I thought it wise to look into the size of narrow boats.
This link - www.abnb.co.uk/submenupages/length.html - has provided some very useful information on the general size of different canals and as such what size boats can use them. It helps to grasp an idea of what is considered large or small.
I have also looked at boat plans too.
I have also looked at boat plans too.
Sources
http://www.abnb.co.uk/submenupages/length.html
http://www.virtualperspective.co.uk/img/images/canal_boat_layouts/Canal_Narrow_Boat_layout_designer_60ftlayout_eg.gif
http://www.abnb.co.uk/submenupages/length.html
http://www.virtualperspective.co.uk/img/images/canal_boat_layouts/Canal_Narrow_Boat_layout_designer_60ftlayout_eg.gif