Running a 82l twin RRD and now using RRD four sails. Having the issue of board bouncing around when on a the wave since i changed to the RRD four sails as if more power is being forced into the fins.
I'm 75-77kg. Only use to encounter his when maxed out on 4m sails North ICE but now I'm getting it with the 4.5 when the sail is comfortably powered up. (love this RRD sails, highly recommended). Mast track forward improves it but the trade off is the board is then not so neutral when jumping. I've dropped from 16.5cm to 15cm fins and still bounce.

I like the 82 as my allround waveboard as it was comfortable from 5.3-4.2 weather and ideal for perth but with the sail change I'm over powering the board it seems

So what size waveboards compared to sailor weight are people running when at 4.5m sails on 4 batten sails and multi fin boards. Do i need to drop to 75l board or swap to a quad? makers seem to suggest a little more volume with mutli-fin boards than sailor weight.

any suggestion welcome. I'm trying to keep to 2 boards 1 wave and 1 FSW 95l

I would definitely consider that to be a light wind volume board for your weight. That said, the difference you are experiencing with the new sails is probably much more related to the sail itself having a centre of effort further aft which is effecting the way you load the fins. I am not familiar with those sails but if they are even half decent you probably just need to get used to them and adjust your style a bit.

Agree with Brien, also seeing as it seems to have some relationship to the sails just play with the rigging a little, more downhaul/less... more out/less.

See what you can come up with that works.

cheers for info. These RRD sails are far more powerful per size than my old North ICE sails, the 5.3 is same as a 5.6m wind strength wise. Plus as you mention the CoE is more aft. I'm a very front footed sailor so think I'm just using too big a board for the conditions but its hard to tell as the sails are really comfortable to sail and I'm not feeling overpowered but the board is telling me otherwise.

So time to expand the board quiver i think as i like a secure feeling on a wave.

So 75l cult quad for me.

Some sails create more lift/ less downforce as others. they lift you board higher out of the water and make your gear start bounce more easily.This doesnt mean its a bad sail, it just needs a different type of board, that is more attached to the water or fins with less lift.
Like Brien I think you are sailing too big boards.With 75kg an 84-90l would be a really light wind board while you can easily use a 70-75l as mid/highwindboard.As example, i,m a 90kg and my lightwind board is custom 96l trifin and my mid/highwindboard is an custom 84l quad.