Trailering, engines up or down?

C-Green":2k1kshy8 said:
I agree with sssobol on the transom saver analysis except for his comment that says the stress will be on the transom if the saver is attached to the transom instead of the trailer. If attached at the base of the transom, there could be no movement because of the hull/stern attachment at that point and therefore no movement at all by the OB when hitting a pothole or bump. Seems to me to be better than an attachment to the trailer except for the stern/hull penetrations to make an adequate attachment point for the saver. ...
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But if the transom saver is attached to the boat, then you are not unloading the weight of the engine off the transom, maybe you are just bracing it better. The advertised purpose of the transom saver is to relieve the transom of some of the weight of the engine when the boat is trailered.
 
I thought the purpose of a transom saver was to reduce the twisting force of the motor on the top of the transom and the tilt mechanism if the motor is carried tilted up and the road is bouncy.

If the boat is securely strapped to the trailer (which it should be), and the transom saver securely connects the lower unit to the trailer, then the motor should not be able to put a twisting force on the top of the transom.

See picture in this link:

https://www.ebay.com/i/302314456705?chn ... gLAYPD_BwE
 
My thought is that the transom saver supports minimal weight and its main purpose is to prevent twisting of the transom caused by the motor bouncing (actually the lower unit moving up and down thus flexing the top of the transom at the OB's attachment point)when the OB's lower unit is raised and not supported. This twisting is minimal if the OB is not raised. Admittedly if the boat is tightly secured to the trailer, the saver will work as advertised but it seems to me that with the sum of hull flex, trailer frame flex and bunk or roller support flex on road bumps/pot holes there is inevitably some movement between the trailer and the boat.

MTCW, Jay
 
The power head is where a lot of the mass is. The motor rotates around the motor mount. Any time the CG of the motor is not over the centerline of the transom there is going to be a torque applied to the transom from vertical bumps. In the normal position the motor is behind the transom and applies a torque on the transom just sitting there. Even if the motor is aligned vertically, you'll still have torque applied when the vehicle accelerates and decelerates. Although this torque could be less and will be applied less sharply.
 
ssolbol, I fully agree with your last post. Note that I said "This twisting is minimal if the OB is not raised." So I agree there is always some twist. As for the saver's advertised functions, marketing guys/gals are sales people not engineers/scientists and are addressing the general public in general.

Jay
 
ssobol":1y5jb8t9 said:
The power head is where a lot of the mass is. The motor rotates around the motor mount. Any time the CG of the motor is not over the centerline of the transom there is going to be a torque applied to the transom from vertical bumps. In the normal position the motor is behind the transom and applies a torque on the transom just sitting there. Even if the motor is aligned vertically, you'll still have torque applied when the vehicle accelerates and decelerates. Although this torque could be less and will be applied less sharply.
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This is a good point, but is the motor center of gravity over the transom centerline when running on the water or down position? I suspect the motor trimmed up is the point where the CG is over the transom, not in the running or "down" position.

In any case it is a good idea to have the motor locked to one side or the center when trailering and a hydraulic system. If the motor is not locked--then the pressure of bumps along the road, could cause damage to seals in the cylinder or valves in the steering pump.
 
thataway":2ggmyqi2 said:
... This is a good point, but is the motor center of gravity over the transom centerline when running on the water or down position? I suspect the motor trimmed up is the point where the CG is over the transom, not in the running or "down" position. ...
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The CG of the motor in the trimmed position is probably not over the centerline of the transom, although this probably varies by engine model. However, if the engine it running and pushing the boat, the torque on the transom from the engine thrust is WAY more than the force caused by the engine CG position.

I suppose if you really wanted to find out the CG of your engine you could disconnect the tilt linkage and manually tilt the engine until it balances. In some tilt systems you can manually open a bypass in the tilt hydraulics that let you manually tilt the engine without disconnecting things.
 
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