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Author Topic: Calculations  (Read 12578 times)
sonosail
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« on: November 10, 2011, 09:41:44 am »

http://sailboatdata.com/viewrecord.asp?class_id=3630

The class or company website has the SA listed as 637sf which is missing from the entry.

http://www.samlmorse.com/?a=bcc_specification
Thanks. It has been entered. 
As always, your comments, corrections etc., are greatly appreciated.
I really need to get the program to be smart enough to use a 'listed SA' to perform some calculations when rig dimensions aren't available.
Again, thanks.
Randy Browning
sailboatdta.com
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Adelie
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« Reply #1 on: November 10, 2011, 12:00:07 pm »

I've created a dbase in Excel that does it.
If you are running something similar, I could help.
What's the software handling the data behind the website?
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sonosail
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« Reply #2 on: November 11, 2011, 11:50:28 am »

I've created a dbase in Excel that does it.
If you are running something similar, I could help.
What's the software handling the data behind the website?

Tables are MS SQL server, but queries, joins etc. are done in .asp.
I received an Email from someone yesterday asking if I'd take the whole thing and give it him in Excel? (or Access). No indication about why he needed it or why I would ever do it. 
There are one or 2 sites that have been continually stealing my content. Though the site that had been most blatant, just recently took it all down.
RE: calculations - The only calculations I have currently are just sail area from rig dimensions (if they exist), and sail to disp ratio. Neither one is stored in a table but made on the fly when the page loads. I'd like to add more. I guess the most basic one that I should have is ballast to displ.  Of course the search/sort function needs to be a bit more sophisticated.  Just the same, I'm not intested in making the site a vehicle for comparisons. It's mainly to allow people to look up a single boat to get information about that one boat.
What do you have on this spreadsheet?
rb
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Adelie
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« Reply #3 on: November 13, 2011, 02:35:23 pm »

Have you considered running the data thru Excel, which can easily do the math including all the if/then stuff I have, before it goes into SM-sql.  The the math is done upfront,  and some error checking can be done like calcing SA from rig dimensions and comparing against advertised SA.  I don't know how you would keep photos and line-drawings properly sync'd.

 I don't know SQL and am hesitant to put the effort into learning since I have plenty of other things demanding my attention.  Is there an on-line tutorial I could peruse?  I could at least take a whack at the math side of it for you.
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sonosail
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« Reply #4 on: November 14, 2011, 10:17:07 am »

Have you considered running the data thru Excel, which can easily do the math including all the if/then stuff I have, before it goes into SM-sql.  The the math is done upfront,  and some error checking can be done like calcing SA from rig dimensions and comparing against advertised SA.  I don't know how you would keep photos and line-drawings properly sync'd.

 I don't know SQL and am hesitant to put the effort into learning since I have plenty of other things demanding my attention.  Is there an on-line tutorial I could peruse?  I could at least take a whack at the math side of it for you.
Just maybe, in your opinion, some of more important formulas. 
Besides bal/disp and sa/disp. based on listed sa which I know I should have.
These would displayed for each individual record. Just remember that having the the program list or sort by these numbers would require a complete rewrite.  Not something that I want to do right now.
Creating graphs etc. on the server side, based on selected records to simulate something you can do relatively easily with excel is way out of my league.  If I ever thought I needed this capabilty, I would probably just hire someone who specialized in this kind of thing. A knowledge of SQL would be a relatively small part of it.
That doesn't mean that I can't improve on the search/sort terms in the user interface, although I am having a bit of trouble even with that.  As programer, I'm little more than a hack.
rb
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Adelie
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« Reply #5 on: November 14, 2011, 12:12:35 pm »

What I meant was have the base data (name, LOD, LWL, Beam...) in excel which can do math for various ratios (DLR, SA/D,...) and error checking.  Excel uploads daily or weekly to SQL.  Uploaded data includes basic values as well as computed values.  SQL and ASP don't do any calc's on the fly, they just manage the query and display functions.  The trick is getting Excel and SQL to talk to each other, and better yet automate the process.  Given that they are both MS products I can see how MS may have put in functions so they can get along.  Then again this is MS I am talking about.

Doing so would add steps to the process.

As you have indicated elsewhere, you are not interested in becoming a boat comparison site, so I don't see you installing options for specialized queries, let alone graphs.
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Adelie
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« Reply #6 on: November 14, 2011, 01:32:32 pm »

Here are 2 links from microsoft.

This one details how to convert Excel spreadsheet to an SQL database file.
http://support.microsoft.com/kb/321686

Apparently you can buy apps that can do this too, perhaps more easily than using the MS method.

