i can't really help there. there are too many thing that effect volume like thickness and rail shape. but i can say you should be albe to get a 95lt board from your dimensions without too much trouble.
also with volume don't forget to take into account the weight of the board. your volume is the boyancy of the foam minus the board weight.
also, with regards tail rocker. in a freestyle board with wave aspirations i wouldn't use tail kick at all. i'd design a flatish continuous rocker and put a 350-400mm flat into it under the straps area. or there abouts. sort of..... 
edit*** are you vac bagging the board? you need a template or the rocker will not be as shaped once it's been bagged.
Yeah I'm gonna vacuum it at a shaper I know (he doesn't want to tell me anything about the shape though, said it was my thing to figure out ). I will keep the templates from cutting in order to keep the shape of the rocker.
So basically I can prolongue the tail kick into tail rocker a bit further, so it would shorten the flat part allong with this.
What's the opinion on twin fin version?
ok, i'd look at some board you've sailed and measure them to get a feel for what you like. a freetyle board doesn't want a lot of tail rocker at all. and a freestyle wave board is only really about another 2-3mm more tail rocker.
the biggest difference between the 2 is the length of flat and the shape of the tail in plan. but i can't say do this or do that as it's a combination of everything.
basically design the rocker and then insert the flat.
twin fins are not my specialty either. i've only ever sailed one and it was too loose for me. twin fins are hard to get right.
it is easer to do a single fin or a widow maker. use it as a single fin for freestyle and a widow maker for waves.
also, you really need to allow for 3 boards to get things right. 4-5 boards to really get things right if you are starting from scratch without a known working rocker
my current freestyle board is version 3 in this volume and version 8-9 if you take other sizes into account. the shaper already had a rocker that was proven etc.
even now with my current board there are little tweaks i'd do here and there and i love it. so it's an endless loop.
Does it really need to be that complicated? Get a nice curve similar to a board you already like, tweak it to what you think it needs to be and you're done.
I see, I also don't want to end with trying to build only 1 board, but don't know how the result will be... if I make something that will be good enough for me, I will keep trying and improving, however it's going to be a slow process it took me more than a year to even start the first one 
@ hoops
no hoops it doesn't have to be complicated. everyones gotta start somewhere though and we've gotten away from a 900mm flat so were are already moving forward.
@ sideskirt.
there's only one way to find out. build it sail it, take your saw, cut it, sail it, and enjoy.
if you do what hoops suggests and template a board you like and then tweak it you will still enjoy the process and it's probably the best advice.
it is not my goal to copy a board but more like getting the experience, to feel what you're making... to be able to say I designed it and made it and if it works close to expectations at the end,the satisfaction is bigger... to copy a board is only semi self build thingie.
I said I will fully commit to it, if I start,not just partially... I have a great chance of fail I am aware, but it is something I gotta do, it is a great learning experience with the whole process as well.
@cjw, - i believe so. all of my boards are done that way and that's the way the shaper explained it.
@ sideskirt, - agree. 
ORLY?? I always thought volume is volume not +/- weight... so the board could have +volume in sea and -volume in fresh water, because of salt (not) being poresent. We could say 88L on sea and 82L on a lake.
So I'm counting on actual volume let's say 93L foam + volume from laminates about 2L - weigth hopefuly 88L to 90L :)
I could measure the volume of a production board to check, but my bath tub is too short 
i think maybe i got the terminology wrong.
what i meant was volume is boyancy of materials - weight of materials. so if your board has 90lt boyancy in the materials and the materials weigh 5kg then the volume is 85lt. which will vary from fresh to salt water.
which is what your saying also i think
overall the volume written on the board is not the actual space volume, like a 1L beer pint?
I'm asking since I plan a bit over 90L volume of foam.... density=15kg/m^3, weight 1,4kg gives 93L of actual volume.... weight/density=Vol. I don't understand why complicating the volume info when you can have a simple way out and it's clear to almost everyone :)
i guess every manufacturer has a different take on things, starboard for had this virtual volume thing going on. sail manufacturers over the years have stretched the size reality also.
but as i understand it. your boards volume is the litres of the board minus it's weight.
1 litre will support 1 kg.
