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Fat Guy Physics
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Brian.bigfella@gmail.com



Joined: 11 Jun 2012
Posts: 127

PostPosted: Wed Jan 28, 2015 10:49 pm    Post subject: Fat Guy Physics Reply with quote

Last summer I was weighing in at about 305 pounds. I've managed to lose about 30 pounds, or about 10% of my weight. So my question is this...

Is the relationship between sailor weight and sail, board, wind speed, etc. linear?

In other words, I was going on my JP SLW with a 9.5 sail in 15 mph wind last summer. Will that same setup get me going in 13.5 mph this summer? Will my 130 now sail like a 143? Or is there a bunch of physics I'm ignoring?
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isobars



Joined: 12 Dec 1999
Posts: 20935

PostPosted: Wed Jan 28, 2015 11:06 pm    Post subject: Reply with quote

Sail power is proportional to windspeed squared, the effect on planing of board displacement due to rider weight varies with the price of juniper berries in Kathmandu, and wind speed on the water is only slightly correlated with that measured on land. You ain't gonna feel much difference.

Now, about that weight. Do you like sweets, breads, pasta, potatoes, etc? If so, the solution is probably Atkins ... presuming you aren't 11 feet tall.
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Brian.bigfella@gmail.com



Joined: 11 Jun 2012
Posts: 127

PostPosted: Thu Jan 29, 2015 12:52 am    Post subject: Reply with quote

isobars wrote:
Sail power is proportional to windspeed squared, the effect on planing of board displacement due to rider weight varies with the price of juniper berries in Kathmandu, and wind speed on the water is only slightly correlated with that measured on land. You ain't gonna feel much difference.

Now, about that weight. Do you like sweets, breads, pasta, potatoes, etc? If so, the solution is probably Atkins ... presuming you aren't 11 feet tall.


Beer. And cutting back on it dramatically is what shed the 30 pounds. I'm 6'3", and my ideal weight is about 220#. At least, that's what I weighed when I graduated boot camp 25 years ago and could run a half mile in two minutes.
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chophop



Joined: 16 Apr 1996
Posts: 230

PostPosted: Thu Jan 29, 2015 3:37 am    Post subject: Reply with quote

In my experience every pound matters in planing. But that experience is going from 144 to 174. I think that your 130 should now feel like a 143 would at 305.Maybe not quite but close Laughing
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joethewindsufa



Joined: 10 Oct 2010
Posts: 1190
Location: Montréal

PostPosted: Thu Jan 29, 2015 6:18 am    Post subject: Reply with quote

using james douglass' sail calculator
http://jimbodouglass.blogspot.ca/2010/11/updated-windsurf-calculator-online.html

9.5 is good in 19.6 knots @ 305 pounds
it is good at 17.6 knots @ 275 pounds

these are approximate numbers, but give one the idea of what impact weight loss has on early planing, wind requirements , etc

would like to say you basically need 2 knots less wind to get going
as you suggested
however, planing in 13.5 mph with 275 pounds and a 9.5 sail ??
you better have good technique ...based on what you write, i guess you do
i weigh about 230 pounds and that is about when i plane with my JP SLW - 12 knots +

when i lose weight i notice it more in early planing and ability to maneuver - NOT so much on smaller board in bigger winds ie i do not feel the weight difference there - except in my body maneuverability - less belly in the way
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d0uglass



Joined: 28 May 2004
Posts: 1286
Location: Bonita Springs, Florida

PostPosted: Thu Jan 29, 2015 11:33 am    Post subject: Reply with quote

Weight definitely matters, and my calculator seems to be pretty good at telling exactly how much difference every pound makes in terms of what sail size you need and how much wind it will take to plane.

Jogging and paddleboarding, combined with not drinking beer or sugary beverages, helped me lose about 5 pounds this year, and I think even that little bit made a difference in my planing.

_________________
James' Blog: Windsurfing Equipment Size Calculator
http://jimbodouglass.blogspot.com/2010/11/updated-windsurf-calculator-online.html
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isobars



Joined: 12 Dec 1999
Posts: 20935

PostPosted: Thu Jan 29, 2015 1:00 pm    Post subject: Reply with quote

Welllll, actually, WSMag testing with weighted boards found that weight differences in the 5# range are inconsequential unless ooching is used effectively, and even that wouldn't matter with rider weight differences. By FAR ... I mean by scores of pounds ... the biggest factor I see every day in planing thresholds and top speed is rider skill.

Where weight matters most is in how long we can sail, as measured in years to decades.
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westender



Joined: 02 Aug 2007
Posts: 1288
Location: Portland / Gorge

PostPosted: Thu Jan 29, 2015 1:26 pm    Post subject: Reply with quote

You can't blame a guy for asking. A large number of the questions on this forum can only be answered by the person asking the question. Shocked

My hat's off to any large person who can enjoy windsurfing. I see people a lot smaller than Brian that make it look impossible.
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dllee



Joined: 03 Jul 2009
Posts: 5328
Location: East Bay

PostPosted: Thu Jan 29, 2015 1:33 pm    Post subject: Reply with quote

Remember, pumping can account for around 20% in earlier planing, while skill can account for at least that much.
Some 270lbs'ers can plane easily as early as some 175 lbs non active windsurfers.
Guys like AntoineAlbeau, at 235, can plane within 5mph winds of guys weighing 150 lbs., using the same equipement....board floaty enough for him.
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Brian.bigfella@gmail.com



Joined: 11 Jun 2012
Posts: 127

PostPosted: Thu Jan 29, 2015 1:47 pm    Post subject: Reply with quote

joethewindsufa wrote:
using james douglass' sail calculator
http://jimbodouglass.blogspot.ca/2010/11/updated-windsurf-calculator-online.html

9.5 is good in 19.6 knots @ 305 pounds
it is good at 17.6 knots @ 275 pounds

these are approximate numbers, but give one the idea of what impact weight loss has on early planing, wind requirements , etc

would like to say you basically need 2 knots less wind to get going
as you suggested
however, planing in 13.5 mph with 275 pounds and a 9.5 sail ??
you better have good technique ...based on what you write, i guess you do
i weigh about 230 pounds and that is about when i plane with my JP SLW - 12 knots +

when i lose weight i notice it more in early planing and ability to maneuver - NOT so much on smaller board in bigger winds ie i do not feel the weight difference there - except in my body maneuverability - less belly in the way


When you're my size you actually become fairly efficient out of necessity. You also get equipment that works for you and not what works for a 170# tester.

In 15mph I can marginally get my 9.5 going with my Super Light Wind, which is 92cm wide, and with a 70cm formula fin. One of the reasons I'm losing weight is because up to about 25 knots windsurfing is pretty uncomfortable because the size sail and board I'm on. At about 30 things become really easy and I can rig my 5.8.

I would encourage heavyweights to sail, provided they know to shrug off most people's advice after they can plane in the straps. It's just a totally different deal for big guys. I could link all the oft-cited stuff from Dave White, but everyone's probably seen it.
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