Curls....

If you work out 'just' what the righting weight would have to be for a board 1.5 m ( 5 ft) X 0.5m (20") X 0.05m (2"s) - for it to be able to sink on its rail, down to its 'rotational axis line. ( water surface - center line - rotational axis)

Righting Buoyancy to be overcome = (Volume / 2) X (shape percentage) X salt water density

= (1.5 x 0.5 x 0.05) /2 x 80% x 1030 kg/m cubed

= 16 kg's ( roughly 35 lbs)

Its interesting to see how the required weight to 'sink' the board, as it increases in size - grows exponentially, relative to the boards volume.
ie some my have thought because a 2 ft board only needing 2 kg's - if you tripled the length to 6ft - it would only need 6kg's - but - we need to remember that the width and thickness increase - increasing the whole of the volume volumetrically....

You can play around with the numbers - you will find shortening the board has far less impact on the required weight compared to the actual 'thickness' of the board....so keeping it as thin as possible will be ideal.

Bro ********. ...
Share the STOKE !

PS ....You may be' Professor Curls'....once you get this one done.......LOL

It might be an idea to simply pick up a Kids Board - 4-5ft in size - I reckon you could work with it for starters....