Assembly in Action: Epoxy Helps Build Ships
Tim Hodgdon is the owner of the company and the fifth generation of his family to carry on the name. When he took over the business from his father, Sonny, the time-honored method of fastening planks on frames was still being practiced.
When work began on the 154-foot 7-inch ketch Scheherazade, Hodgdon knew that to compete in an increasingly high-tech market, it was imperative to implement the latest technologies and processes into designing and constructing yachts. That research led to the use of cold molding. This process uses epoxy to bond a successive series of thin wood laminates to a wood frame, providing a strong and stable hull.
Traditional methods are used to fasten the first layer of planking, which also serves as the finished interior, to the frames. Then, wood laminate strips are coated with epoxy and stapled over the planks. Successive layers of laminates ultimately yield a hull thickness of 3-1/2 inches or more depending on the hull size.
Following the application of each laminate series, the strips are held in place to achieve full bond strength by using a method known as "vacuum bagging." This method involves large sheets of plastic bubble wrap being laid over the wood and sealed around the perimeter. A vacuum pump is connected to the plastic "tent," and the air is pumped out. This yields a uniform clamping force over the entire surface.
Having built two yachts using this process, Hodgdon knew that to ensure optimal bonding, mixing large quantities of epoxy in a timely fashion and maintaining the mix ratio during the entire planking process was important.
On previous boats, the standard practice was to hand mix about 5 gallons of epoxy and then pour it into paint trays. Workers would then roll the adhesive onto the wood strips. The drawbacks included difficulty maintaining correct mix ratio, loss of working time from mix to application, and excessive handling, waste and mess. However, the primary concerns were that an incorrect mix ratio could cause loss of critical bonding properties and delamination. Repairing delaminations is time-consuming and costly.
For these reasons, Hodgdon purchased a meter, mix and dispense system from Sheepscot Machine Works (Newcastle, ME). The Model 9450 double-acting meter, mix and dispense system provides continuous fluid output, which is a critical feature for satisfying the large output demand. With pneumatic supply pumps, and a low-viscosity epoxy supplied by Gougeon Brothers (Bay City, MI), Sheepscot determined that the Model 9450 could deliver upward of 1 gallon per minute of mixed material.
A cart with casters allows moving the system and its associated feed drum throughout the building, depending on where the planking is taking place. It can also be moved between the two buildings that are used for various bonding tasks.
Although the system was chosen primarily for its ability to optimize the cold molding process, the staff at Hodgdon’s is now using the system on miscellaneous bonding projects on interior components. Now that the Scheherazade’s hull has been molded and turned upright, work will start on other projects, including epoxy saturation of carbon fiber sheets used to fabricate deck tops and interior partitions. Wherever medium to large quantities of adhesive are needed, the 9450 system will be used.
For more information on metering, mixing and dispensing equipment, call 207-563-2299 or visit www.sheepscotmachine.com.
For more information on epoxies, call 989-684-6881 or visit www.gougeon.com.