Hardest Part Of Learning To Sail

Sep 20, 2014
1,284
Rob Legg RL24 Chain O'Lakes
Daveinet makes a good point about the diagramming of lift being problematic for beginners. However, that is typical for a force diagram. Arrows are used to represent the direction and magnitude of the force, not necessarily the origin. They are placed at the central point of mass to show the effects of the force on that mass. In the case of an explanatory diagram for lift, they choose to place the arrow's origin at the outer curve to help suggest that is where the action is. But, it takes both the lower pressure surface and the higher pressure surface to achieve lift.
...Will (Dragonfly)
Bingo. Most beginners are not used to seeing vector diagrams, so that adds to the confusion. While technically correct, it is confusing, as they try to imagine air pulling on the sail, which they know is impossible.

Thanks for posting, as I was enjoying Thanksgiving in an area without internet.
 
Oct 19, 2017
7,019
O'Day 19 Littleton, NH
air pulling on the sail, which they know is impossible.
I know I'm sort of taking this out of context, but I want to make sure we are all saying the same thing. The beginner may believe it is impossible, but they likely took junior high science and should understand that it isn't the suction cup that pulls on a piece of glass, but the low air pressure inside the suction cup. In both cases, the suction cup and the sail, it is the difference in air pressure that is doing the work, a suction cup won't work in a vacuum. Both high and low pressure must be present, but pulling is just as possible and important as pushing.

-Will (Dragonfly)
 
Oct 31, 2012
441
Hunter 2008 H25 Lake Wabamun
but pulling is just as possible and important as pushing.
A simple comparison is a Vacume cleaner. All ads talk about how well they suck but it only creates a low pressure area which forces air in from the high pressure outside. The air, on route, PUSHES the dirt into the low pressure vacuum bag. The only force that can PULL something would be a magnetic force on iron.
 
May 17, 2004
3,539
Beneteau Oceanis 37 LE Havre de Grace
The only force that can PULL something would be a magnetic force on iron.
Also gravitational and electrical fields, but you probably can't propel a sailboat with them. (At least not in the intended direction.)
 
Sep 20, 2014
1,284
Rob Legg RL24 Chain O'Lakes
That still exists??? Please tell me where! ;^)
Yes, in the middle of Wisconsin - Southeast of you. There are no internet providers, and cell phone is sketchy at best. About 2 miles away is the cutoff for both cable and DSL. There are some advantages to going on vacation without cell service. Seems most of the places we go, that is the case. The big disadvantage is when kids have to do homework for college.