Really guys, that is is non-sense.

I hardly never refer to my myself as a fully schooled mechanical engineer, but I am. And that rivet and hole did not make weaken the pole by any significant amount. That pole is under normal sailing circumstances under compression, in that situation it is practicall impossile to snap it as is show in the pictures.

The break surface is smooth without any deformantion that would occur when it snapped under compression. This pole snapped under tension, which can only mean that the (initial) damage was fully caused by a loading situation unrelated to sailing or the spinnaker. Additionally crack growth can not happen under compression as the crack itself is closed by the compressional forces. If robi broke this pole with only a very small amount of force then a small crack must have been have present already AND the pole was broken in a way you tear a piece of paper. It is very hard to pull part apart when it is loaded in its plane, but by tearing it (skewed loads) it is alot more easier. This directly points to a misloading of the pole as again spi forces while sailing will never lead to unskewed forces. Most likely Robi could have sailed with this pole and have it survive even with the prior damage being there. The spi pole design is actually very well made from the spi loads point of view. Especially with the stabilizing lines from the bridle chainplates to the strut.

This pole was certainly broken (or initial damaged) by a force that was put on it outside of the upper vertical plane. Either a downward force or a horizontal force with a downward component.

The rivet hole, errornously refered to as weakening the pole, is of no consequence under spi loads as the compression forces in the pole do not allow a crack to develop around this hole. Therefor the hole is perfectly acceptable for sailing. Even when it is fitted under prebend. Metal fatique is not an issue either again because of the compression loads and the the fact that there are only very small fluctuations in the loading while sailing. Both of these work again crack growth with the last even delaying crack initiation to many many many fluctuations, properly in the order of 100.000's or millions of them. These will very easily make up 10 or more years of hard use.

The rivet hole is also insignificant because under spi loads the pole is not under bending at all. The tip support lines transform all possible bending into compression loads. Ergo the material around the full circumference of the pole is under loading and not just predominantly the part on the top and bottom as would be the case in bending. The crosssectional area of the whole is ONLY 5 % of the total crossectional area of the ring of material. This is downright negligiable.

However this whole situation changes when the pole is not loaded by the spi, but by a unrelated to sailing force that has a downward component when the spi pole tip is unsupported in that direction by tying the two halyards to eachother and tensioning them up. The support wires will now hang slack and all the load on the pole, with a very significant leverage, must be taking up by bending. It will be as if the pole it just stuck into a wall with 2 mtr sticking up and somebody is pushing down on its end. It will bend downward to same degree, as far as its elasticity will allow, and then bend permanently or break. Many of us use this principle when breaking and dividing a bar of chocolat on the corner of a table or bending waterpipes or steel garden wires.

I can assure everybody that a pole supported by a nacra ring will bend and break just as easily in this situation. So don't blame the rivet hole, it is really not the culprit

Wouter