There was an earlier post on tandems at Sandy Point, but I couldn't resurrect it, so starting a new topic. We will need to get this one out on the water again:
Very nice Perks. The fin set up is exactly what we were thinking. Daffy and I hit 35 with his at the Pit but no joy at LG. Just couldn't get the fin out of the weed enough to get going. I'd be happy to jump onto the front with you.
Geez Perks, you're not just a pretty face! That looks awesome and the fin setup....genius.
Dave loves a tight hole apparently 
Now my brain is ticking over.
2 ideas.
1/ Front guy gets more vertical lift from sail, by raking more to windward than usual? Should reduce whetted area.
2/ a stepped bottom, so there are 2 planing areas, fore and aft. I think there was a boat made like this so there was always a 7deg angle of attack, almost independent of weight distribution. Not sure how you'd turn it though. might need a turning flap on the fin.
I was wave sailing at Lancelin with a mate in the 80's. We were dicking around one the way back to the beach and I sat on the nose of his board. The acceleration was surprising.
I dig the vid
aussie speed sailors seem a breed of their own, cool to see the legendary ones mugs speak.
Select to expand quotedecrepit said..
Now my brain is ticking over.
2 ideas.
1/ Front guy gets more vertical lift from sail, by raking more to windward than usual? Should reduce whetted area.
2/ a stepped bottom, so there are 2 planing areas, fore and aft. I think there was a boat made like this so there was always a 7deg angle of attack, almost independent of weight distribution. Not sure how you'd turn it though. might need a turning flap on the fin.
Hi decrepit Yes it got to the plane easy And accelerated well but when it hit 30 knots it tended to die and then try to come Back again ,not sure why
Select to expand quotered said..
Get Izaak on the front ... fastest father/son duo in Australia!!
Yes Red He was on the front the first time but tough to get him back there
Select to expand quoteanthony perkins said..
Hi decrepit Yes it got to the plane easy And accelerated well but when it hit 30 knots it tended to die and then try to come Back again ,not sure why
That sounds like the old negative rocker problem, too much lift behind the centre of gravity pushing the nose down.
But in this case, you don't need -ve rocker to do that. you have all the weight of that front sailor.
That's why I think the front sailor needs vertical lift, either the stepped hull idea or a more raked sail. In this day and age though a foil may work. You need somebody smarter than me to work that all out.
I read somewhere a long time ago, the American navy worked out, the fastest setup for planning hulls was a 7deg angle of attack. That means the faster you go the less hull is in the water, so less drag. So if it was me experimenting. I'd modify the bottom with some extra foam under the front rider's feet at 7 deg. Just how thick that should be, would need to be worked out. I guess so that when planing on it, the rear planing are would be optimum as well. All about getting front and back whetted area's minimal.
Select to expand quotedecrepit said..
Now my brain is ticking over.
2 ideas.
1/ Front guy gets more vertical lift from sail, by raking more to windward than usual? Should reduce whetted area.
2/ a stepped bottom, so there are 2 planing areas, fore and aft. I think there was a boat made like this so there was always a 7deg angle of attack, almost independent of weight distribution. Not sure how you'd turn it though. might need a turning flap on the fin.
Ha,Ha! Good stuff to brainstorm isn't it.
We have always found on both the speed and the Gemini tandem, that the front person tends to stand more upright and the rear person more back leaning.
I noticed a definite change in trim with Mathew on the front at 70kg and Kato on the front at 80+ kg. (I was about 73Kg at this time). It seemed more pitch stable with Kato. But the original partner and co-constructor Peter Smith was the same weight as me and we had some great runs on it in the early 90's. Albeit, in stronger winds with much smaller sails!!
Anthony's design looks excellent to me. 
I recon they are both capable of 40 knots in the right conditions.
Our board is 10'8" (325cm) x 20" (50.5cm). It's Polyurethane/Polyester construction, so quite heavy!
Our big limitation is the US type finbox, especially for Lake George. Anthony's adjustable Tuttle box is a huge step forward.
Yes alot to brain storm my head is spinning, the complexity of an adjustable fin forward or back is just one,the weight distribution next run will be close to you and kato as Dave will jump on the front, I think before with izaak I was the heavier, on the back,just need more runs
This is quite an interesting build. I'm in awe.
Happy with my ancient F2 Tandem, but building something faster would be appealing. I've thought about converting a raceboard like a Cat, Viper , Lightning or similar, but taking out a strip in the middle has never occurred to me. Great idea. Was the donor board something stock?
And are there any pics or vids of the conversion process? Would love to see these.
Oooops, sorry,
I had not listened properly when you said "Speed 250".
Still interested in pics of the conversion.
Select to expand quoteZeeGerman said..
Oooops, sorry,
I had not listened properly when you said "Speed 250".
Still interested in pics of the conversion.
Sorry Zee didn't take any photos I just didn't think of it at the time, The other reason why I liked that board was that it had very Flat and upright sides So by putting carbon on them and a carbon Stringer in the middle I felt it was making it stiff enough to carry 2 people without flex
No worries. Being lazy on documenting things myself, I can understand.
But I take it you decided on an angle that was obviously not exactly perpendicular because you wanted less (or more?) vee, somehow fixated it to the surface and ran a circular saw along it on both sides of the middle. If I'm wrong here, please correct me. I love the idea. One could even run the saw closer to the middle in the front or tail to give it more or less volume for the rear or front rider. Or is this a nonsense idea?
A stationary saw through which you can feed the board might be handier, but is it mandatory?
The rest would be a lot of work but s more or less straightforward. And yes, I guess with their steep sidewalls they will all be stiff enough, especially with a stringer down the middle.
I hope this will wear off soon or else I can already picture myself with another winter project.
Yes zee I think all of The above would work , I used a hand saw its Nice and slow with some control I then touched it up with an electric plane, Basically a centre line down the middle of the bottom ,I Mark the width of the piece to come out to give me the board shape I wanted Then the same on the top plus or minus a little bit just to set the V that you want on the bottom and yes I think the piece in the front was a lot wider than the piece in the back to achieve my final shape,all not hard just need to think about it, it sounds like you're on to it.
Thanks a lot Anthony,
probably a good idea to first saw straight down the middle in order to then produce two symmetrical halves. It'll make it easier to be accurate.
Still one of the best build ideas I've come acroiss for a long time.
