Swain BS_36 Stability curve

Wynand
Never Ever say you are JUST a tradesman
Be proud of it as I am with 45 years hands on
We make it happen

 

Maybe that explains somewhat wide range of the displacements of BS36's.. 22klbs might be due wet Styro.. so that argument might have a lot of weight after all..

 

This train is derailed.

BS offers the plate and foam example to make this point:

He proves the point for floating his plate but why make this argument?
Is not the issue more of how the CG is effected by raising the existing deck structure?

The deck plate exists in either configuration eh?

His point should be: 'the additional volume more than offsets raising the CG'???

 

..Because that's an excellent basis for designing a vessel!

How exactly do you run halyards inside a mast if it is sealed? Please provide pictures. I personally have never seen a metal sailboat mast outfitted that way.

 

You don't . You run them externally like they have been done for millenia. Easier to replace and keep an eye on.

 

Well, that's probably the route I'd go if I ever got up into boats that size, although the lines are noisier and more prone to chafing.

But I wouldn't count on the watertight integrity of a hollow mast, anyway. I'd regard any buoyancy it might provide in a knockdown as a possible gift from Providence, rather than something to be relied upon.

 

Absolutely! If more boats were designed by guys who get their hands dirty building them ,instead of armchair academics, they would be far easier to build and far better boats.
A friend spent three years building a Roberts Spray. He didn't like it, so built a boat designed by Denis Ganley, a designer who got his hands dirty building his own designs, and worked alongside others who did. The Ganley took about six months, and practically fell together. No hangups or surprises.
I've seen armchair academics, who neither sail nor build, design bilge keels, which, according to their computers, are as good as one can get . Unfortunately, the keels are so badly designed from a practical point that it would be impossible to unfoul an anchor rode around them, something about which their computer calculations will tel them nothing.
The first step in choosing a design, is to ask what experience your designer has in building and sailing a similar boat over several ocean crossings, boats of his own design.

 

It's amazing how many calculations some will post, without simply taping a piece of styrofoam to a piece of plate and throwing it in a sink full of water. It's amazing to see people propose a square meter of plate and a square meter of high tec, expensive foam, to resolve what a 3 inch square of plate on a 3 inch square of one inch stryrofoam will accomplish . Is that the kind of thinking which makes boats so horrendously expensive?
Once you have done the test, calculations are irrellevant in determining if the works will float ,and thus calculations are definitely" ASIDE. "
Tad
Do your calculations take into account the engine weight and stowage of thousands of pounds of water , fuel and personal effects below the waterline?
Yes I stand corrected . The rigging wire has an effect of 1422b ft lbs , which ,subtracted from the 5783 for the mast, equals 4631 ft pounds of righting moment for the mast buoyancy, close to the roughly 4,000 ft pounds I originally mentioned. .

It would take a pretty poor welder to enable a significant amount of water in a mast in the time it takes for a boat to right itself, if it were welded with the intent of making it watertight.

 

Well... take the offer that was mentioned in post#5.

Cheers,
Angel

 

Absolutely! That's why I decided to build a Tom Colvin design. Not only is it a design that was built by the designer multiple times, Tom also could provide the calculations behind the design.

Unlike, for example, a BS design...

PDW

 

Exactly "Jack".Same old, same old.
To recap:"Jack" says an inch of air floats 1/8"plate.Many calculations are made."Jack" pops back in and says[paraphrased],"Hey,just strap some foam onto any size 1/8 steel plate [cut to its shape] and see..."
Then the calculators come out and failing that,the argument is about what kind of foam.You'd think the obvious "foam" would be the lightest and most similar to plain air (the incredibly common styrofoam)but no...people hunt around for the densest stuff they can find and defend it for two pages.I remember this.

I don't know about empty dive tanks,but empty propane bottles float.I find em on the beach....go ahead and prove they didn't float onto them.

 

And then there's a sidebar metric versus imperial.Both are totally arbitrary measures.Each has their good points,in usage,but the root of each is totally arbitrary.Anyone can invent their own.How about hexadecimal for instance?And while we're at it, let's get a metric clock,too.