This one details how to link an Excel sheet so that SQL uses it directly as a database.
http://support.microsoft.com/kb/306397/EN-US

Not knowing SQL I have no idea which one would be easier for you to use or whether getting SQL/asp to do the math to get the calculated ratios would be easier.
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sonosail
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« Reply #7 on: November 15, 2011, 09:40:03 am »

All the problems with .asp and SQL aside, I was only wondering if there are 1 or 2 extra calculations that you find particularly relavent, that I don't currenty have.  For example, ballast/disp is one that would be relatively easy to implement. Of course, it would only be displayed for boats that are ballasted or, for which ballast is listed.  (In effect such a number would not be displayed for all dinghies and most multihulls.) 
On the other hand, any calculation that uses beam at the waterline would not be possible since this is not a number that exists in the data.
rb
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Adelie
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« Reply #8 on: November 15, 2011, 02:00:34 pm »

OH, sorry, missed that.

For sure I would add:
DLR aka D/L- I'm not a big fan of this number since it uses LWL rather than LOD and becomes misleading for boats with huge overhangs or very short/no overhangs.  However it is the generally understood ratio that people look at to figure out if the boat is heavy or light for it's length.  The history of the ratio goes back to early handicapping rules which looked at LWL a lot rather than LOD.
Capsize Screen aka CSF- I know you are not interested in becoming a comparison site, but if you are going to do SA/D which is what racers are really interested in, CSF is the corollary the cruisers are going to be interested in.  Another way to look at is that SA/D serves racers mostly, and cruisers some, whereas CSF only serves racers.  Another thought is that all the numbers you include are going to confuse newbies or spur them to learn more so they can understand things better.  I think I've covered all the possible arguements here.  I would put it in because I am interested in it, my logic for it is just trying to look like I have a rational reason for it.

Likely I would add:
Hull speed
LoD/Bm
%Ballast

Less likely I would add:
Hull Wt
DLR variant using LOD rather than LWL for reasons discussed above
hp for hull speed
Fuel efficiency at Hull speed and 4.5kt.  There is a huge disparity in fuel consumption between those speeds and most people don't realize it.  Most people's experience is with cars where the difference between driving 60mph and 75mph (I live in CA) is on the order of an extra 10-20% fuel.  In boats the difference between 4.5kt and Hull speed it on the order of double the fuel consumption for boats over about 27'. If it sunk in with people how much more fuel they use as they approach HS, I think they would slow down at least some.  Once again this is just a rationalization, I would put it in because it intreests me.
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sonosail
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« Reply #9 on: November 16, 2011, 09:21:45 am »

Before I say anything about this, I'm going to try to move this part of the thread to the General Discussion Area, if you don't mind.  Actually, I've never done this before so it may not work.

rb
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sonosail
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« Reply #10 on: November 16, 2011, 10:15:02 am »

Seems like it did work. 
Back to the topic at hand.
LOA:
As you probably have noticed, the number given for the length of the vessel, which I call LOA is a big problem, because the way it is measured  in most media is never the same.  I made the decision, (maybe not the right one) that if a designer or builder is CALLING the number LOA, that's what I use, whether it includes bowsprits, pulpits etc., or not. In some cases, a separate LOD number if also available, but I still use LOA.  I could create a separate field for LOD, but it would end being blank most of the time.
Because I've made it a policy to never make a GUESS on a number. Everything has to be somewhat authoritative even if it might be wrong.  If the number is not available, I leave it out. 
Actually, I should probably state this somewhere on the site.
For this reason, any calculation based on LOA is not going to be very meaningful.
 
Let me get back to you with my comments on the various formulas you have listed.
And thank you very much for posting them.   

Randy Browning
sailboatdata.com   
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Adelie
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« Reply #11 on: November 16, 2011, 10:35:57 am »

If you do decide to go with some of the more esoteric calc'd values like HP and fuel consumption, I have the equations and the sources I got them from.  Since my sources aren't first souces I would be happy if someone checked them before they went very public, might be very embarassing. :o


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Cormorant
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« Reply #12 on: November 16, 2011, 04:14:57 pm »

For this reason, any calculation based on LOA is not going to be very meaningful.

+1
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sonosail
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« Reply #13 on: November 17, 2011, 10:27:51 am »

OH, sorry, missed that.

