Swain BS_36 Stability curve

This math is confusing
Our 8" pipe 3/16" wall has 8.25" ID
I came up with 6.8 Lbs per foot positive flotation if sealed.
Tom

 

Tom

Can't do imperial units..no idea how to use them.

Dimensions given:

Diameter of 165.1mm

Area = pi*dia^2/4 = 3.14159*(165.1^2)/4 = 21408mm^2

or 0.0214m^2

If 13.6m long vol = 13.6 x 0.0214 = 0.291m^3

SW = 1025 kg/m^3

Therefore displacement/buoyancy in SW is 1025 x 0.291 = 299kg

 

Ad Hoc
When you calculate would you use OD or ID of the pipe to figure the flotation ?
Tom

 

Just two points here.....

Mast self weight is (should*) be ignored at this point (in the context of the thread) since it should already be included within any displacement/vcg estimate or calc.


Secondly, unless the mast itself can be shown to be watertight or buoyant to a pressure equivalent to a head of 13.6m seawater (mast height), then it should not be included in any buoyancy/rm calcs imo especially if claims of positive stability to near 180 are to be verified..

 

Eaxctly..that's why all the twists and turns from from BS is just that, BS, and should be ignored. Except for fun by pointing out the obvious errors in his mis-direction.

Always OD...buoyancy is the volume of the immersed 'body'.

Think this way. If you had a boat floating in the sea, then froze the sea. Take out the boat you're left with a "hole" or "groove" in the ice. This 'hole' is up to the hull plating (i.e. the OD). If you now fill the hole with water, and then pour that water onto a scales....it weighs the same as the boat.

 

Thanks Ad Hoc
My calcs on the 8" were ID Little off there
Checked the 6" pipe 168 mm od 3/16" 4.77 mm wall and yep it only came out little over a pound a foot positive Not much .
Tom

 

It's a mute point anyway.

A knockdown resulting in an inversion is usually a violent event, few sailboats boats have managed to fully roll without losing their masts.

 

I used light wall as this is more than strong enough - 3.5mm wall, 13.95kg/m according to my edcon steel catalog.

As I thought - 4000lbs buoyancy is total crap. The mast would have to be made of that rare & unusual antigravitic unobtanium to give that sort of positive buoyancy.

Tazmann, sorry, but I'm really not going to bother calculating anything expressed in antique units. I realise you live in one of the 2 last remaining backward countries but you have to come into the 21st century sooner or later, preferably well before the 22C.

PDW

 

It was ftlbs.. so quite close. Thou stability would be better when dismasted

 

Is this true?
Did I miss something when away from the forum?

If so- Brent it is destructive to your case to use such falsehoods to present your ideals.

You have long experience. Stand toe to the line and speak.

 

I would rather settle for different than backwards ?
Reguardless If I was going to build a mast from pipe I would
need to go by what is available here.
Tom

 

This is not so; the whole of the boat should be considered.

Evaluation of whether you can expect the deck house to remain watertight when inverted should be done when examining the structure of the boat as a whole.

But most importantly, assuming the boat to have a flush deck wouldn't give you any meaningful insight into how the boat would behave if the deckhouse didn't remain watertight.

If Dehler can use the deckhouse of the Moody 45 to give an AVS of 180 degrees, then we should extend this liberty to everyone.

 

liberty or death

 

With regard to most things, the USA is a leader and an innovator. With regard to sticking to inch based measurements, it's backward. Sorry but that's how I and most other people see it.

I agree that you've got no choice when it comes to buying materials however.

If you're planning on taking your boat outside US waters I hope you've made provision for 220V 50Hz power because that's far more common.

How are you going with the Roberts hull?

PDW

 

Yep I could see our system would be tough if you are use to metric same the other way too.
The Roberts hull I modeled it but that was as far as I got with it, change of plans.

Tom