In your post, you mention flexible conduit. Screwfix supply rigid and flexible conduit, mostly plastic type. The rigid type is good for use on a boat, as it has smooth inner surface and cables pull through easily. It can be bent, but you need to take care.
Flexible conduit has ridges, so can damage cable insulation when pulling cables (especially when there are lots of other cables already in the conduit).
Some electrical wholesalers sell Marshall Tufflex supertube, which is a flexible conduit but with smooth surfaces. It comes on a 10m roll but most wholesalers would sell smaller quantities.