Swain BS_36 Stability curve

What are? I'm querying TAD's assertion that increased freeboard and the inclusion of a large cabin house in the large angle stability calculations will lower the AVS.

I've already said that through the stability range up to the immersion of the old sheerline, the "rise in the CofG will result in a decrease in stability" and this obviously comes from the weight of the extra steel and fully implies the sail carrying ability will also decline. I've added that the 'trim will alter' but the influences of this will quite complex at small angles of heel as the model shows quite flared topsides so there will be an increase in the WLB.

But when determining the AVS, I believe the changes in the CofB of the new (upside down immersed body) will have more of a positive influence than the detrimental change in the CofG. Tad's use of the basic stability formula does not take into account the changes to BM at angles approaching the original AVS, of the new, larger, upside down, immersed body.

 

Sorry, only the first assumption.. I reread your posts so I understand now what you meant.

 

Tad
Did not mean to piss you off
What am I doing wrong
If a cubic foot 1728 square inches has 62 Lbs buoyancy
62 devided by 1728 = 0.035879629 per square inch buoyancy
0.035879629 x 144 square inches = 5.166666576 Lbs buoyancy

 

Crag,

My thinking is that the rise of G will offset any rise of M, but you're right, at high angles different things happen .......The house is already included.......if one took steps to lighten the house structure and maintain the G position, stability would obviously be increased........

So lets look at it......I'll increase (scale the topsides in z, then in y to reduce beam back to spec.) I'll add the additional topsides plate weight and center, and increase VCG of the deck and everything on it plus the rig 5.5".......

 

This is a bit rushed and I reserve the right to correct any mistakes in future......I was wrong and learned something today, never having had the occasion to stretch a boat vertically and do the associated calculations.

Stretching the topsides 5.5" resulted in raising overall VCG 2" and increasing displacement 300 pounds, the curves below are both at half-load condition......

T = 5.06', VCG is 7.5" above WL, 19,000 lbs (from the drawings)
T = 5.08', VCG is 9.5" above WL, 19,300 lbs (stretched)pounds.

As can be seen in the curves, the higher G means righting arms are shorter at normal sailing heel angles, up to 60 degrees. Then the arms cross, max righting arm is still at 75 degrees and is about 1" longer (max RA = 1.07').......AVS for the original model is about 131 degrees and for the stretched version is about 148 degrees.........a substantial improvement........

Perhaps if the pilothouse is stretched up another couple of feet we can get Jack/Brent's 175 degrees?.......but I'll save that for another day.......

Some conclusions........

Increased freeboard is not going to help with ISO wind heeling requirements.....
Increased freeboard will not help with Transport Canada stability requirements.....
Increased freeboard and windage will not help sailing to windward (unless conditions are really bad and the boat is being knocked down...Fastnet 79?).......
Increased freeboard may increase righting arms in some cases at over 60 degrees heel........

Obviously all of this is dependent on everything remaining intact.......in reality the good news is that over 110 or so everything on deck gets washed away and G goes down..........But as it washes away it breaks windows......not good......

 

Tape an inch of foam to a piece of 1/8th inch plate the same size and shape. Throw it in water and it will float, marginally. Settles that point.
Water has 64 lbs buoyancy per cubic foot. A six inch pipe has 12.56 lbs of buoyancy per linear foot.
6 inch tubing with a 11 guage wall weighs 7.54 lbs per foot. leaving 5.02 lbs per foot remaining buoyancy. A 48 ft steel tube has 240.96 lbs total buoyancy, centered half way along it, at 24 feet . 24 feet times 240.96 lbs, leaves 5783 ft lbs of righting moment , when the mast first hits the water.

I remember reading about a Sparkman and Stephens design, which capsized and rolled in the Atlantic back in the late 70's , After righting itself ,the floorboards gushed up on surge of water. After pumping the bilges dry, no more water came in. The skipper figured out that the hollow aluminum mast had filled with water ,which had gushed out the bottom when the boat righted itself Scared the hell out of him till then. He was sure he was holed .
The rig stayed intact.
That stability curve looks much better, not exactly unseaworthy. Include the buoyancy of the mast, and you will be even closer.
If one keeps windows small, and made out of 1/2 inch plexi ,there is little chance of their breaking. A guy in the plastics business for many years , told me that plexi has 25 times the impact strength of the same thickness of standard glass.
When raising buoyancy 5 times any increase in the raising of weights , that raising of buoyancy over rules the weight factor ,in ultimate stability , by a factor of five.

 

Relax, PDW. Bit of an evangelical streak in you, I see.

As I thought I said, I have nothing against the metric system and I'm not fighting it. I was simply pointing out that to people in the building trades who are used to feet and inches, they aren't as impractical or unusable as some folks assume...

It's nice that you've built three houses. My father and grandfather were both carpenters, most of my relatives on both sides were in one or another of the building trades, and I grew up in construction. In fact, I was a General Contractor for years (CA lic. #468972). So I have a fair amount of building experience myself...

 

Wow, this is like the steel thread..full of utter nonsense…yet the acolytes still ignore facts and believe the messiah!

What point is that..?

Er..one “floating” in air and one is “floating” in sea water….the steel does not float away in air, shown here:
http://www.boatdesign.net/forums/stability/swain-bs_36-stability-curve-37070-8.html#post453087

….so again, what’s your point..?

