il Mostro Bulb Project
"PUMA’s il Mostro finished 2nd in the 2008-2009 Volvo Ocean Race. Since this amazing feat, the boat has steadily been updated while being used as a training platform for PUMA Ocean Racing during the summer of 2010. During that summer il Mostro placed 2nd in the Newport-Bermuda Race under ORR …" says SailSpeed in a 2011 arcticle.
We were very pleased to be asked to construct a replacement bulb for this 2008 70′ Goetz Custom Boats "speedster" which was delivered well within 0.01% of the total specified weight. This replacement was not a typical simple cast replacement bulb because of the very high precision CNC machined bulb. The general process of manufacturing the bulb is similar to other standard "cast bulbs" with a few major exceptions. Because the bulb was to be machined after casting the pattern process was slightly altered, the needed pattern was not simply the offered shape plus the needed shrinkage added. This project required the added step of increasing the pattern size in all dimensions to enable material to be added allowed the final shape to be cut.
There was also the need for a custom designed and manufactured internal weldment (using 17-4 Ph SS) to be located in the bulb, which was used to secure the fin. This part also required modified casting fixtures, not a large departure from what we normally do, but we were using new geometry that made production more complicated. All of the process was worked through under the direction and acceptance for the yacht design firm Juan Yacht Design of Spain. It was a pleasure to work with them on this project. The casting process required great attention to detail as the casting was to have the highest density that was possible from the process. The final part was in fact within 0.01% of weight estimate. Once the casting process was complete the process moved to the machine shop which had manufactured the necessary fixture to support and locate the bulb on the boring mill ahead of time. The general process was to locate the needed reference point on the bulb and then adjust the position of the bulb so that there is material on all surfaces to be cut off. All parts had to be "dialed off" to ensure the digital surface model fits on the rough material provided. The actual cutting process was completed by a 5 axis horizontal boring mill, in 2 stages with a roughing cut and a finishing cut, with the level of accuracy better than 0.004" from the surface file.
Once the cutting was complete the remaining scallops were removed carefully, making the surface both accurate and smooth. The bulb was then released to the finishing department, where the coating process was completed. This was simply a careful buildup of epoxy based barrier coats put on in a manner to add very little surface roughness. The aim is to protect the bulb and put virtually no "orange peel" on it so you don’t have to have to sand the surface, running the risk of changing the shape. The bulb was then left in the heat room to allow a full and complete cure to the paint.
And finally the il Mostro bulb was packaged on a custom made cradle with shipping crate, loaded on a truck and delivered to the customer for installation.