Monday, June 29, 2015

Types of Ballast and How it was Installed

Lord Nelson sail boats came standard with cast iron ballast but had a lead ballast option.  Tommy Chen said you can tell which ballast material was used by the depth of the bilge (as measured from the floor boards).  A lead ballasted boat will have a deeper bilge than a cast iron ballasted boat.  Because lead is denser, and therefore a lead ballasted boat will have a lower center of gravity, less volume of lead was used--thus the deeper bilge.  Tommy said that 5.2 metric tons of cast iron or 4.2 metric tons of lead was used.   The manner of ballast placement depended on the type of ballast used.

For a lead ballasted boat, the inside of the keel was first covered with a slurry of dry sand and heat resistant resin.  It was critical that the sand be dry and so the yard had a special, large wok just for heating sand.  Tommy assured me that this was a different wok from which meals were prepared ;-).  Lead pigs were then tightly stacked inside the keel.  Finally, molten lead was poured into the keel fixing everything into place.   

The iron ballast was sand casted, off site by a subcontractor to shapes specified by the yard.  Three separate castings make up the ballast for a Lord Nelson 41.  After the castings were placed inside the keel a sand and resin slurry was poured around them to lock them into place.

Dave Howell, Nellie D. 37VT63

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