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master OM Tartan 3400 2012.doc
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3.5 Ballast
The keel of your Tartan Yacht is of lead alloyed with antimony for added strength and cast to exacting
tolerances. In addition to providing the yacht's stability, the foil shape of the keel produces hydrodynamic
lift while sailing to weather, enhancing upwind performance.
The keel is fastened to the hull by means of stainless steel bolts, which are cast into the lead. These bolts
project through the bottom of the boat and are bedded with sealing material to prevent water leaks. The
bolts are secured by stainless steel nuts and washers, which are visible in the bilge.
4.0 RIGGING
4.1
General Description
In order to tune your mast effectively, it is important that you are familiar with the basic associated
principles. Some definitions and explanations follow: The term 'standing rigging' refers to fixed pieces
of stainless steel rod or wire supporting the mast. Those, which offer fore and aft support, are called
'stays' (backstay, forestay, etc.). Those, which provide transverse support, are called 'shrouds'.
The shroud running from the masthead to a chainplate on the deck near the rail is called the main or upper
shroud. If it were to travel this route directly, the angle of support would be so fine as to induce
extremely large tensile forces in the shroud and equally large compressive forces in the mast. To increase
this angle of support, a spreader is positioned according to load requirements. This spreader should be
angled upwards to bisect the angle formed by the shroud as it bends over the spreader tip. A horizontal
spreader, or worse still a spreader angled downwards, is dangerous. The spreader may be forced to slip
further down the shroud resulting in the loss of the spreader and possible collapse of the mast.
The spreader becomes a compressive member, and when properly loaded tends to push the middle of the
mast to leeward. To eliminate such a leeward bow, a lower shroud is installed running from the mast at
the base of the spreader down to the deck near the upper shroud chainplate. The primary purpose of the
lower shroud is to provide athwartship support. The addition of the spreader and the lower shroud means
that the mast is supported at more places transversely than fore and aft. Therefore, the mast itself need
not be as strong transversely as fore and aft. The mast then may have a lesser (more aerodynamically
advantageous) transverse dimension than fore and aft dimension.
4.2
Spars
Based upon the relationships described above, the more spreaders and shrouds used transversely, and the
more intermediate forestays and running backstays used longitudinally, the smaller the allowable mast
section may be. This can be advantageous as weight aloft and windage may be reduced in addition to
minimizing the undesirable aerodynamic effect of the mast on the mainsail. The smaller the mast section,
the less disturbed is the air flow across the main. However, a practical and functional balance of rig
complexity and aerodynamic efficiency has governed the design of the rig of the Tartan 3400. The spar
section and carbon fiber laminate schedule have been engineered to provide a strong, stiff and safe mast
while minimizing weight aloft.