1) Is there a rule of thumb on what size cleats you need for a particular size boat? i.e size cleat you need for a 20 ft boat? size you need for a 40 ft boat , size you need for 60 ft boat, 100 ft boat etc. etc.
Answer: There is no standard Cleat size per boat size because cleats can be used for different purposes, but as a general rule of thumb you should gauge by the amount of force you will have on the cleat and the use. For example, are you Towing with the Cleat or just tying to a dock? You need to examine the load that will be displaced on the cleat. You also need to carefully examine how the cleat is fastened to insure it will hold to the load desired. In our opinion you should always through bolt a cleat and use a backing plate if substantial load will be applied. Another consideration is what size line will be used, and this can also be a guide regarding the load that may be expected. Bow cleats need to be generous to accept large mooring pendants of up to 1" . Stern and spring cleats depend on dock line sizes.
You will likely want to consult a marine contractor or boat yard unless you are experienced with hardware selection.
2) I have noticed some cleats have different Bolt patterns, even some that are the same size? i.e 8" Herreshoff cleat bolt pattern is 2.82" and 8" Blue water cleat bolt pattern is 3.32" why the difference in sizes? Does that have to do with what kind of boat it's going on?
Answer: The bolt pattern on cleats has to do with the size and assumed work load that will be displaced on the cleat. Blue water cleats are heavier duty and have a wider base that allows for stronger mounting.
3) What is the most common size bolt patterns for 6" , 8" , 10" , 12" & 15" size cleats?
Answer:These will vary slightly from manufacturer to manufacturer, but Suncor product represents a very common configuration.