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Author Topic: Calculations  (Read 11783 times)
Adelie
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Ahrrrrrr!!!!

« Reply #15 on: November 18, 2011, 10:13:58 am »

CSF results below 2 are considered more appropriate for offshore.
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A house is but a boat so poorly built and so firmly run aground that no one would think to try and refloat it.
Cormorant
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« Reply #16 on: November 18, 2011, 11:28:48 am »

Not to sound like a party pooper, but over here sailboats fall into one of two categories: "marin" or "pas marin". It could be that the sailing culture is a bit different, but rather than fancy numbers, an experience-based rating system (rather than calculator-based) is probably more reliable, like: "Sails with the grace of my sofabed" or "sails very well". I don't know. In my experience too, sailboats either suck or don't suck. But adding such a value would require an interactive social-media type voting system added to the pages or something of the sort.

Not to belittle the theory and calculations, after all engineering has its place, but after all is said and done, to use the language of the day, they do tend to either #fail or #win...

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I'd rather be sailing
Adelie
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Ahrrrrrr!!!!

« Reply #17 on: November 18, 2011, 12:04:19 pm »

I would see voting on a boat's capsize resistance as akin to voting on climate change.  The science for each is fairly strong and voting on physics is pretty pointless.

Voting on what you do about each is another story.  In sailing you vote by choosing the boat you want to sail and paying the money to get that boat.

Keep in mind that Capsize resistance is not the be all and end all of seaworthiness which is a larger and harder to pin down quality, encompassing boat motion, quality of construction, strength of construction, ability to suffer groundings without major damage, strength of sails, ease of setting or dousing sails .......  But capsize resistance is a significant part of that.

Like I say, this topic can attract controversy and you may wish to just completely avoid the issue by not including the value.
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A house is but a boat so poorly built and so firmly run aground that no one would think to try and refloat it.
Cormorant
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« Reply #18 on: November 20, 2011, 05:02:46 am »

Well spoken :)

It would be awesome if boats were attributed a suck coefficient ;) 

"What? you bough the Yoyotte 35? damn, she has a suck coefficient of 23. Your trips must suck."

hahaha (just having a bit of fun with this)  ;D
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sonosail
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« Reply #19 on: November 20, 2011, 01:09:20 pm »

CSF results below 2 are considered more appropriate for offshore.

Excellent explanation of your formulas. Thanks for taking the time. It just might take a bit to digest it all.
Sorry.

Randy Browning
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sonosail
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« Reply #20 on: November 20, 2011, 01:14:33 pm »

Not to sound like a party pooper, but over here sailboats fall into one of two categories: "marin" or "pas marin". It could be that the sailing culture is a bit different, but rather than fancy numbers, an experience-based rating system (rather than calculator-based) is probably more reliable, like: "Sails with the grace of my sofabed" or "sails very well". I don't know. In my experience too, sailboats either suck or don't suck. But adding such a value would require an interactive social-media type voting system added to the pages or something of the sort.

Not to belittle the theory and calculations, after all engineering has its place, but after all is said and done, to use the language of the day, they do tend to either #fail or #win...

For one thing, I need to have a comments window below each record. Just need to figure out the right way to do it. (making it relatively easy, but still discourage spam etc.)

Randy Browning
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Cormorant
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« Reply #21 on: November 20, 2011, 02:36:05 pm »

you know, you probably *could* add a facebook 'like' button under each record without much work, now that I think about it.
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sonosail
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« Reply #22 on: November 26, 2011, 07:31:07 pm »

you know, you probably *could* add a facebook 'like' button under each record without much work, now that I think about it.

Yes. But I don't don't know how I'd do it with Facebook and maintaining an association with a particular boat/record.
rb 
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sonosail
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« Reply #23 on: November 28, 2011, 03:48:47 pm »

I minor start I guess,
but I have now added sa/disp for 'listed' sa. AND ballast/disp.
If the necessary informaiton is not present the field is just blank. I COULD make it display as 'NA'. 90% of the records should at least display the former. The latter will, of course, be blank for all 'non ballasted boats'.
When you get a chance, you can check if you think it's displayed correctly. Ballast/Dsp. appears as a number .xx (rounded to 2 dec. places)   rather than a percentage. I don't know if this is the general convention. These numbers are calculated by the server every time the page is displayed. (probably not the best way to do it but it works for now.)

I was thinking of doing one more for now. Possibly beam/lwl.

rb
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Adelie
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Ahrrrrrr!!!!

