I have been triing to find some advice or information regarding sail shape. I have 2 sails, the first one is fairly old and has a flat shape, ie when on the beach and sheeted in the top section of the sail(up to batton number 3)is very flat, then from there on to the bottom of the sail a decent pocket is formed. I had a new sail made by north sails about a year ago. This sail is not flat at the top, and has a very curved shape causing a very closed shape to the sail, and boy o boy i cannot get it to perform. I have tried everything to get the top of the sail flatter as i find up wind the boat wants to stall very easily compared to the older sail.i Have tried less to no batton tension i have tried lots of downhaul! What sail shape should a hobie16 have to perform well?

That's your problem right there. North doesn't know how to make catamaran sails. You're not going to get much advice from racers, because only Hobie sails are class legal.

Not to be a smart butt, but the shape that Hobie gives them works pretty well. The top is fairly flat, since the mast gives you most of your camber. Downhaul frees up the leech. Outhaul does next to nothing. Oversheeting will stall the top of the sail. You need to have tell-tales high up on the sail and a couple on the leech to tell you when you're oversheeting.

OK, this is about as good a picture as you're going to get:


That's 2 x North American Champion Armando Noriega going upwind in about 15 kts, big waves.

He's moderately de-powered (traveller's about 8" out; jib traveller is in the "middle" position for upwind (see the tape on his front crossbar)) Can't really tell, but it looks like he's got a lot of downhaul on - gooseneck slide is right near the black band.

Nice picture Matt.

Thank you for the info so far, i Am in South Africa, North Sails are contracted by Hobie for the class legal sails here. As you will see from the pic, Batton 1,2,3 hook shape, this was on the beach completley rigged with no batton tension and sheeted in. Yes there was very little wind on the sail BUT more wind does not seem to open the slot at the top much more, it has a hooked shape to me compared with my other sail. I don't have a pic of the other sail but i can tell you that the first 3 battons would be almost straight compared to this. Have i got a badley cut sail from North do you think?

I would try some stiffer battens, are you using the ones from the old sail?