Momentum Discussion

Posted by Grant Headifen on February 19, 2009 under Maneuvering Under Power, Skipper | 2 Comments to Read

Here is an exercise that everyone should do. It’s taken from the Maneuvering a Sailboat Under Power clinic which gives 20 different exercises to be able to confidently maneuver a sailboat.

Exercise 1: Under power, and going down wind, move towards a marker or buoy and stop the boat with the buoy abeam of the boat. You’ll invariably overshoot. No problem though because you’re in deep water and nowhere near a marina.

Sailboat moving downwind under power

Sailboat moving downwind under power

What you learned: You overshot for two reasons the boat has a massive amount of momentum and the wind is pushing you from behind. To do it better next time, put the engine into reverse about 5 boat lengths back at about 1000 rpm. As the boat begins to slow, gauge whether you should increase the engine speed against the approaching speed of the buoy. Work the engine up to 2500 rpm and down to ensure you stop in the desired place. Most people make the mistake of putting the engine in reverse too late and then have to overpower the engine at the last minute.

Exercise 2: Repeat exercise 1 above but headed into wind.

What you learned: You still run the possibility of overshooting your mark largely again because of the momentum of the boat. The exact same principles apply. Use reverse with plenty of space and work the engine to gauge your approach.

Sailboat moving upwind under power

Sailboat moving upwind under power

The bottom line here is that the boat does not work very well in reverse. As another example – from stand still notice the acceleration of the boat in both forward and reverse. You’ll see that the boat takes off much faster in forward. Why, well that’s easy – because the propeller is mostly used in forward the shape of the prop is engineered to have its greatest efficiency in forward. The trade off is poor performance in reverse. However – enter the innovative reversing propeller. The following video shows a reversing propeller turning and then flipping it’s blades entirely around so that the blades always work in their most efficient mode.

 

This video is courtesy of MaxProp who manufacture the reversing prop. You can visit their website at http://www.pyiinc.com.

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