Backing plate
- Thread starter slowdog
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Sorry Slowdog, you are going to have to throw us a bone. There are potentally hundreds of things on a 9.9 that would need a backing plate.
As a general rule you want the backing plate to do two things,
1. have enough area to spread out the max load so it does not crush the supporting material and
2. Have enough perimeter (measured around the edges of the backing plate) so that the supporting material does not fail in shear at max load. The first is usually not the controlling equation so focus on making the perimeter large enough and keeping the corners well rounded. The thickness of the supporting material times the perimeter is the shear area. the max load times a safety factor (1.5-2.0) divided by the shear area must be less than the allowable shear stress in the supporting material.
Now if you could give the type of load, and supporting material type and thickness it is a simple matter of figuring the backing plate size.
As a general rule you want the backing plate to do two things,
1. have enough area to spread out the max load so it does not crush the supporting material and
2. Have enough perimeter (measured around the edges of the backing plate) so that the supporting material does not fail in shear at max load. The first is usually not the controlling equation so focus on making the perimeter large enough and keeping the corners well rounded. The thickness of the supporting material times the perimeter is the shear area. the max load times a safety factor (1.5-2.0) divided by the shear area must be less than the allowable shear stress in the supporting material.
Now if you could give the type of load, and supporting material type and thickness it is a simple matter of figuring the backing plate size.
Ok I wil try it's going on a macgregor 22 it's a OMC mount rated for 15 hp I don't know how much pounds it will hold my motor is a Nissan 9.9 long shaft elec start 4 strok I had some pic of the old mount and the new mount but I do not know how to link them in one post
Ahh! a motor mount to the stern of the boat. that is a little more complicated as you also have torques (bending moments) with the motor thrust and the weight being not in line with the bolts.
Going to need the hull thickness and the mount width and breadth and if the hull is cored (and with what) or not.
Going to need the hull thickness and the mount width and breadth and if the hull is cored (and with what) or not.
It can't be too big.
If in doubt, just make it as big is is possible with the room you have. Bigger is almost always better.
If in doubt, just make it as big is is possible with the room you have. Bigger is almost always better.
Mine has 3/4" plywood that was glassed in on the aft port side during mfg by MacGregor. I also had to build the mount out 3" with composite to get the tilt out to work right for my motor.
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