Swain BS_36 Stability curve

I grew up with the old system so I know both well and use both still as most of my machine tools are old ones with inch graduations. Metric is a lot more logical and easy to use IMO.

What if anything are you building now or have you gone back to work on your BS hull?

I've finished welding the hull of my Colvin design now. Lotta work and still more to go but it's entertainment.

PDW

 

Well at the moment nothing but waiting for the weather to get a little better then I will start lofting up a stretched spray 28, I think I will go aluminum on this one. Should make for a fun project.
Have any pictures of your Colvin ?

Back on the topic of the pipe mast, I found a PDF chart online showing the
cubic feet in different sizes of pipe, showed 1-1/2 cubic feet per foot of 6" pipe. Maybe that was the one used for the 4000 lbs LOL
Tom

 

You can find all kinds of pictures of these boats, and further info, on the origamiboats site. ( yahoo groups)
A steel scuba tank, with a thicker wall ,will float, when empty. A steel mast has a much thinner wall.
The first post here looks like the 36 with the cut sheer , 5 1/2 inches less freeboard. Calculations with the higher freeboard brought the AVS close to 175 degrees.

 

Just wanted to inform the observers/contributors to this thread that I've been occupying Tad's time for the past week: http://www.boatdesign.net/forums/education/yacht-design-short-course-36821.html#post452497

 

You've already been told that a steel 72 ft^3 scuba tank will not float. This matches my own personal experience in the past. Aluminium tanks will float.

If you want to argue about it, please post the exact capacity & model of tanks that you claim will float rather than just making general statements. It's only fair to tell you that one of my clients owns a large dive equipment servicing business and I can easily cross-check anything you post on this topic.

PDW

 

Here is some info on tanks.
Though not the norm, there are a couple of steel tanks which are barely positive buoyant when empty.

Why make the comparison though???

Why not calculate the buoyancy of the mast which is installed on the vessel with all of its ancillary bits?


"Buoyancy Characteristics of Steel and Aluminum Tanks:

Steel tanks are generally more negatively buoyant than aluminum tanks.

As a diver empties his tank by breathing from it, the tank becomes lighter. One difference between steel and aluminum tanks is that aluminum tanks become positively buoyant (float) as they are emptied while steel tanks only become less negatively buoyant (don't sink so much) as they are emptied. Whether he dives with a steel or an aluminum tank, a diver must compensate for the increased buoyancy of his tanks near the end of a dive. However, a diver using a steel tank will need significantly less weight than a diver using an aluminum tank, because steel tanks are more negatively buoyant overall.

The exception to this rule is the "Compact Neutral" Al 80, which is designed with thick tank walls and a higher working pressure. The Sherwood Compact Neutral Al 80 is smaller than the average aluminum tank, and remains slightly negatively buoyant when empty.

The following list assumes all tanks are in salt water.
• Catalina Al 80 - 1.6 lbs negative full and 4.1 lbs positive empty
• Sherwood Compact Neutral HP Al 80 - 5.9 lbs negative full and 1.4 lbs negative empty
• Worthington Steel LP 85 - 7.1 lbs negative full and 0.7 lbs negative empty
• Worthington Steel HP 80 - 9 lbs negative full and 3 lbs negative empty"

 

General stability theory tells us that raising the freeboard will reduce AVS, because you are raising G........ GZ max will increase, as will the angle of deck edge immersion, but at higher angles the higher VCG (shorter GM) will mean larger RM area under zero GZ.

So Jack you are postulating that the design drawings do not represent the actual boats? Where does this 5 1/2" come from? Do you have a reference with Brent Swain's signature on it? I have the lines drawings, the sail plan drawing, and the profile published in the construction book. None of them bear any resemblance to the others.......Things like the sheer shape, the stem profile, and the draft....all different.......

Here's the model overlaid on the sailplan drawing.......at this waterline the boat displaces 20,000 pounds (draft = 5'1.375")......Note the sheer and profile match almost perfectly..........

 

I didn't ask for "all kinds" of pictures... I asked for pictures about the boat you claimed to have measured in post#68.

About the talk about mast buoyancy... post#82 tells it all...

Well... show these calculations... together with the figures they are based on... I would love to see them discused here...

Without underpinning these so called "calculations" are baseless claims.

Cheers,
Angel

 

I suppose that overall, the metric system is more logical. But the decimal system it's based on isn't all that practical in itself, for builders. For example, the number ten isn't evenly divisible by any other numbers but two, five and itself.

On the other hand, a foot is twelve inches. Twelve can be evenly divided by two, three, four, six and itself. And the inches themselves have an infinite number of divisions. They can be divided into halves, quarters, eighths, sixteenths, thirty seconds, sixty fourths.... And if you have a measurement that's feet and inches combined, it's simple enough to convert it to inches while you're working on it.

People who haven't built houses, garages, decks, cabinets, shelves, etc. would probably be surprised at how often you wind up trying to divide a measurement into equal segments of one sort or another.

I usually manage just fine when I have to cope with the metric system. But since it isn't my 'native language,' so to speak, I still find myself doing very rough conversions in my head to keep things in scale (e.g., a meter is a little more than a yard, two and a half centimeters are an inch, 65 miles per hour is a little over 100 kph, etc).

