Do they rent kayaks outside of the tours for personal use?

Is there weight restrictions

We don't do unguided rentals unless customers have a sea kayaking certification equivalent to 3 stars in the American Canoe Association, or comparable skills. The Mountaineers Sea Kayaking endorsement is valid for example.

From the FAQ: Can I rent a kayak to use without a guide? ​ Generally no but we will rent boats if you have a certification of a 3 star rating in the BCU or ACA systems or equivalent international rating. Further if you can demonstrate that you possess the skills indicated by a 3 star rating or higher we will rent to you. If you don't possess these certifications we will not be able to make an unguided rental to you.