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engine. I used the uppermost step of the companionway and drew a line at the midpoint. If you have leveled the boat, hang a plumb bob from the center mark and align the engine using the center of the engine crankshaft pulley. If you have not leveled the boat - use a large carpenter's square at the midway mark and go down 90 degrees to the center of the engine crankshaft pulley. Centering the engine crankshaft and temporarily installing the prop shaft/stern tube will center the engine the "yaw" direction.
Double check the alignment. Mark the engine mount bolt locations (8 places). Remove the engine and prop shaft. Drill eight 1/8" pilot holes on the mounting hole centerlines - DO NOT DRILL THROUGH THE HULL. At this point you will discover if there is a steel plate cast inside the engine bed by looking at the shavings the drill bit is bringing up. If there are steel bits in the fiberglass dust then you have a steel plate inside the bed. If there are no steel bits coming from the drill bit, you will have to make your own plates. If your engine bed has a steel plate already cast inside the engine bed all you have to do is drill and tap for 3/8-16 bolts. Use the drill bit recommended on the tap and then use the tap. Use a little oil, go slow, a quarter turn in and a quarter out to remove metal bits and you'll be fine. This will make it easier to install the bolts. If your engine bed does not have plates cast inside the bed you will have to make plates with the proper hole locations and holes drilled and tapped for 3/8-16 bolts. I would use approx. 3/8" x 1" x 15" bronze. Use the engine mounts for the proper hole locations. Drill the 8 mounting holes in the engine bed to 1/2" diameter to allow easier installation. Cut a small rectangle in the end of the bed and insert the plate inside the bed and fasten the engine mounting bolts to the plate. If you have access to the underside of the engine bed you may be able to use regular nuts, fender washers and lock washers instead of plates (much easier). Reinstall the engine. Install the engine mounting bolts. Use 3/8-16 stainless steel bolts, washers and lock washers. Grease them heavily. Reinstall the prop shaft, bearings and stern tube.
HORIZONTAL ALIGNMENT
The engine now needs to be aligned to the correct angle in relation to the water. This is what I call the horizontal direction. Your Yanmar should not be mounted more than 15 degrees relative to the water level since the oil pump will be ineffective. The optimum angle to the water would be 0 degrees but that's rarely possible. Between 5 and 10 degrees would be good. Yanmar specs their engine out at 8 degrees. This alignment will be accomplished through the use of the adjustable engine mounts. With a protractor and an adjustable square, mark off whatever angle you desire (I used 5 degrees). If you have leveled the boat, use the adjustable square in conjunction with a bubble level to establish the correct angle. If you have not leveled your boat, use the engine bed as a level reference point and then use the adjustable square and bubble level to establish the correct angle of the engine. With the bubble level/adjustable square on top of the prop shaft, adjust the engine mounts up or down as required until you get the correct angle.
VERTICAL ALIGNMENT
The next step is to ensure correct vertical direction. This is accomplished by making sure the two front mounts have equal amount of threads showing (example: 3/8" port and starboard). Next, the two rear mounts need to have the same amount of threads showing (example: 1/2" port and starboard). Adjust the mounts until you have achieved horizontal and vertical alignment. This might take a while. Once all the directions are correct, tighten the locking nuts. Double check the alignment.
Now you must make a structural support to hold the stern tube in place. This will be accomplished by making a plywood dam (or bulkhead if you wish to call it that) near the end of the stern tube and filling the cavity aft of the dam with chopped fiberglass strand and resin. Using 1/8" plywood, fashion a dam with a slot large enough for the stern tube and curves that match the curves of the bilge. It will take quite a few tries to accomplish this. You can use popsicle sticks and hot melt glue or cardboard to fashion
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