Fixing Ship Ramp: Winch vs Windlass

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Discussion Overview

The discussion revolves around the mechanics of fixing a ship's ramp, specifically debating the optimal attachment point for a winch cable. Participants explore the implications of different attachment points on the ramp's operation, considering both theoretical and practical aspects of the setup.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests connecting the winch cable to the edge of the ramp for better operation, while acknowledging that this may cause the winch to pull the ramp instead of lifting it.
  • Another participant clarifies that attaching the cable at the far end of the ramp would result in the cable pulling down when the ramp is raised nearly vertical, rather than pulling horizontally.
  • A later reply proposes that while the suggested attachment point is a good rule of thumb, real-world mechanisms may not always adhere to this principle, and detailed calculations of moments at various angles could provide better insights.
  • There is a mention of the potential for adding a pulley system to increase mechanical advantage, although this may slow down the ramp's lifting process.
  • One participant humorously points out that the schematic shared resembles that of the Enterprise, questioning the shipyard's authenticity.

Areas of Agreement / Disagreement

Participants express differing views on the optimal attachment point for the winch cable, with no consensus reached on the best approach. The discussion includes both theoretical considerations and practical implications, indicating ongoing uncertainty.

Contextual Notes

Participants note that practical details of the ship's layout may limit options for cable attachment, and there are unresolved questions regarding the effects of additional loads when starting the lift.

rodoka
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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
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:welcome:

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.
 
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thank you very much!
 
anorlunda said:
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?
 
Hey wait a minute, that’s a hull schematic of the Enterprise! (At What ship yard do you work?)
 
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