Tube diameter: better big or small?
The diameter of the tubes is generally functional to the size of the boat.
If the dinghy has a tubular section that is too small it becomes a boat, while if it is too large it becomes a balloon. The dimensional range usually fluctuates from a minimum of 40 cm in diameter at the stern to 70 and beyond for boats over ten meters long.
The diameter, and therefore the section, affects what the volume of air is and, therefore, the buoyancy reserve.
The smaller inflatable boats, therefore subject to greater load, have generously sized and proportionally larger tubulars, while those used on the maxi-ribs appear more exhausted and less bulky.
Obviously, each shipyard makes its own choices, often linked not only to technical but also commercial or convenience needs.
The “fender” tubulars, that is, of small section, have little sense when mounted at the bottom, since their purpose is not to affect the attitude but only to provide a buoyancy reserve in a dangerous situation, or they are useful for boarding vehicles. for work (they are often also foamed and cut resistant); in some cases, finally, they only serve to “make a scene” and allow the builder to “sell” it to a rubber dinghy even if, in reality, this is not.
Tubes of generous dimensions, even on inflatable boats that are not exactly small, are usually the prerogative of transport boats, called to bear heavy loads, while on a semi-rigid pleasure boat, which often travels in light weight, they protect better from splashes and also provide a reassuring sense of protection to passengers, but they have two flaws: they offer a remarkable wind grip, which means a high leeway in strong wind and a broken attitude on rough or strong wind in the bow, which in extreme cases can lead to overturning of the medium.
The second flaw is that the very large tubulars greatly reduce the internal space. To overcome this limitation, but also to give the boat a more slender and sporty line, it is customary to taper the sections towards the bow by up to 20%.
To do this, however, requires considerable skill on the part of the builder and affects the final cost of the artifact.