I just purchased a Ritchie bulkhead compass for my 1984 MacGregor 25. The mounting specifications specify a shim to create a 90-degree angle to the water surface. Does anyone out there know what represents a true angle for the port-side bulkhead (which also serves at the forward wall of the cockpit and stern wall of the cabin? There are no reference points to work off of since it appears when the boat is at rest on the water there are no straight lines or vertical lines relative to what may be the water surface or even to the centerline of the boat. The bulkhead I’m referencing is angled slightly forward (vertical axis) and very slightly forward (overhead axis, working from companionway entrance to port side of the boat.
It sounds like you need to use a plumb-bob or level to find “straight up” at the port-side bulkhead. Then you need to make a shim that matches the angle that forms with the bulkhead, and use it when mounting the compass on the bulkhead. There is no set “angle” that anyone can give you, because each boat will float a little differently. Some may have more chain in the anchor locker, or stow diving gear aft. This is a custom installation.
Plum bob is the way to go. simply a string and a weight. load you boat as you would normally have it loaded and use the plum bob to create the correct angle for your wedge piece. transfer it to wood or other medium, (3d printed would be my choice) and attach. Non ferrous materials only please
Follow-up question: So, with the boat on the trailer, could one assume that if I leveled the boat by using the trailer jack and boot stripe as likely the only thing remotely parallel to the water–and then used the plumb bob, I would be about as close as I can get to a perpendicular mount? Fortunately, I have access to a 3-D printer and some folks who know how to program the needed sizes and angles at our local Great Plains MakerSpace.,