« Reply #24 on: December 18, 2011, 10:14:54 pm »

I don't think bm/lwl is the way to go, the water sees WLBeam/lwl, but since water line beam is not generally published I feel the closer approximation is Beam/LOA.  Generally I recall seeing the ratio as LOA/beam so the number is greater than 1, same relationship expressed a different way.  I suspect the preference for this format is that if you double the length of the vessel keeping the beam the same the ratio doubles too, whereas the other way it halves.  Also the beam/Length ratio is asymptotic to zero and it's easier to lose a mental sense of what's going on as the ratio gets very small.

As far as number of significant digits in Bal/Disp, 2 seems appropriate.  For LOA/Beam or LWL/Beam, I would go 2 places past the decimal point.
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A house is but a boat so poorly built and so firmly run aground that no one would think to try and refloat it.
sonosail
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« Reply #25 on: December 19, 2011, 12:02:27 pm »

I don't think bm/lwl is the way to go, the water sees WLBeam/lwl, but since water line beam is not generally published I feel the closer approximation is Beam/LOA.  Generally I recall seeing the ratio as LOA/beam so the number is greater than 1, same relationship expressed a different way.  I suspect the preference for this format is that if you double the length of the vessel keeping the beam the same the ratio doubles too, whereas the other way it halves.  Also the beam/Length ratio is asymptotic to zero and it's easier to lose a mental sense of what's going on as the ratio gets very small.

As far as number of significant digits in Bal/Disp, 2 seems appropriate.  For LOA/Beam or LWL/Beam, I would go 2 places past the decimal point.
Right. I am now displaying bal/disp ratio as a value less than 1. So a boat that weighs 1000 lbs, with 250 lbs. of ballast is shown as .25.
You think that is OK?  I could just format it as %. I think I would like to do the LOA/Beam, but I'm not following you completely about the standard way to display it.  A 'narrower' boat has a HIGHER number than a fatter one? A boat with a 50' LOA and a 10' Beam should be displayed as a what?

Thanks
rb
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Adelie
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Ahrrrrrr!!!!

« Reply #26 on: December 27, 2011, 11:14:08 pm »

A 'narrower' boat has a HIGHER number than a fatter one? Correct.

And a longer boat for that same beam has a higher number.  Same physical change but a different cognitive way of thinking about it.

A boat with a 50' LOA and a 10' Beam should be displayed as a what? 5.0

So I just checked a number of sources looking for what is the most common way to express the ratio between length and beam.

Of the 5 design books that I have only one, Larsson & Eliasson, discusses the ratio and uses the form Length/Beam (>1).

In the magazine Good Old Boat, Ted Brewer, regularly compares 3 boats and he uses the B/L form (<1).

Doing google search for "beam to length ratio"  seemed to favor L/B (>1) by 6:1 or better, academic articles more so.

For monohull sailboats the typical ratios tend to fall into a range of 2.4 to 5 or so.  But for other vessels such as catamarans or military vessels the ratio can go much higher.  Catamarans can be into the 20's, military vessels over 10.

When comparing ratios for very long  and narrow vessels, it is easier to visualize a change from 10:1 to 11:1 than .10 to .09.

I expect that L/B is easier to use when dealing with these sort of vessels so that is the form that is used for most design work for consistencies sake.
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A house is but a boat so poorly built and so firmly run aground that no one would think to try and refloat it.
sonosail
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« Reply #27 on: December 28, 2011, 09:07:19 am »

Thanks.
Length/Beam (>1) makes more sense to me. I guess that's how I'll display it.

RB
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sonosail
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« Reply #28 on: January 31, 2012, 01:15:56 pm »

I'm thinking now that the calculation I want to add next is the displacement/length ratio.
As I understand it, the calculation is made by dividing a boat's displacement in long tons (2,240 pounds) by one one-hundredth of the waterline length (in feet) cubed:

I just noticed that a lot of boat reviews include it and it is based on numbers that that are available in majority of the listings.  I think you included it in one of your earlier posts.

rb
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Ken H.
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« Reply #29 on: February 01, 2012, 01:04:30 pm »

Hi Randy, have seen this online calculator form US Sailing?  It gives all the formulas and you can run numbers on their site to check your numbers.

http://www.sailingusa.info/cal__dl_ratio.htm
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S/V Salazar - CAN 54955
1990 - C&C 37/40 XL #67
Cape Breton Island, Nova Scotia
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