Monday, February 10, 2014

Do the Math

Can anyone explain to me what this means?

Is this the secret formula for Laser boat speed?

Originally posted here.


Anonymous said...

It means if you are tall and can hike hard and about 84kgs, you've got no excuses for not winning every race

I've been blessed with genes that make me short, fat and unfit. The fact I can even get on a laser is a miracle

O Docker said...

I think they're trying to prove that it is theoretically possible not to capsize a Laser in a jibe.

Anonymous said...

No its a secret formula for keeping your laser upright... which I guess is the beginning of boat speed >0

"Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing it is stupid." - Albert Einstein

Pandabonium said...

Sailing isn't rocket science. If you spend your life thinking of it as such, you've missed the point entirely. Be the Laser.

JP said...

Doh! Define your terms! It doesn't help that some symbols such as a & b are not shown.

The first two equations seem to be force equations and the third moment or torque (distance x force). In a balanced boat all equations add up to zero.

In this case the sailor's weight has been split into several components (body, upper legs, lower legs) each with a separate gravitational weight (G) and distance from Laser axis.

The forces are:
F2 = the force coming from the main sheet which is at an angle of 50 degrees hence part horizontal and part vertical
Fnx = the force of the sailor against the hull horizontally (sore bum time)
Fny = the force of the sailor against the hull vertically (ditto)

Hence the first equation says the horizontal forces must balance (i.e. pull of sheet is balanced by bum on hull), the second the vertical forces must balance (weight of sailor plus part of pull of sheet) and the third the moment must balance.

I have no idea if this helps sail faster.

"Vorsprung durch Technik" and all that but to be honest it looks like a "how sore will my bum get?" type of equation.

Tillerman said...

When Tiller Extension #1 was at MIT we were invited to go one of his lectures there on some parents' day thingie. The subject was refrigeration and the professor explained how refrigeration works with a whole blackboard full of equations like this. Exactly like this because every one of them had a zero on the right hand side of the equation.

After about 40 minutes, Tillerwoman was looking very puzzled and asked, 'If it all adds up to nothing, what's the point?"

She is a very wise woman. She married me after all.

Me, I still wonder who turns the light off when you close the fridge door.

Albert E said...

Hike harder = go faster

Tillerman said...

Seriously, I think JP has got to the bottom of this mystery (pun intended.)

The sailor weighs 84kg but the vertical force he exerts on the hull through his hiking pads is 1227.55 Newtons, which is the force that gravity would exert on a body of approximately 125 kg. Sort of counterintuitive but I think that anyone who has ever hiked on a Laser without hiking pants and using a hiking posture where there is only one point of contact with the thigh, can relate to the truth of this. It fricking hurts!

The calculation also gives us the force on the mainsheet, 527.11 N which is the force exerted by gravity on a weight of about 54 kg.

The takeaway for me is that if you want to sail a Laser you had better have good hiking pants and a good ratchet block. Or muscles of steel and infinite tolerance for pain.

Joe said...

Thank God JP came up to the plate and knocked it out the park. I hate a math quiz in the morning.

Tillerman said...

JP knows his math. I think he even has a degree in mathematics from one of those fancy schmancy English universities.

JP said...

If only the department had a couple of Lasers. There was all this emphasis at the university on rowing which is not really my thing. All that getting up early in the morning.

Tillerman said...

Sounds like they have made some progress since your time JP. Looks like they now have one Laser!.

JP said...

They might have had Lasers at the time, I just wasn't aware of it. I didn't get into sailing until after uni and I didn't meet anyone there who was.

Tillerman said...

Same here. I didn't know anyone who was sailing at college and was barely aware of the existence of the Cruising Club.

Strangely enough 2 years after graduating I ended up working with a couple of sailors who had overlapped in time with me at college, but I never knew them there. And both of them went on to sail in the Olympics. Who knows what would have happened if I had taken up sailing at college!

my2fish said...

My day job is as a structural engineer, so I do stuff like this often (not with sailboats, but...) My conclusion: it's mostly just gibberish. I think the intent is maybe to show the amount of resisting force a sailor provides by hiking out, but there are several items missing and not clear.

JP covered a lot of it, but it is basically a free body diagram and equilibrium equations - usually taught in a class about vector mechanics (or statics).

Tillerman also makes note of the fact that a lighter sailor, by hiking further out, can produce the same resisting force as a heavier sailor that just sits on the deck.

The F2 force is confusing to me - I'm not sure it relates to the mainsheet, but it should more realistically be the force due to wind pressure on the sail. I don't understand why the diagram applies it where it does, though.

Also, no force is shown on the sail, or acting on the daggerboard. I think those would be present as well for force equilibrium.

Anonymous said...

Could it be that F2 is the force that the feet must do on the toestrap to balance the weight hiking outboard ? It seems to me that all the forces are refered to the body of the sailor, and they must be balanced... The body of the sailor is divided in three weights G1 (chest), G2(bum and higher legs) and G3(low legs and feet), with diferent distances from the points in contact with the boat (2, the toestrap and the side), all the vertical forces must be balanced by the side of the boat, higher than the weight of the sailor because the torque made by the legs on the toestrap...(54kg+84kg = 138kg , aprox 124 kg because the sailor isn't hiking straight !!)

Anyway ,the truth is that larger sailors, and hiking harder involve higher forces , with heavy stress of the body !! More beer please !!!
Juan, Lanzarote

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