Here's the thing , it comes down to maths .
Lets say 250 mm is a good spacing with a pool noodle over the dowl , could go 220 with straps and still be smiling.
Thats what I have with a little to spare . Horizontal.
It depends on the amount of boards .
A 3m garage ceiling can hold 11 boards
If you have less than 11, standing up is better .
Standing up between dowls , at least 16 sails and 8 masts . 1 m wide .
A few booms hanging on 1 dowl.
A car length garage wall can hold a lot of stuff , no wider than your widest board.
Your welcome