1 litre is 10cm3
after you've got the volume you then subtract the weight of all materials and that's your volume.
the boards is use are tested in a pool and loaded up with weights to confirm the volume;
Actualy 1L = 1000cm^3; 1L = 1dm^3 ---> 1dm^3 = 1000cm^3
but I get your point here, actual volume - board weight=board volume... so I will get a smaller board by wsurf standards then I planned... still good though :)
yes
10cm3 was a slack way of writing 10x10x10
depending on your construction weights that could be anywhere from 5-8lt difference which in my mind is significant.
other than performance, this is one of the driving factors behind board manufacturers building lighter boards. ie. they get to build smaller boards with high relative volumes.
litres from a windsurfer point of view is referring to how much water the board displaces (isaf) when submerged in fresh water.
prior to computers this was calculated by putting the board in the water and adding weights to it until it was level with the water.
if board manufacturers are now calling board volume from computer models then they are taking the piss.
is it because the boards aren't built accurately to the computer model?
volume and bouyancy are two different things.
yes, volume and bouyancy are technically 2 different things.
in windsurfing edit* generally, volume was actually referring to bouyancy. same with surfing. in which case the weight is part of the equation. and to take that further the weight of the layup must be taken into account.
i can say with absolute confidence that my custom boards are describing the bouyancy. so when i buy a 100lt board i know it will float 100kg
it is in the manufacturers interest to talk volume rather than bouyancy for obvious reasons.
yes barn, i am aware that board manufacturers are referring to the actual volume as described in a dictionary or a science lab and not the bouyancy.
as i said a couple of times above before computers calculated volumes a boards volume was a reference to it's floatation. shapers checked the floatation by loading up the board with weights and the weight needed to submerge the board was considered it's volume.
at some point this changed.
to troll it further,
volume tells you nothing about a board. it doesn't tell you it's dimensions, it's boyancy, volume distribution or rocker etc.
when someone buys a board of a particular volume they are interested in it's bouyancy or it's floatation. that is the reason starboard copped so much flack about talking in terms of virtual volume. people bought boards they thought were 122lt when they were acutally 113lt or there abouts and they discovered they cound't plane early or dredge home. in starboards defence they understood that volume tells you nothing about a board so they tried to talk in terms of virtual volume. things like rail volume, board width, volume distribution, the relationship of the centre of bouyancy and the centre of mass etc all effect bouyancy. volume doesn't describe any of these things.
buy 2 boards of the same volume where 1 is 10kg heavier and see what the difference is. they are both the same volume though.
at the end of the day when people talk volume they are indirectly talking adout floatation. same reason why old scholl volume was a referrence to floatation.
yeah if weights were added on to of a board in a tank, the amount needed to sink it gives you the buoyancy (as long as the weights themselves don't touch the water) I don't dispute this... But why would they ever have called it volume?? (because they didn't) ...
This is how you measure the volume of a windsurf board (before computers?? hmm).. What they do is submerge the board in a tank and the amount of water displaced is measured.. giving you the volume.. in litres.. done.. or as Archimedes would say in this exact situation.. EUREKA!!!
Also 'Old school volume' (buoyancy) cant be measured in litres anyway!!.. As its the force needed to submerge and object, so its probably in Newtons or something.. But that is irrelephant..
So at the end of the day volume is volume and it always has been since archenemies..
not sure how Starboard, JP etc do it but I remember reading an article in the German Windsurf Magazine a few years back that described what method they used.
They used a certified lab to determine the exact volume of each tested board. The volume was measured without foot straps and fins. During the test the board was placed into a tank filled with water. A stamp would push down onto the board. The displaced water then would be equal the volume of the board. The tanks gage automatically subtracked the volume the stamp would displace. They usually would do a test series of several measurements and take the median then calculate the error factor... the resulting volume was quotes as:
xx Liters +/- yy liters.
well if the calc is subtracting the volume the stamp displaces then it is measuring bouyancy. which is how the weights on the board in the pool works.
if they measured the volume change of the board + the stamp then they are measuring volume.
maybe they were giving both.
but again, the volume measuremtn tells you nothing as it doesn't describe bouyancy which is what everyone is actually interested in when the look at a boards volume.
i am not arguing that bouyancy is not preffixed by litres. i would suggest the confusion came about because bouyancy = weight of displaced liquid and 1kg of water = 1lt. reality is boards should be sized in newtons or something but whos going to buy a board that says 120 newtons (other than hardcore gps dudes)
there's also cohesion and surface tension
it all comes back to the same piont. voilume doesn't tell you what you need to know about a board.
Hi Gestalt
check out the number of posts next to your profile pic - you MAY have a problem..
now please go sailing
