Velvia 50 fast enough with a single strobe?

I'm a newbie, and have a Nikonos V with 35mm and 15mm lenses, and a single SB-105 strobe in my arsenal. Never tried shooting Velvia 50 before, but am tempted. Will it give me good results or will I struggle with insufficient light? I'm planning to do some shallow dives with rays and sharks, and but may venture out deeper to some sea mounts (25-35m).

It worked fine for me - it all depends on your aperture. The 105 is a great strobe but will struggle to cover the 15mm.

Should be fine - partic as you are not planning to light the entire shot with this strobe. There will be plenty of ambient light about which you should use.