Improving the design and functionality of an older vessel.

Old Shaft of the Yacht

While fabricating new 125mm (near 5 inch) shafts for a 1988 145 foot NQEA Lloyd’s Registered yacht, we had an opportunity to improve the design and functionality of the vessel.

The boat used a coupler nut attachment with one big nut on the coupler end in the engine room. The nut that was used would be similar to a propeller nut. Since the coupler nut is usually recessed into the coupler, it takes a very large socket to tighten or loosen it. In order to perform the work, we would have to make custom sockets that would fit on a 1” wrench and then, because of the amount of torque required, put a 3 foot long pipe on the wrench to get the leverage.  Because this work is happening in the engine room between the engine and the shaft, we often find that do not have enough room to swing a long pipe or get the socket in place.

A more modern approach is the keeper plate or shaft locking plate.  The end of the shaft

New couplet

is cut flush, drilled and tapped for much smaller bolts.  Three ¾” hardened bolts are torqued down in a circle to draw the plate and coupler onto the shaft taper.  A common ¾” socket can be used on a regular ½” or ¾” wrench.  We no longer needed long cheater pipes since the torque required to draw up the plate is considerably less than that required on one big nut.

Since we were making new shafts, we wanted to take the opportunity to improve on this 1988 vessel.  We used a naval architect to make the drawings and got everything approved by Lloyd’s surveyors in advance.