Replacing an Oil Bath Shaft System

2014 May 27
by Chris Brown

strut mold, mock-up and new stainless steel strutThere is a 61 foot Blackwell “Carolina” fishing boat that is going through a major refit in our yard due to fire damage. During this time the owner wanted to return the vessel back to the original shafting arrangement. The vessel was repowered a few years ago and had an Oil Bath Shaft System installed which the owner wanted removed. This job required us to machine new shafts and couplers in our machine shop (Straight Line), order new stainless steel struts, new Veem propellers and a new Tides Marine shaft seal system. In addition to replacing the entire system, we also moved the engines back 8 inches in order to change the trim and stability of the yacht.

Comparing Naval Architect's drawing with plywood mock-up

Comparing Naval Architect’s drawing with plywood mock-up

Since we were making a major change to the running gear we engaged a Naval Architect to redraw the running gear configuration, check all the shafting calculations and design new struts for the boat. The Naval Architect provided us with drawings and dimensions for the struts. However, that was based on limited detailed drawings of the vessel’s hull. From the design, we made a plywood mock-up of the new strut which we hung under the boat in order to refine the measurements. With the plywood in place we are able to set up the optical scope for a perfect alignment and find the exact location of the shaft centerline. Initial drawings from Naval Architects can be +/- .25 inches from the actual numbers needed for installation. Since the strut was molded and cast in stainless steel we needed to be absolutely sure the dimensions were accurate before placing an order with the foundry. Stay tuned for more articles as we align and assemble this vessel.

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