Nto over thinking it. Just want to get the right stuff. Am familiar with mooring a boat, knots etc, but never kitted a boat before as always used someone elses.
What is confusing is that on the web the strength (i.e. diamaeter) of rope is generally by length of boat, and I guess they mean a yacht. As a RIB is a lot lighter than a yacht, I guess you can go for thinner, less bulky rope.
So, what diameter rope for a 6.5m RIB?
My list so far for my 6.5m RIB is:
1off x 7m for Painter = 7m
2off x 7m for Springs = 14m
2off x 3.5m for Bow & Stern = 7m
2off x 15m for towing, quay walls etc. = 30m
Total length is 58m. So might as well get a 100m reel of Nylon and use the rest for anchor line and spare. Cheap at £57 from Mooring Ropes from Boat Gear Direct
Grateful for for the view on this approach on here. Ta.
Apologies if I came across rude when suggesting you were over thinking it.
I think that your numbers and lengths are good but think the line is too thin. Not strength wise but for ease of handling.
I would go a lot thicker for the painter and probably 14 or 16 mm for the mooring lines.
I would agree that you could use floating line for the anchor and it will make no real world difference.
Yes you can get much expensive ropes for particular purposes that will "perform" better but for general stuff like this, I don't see the point TBH.