of the keel panel is in effect 18 mm thick. I probably had to shape the curve of these small bits with the belt sander. You can see the join in later photos eg Oct 2012.
I installed the stem pieces, the upper and lower stringers onto the outer hull side panel before assembly, checking out the top and bottom of the bulkheads accordingly to receive them. I installed the angled hull stringers in the outer hull panels AFTER the hulls were together (note: a horizontal outer hull stringer is an option but harder to do so I chose the angled stringer method at Bernd's reccomendation.)
Alternatively, the outer hull panel could be made taller by the thickness of the ply top and bottom, but I found when I build my test half size hull in cheap fibre board it was MUCH easier to keep things aligned by doing it with the panels and bulkheads cut as per the plans. I strongly reccomend to never reduce the size of the bulkheads as it just makes the boat smaller and creates many possibilities for errors.
The only exception I made to the above was the inner hull panels which I scribed onto the boat, but this comes later when the hulls are joined by the bridgedeck panel.
I had to decide whether to make up the pieces for one hull or do both as I went. I decided to make up the panels for both hulls, but then to only to actually build one hull at a time, for space reasons. Also I had to decide on pre coating with epoxy resin all the sheets of plywood for the boat first, or to coat the panels as I made them. I did the latter but with hindsight it would have been quicker overall to pre coat the full sheets of ply in advance, at the expense of the wastage of the epoxy on the offcuts. One side benefit of coating the made up panels is that the CWL and centre lines , which are pencilled on the components are trapped under the epoxy coating and are unlikely to be obliterated during the building process. Marking all the bulkhead locations plus CL on BOTH sides of the deck panel is important too for the construction of the superstructure after the boat is turned.
Plywood on my boat is Gaboon marine ply, a combo of 6 and 9 mm thick as specified in the plans. I also precoated all my Macrocarpa stringer material. Mostly a 3 coat minimum for the internal coating. All the bulkhead panels have wood stringers around them to provide a big enough surface for the hull panels to be glued onto. From the halfway point of each hull the bulkheads towards the front of the hull have the stringers glued onto the front of the bulkhead, and those in the rear section must have the pieces glued to the rear of each BH. This allows for fairing off . The long stringers on the hull panels must also be faired off before the hull panels are assembled.
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