Other than you are talking nonsense??

Going back to this gem:

… Let’s examine this pearl of wisdom…does the Emperor have clothes?

So, line by line for those that still wish to believe the smoke and mirrors from Brent.

1” of foam ontop of 1/8” steel.

Lets assume, for sake of simplicity, that the steel and foam is 1.0 x 1.0m…one square metre.

The total volume of this steel/foam is?

Well …1” = 25.4mm and 1/8” = 3.175mm..therefore total depth = 28.575mm

Or 0.02875m or (28.575/1000) m…pick which ever presentation you like, but its now in metres.

Volume is therefore 1.0 x 1.0 x (28.575/1000) = 0.028575m^3

If floating in SW of 1025kg/m^3 density,

The total displacement is density x volume = 0.028575 x 1025 = 29.3kg

So, now lets look at the total weight.

1/8” steel thick = 3.175mm thick. The volume = 1 x 1 x (3.175/1000) =0.003175m^3

Density of steel = 7800kg/m^3

Weight of steel = 0.003175 x 7800 = 24.8kg.

1” foam = 25.4mm thick. The volume is 1 x 1 x (25.4/1000) = 0.0254m^3

Density of say Syntactic foam (nominally) 800 kg/m^3

Weight of foam = 0.0254 x 800 = 20.3kg

Total weight = 24.8 + 20.3 = 45.1 kg

Oh dear…it weighs more than it displaces..ergo..it sinks!

Wrong again.

 

Hi Brent (Jack Hickson).

I didn't want to wade into this stuff, but aren't these new results "acceptable enough" for a fairly easily built steel sailboat?

I know I risk stirring the pot and some wrath, but Brent's an OK guy. He isn't formally trained like many of the posters in these threads, but he did come up with a kind of cool boat, for it's intended purpose and method of construction.

I know some of his claims about the boat itself are a bit out there and colorful, but why is everyone after him?

He's got a lot of good ideas when it comes to fitting the equipment on these boats and such, on a budget.

 

Not in anyway giving credence to anything this brent (jack) fella says, but

Do you want to try that using a density more in line with foams used for buoyancy purposes? (say ~30kg/m^3)?




Oh, and good work Tad.

 

I’m glad someone picked up on this. I was hoping BS himself would.

The point being…cherry picking. If he doesn’t like the use of syntactic foam in my calculation to debunk his argument, saying it is incorrect foam I must use the PVC (nominally 75 kg/m^3), then he must extend the same courtesy to Tad, in providing the exact correct numbers for his hydrostatic model to perform the stability calculations in his software.

Otherwise he has no place in the debate.

 

I'm not sure who is right here Ad hoc or if it is something in the metric conversion
Using the USCG boatbuilder hand book
Flotation foam is about a 2 Lbs density plus you subtract a small % for moisture, according to them you would use 60.3 Lbs per cubic foot of foam.
To keep it simple 12 square feet of 1/8" steel sheet would weigh 60 Lbs.
60 Lbs x .88 for the submerged weight =52.8 Lbs
52.8 Lbs devided by 60.3 = 0.8756 cubic feet of foam
with this it would float or at least stay at the surface
Tom

 

As I said this topic has been thrashed to death a number of times on a machining forum. People in the USA don't seem to realise just how quaint and out of touch it seems to everyone else. Look at this thread even, who uses inch based measurements? Others won't even look at calcs done in them.

I learnt a valuable lesson after house 2. Don't build any more Unfortunately the lesson wore off but the salient part didn't - do NOT build multi-storey houses as the time & aggravation outweigh any possible benefit. The reason I mentioned house building was just to show that I did have some hands-on experience in that field and yeah, guess what the standard stud size is? 50x100mm....

Back to the stability topic, the interesting question for me is, what can be done with the basic hull design/concept to get it to where it *is* compliant with the statutory/ISO requirements?

I'm not taking any notice of Jack/Brent's claims because:

1. They're incoherent & nonsensical (try this mind experiment. Throw a 1m^2 sheet of 1mm thick steel into the water. What happens? Throw a 1m^2 sheet of 25mm thick polystrene into the water. What happens? Glue the 2 together and throw them into the water. What happens? How buoyant is the steel alone?)

2. He *clearly* does not understand Archimedes Law.

3. He doesn't use ISO units

PDW

 

Brent didn't specify *what* foam so he can't complain when his example sinks. There are very dense foams.

Point is, the details are important and arm waving ******** doesn't get you far.

It's also completely irrelevant as we already *did* the calcs for mass of steel pipe vs volume of steel pipe. When it comes to displacement those are the only 2 things that really count. Think about it....

PDW

 

It is Brent who criticizes engineers, naval architects, professional boatbuilders, welders, etc., on these & other forums, while making statements which exaggerate the abilities of his own design or are incorrect in some other manner. The thread was started with an incorrect set of calcs & Brent at least owes Tad & others "thanks" for doing the work that he should have done & been able to explain. Further, the thread benefits those who have or plan to build to such designs in many ways. Perhaps, if Brent showed some reasonable amount of respect toward others, the responses would be in kind. But, you know Brent, so what are the chances that he'll ignore what he has been shown & continue with erroneous values?