[R. Kolick]

i've read a few articles on antique swords mainly about ancient and dark age swords so my understandung on fullers is very minimal and i was wondering what advantage does double and triple fullers have over broad-fuller or opposing fullers and what about narrow fullers if anyone could tell me the differnt purpose and advantages of each of these types of fullers thanks

[J.D. Crawford]

Here is my understanding: A fullered blade has sometimes been likened to an I beam in terms of optimizing between strength and mass. In two blades of the same width and thickness, multple fullers compared to a wide fuller is like a stack of narrow I beams compared to one wider I beam, so should be stronger. But the price is greater mass. Likewise a narrow fuller (in blade with otherwise the same cross section) means more strength but proportionately more mass. This might be what you want for some purposes, but this could co-vary with other factors like blade width and cross section. Multiple fullers have appeard throughout the history of the sword but in the Viking and high medieval periods single fullers were far more common, probably because of weight and simplicty of manufacture. One other factor is that multiple fullers just look cool (or so some of us think) - so they may have been done for esthetic purposes in some or even most cases.

[Justin King]

Any time you remove material from the cross section of a blade, you will reduce both the weight and the rigidity. The amount of wieght removed can be considered a fixed value, calculated by the amount of material removed. The effect on rigidity is variable, according to how it affects the cross section as a whole. So the affect of fullers is dependent not only on the number and size of the fullers, but the cross section of the blade itself.
A single wide fuller, if applied to a diamond section blade, will make it lighter but will reduce the maximum thickness of the blade and make it much more flexible as well. Twin side-by side fullers on the same blade can be made so as to not reduce the thickness of the blade at the central ridge, and therefore will have less effect on rigidity. This principle is well-developed in the hollow-ground diamond section blades that can be seen on a lot of 15th century swords, where the twin fullers encompass the entire width and length of the bevels.
When dealing with a blade of hexagonal section, the number and configuration of the fullers generally have less effect on rigidity because the ridges in between the fullers still retain the original thickness of the flat central area. It is notable that the complex fuller configurations that you can see on a lot of 16th century swords are, more often than not, combined with a blade of hexagonal section.