Winch

There are many situations in which it is useful to apply a strong pulling force. This is particularly true on sailing boats. The device that is used for this is the winch. These can be small hand operated devices used for raising and lowering sails, and for altering the angle of the sail to the wind. More powerful motor driven winches are used for raising and lowering the anchor and even moving the boat itself along the slipway. They need to be powerful because boats are heavy and reliable as it would be very dangerous if the winch failed and the boat moved uncontrollably back into the water.

Your task is to design and build a motorized winch to be used to pull a boat out of the water onto a slipway.

Motivation
To help in the design process, instruct the students to look at the picture on the front of the unit and read the accompanying text.
Alternatively, let the students search the Internet to learn more about the appearance, structure and function of different sorts of motorized winch systems used to haul or launch boats in different parts of the world.
Discuss the constraints and functions the ancient engineers would have had to take into account.

Note: You are advised not to share this image with students.

While the activity is in progress, encourage the students to relate their knowledge, skills and understanding to the task at hand by asking:

How will your winch work?
What sort of structure will you use to support the motor?
What sort of structure will you use to hold the cable?
How will you attach the cable to the boat?
How will you ensure that the winch doesn’t pull too fast?
How will you ensure that the winch doesn’t pull too slowly?
How will you ensure that the winch is powerful enough?
How will you ensure that the winch will be able to launch boats as well as pull them from the water?

When the activity is almost finished, encourage the students to reflect on both the product that they have produced and the processes they have used by encouraging the students to:

Carry out tests to evaluate the performance of the winch:

• What is the largest load it can move?
• Does it work well both ways – hauling and launching?
• Does it work reliably, without slip?

Record their design by drawing it or taking digital photos of it.
Add notes describing the way the model works and how this might be improved to get better performance.
Describe how to ensure safe use of the model.
Write briefly on what went well in their design task and what they could have done to improve it.

Look at:

Tower Crane (Building Instruction)

Principle Models: Pulley (Building Instruction)