I can understand that to someone not used to it, measuring in a mishmash of feet, inches and fractions of an inch sounds very confusing. But having done it all my life, it's completely automatic for me -- and I don't think it slows me down one whit.

It's somewhat like the qwerty keyboard. People have come up with numerous more logical and supposedly more practical keyboard layouts. And what's the final verdict on them? Although the qwerty keyboard may look more confusing, it turns out that in real life people wind up typing about the same speed no matter what keyboard layout they're using, as long as it's the one they're used to.

 

As I said I grew up with the inch based measurement system and had to switch to metric in my teens. I understand both systems well and can use them interchangeably.

I've built (and I mean, built, not supervised other people) 3 houses including one of 3 storeys with a structural steel post & beam skeleton. How often have you ever needed to measure anything in a building to closer than 1mm? Pretty much never I'd bet so a metric tape measure works fine. I'm a metalworker by hobby and have a lot of machine tools. I can & do work down to 0.001" or 0.01mm, makes little difference to me.

As for equal divisions, come on. I learnt to do mental arithmetic in primary school and if I can't figure it that way I use a calculator.

First thing I did when I got my boat plans was dump all the offsets into a spreadsheet and convert the inch-eighth values into millimeters. Lot simpler and less error-prone when doing the layout.

Your space people augered a very expensive spacecraft into Mars because of a measurement error, solely due to the idiotic mishmash of units in use. Your industrial base is starting to hit problems selling equipment that's not based on metric units.

I'm not just trolling about this, I'm serious. You guys staying on an inch based system makes you incompatible with the rest of the industrialised world and that world is both bigger than you and rapidly becoming more technically sophisticated. The topic comes up regularly on one of the industrial machining forums I belong to and has been thrashed to death there.

PDW

 

A bit offtopic, but while we're waiting for the results I think I'll stick my spoon in the soop anyway.

I grown to metric system, but also partially to the imperial, as we have a saw mill. In literature all lumber is measured in metric (millimetres) but in talk it turns to inches, probabaly because the measures are in single numbers (like 2 by 4 vs. 50 x 100). Also imperial comes up in pipes and threads quite often. Basically all threaded plumbing gear is still identified imperial units. As I have been involved with all of these things most of my life I am pretty fluent in both measurement systems. Not many are.

As for ease of use, the units that are almost exlusively used in building anything (in metric) are millimetres, that's 1/25.4 inches, how often you need that much accuracy? Dividing anything over 200 mm in three parts (the hardest in metric, IMO) no one will be able to tell that you divided it into 66+67+66 mm. Half a millimeter is usually the smallest measure I use, in wood working you'll be hard pressed to get to that accuracy with the common hand and power tools.

As for the whole metric vs. imperial deal, dealing with people globally (as we're doing here) would be a lot easier if everybody used the same units. But on the other hand I would surely miss imperial units if they were to disappear.

Just an oppinion.
Lurvio

edit, well, PD was a bit quicker.

 

Concur.. rowing boats are measured in meters, seagoing in ft, ships again in meters. Sail area in m2 (everybody knows sqm classes). Tit's are measured in alfabetes, lubbers in SML..
Wonderfull world

 

You all are slowing coming around to the superior language and will eventually get up to speed with how we measure the world...


I was in high school when one of the movements to 'go metric' blew through.
There was a sudden hubbub and dismay over the strangeness of it all for us kids and some effort to get us up to speed so we could buy a qt of milk (opps I mean liter...)

Of course as soon as I got into college much of my science and engineering course work was metric and no thought was given to any other system.

"The Metric Conversion Act of 1975 (later amended by the Omnibus Trade and Competitiveness Act of 1988, the Savings in Construction Act of 1996, and the Department of Energy High-End Computing Revitalization Act of 2004) designated the metric system as the preferred system of weights and measures for US trade and commerce, and directed federal agencies to convert to the metric system, to the extent feasible, including the use of metric in construction of federal facilities."
http://lamar.colostate.edu/~hillger/laws/metric-conv.html

Thirty five years later we now have metric and imperial on all the food packaging.. it takes time. We don't want to confuse the old ladies buying milk.



Give it time and don't fuss when you see all the 40's vintage imperial machine tools in my shop..

 

So here is a tentative weight study.....not comprehensive but reasonably close.....please check for mistakes or revise as you wish and resubmit.........all steel plate weights and centers are from the Rhino model........

Current results are
Light ship is 17,000 pounds, with KG at 5'7"
Half Load is 19,000 pounds and KG is 5'8"
Full Load is 19,500 pounds and KG is 5'7

View attachment S36weights01.xls

 

So at.......
Lightship KG =5.59', LCG = 16.4', Disp. = 17,000, draft = 4.91', and VCG = 0.68'

Half Load KG =5.67', LCG = 16.3', Disp. = 19,000, draft = 5.06', and VCG = 0.61'

Full Load KG =5.6', LCG = 16.26', Disp. = 19,500, draft =5.1', and VCG = 0.5'

Righting arm curve at half-load condition shows max RA of 1.0' at 78 degrees and AVS of 131 degrees.......