Freeride/slalom style , goal early planing in light winds (starting at 8-9kn)
No dagger sword, but 2x tuttle box, able to carry 2x 9.5 sails.
Sandwich glas construction.
With a team of 3 guys from The Netherlands we build our own tandem from scratch.
Gluwed foam blocks together , hot wire the rocker and outline , shape and sand it.
The stiffness was not good, so we hot wire the board in 3 pieces put stinger in and glu back together.
Then we put 1 layer glas around the core 5mm pvc foam at the bottom and 3 mm pvc foam on the deck.
Put in the insert for footstraps and finboxes.
Afther sandig 3 layers glas epoxy for outher layer.
Sanding again before painting the bottom and rail.
Put EVA soft deck on top and finish putting on mast tracks , footstraps and stickers.
Special tools as vacuüm bag , dril for mastrack and finbox , ect are self made.
First test being made pure fun in low winds, able to carry 2x 9,5 sail planing at 11knts bigger sail at the back up to 11.8 and 8.5 in front , planig in 8 knts.
For any questions or details your welcome.
This a great looking bit of kit.
We have Gemini mk2 here at Low Head in northern Tas and it's great for a learning platform and also pretty frightening when fired up. Maxed it at 24kts ( it's 4m long X 1m wide) and improving alphas is this season's challenge.
Not sure it's my favourite board but it's certainly the most social and gets more onboard laughs than anything else. Everyone gets excited when it turns up at the beach.
Up until now it hasn't occurred to me that I'd want it to be a different shape but Peter's is looking interesting.
Who else has a tandem?. (Sailquik?)
I think the best speed Daffy and I did was a 34 lt 10 sec. Only got scary when we got the speed wobbles .
Thank for the nice comments.
We didn´t put it on a scale yet, I think its ± 30 kilo.
I am sure we can reduce the weight to 20 kilo or less by using carbon in a next one.
We take the rest off this windsurfing season and next year to testing this one in all its options.
Its our first windsurf board ever we self build.
We had a lot of fun building it and learned many things on our way, and we are very happy about perfomance so far.
Our wishes are filled in so far.
Goals early planing in light winds (starting at 8-9kn)
No dagger sword, but 2x tuttle box,
able to carry 2x 9.5 sails.
And use this proto type for teaching in the future.
For this last reason its ultra stiff, school friendly by using EVA deck and impact proof build.
Maybe its to heavy in slalom and speed surfers minds, we will take its to a speed spot like Strand Horst in West or North West wind direction to do some speed runs.
We have to experience and learn with sails and fins to find out the reaction off this board when speeded up.
Thanks for the reply guys. It looks great by the way.You should be able to save a bit of weight with using regular mast track as well.PS: You should put some foils on it is fashion at the moment 
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We take the rest off this windsurfing season and next year to testing this one in all its options.
Building a tandem foil ?? would be a intresting winter project. 
Back in '88 a school friend & I built one from scratch in his parents garage . At 17 we had no idea about working with foam or fibreglass but decided to give it a go anyway. We started like you but the 'design' we created was as simple as laying my board (John Hall 295) and my mates board (Bombora Astro Toy) on top of each other and sliding them backwards and forwards until the rails lined up!! The astro toy was at the back - it ending up being over 13foot long and about 700mm wide.
Next step was to glue 2 blanks together which turned out to be little harder than we thought....we had a nice join on the deck but the bottom had a 50mm gap (we cut them at a 45deg angle). No problem - fixed with builders bog and duct tape!!
Stringers - this we outsourced to the local surfboard blank company who I am sure thought we were not all there when we asked for 2 x 50mm stringers cut into this monstrosity 
Mast tracks and foot straps - again a lot of thought went into this improtnat step - we simply put them where they were in the boards we used as a template.
The all important bottom shape - a double concave with steps on the rails - and when i say steps i mean about a 20mm step!!!!
Fin - same deal for the fin box as the footstraps but we splashed out on the latest fin design at the time and bought a Multifin slot fin.
Cant recall much about the glassing process only that we raised the floor of the garage by about a foot with all the excess .
At this point we didn't even know if the thing would float let alone be able to be sailed, bbut we decided to name it any.....the "MAJK BAJK (BAJK being a combination of our initials)
First test - this launch was done with much fanfare with family and fiends all gathered at Narrabeen Lake to see if what we made (whilst we were supposed to be studying for the HSC) would actually work.
Well....it did float and went like a dream 
.
We set it up with 2 wave sails and had an absolute ball.
Gybing - all i can say is you need to know your partners skill set very well and give yourself a lot of room (back sailor duck gybed) but it did do carve gybes after a while of dialing it in.
Not content with keeping it on flatwater, we took it for a spin at long reef in gentle 1-2foot to see what we could do....well...the first jump was enough to scare the s*&% out of me. As I was up the front I was 6 foot in the air before the back half had even left the top of the wave and the flex was enough for us to keep it as a flat water board only.
I still have it under the house nearly 30 year later and yes it still does come out occasional in a strong westerly in the Lake and even though my design partner has stopped sailing there are a few willing guys to take it. Here is a photo of about 5 years ago of me and a well regarded wavesailor giving it a blast.
Great story and good to hear and see other tandem enthusiasts. Tandem surfing lots of fun , we even did a high five while powerd up sailing .
We like to see some pictures from the board on shore, to learn even more about tandem design .
Last test was last sunday, 7.5 and 8.5 same type of sails . 2 persons 78 (leight weight,lw) and 92 kilo (heavy weight ,hw) . 30+44 freeride fins
1e test 7.5 and lw in front position ,nose came out the water like pictuce above in planing. 2e test 8.5 and lw in front, same but with tacking and jibe sifnificant better performance in manouvers. 3e test 8.5 and hw in front, while planing the board is a lot flatter on the water surface and faster.
Next time fins test ( bigger ,slalom)
Keep tandem sailing, keep smiling
Thanks Peter - I will dig it out over the weekend and post some shots so you can get a laugh.
Absolute classic Chub, I remember that thing pretty well. You and Brett were killing it!!!
Wouldnt mind getting it out at Budgewoi Lake next winter in the westerly and see what it could be wound up to???
Colour left a lot to be desired 
Larko.
