Swain BS_36 Stability curve

[bntii]

The stability of a vessel as shown by measurement defines the response the hull will exhibit through the range of fit outs and loadings which it may be subjected to over its service life.

It appears to be a required starting place.
I trust the designers here will elaborate?

Originally Posted by Jack Hickson

I saw a very similar stability curve for a Contessa 32, a very similar deadrise, and hull shape. I suspect most boats of that era have a very similar stability curve.

Originally Posted by Jack Hickson

There is a huge difference in what any two owners will put aboard a boat, something that no designer can predict, which makes micro calculations,and measurements , meaningless, in the real world.

Is not the stability curve for the Contessa 32 a product of "micro calculations" and "measurements"?
So do you agree with their utility or not?

And further, how does one know that the BS_36 exhibits a "similar stability curve" as the Contessa 32 without subjecting it to calculations and measurements?

[Tad]

taz......

Thanks for that, those dimensions published in the book are some of the source material I'm using.......

bn,

The Contessa 32 curve referred to is published in Tony Marchaj's book, Seaworthiness, The forgotten Factor. That data is presented with VCG at -.75' (9" below dwl). I have no idea how realistic that is, but it's suspect.......perhaps possible for a stripped racing boat but unlikely with 6-8 big guys on the deck.......The Swain 36 will be considerably different due to loading and construction..........

[TeddyDiver]

Originally Posted by Jack Hickson

similar stability curve;very similar deadrise;a very similar stability curve;huge distance from a plank on edge; the huge effect of the buoyancy in a pilot house;a huge difference in what any two owners will put aboard a boat
A steel scuba tank, empty, with far thicker wall will float .

You never learn Brent Words like "similar" and "huge" are used instead of a single fact in your claims..
and steel scuba tanks don't float. 15L 200bar tank is the only standard steel tank with ~1kg of positive boyancy (with regulators attached it's neutral) when other more common 12 and 10 liter tanks are all well negatively boyant.

[Wynand N]

Originally Posted by Jack Hickson

A steel scuba tank, empty, with far thicker wall will float .

One liter of flotation/buoyancy will float one kg minus the weigh of flotation medium used in freshwater, fact. In saltwater the difference is minuscule and not really a factor.
Secondly, due to the density of water the specific gravity of submerged steel is about 0.88, in other words, one kg steel will weigh 880 grams submerged.

Now make the sum and see if the scuba tank will float....

[Dean Smith]

Originally Posted by Wynand N

One liter of flotation/buoyancy will float one kg minus the weigh of flotation medium used in freshwater, fact. In saltwater the difference is minuscule and not really a factor.
Secondly, due to the density of water the specific gravity of submerged steel is about 0.88, in other words, one kg steel will weigh 880 grams submerged.

Now make the sum and see if the scuba tank will float....

SMILE
often I had to dive for the tank I let go

[peter radclyffe]

quote

hear Dudly Dix is now giving different stability curves for boats with pilot houses and those without, taking into account the huge effect of the buoyancy in a pilot house on stability


this is unwise, as pilot houses are rarely watertight,

[Dean Smith]

Originally Posted by peter radclyffe

quote

hear Dudly Dix is now giving different stability curves for boats with pilot houses and those without, taking into account the huge effect of the buoyancy in a pilot house on stability


this is unwise, as pilot houses are rarely watertight,

that depends, many metal boats are ar wt as can be esp those build under Lloyds
I did one once and they turned a hose on it to test the integrity of the house egress,s
And this should be a test for all yachts going , not only Offshore but out of the river?

[Paul Kotzebue]

Originally Posted by peter radclyffe

quote

hear Dudly Dix is now giving different stability curves for boats with pilot houses and those without, taking into account the huge effect of the buoyancy in a pilot house on stability


this is unwise, as pilot houses are rarely watertight,

This a good observation that some may not be considering. The only time the volume of a pilot house should be used in stability calculations is if the structure of the pilot house is designed to withstand the loads of being immersed and downflooding can be prevented.

While the volume of a structurally sound and watertight pilot house will help right a capsized vessel, its weight and windage may make it more prone to capsize in the first place.

[Dean Smith]

Originally Posted by Paul Kotzebue

This a good observation that some may not be considering. The only time the volume of a pilot house should be used in stability calculations is if the structure of the pilot house is designed to withstand the loads of being immersed and downflooding can be prevented.

While the volume of a structurally sound and watertight pilot house will help right a capsized vessel, its weight and windage may make it more prone to capsize in the first place.

it depends upon what you call a pilothouse, or decksaloon
the (house) if you may call it that on an open 60 for instance is a very important part of the test(righting roll over)
Once again we assume that the structure is in keeping with standards
And if we then go on to extremes , albeit very common ones, the stabilty of say a 20,ooo tonne ferry is calculated with those windows high above the water as being submerged and part of the heeled waterplane

[peter radclyffe]

Originally Posted by Dean Smith

that depends, many metal boats are ar wt as can be esp those build under Lloyds
I did one once and they turned a hose on it to test the integrity of the house egress,s
And this should be a test for all yachts going , not only Offshore but out of the river?

the wracking strains on a boat at sea with big windows, even if they are bench tested watertight, prove a hose test is just that, a hose test

[Dean Smith]

Originally Posted by peter radclyffe

the wracking strains on a boat at sea with big windows, even if they are bench tested watertight, prove a hose test is just that, a hose test

perhaps you are used to timber, which wracks
small metal structures do not wrack, unlike ships. they are quite the module
Having been to sea in full gales for days on nose, I assure you it was more than a hose test

[Tad]

This is the model so far....bit of a struggle.....I had little faith in it as I built it, but upon expanding the surfaces I find it fits the "half pattern" (the only dimensioned drawing I have) rather well..........surprise........

Now for the deck, house, and cockpit.......

[Ad Hoc]

Originally Posted by Dean Smith

And if we then go on to extremes , albeit very common ones, the stabilty of say a 20,ooo tonne ferry is calculated with those windows high above the water as being submerged and part of the heeled waterplane

Not correct.

Windows and any other openings where progressive flooding may take place, is called downflooding. All these locations must have a freeboard and/or an angle from the damaged condition to the angle of downflood (or freeboard) in excess of that given by the administration.

Windows etc are not considered part of a stability calculation. Only the hull below the margin line. In other words, the superstructure is non-contributary. It may assist, but it is not considered as being "effective" by the administration. You just need to ensure progress flooding does not occur.

[peter radclyffe]

Originally Posted by Dean Smith

perhaps you are used to timber, which wracks
small metal structures do not wrack, unlike ships. they are quite the module
Having been to sea in full gales for days on nose, I assure you it was more than a hose test

i started working on steel boats 35 years ago, and windows on steel boats are often the weak point

[Dean Smith]

Originally Posted by peter radclyffe

i started working on steel boats 35 years ago, and windows on steel boats are often the weak point, perhaps you are used to ignoring facts

the issue is wracking
yes a full sized ship had her fore facing windows stove by a 100 ft wave in the Sourthern Ocean, which knocked out her mains, she lay broadsize until they did start her mains
So how far would you care to go
btway I am 65, so please be slightly polite