And another thing, Jeff says - ensure that the rope you are using is dry, then your fender will firm up nicely. If you do use damp or wet rope, your fender will end up with ‘brewer’s droop’ when dry. 
Wow you guys are great!! Thanks for all the info. For those of you who asked questions this is what the fender will be going on:
I have a 37 ft morgan sailboat. 1976, Solid fiberglass hull, Will be used in salt and brackish water on the connecticut river in the U.S. Boat weighs about 9 tons. Has a thick black rubber rub rail built in but it is up high. I had the boat at a mooring last summer and am not sure wether i will be at a mooring or a slip in the spring. These fenders will probably not be my fenders used at my home slip ( if there is one). Will be used when going somewhere (to another port). Basically for show. i have inflatable fenders for when i am not around. (although i do like the idea of covering those fenders as previously mentioned) I really like the look of the rope fenders and thought it might be fun to make a few myself for the boat. I like the look of hemp but was hoping for something more durable like poly. I am in the us so rope in the uK is not practical for me. There is however west marine, defender and boaters world in my area. and also several chain hardware stores like home depot and lowels. I was looking mostly for side fenders but a nice bow fender for the occasion when i am pulling into a slip would be really nice.
I am not a master at knotcraft by any means so i appreciate any and all advice. I plan on getting the book mentioned previously. But if anybody had any clear and easy instructions, plans, pics or diagrams they could share that would be greatly appreciated.
Thanks for the great responses again and i look forward to more conversations with all of you.
jason
is there another name for “coir” i have never heard of that.
jason
Coir is coconut fiber
Have a great time with your fender making!
I have a 27 ft Morgan and mine would definitely not do well with rope fenders, but I know of others with a 37 ft Morgan - very solid construction! Be sure to mark the places on the hull (or at least know where they are) where the bulkheads are situated so that you don’t put a fender where there is little to no real support! ;D
Lindsey
Jason,
If you like the look of hemp but want to get the quality of modern fibres, look for the hemp look-alikes.
There are several brands that have the kind of rope, all under different names.
And there is a lot of difference in how ‘hemp’ they look. It pays to have a good look around before you buy large quantities.
Willeke
i am curious as to why you say your boat will not do well with rope fenders?
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.