Bimini Babe 0 Posted April 2, 2012 Share Posted April 2, 2012 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? First correct answer wins my undying admiration! Sorry, we're all out of rum. Link to post Share on other sites
Guest Posted April 2, 2012 Share Posted April 2, 2012 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. Link to post Share on other sites
Bimini Babe 0 Posted April 2, 2012 Author Share Posted April 2, 2012 And I have to do it in sq. feet, not sq. metres? Link to post Share on other sites
Megwyn 2 Posted April 2, 2012 Share Posted April 2, 2012 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 Link to post Share on other sites
Fogg 427 Posted April 2, 2012 Share Posted April 2, 2012 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? Link to post Share on other sites
Guest Posted April 2, 2012 Share Posted April 2, 2012 Sounds right - is it a Whiting 29, or an old half tonner , or something like that? Link to post Share on other sites
chic014 0 Posted April 2, 2012 Share Posted April 2, 2012 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 Link to post Share on other sites
w44vi 17 Posted April 2, 2012 Share Posted April 2, 2012 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! Link to post Share on other sites
rigger 47 Posted April 2, 2012 Share Posted April 2, 2012 density of salt water is normally (where I have worked) taken to be 1025kg/m^3 for all calculations. Link to post Share on other sites
chic014 0 Posted April 2, 2012 Share Posted April 2, 2012 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. Link to post Share on other sites
chic014 0 Posted April 2, 2012 Share Posted April 2, 2012 Actually make that 21st Link to post Share on other sites
Megwyn 2 Posted April 2, 2012 Share Posted April 2, 2012 Actually make that 21st Sounds like a celebration is due. Link to post Share on other sites
Bimini Babe 0 Posted April 2, 2012 Author Share Posted April 2, 2012 Oh wow, I love this place. 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! Link to post Share on other sites
rigger 47 Posted April 2, 2012 Share Posted April 2, 2012 next time you lift the boat out of the water see if the travel lift operater can give you the weight - the weight is the displacement. Link to post Share on other sites
Bimini Babe 0 Posted April 2, 2012 Author Share Posted April 2, 2012 Yeah I was going to do that - Ashby's new travelift in Opua can give weight I think, but the pre-cruise haul-out just got cut from the to-do list due to budget constraints. Link to post Share on other sites
wheels 543 Posted April 2, 2012 Share Posted April 2, 2012 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. Link to post Share on other sites
Fogg 427 Posted April 2, 2012 Share Posted April 2, 2012 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? Link to post Share on other sites
Bimini Babe 0 Posted April 3, 2012 Author Share Posted April 3, 2012 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. Link to post Share on other sites
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