I'm starting out in this tarrific sport I weight 104 kg. My question is what size board should I be using, i have a bic 210s it's a fairly big long thick old school board i also have a bombora 270 a couple of old shorter boards
Any help would be appreciated

135 liters and if you can afford it, wider than 80 cm's.

A little more info

how far have you progressed on boards you mentioned

can you waterstart?

wind conditions

sail sizes you have

lots of usefull info in this thread
www.seabreeze.com.au/forums/Windsurfing/General/Just-getting-started?page=1

I'm of a similar weight and looking back at my struggles and mistakes...

Learn basics on your large board.
Once you get more confident and you start thinking about planing, straps and harness, get a board of around 160L, couple it with a freeride 6m sail and stick with it until you learn to plan safely in straps and harness. Then consider an additional smaller board.

^ +1

am a 100+ kilo sailor
learn as much as you can on your current board(s)
and do not rush to downsize
i only recently sold my last BIC Dufour Wing
but was still having fun with it on a small lake 20 years after starting



from there I went to a 160 liter freeride of 80 cm width
as i was accustomed to not dropping the sail too often, i went with an 8.0 freeride sail (NO cambers)
after about 3 years I was comfortable planing
and even bought this 8.4 race sail with 4 cambers



there is always something to learn in the sport and always new condtions
patience and practice, practice = lots of TOW required
TOW= time on water

ENJOY !!

Joe Windsurf and Obelix are spot on. Cheaper way to go since you already have gear. I learned on a floaty, long Bic board as well and it paid off fine for me. Been windsurfing for 14 years now and have been on short boards 12 of those 14 years and loving it! Enjoy the adventure of windsurfing!