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Old 20-05-2019, 17:34   #1
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How's your math?

SA/DSPL for a 4400# boat w/283 sq ' sail area?
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Old 20-05-2019, 18:23   #2
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Re: How's your math?

My ol' Columbia 24 had a SA of 285 and a D of 4000 or a little over which supposedly gave it a SA/D of 18 so I'll bet yours is 17 as a guess. Otherwise here's the formula, good luck!

To then find the boat's SA/D ratio, just divide its sail-area in square feet (SA) by its displacement in cubic feet taken to the two-thirds power (SA/D ratio = SA ÷ DCF↑.667)
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Old 20-05-2019, 18:24   #3
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Re: How's your math?

15.5



Sailboatdata.com will give you all the answers ye seek
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Old 20-05-2019, 18:29   #4
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Re: How's your math?

OK, got it, 16.8. Hey I was pretty darn close!
What did I win?

https://wavetrain.net/2011/03/17/cru...acement-ratio/
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Old 20-05-2019, 19:19   #5
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Unhappy Re: How's your math?

Quote:
Originally Posted by RGN View Post
15.5



Sailboatdata.com will give you all the answers ye seek
It don't. https://sailboatdata.com/sailboat/mirage-25-perry

I hope you other guys do bad math 'cause Mirage 25 supposed to have reasonable perfomance for what it is..... http://www.canadianyachting.ca/boat-...il-boat-review

Meh...I'll just buy the Olson 25 and re-learn to crouch.
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Old 20-05-2019, 19:22   #6
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Re: How's your math?

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Originally Posted by Drinky Crow View Post
It don't. https://sailboatdata.com/sailboat/mirage-25-perry

I hope you other guys do bad math 'cause Mirage 25 supposed to have reasonable perfomance for what it is.....
Reasonable is the word 17 is not bad for a small cruising boat.
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Old 20-05-2019, 19:49   #7
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Re: How's your math?

Quote:
Originally Posted by Drinky Crow View Post
SA/DSPL for a 4400# boat w/283 sq ' sail area?

DCuft = 4400 / 64 = 68.75 ft^3
DSPL = DCuF ^2/3 = 16.78


SA/DSPL = 283 / 16.78 = 16.87
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Old 20-05-2019, 19:53   #8
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Re: How's your math?

You'd be surprised how much that ratio can vary with fairly small changes in the displacement.
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Old 20-05-2019, 20:01   #9
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Re: How's your math?

Is this to give a performance comparison ?

What if your comparing a short fat boat to a long skinny one.
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Old 20-05-2019, 20:03   #10
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Re: How's your math?

You're comparing it to an Olson 25?
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Old 20-05-2019, 21:40   #11
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Re: How's your math?

Quote:
Originally Posted by sandy stone View Post
You'd be surprised how much that ratio can vary with fairly small changes in the displacement.
On a percentage basis, I'd be surprise if it wasn't less than linear.



Let's see.
-20% = 3520lb = 19.57 = +16%
-10% = 3960lb = 18.09 = +7%
-5% = 4180 = 17.45 = +3%
100% = 4400lb = 16.86
+5% = 4620 = 16.32 = -3%
+10% = 4840lb = 15.82 = -6%
+20% = 5280lb = 14.93 = -11%
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Old 21-05-2019, 00:16   #12
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Re: How's your math?

Quote:
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You're comparing it to an Olson 25?
Comparable insomuch as price and fit-to-the-slip but no, completely different animals....all boats being a compromise.

.........
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Old 21-05-2019, 02:49   #13
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Re: How's your math?

According to Carl’s Sail Calculator v3.55. Performance Comparison
Sail Calculator Pro v3.54 - 3200+ boats
Mirage 25 vs Olson 25
SAIL AREA*: Mirage 25 =275 ~ Olson 25 = 308
DISPLACEMENT: Mirage 25 = 4226 ~ Olson 25 = 2900
SA/DISP*: Mirage 25 = 16.83 ~ Olson 25 = 24.23

*The sail area is the total of the main sail and the area of the front triangle. I cannot be sure that this datum was entered correctly for each listed boat.
High performance boats would be around 18 or higher SA/D.
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Old 21-05-2019, 03:28   #14
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Re: How's your math?

Just one basic fact regarding boats (there are exceptions):

Faster = less comfortable
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Old 21-05-2019, 04:59   #15
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Re: How's your math?

Quote:
Originally Posted by MartinR View Post
Just one basic fact regarding boats (there are exceptions):

Faster = less comfortable

That kind of goes against the concept of hull speed as a factor of LWL.



As a general rule:
The bigger the boat, the faster.
The bigger the boat, the more comfortable.
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