For sure I would add:
DLR aka D/L- I'm not a big fan of this number since it uses LWL rather than LOD and becomes misleading for boats with huge overhangs or very short/no overhangs.  However it is the generally understood ratio that people look at to figure out if the boat is heavy or light for it's length.  The history of the ratio goes back to early handicapping rules which looked at LWL a lot rather than LOD.
Capsize Screen aka CSF- I know you are not interested in becoming a comparison site, but if you are going to do SA/D which is what racers are really interested in, CSF is the corollary the cruisers are going to be interested in.  Another way to look at is that SA/D serves racers mostly, and cruisers some, whereas CSF only serves racers.  Another thought is that all the numbers you include are going to confuse newbies or spur them to learn more so they can understand things better.  I think I've covered all the possible arguements here.  I would put it in because I am interested in it, my logic for it is just trying to look like I have a rational reason for it.
Quote
So this one is just lwl /disp? Shouldn't be that hard.


Likely I would add:
Hull speed
Quote
So we are just taking sq rt of LWL and multiplying by a constant? I have to say I've never been a big fan of this one unless we're talking about ships or something.

LoD/Bm
Quote
I could do LOA/Beam?

%Ballast
Quote
Isn't this just Bal/Disp? - which I would like to do.


Less likely I would add:
Hull Wt
Quote
The only thing I have is listed disp.??

DLR variant using LOD rather than LWL for reasons discussed above
Quote
I only have LOA. You think that might work?/
hp for hull speed
Fuel efficiency at Hull speed and 4.5kt.  There is a huge disparity in fuel consumption between those speeds and most people don't realize it.  Most people's experience is with cars where the difference between driving 60mph and 75mph (I live in CA) is on the order of an extra 10-20% fuel.  In boats the difference between 4.5kt and Hull speed it on the order of double the fuel consumption for boats over about 27'. If it sunk in with people how much more fuel they use as they approach HS, I think they would slow down at least some.  Once again this is just a rationalization, I would put it in because it intreests me.
You'll have to explain these last 2 and how they could be derived from available data.

Also, maybe I'm not really sure how you do capsize screening.
It seems like I could do 2 and possibly 3 of these as I understand them.
For some of the others, you might need to explain how the calculations are actually made.
I'll probably start trying to implement one like bal/disp. to how it works out.

Thanks once again for your suggestions.

Randy Browning
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Adelie
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« Reply #14 on: November 18, 2011, 09:51:03 am »

I see your reasoning about Hull Speed but:
A. People kind of expect it. 
B. Undersail it is kind of meaningless since a significant number of boats can surf or even plane.
C. Under power it gives people a resaonable idea of how fast they really can motor, except for a few freak boats, no one is going to have the HP needed to go much faster.
D. This is your site so people can just bugger off.

LoA/D - Yes, what people expect.  I keep using LOD out of habit.  Pays to be precise/accurate in my job, rubs off on the rest of my life, just read LoA when I write LOD.  Sorry.

Bal/Disp is %Bal.

Hull weight is Disp - Ballast.  The amount of weight devoted to structure.  For boats of a similar length and build quality, the boat with the heavier hull weight will be stronger.  I would be less likely to put this in.  As mentioned I am trying to find a formula like DLR that indicates structural weight in the boat irrelavant to the boat's length.

HP at any given speed can be estimated from LWL, Displ, and some indication of the hull type.  The formulas originate in one of Gerr's books.  The formula I have is HP=Disp/((2.3-(Speed/(LWL)^0.5))*8.11)^3
2.3 and 8.11 are constants
One is for the hull type, sailboats are going to be displacement vessels under power.  I don't remember what the other one is, probably something to make the units work out.
The formula doesn't take into account L/Bm (but most sailboats are similar in that regards) or whether the hullshape is a bath tube.

For a diesel engine, 1 gal of fuel will give you about 10hp for 1 hour.  Taken from some of John Vigor's books, and I think I checked this on-line a couple of places.

Using the HP required for the speed and dividing by 10 gives you gal/hr.
Dividing speed by gal/hr give you nm/gal

All rolled up into one equation you have mpg = 10*Speed/[Disp/((2.3-(Speed/(LWL)^0.5))*8.11)^3].

Good for reasonable estimate.


Capsize Screening Formula - CSF=Beam/(Disp/64)^.333  results below are generally considered more suitable for offshore boats.
64 is the density of seawater.
Disp/64 is a volume, cubic feet.
Cube root of that is a length, feet.
Beam in feet divided by above cube root in feet gives you a number with no dimension.
Following the Fastnet debacle in '79 some parties did a bunch of research on boats in breaking waves.  They found that beam is detrimental to capsize resistance, it provides a longer lever arm for breaking waves to act on.
Good for capsize resistance is roll inertia and roll damping.
Displacement itself has a minor positive influence, but it is a very good predictor of the other 2 and is much more readily available.

There is actually a better formula that explicitly uses roll inertia, but the input values are so hard to come by that it is worthless for general use.

Debates about this formula can be a bit heated shall we say, and even providing the result may attract some ire which I can see as a reason for you to not go there in the first place.
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