 

That's just nonsense noise junk2lee what comes from Brent every time there's a question about BS boats.. Instead of throwing styrofoam blocks strapped to steel plates he could do a proper inclining experiment with one of his boats as been suggested a loooong time ago...
The real point here is that Brent hasn't provided hard facts about the boat characteristics, just sailed once over the pacific and liveaboard since PNW and thats his argument..
Meanwhile others are trying to get some "flesh over the bones" what benefits every BS boat owner out there.

 

I think you're missing the point.

Can you tell me what relevance the buoyancy of a FLAT sheet of steel glued, taped or whatever, to some styrofoam has to the question at hand?

No? I didn't think so. It's simply a red herring and you're right, we should just have ignored it.

I just cut a steel SCUBA tank in half so now I know what at least 1 model is made up of WRT wall thickness etc. I'm still waiting on Jack on the details of which ones float. This one didn't even before I cut it up. Nice bit of pipe now, though.

The point YOU are missing, junk2lee, is that Archimedes Principle has been around for a very long time, nobody has ever found a case where it doesn't apply, calculation of volume and mass is also straightforward, so just what in hell do you think people who are numerate are going to believe? You and 'Jack' or calculations where the assumptions, values and results are all laid out in front of them?

On that point I looked up the rigging details in Brent's book. Turns out the mast section is 125NB tube not 150NB, wall thickness 3.5mm, length 13.8m. Also the rigging wire is 8mm not 6mm, and the masthead sheave box has to be every bit of 5kg at least. So, here's some more numbers:

Volume of mast: 3.1.41*49*1380 = 212934 cm^3.

Equivalent mass of water: 212.93kg.

Mass of mast from Edcon Steel tables: 11.76*13.8 = 162.88kg

Mass of 8mm rigging wire: 26.33kg

Est. mass of masthead box: 5kg

Total mass of mast & rigging: 194.2kg

Total positive buoyancy: 18.7kg.

Conclusion: the mast adds at most 18kg of positive buoyancy when immersed.

Now if you want to dispute my calculations, by all means do so and post your figures. Until then, mine stand and Brent's claims are wrong.

I haven't even started in on the foot-lbs part of this because once again the figure quoted is meaningless. I know that you have no math and don't understand any of this, but there's a ton of information available on the net so you really have no excuse for just believing ********.

Here's another little thought experiment: if the boat is inverted (mast 180deg from vertical), how much torque and in what direction is the mast buoyancy having on the inverted hull? How about a mast angle of 90deg from vertical? Hint: you need to know the force acting, the radius of that force and the angle through which the force is applied.

I won't wait up for the answer from either you or Jack.

PDW

 

PDW, Lets make it easier for the two chaps I will "donate" three sets of calculation formulas with pointers to help the on their way. The rest they can work out for themselves.
Some other formulas also exist and this is only supplied as examples...

MOMENT OF INERTIA (I) = disp^1.744/35.5 (A heavy rig can greatly increase I, with little impact on displacement.)

ROLL PERIOD (T) = 2*PI*(I/(82.43*lwl*(.82*beam)^3))^.5
The roll period is based on the moment of inertia. The term ".82*beam" has been substituted for the waterline beam due to lack of data. Using ".82" results in a close match for the few boats with measured periods
Simply stated, a sailboat’s roll period, in seconds, is inversely proportional to its stability. Unstable boats have long periods, stable boats have short periods. The roll period is very easy to determine, you simply grab a shroud and push / pull until the boat is rocking over a few degrees. Then count the number of full cycles in one minute, and divide into 60. The general rule of thumb is that boats with periods less than 4 seconds are stiff and periods greater than 8 seconds are tender.
A value of 4.05 is near the stiff end of the range, indicating good static stability..

STABILITY INDEX = T / (beam*.3048) This is an empirical term relating period and beam to stability. Values less than 1.0 are considered stiff. Values greater than 1.5 are considered tender.