Fixing Ship Ramp: Winch vs Windlass

[rodoka]

Hi i got a problem and i want to share it with you guys. i am new in the forum. Today i was in a shipyard trying to fix a ship's ramp.

The sketch shows that the wire rope is connected to the middle of the ramp. But i think that it is better to connect it to the edge of the ramp because the winch will work more restful. But in the other hand if i put it on the edge, the winch will not bring the ramp up instead of pulling it. what's your opinion? what if the Block-pulley should be placed little bit right? The ramp is about 250kg weight Sorry for bad the english its not my native language

 

[anorlunda]

By edge, I assume you mean the far end of the ramp. In your drawing, the end of the ramp will be high above the pulley when the ramp is up nearly 90 degrees. At that angle, the cable will be pulling down on the ramp, not pulling to the left.

The best place to attach the cable is the point where the end of the cable is near the pulley when the ramp is fully raised.

 

[rodoka]

thank you very much!

 

[sophiecentaur]

The best place to attach the cable is the point where the end of the cable is near the pulley when the ramp is fully raised.

That would be very good as a rule of thumb but you can see mechanisms all over the place that don't follow that rule. The angles that are used in Hydraulic Cranes often appear far from optimal (intuitively) so you would need to do some detailed calculations of a range of ramp angles. Using simple calculations of Moments about the pivot for various angles would allow you to put points on a graph. That would be a good exercise to give you an appreciation of the way the force varies according to fixing position and elevation angle. If you don't fancy the Maths, you could draw a number of diagrams for yourself to demonstrate the useful points that @anorlunda makes. There may be a number of practical details of the ship's layout that could limit your options(?).
If you are bothered about available force from the winch, you can always add a pulley system to give you some mechanical advantage (at the expense of time taken to raise the ramp, of course).
PS Could there ever be an extra load, getting the lift started from the grooves in the roadway?

 

[LURCH]

Hey wait a minute, that’s a hull schematic of the Enterprise! (At What ship yard do you work?)