Passport 40 rudder prepared as a mold plug
The rudder on a sailboat is a very important yet often neglected part of the boat. Over 30 years of service and the effects of corrosion (galvanic and electrolytic) caused crevice pitting in the shaft of my friend’s rudder on his Passport 40. The interior had absorbed water as well, which is largely due to the different expansion rates of the stainless steel shaft and fibreglass rudder skins. This rudder is filled with a dense foam, likely poured in after bonding the skins together over the shaft. After considerable discussion, we decided to build a completely new rudder, using the old one as a plug for a mold. We contacted the boat designer whom was very willing to discuss this project. The original rudder drawings were purchased. The mold is used to make completely new skins. New metal parts were ordered and sent to the machine shop. Then the difficult process of preparing the old rudder, expanding in portions from the interior metal deterioration began. Portions had to be ground down and other portions had to be filled to bring the rudder back to “reasonable” and original shape. The picture above is after the fairing process. A parting board seen in the background of the photo was made to provide a flat surface around the centerline of the rudder.
1st half of rudder mold over parting board
Small cracks between the parting board and rudder are plugged with putty and then the whole exposed surface is waxed and coated with mold release (PVA). Black pigmented, thickened resin is coated over the parting board and rudder plug, which is allowed to partially cure. The layers of surface veil, and glass cloth are laminated over top to build up the desired thickness of the mold. Plywood is bonded to the perimeter above the parting board to form a strong and durable flange and glassed over. The ribs are cut and fitted to make a level base so the mold can be turned over and used on a flat table. This is very important to not build the new rudder with an undesirable twist. “X” reinforcements of Styrofoam scraps are glassed over the larger areas to stiffen the mold. When done correctly, the result is a strong, straight and stiff mold.
Completed 1st half of female rudder mold
After cure of the resin, the 1st half is lifted off the parting board and plug, revealing a nearly perfect female mold of the rudder plug. At this point, the mold is cleaned and high spots are lightly sanded. The perimeter flange area is sanded to a smooth, flat surface with a sharply defined edge. Then the surface is waxed 5 times and mold release (PVA) is applied. This prevents and resin that seeps between mold and plug from sticking to the female mold. The plug is placed back into the 1st half and waxed. The edge is sealed with PVA. Because the old shaft was undersized due to corrosion, we decided to make a urethane mold insert at the shaft and bearing portions of the mold. The urethane will compress slightly around the new shaft
Preparing to make the 2nd half of rudder mold
Urethane Mold Insert
Making the 2nd female mold half
After proper preparation, pigmented, thickened resin is again painted onto the plug and flange to form a smooth mold surface. Note, we ran out of black pigment and used grey which I had on hand. Perhaps the contrast in colours will help us in lamination, so we make one of each half and not two of the same. 🙂
Laminated 2nd half of rudder mold
Ribs added to rudder mold
Again, plywood is laminated to the perimeter. Ribs and cross braces are applied. But this time, before removal, registration pin holes are drilled into the flange area. Brass tubing pieces are bonded into the holes. Washers and nuts are glued to the bottom half to receive bolts from the top. This will allow us to bolt the aligned halves together when the time comes to bond the rudder together. When cured, the two halves are separated, cleaned up and waxed.
Completed 2nd half of female rudder mold
The second half as removed from the mold making process.
Now we wait for the metal work to be done so we can trail fit the metal in the mold. To be continued….