Swain BS_36 Stability curve

Everyone should be clear that the curve presented in my post #49 is purely a test. Statements that it's a great curve, a bad boat, or that the boat will remain inverted beyond certain heel angles are totally premature.......

We do not have a realistic displacement range or a VCG yet.....so please don't pass judgment on anything at this time.....for all I know the VCG could be a foot higher and AVS could be 90 degrees.......or it could be a foot lower.......

Thus I am doing a moderately rigorous weight study, with appropriate fudge factors that will establish a displacement range. Also I believe ISO requires VCG be adjusted upwards if you are working from calculation and not an inclining.

 

Tad,
There are 3 Swain 36's presently on Yachtworld, with reported displ/ballast at 7200/18500, 5700/17500, and 5500/18500(no PH). Unfortunately, I'm probably muddying the waters, as I believe that the M.O.M. site listed a lift measurement of 22,000lbs. displ., although I could not find the measurement when I reviewed the site today.
Mike

 

This difficulty allways appears. Why not just keep the dimensions and make a new hull similar to original? The propable errors can't be much bigger than the builder will do. Actually, the hull can be even better... The most significant dimensions are BWL and Tc. If these are approximately right (especially BWL), the stability curve is accurate enough. Far better than from model. The roof and keel volumes have significant influence.

Made one test. Here is the model and her stability curves. Two curves, blue for VCG on design waterline and red when VCG is 100 above DWL. Displacement is approx 8000 kg.

Terho

 

Thanks Mike......
I refuse to believe anything published in brokerage ads, the plans state a ballast weight of 4500 pounds, beyond that I'm calculating every piece I can.......perhaps the 7200/5700/5500 numbers represent the ballast plus the steel box keel and contents of the belly/keel tanks? The 18500 and 17500 numbers are the published (on plans and in book) displacements....they do not represent reality.....I also have a reported 14 (short) ton Travellift weight which I'm not sure I believe either........

Terho......

That would be too easy..................Thank you and I agree, but wanted to minimize the "but it's different" discussion......see post #53 in this thread........I do have measured drawings for the keel and house.....the keel drawing highlights another inconsistency.....published displacement is either 17500 or 18500 at a draft of 5'10", yet with hull and keel matching (as close as I can) the drawings the displacement is 23,700 at a draft of 5'4"......

Curves for your model and that of my Swain 36 are close enough that people will start to see a consistent picture....and one very different from what was represented in the first post of this thread.......for your work I thank you.......

And back to my weights..........got to finish this tonight........

 

145 mile to see and measure for yourself... but you might have seen the ad already... and it would cost a day...

Good luck!
Angel

 

I was reading this post and saw a member name Ad Hoc from Japan.
I just wanted to hope he didn't have, him and his family, to suffer too much from this horrific tragedy.
Lister

 

I am fine, fortunately, thank you for your concern:
http://www.boatdesign.net/forums/open-discussion/japanese-quake-tsunami-37099.html#post449019

 

I just walked over and checked one. They seem to be everywhere on the BC coast.
The measurement , 20 feet back from the bow, from chine to the top of the rail, is 3ft 9 inches.
Check that on your lines, and if it is 5. 1/2 inches higher , redo your stability calculations on that basis, for a more up to date calculation.

It would be quite a stretch to imagine that adding thousands of pounds of water, fuel , interior and personal effects below the waterline, would reduce a boats righting moment from the inverted position.

 

Did you make pictures? Please share... They seem to vary.. like you can see on the one linked in posts#65.. that one has no doghouse for example...

Thanks!
Angel

 

Most have doghouse. The buoyancy in the doghouse is the equivalent in righting effect to adding thousands of pounds to the keel.

 

Do your calculations take into account the roughly 4,000 ft lbs of righting moment when you try to submerge the sealed and buoyant mast?
5 1/2 inches of extra freeboard make a huge difference in AVS

 

Dog house are not to be counted in the calculation due to the lake of strength of the structure, the hatches, window and so on. Only highly professional boat builder sparing no money for the construction have the right to include the dog house in the calculation, providing they gave the necessary documents proving that the windows are in accordance with the body of regulation.
I doubt very much that the backyard yacht are built this way.
Don't put your life on a bet than the doghouse will not explode when hitting the water on a rollover.
Lister

 

Please provide the calculations to validate this throw-away "assumption/statement".

Without providing the calculations to support this statement, (to verify its validity), it is meaningless and baseless....

 

Not buying too far into this because of all the unstated assumptions (and math was never my strong point, that's why I became a biologist) but...

According to my pipe catalog 150NB light pipe weighs 14 kg/m. OD is 16.5 cm.

Scaling the mast height off the plans in Brent Swain's book I get a length above deck of approx 13.6m.

Total weight therefore (ignoring all the crap attached to the mast) 190 kg more or less.

Working in centimeters for convenience:

Mast cross section is 3.141 * (8.25^2) = 214 cm^2.

Mast volume is 214 * 1360 = 290746 cm^3 and as 1 cm^3 masses 1g of water (fresh), we get 291 kg equivalent water volume.

What have I screwed up?

PDW

 

The only screw up is thinking BS has a positive contribution to the stability discussion

Basically you're on the right track, but the numbers a bit skewed.

If the 150NB has the following dims:
165.1 x 5.0 (medium wall) @ 13.6m length
(http://www.edconsteel.com.au/pdfs/products/PIPE.pdf)

Weight (pipe only) = 19.6 kg/m

Total weight = 267kg.

Assume Buoy (vol) inside water tight
Total (inc internal watertight) volume = 0.292m^3 or in SW = 299kg.

Conclusion pipe just floats.

PS...corrected owing to lack of coffee first thing!