There are three principal reasons why: first, the only reinforcement to the hull is in the sandwich forward of the bulkhead by the head where the first four or five feet of the hull in the bow are reinforced with balsa as a core. The fiberglass to the remainder of the hull will "oilcan" or produce ripples or waves along its length if there is too much load on one point - this is a racing hull, not a cruising hull and the fiberglass layup is remarkably thin. Second, the hull shape is such that a fender hanging straight down from the sheer will not touch the hull when the vessel is in the slip. As such, when the vessel moves laterally with a wave or swell, there is a tendency for the hull to suffer from dynamic impact and that needs to be spread as widely as possible. A vertical rope fender would not answer well to this, unless it were very wide (we could always lace two together!) and that is impractical on the basis of weight on the sheer. A horizontal fender would work well, but would tend to droop into the salt water and wear out very quickly, apart from having problems with finding non-abrading suspension points (it is only a 27 ft hull length!). Third, and this is not insurmountable, the hull is painted with a very weak paint. A rope fender rolling or rubbing would quickly strip that paint and start to work through the gelcoat. Until we replace the paint with a substantial epoxy coat (which we do not plan on doing for a couple of years) with more hard-wearing characteristics, we choose not to use traditional materials like manila or coir, both of which are very scratchy to the paint surface - it would be like using a Scotchbrite fender covering! Now, if we had a more substantial hull such as yours or a wood hull, varnished or oiled, it would be more appropriate and would undoubtedly be worth the extra care it would take to keep the hull in great shape while protecting it from the (concrete) dock sides. Meanwhile, we use multiple semi-inflated rubber condoms! An expedient choice until we can do things (perhaps like getting one of those free boats in Classic Boat magazine?!) that will improve our situation.
