You've probably looked at the folded dimensions (cm):
Birdy: 80x34x62
Dahon Jetstream: 83x29x66
BikeFriday pakit: 96x25x61
Hummingbird: 117x20x60
Tern BYB: 81x33x51
Dahon Qix: 67x26x60
Brompton: 58.5x27x56
Dahon Curl: 58x27x54
Listed in descending order of total folded (XYZ) volume. Perhaps there's one dimension that's more critical to your space on your boat or dinghy.
Thanks, that's really useful!!
I'm really surprised the Pakit is so bulky!! That scratches that. And the Birdy it turns out is even bulkier than the Jetstream!!
What's critical on the boat is not really any one dimension, so much as low volume (the Jetstream takes up too big a portion of my lazarette, even on a 54' boat), and even more important -- that bits don't protrude out of it so that it can be smoothly fit in with other stuff (like sailbags), and you don't set it down on vulnerable bits like the chainwheel. And there's no derailleur sticking out like the Jetstream. So a well-fitting bag or case would be a huge plus.
I guess I'm back to the Brommie.