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One for the mathematicians...


Bimini Babe

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OK, so I know the Sail Area / Displacement number for my boat is 17.2. And I know the sail area is 39 sq. m. How do I find the displacement? :think:

 

First correct answer wins my undying admiration! :thumbup: Sorry, we're all out of rum.

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the formula is the square root of SA over cube root of disp. Turn it upside down and start multiplying. Your problem will be the average corn flake box calculator won't do cube roots.

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And I have to do it in sq. feet, not sq. metres?

Your sq feet sail area is 419.8 (from google).

 

I believe you can do a cubic root with google too. Not that I would want to try it :wink:

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Are you just trying to find out your displacement? There might be easier and more reliable ways that reverse engineering the sail area calc.

 

What's the boat?

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Everything has to be in square feet and cubic feet.

 

SA/D Ratio = Sail Area/ (Displacement^(2/3))

 

Therefore:

 

Displacement = (Sail Area/(SA/D Ratio))^(3/2)

 

Sail Area in square feet = 419.79

 

Displacement = 120.57 cubic feet

 

http://www.google.co.nz/search?hl=en&source=hp&biw=1280&bih=918&q=(419.79%2F17.2)%5E(3%2F2)&btnG=Google+Search&aq=f&aqi=&aql=&oq=&gs_rfai=

 

In Cubic Metres = 3.414 cubic metres

 

http://www.google.co.nz/search?hl=en&so ... 80&bih=963

 

Assuming density of saltwater =1020kg/m^3

 

=3.414*1020= 3 482 kg

 

http://www.google.co.nz/search?hl=en&so ... =&gs_rfai=

 

The conversion and calculator in google are quite useful :-)

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Everything has to be in square feet and cubic feet.

 

SA/D Ratio = Sail Area/ (Displacement^(2/3))

 

Therefore:

 

Displacement = (Sail Area/(SA/D Ratio))^(3/2)

 

Sail Area in square feet = 419.79

 

Displacement = 120.57 cubic feet

 

http://www.google.co.nz/search?hl=en&source=hp&biw=1280&bih=918&q=(419.79%2F17.2)%5E(3%2F2)&btnG=Google+Search&aq=f&aqi=&aql=&oq=&gs_rfai=

 

In Cubic Metres = 3.414 cubic metres

 

http://www.google.co.nz/search?hl=en&so ... 80&bih=963

 

Assuming density of saltwater =1020kg/m^3

 

=3.414*1020= 3 482 kg

 

http://www.google.co.nz/search?hl=en&so ... =&gs_rfai=

 

The conversion and calculator in google are quite useful :-)

 

You went to school for more than just your lunch!

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Yea 1025 seems more widely used.

 

That would make it 3500kg. A suspiciously round number, which makes me wonder if that was just an estimate to calculate an estimated Sail Area to Displacement ratio.

 

 

You went to school for more than just your lunch!

 

20th year of continuous education. Yawn.

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Oh wow, I love this place. :thumbup: Thanks guys.

 

Squid - yeah it's a half-tonner. One-off as far as I know - designed by Guy Thompson, built by Ian Franklin (one of his first), launched 1976. I just got hold of the old rig spec sheets from when the new rig went in about 8 or 9 years ago, and I was just curious, as I've always wondered what the displacement is, but never known how to figure it out!

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Easy to work out the displacement. Fill the Bath to the brim and then gently lower the boat into the bath. Then collect all the water that spilled out and Water being 1Kg/ltr, bingo. :wink:

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How long's the cruise, BB? And how long since last haulout and external service/checks? Cos depending on those answers you might regard a pre-departure liftout pretty important rather than nice to have?

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6 months cruise initially AC, then back to NZ before my visa runs out in November and I can apply for an indefinite RRV. Last haul-out was probably about 8 months ago, so not too long. All we'd be doing is antifouling, and propspeeding, probably also re-packing the rudder gland, but I can do that on the water. Quickly!

 

There's plenty that's been moved from the essentials list to the nice-to-have list as time goes on, but it's a case of put it off for yet another year or just do it. And when it comes to antifoul or not-to-antifoul, I think we can sacrifice a bit of speed. Besides, I don't think it'll be that much of a hardship to jump over and give her the occasional scrub once we get to Tonga. :D

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