Below is an excerpt from the "Conclusions" section of the report, specifically addressing the failure of the rudder
5.3 RUDDERSTOCK FAILURE
5.3.1 The chemical composition of the rudderstock material corresponded to the
5.3.2 The mechanical characteristics of yield point and tensile strength determined
are about 10% above the upper limits of the strength class F32, which means
the rudderstock had a reduced toughness leading to fast growth of any fissure
5.3.3 The rudderstock was roughly machined.
A surface finish
of 80mm is rougher than the surface finish
achieved for sand
casting and flame cutting. As stated in the test report in Appendix 7.7 80mm is
"considered as very rough machine work".
5.3.4 The macroscopic findings indicate a fatigue fracture due to a V-notch (approx.
0.3mm) in the circumferential direction with unsymmetrical bending stress at
It is unclear how the initial V notch defect was formed. There are two possible
5.3.5 The defect was caused during manufacturing which resulted in a rough surface
5.3.6 The retrofitted autopilot
tiller arm was clamped to the rudderstock so the
lower edge of the retrofitted tiller arm caught the top of the taper or a
particle was present when the new tiller was clamped onto the rudderstock
causing the initiating V-Notch defect. The presence of an initial defect leads to rapid growth of a fatigue fracture.
Final failure will occur when the original diameter of the rudderstock is
sufficiently reduced to lead to failure. Aluminium does not have a fatigue
endurance limit unlike steel
5.3.7 The surface finish detailed on the designers drawing, see Appendix 7.1, was
specified as "smooth" and the drawing specified no dimensional tolerances.
On a constructional drawing the surface finish and dimensional tolerances
should be specified in accordance with best engineering practice. "Smooth" is
not a recognised engineering specification.
5.3.8 The exposed part of the rudderstock between the underside of the hull
top of the rudder blade was corroded.
The antifouling (Awlgrip Gold) was incompatible with the aluminium
rudderstock. The manufacturers of Awlgrip have advised that Awlgrip Gold
should not be used on aluminium components as it is copper based and causes
if applied to aluminium. Hanse Yachts advised that this type of
has been found on other Hanse Yachts. Continued corrosion of the
rudderstock could eventually lead to failure.
5.3.9 The owners manual does not warn the owner about the use of copper based
What I took away from the report was, if you are going to have an aluminium rudder post it has to be machined and installed to very very standards, which wasn't the case here. Aluminium rudder post can develop microscopic cracks that lead to "rapid growth of a fatigue failure". How do you find these microscopic cracks, on an installed rudder post? I think one would be better off using a material that doesn't require absolute perfection to avoid catastrophic failure.
It also appears that some things have fallen out of favour, rudder tubes that finish above the waterline and water
tight bulkheads, both of which would have prevented the boat from sinking.