Swain BS_36 Stability curve

You are quite right Dean. And I was the person warning others about arguing with a fool....

As said, before, this thread reached its sell by date after the stability claim was disproved by naval architects. Now it is just the usual BS rant and drivel.

I think I will stop posting as well for the time being on this thread because it has been proven that BS stands for bull ****,(ter), proven a fraud many time over in the past, he is the king of insult and the nirvana of everything knowledgeable. He is a dodger of facts par excellence and at the end of the day the lies he sells, borders on criminal.
But that is all well in the universe of BS but it reminds me so much of a hillbilly society.... OK, stone me for that

 

The only difference between that photo & what I saw in Silva Bay last month is that James' boat is moored in a different place & there's no mega trawler yacht in the background in the photo. Not sure that a discussion of Silva Bay helps the OP with his desire to determine the stability, or lack thereof, of a BS 36. I didn't see any anchored there last month & I spent time every evening looking at the boats anchored there. Obviously, Brent & the origami crowd would know who has a completed 36 in the area. If Haiden finished his, why not ask him to supply his boat for the test?

 

So true... I have a keel to sand

 

Seen as how this thread is about the stability of the 36'
Rul books aside simply because it does not have to comply being home built.
Stabiiity wise would you consider it
Safe or Unsafe ?

 

Well, there is the crux of the matter.

To be able to say whether it is safe or unsafe requires 2 things about the boat to be known.

1) The real actual, as inclined displacement, LCG, VCG along with the real hydrostatics
2) What criterion is the boat being measured against to ascertain whether it is a “safe” or “unsafe”…..a pass/fail needs a target to aim at.

To date BS has failed to provide No.1, and as for No.2, you need No.1 as the input, regardless what criteria one uses.

The ‘designer’ is unable to provide simple professional information such as its stability... so, no one can say for sure….and the fact the designer doesn’t seem to want to know and/or answer the simple question...doesn’t that worry you????

 

Yes a lot of varables being home built when it comes to weights but the hull if cut to pattern will not vary much same with keel or keels and balast.
We know the length beam ratio, balast ratio if built within reason. The hull has pretty good deadrise through the center so we would know it is a bit tender. So with that info and say it is built and loaded within reason would you say it is safe or unsafe stability wise.
Has nothing to do with brents claimes or that he can't answer in engineering terms

 

Tom,
As Ad Hoc stated: 1) The real actual, as inclined displacement, LCG, VCG along with the real hydrostatics

(Correct me if I'm wrong, folks) The issue is that an incline test would allow for more accuracy in determining stability. It is not the "ultimate answer" on it's own, but an integral cog in the process. But, the question remains: Why would one who specifically wishes to build in this manner use Brent's plans when there are qualified designers who offer an alternative & will be able to present all of the calculations? (Tad Roberts, Pat Bray, Yves Tanton, etc.)
When I was down in Newport Beach last week, I bought another Cal. I've looked at a lot of boats in the past year, some with greater offshore attributes than this Cal. But I owned/sailed a Cal 3-30 & ultimately decided that it was, for me, a case of "better the devil you know". As Brent promotes his boats for offshore use, wouldn't it be a benefit for the owner to know what they have? The Cal 2-30(different LWL, beam, disp, ballast to 3-30) I bought came with a mast 3 feet longer than "stock". If I keep that mast, the boat is no longer the boat I know about, it is a question mark.

Not to be over-dramatic, but when you buy a design you are placing your life in the hands of the designer, assuming you build to the plans. What we know, and what we can surmise, to this point is that the "hype" has no basis in fact.

Tom, I probably have enough knowledge of design at this stage to be dangerous. I could give you an alternative design to Brent's 36 footer & it would be irresponsible for me to do so, even if the boat seemed to sail well. As I pointed out to "Dean Smith", Mummery, et al, may not have attended an institute of formal education in N.A., but they did cut their teeth with other designers. I realized, while at Tad's office, that finishing any course in design wouldn't qualify me to hang out my shingle, that it is just the start of the education. As well, imho, while offshore experience is a benefit to a designer - hence, my planned trip to Asia on a Cal - it's no substitute for having more qualified individuals guiding one in their education of design. This design business is a constant-learning deal, from what I see, a very long road. As you can probably appreciate, there are no short-cuts in life and there is no substitute for knowledge.

 

As Mike pointed out, this is one aspect of many to consider, since Stability covers many issues with yachts, not just its hull form for intact statically stability.

It has EVERYTHING to do with his claims. Because that is all they are, just claims. A professional designer does not make a claim regarding its stability, a professional designer provides hard facts, facts for the purchaser to make informed judgements and decisions. There is no room for guess work when it comes to Stability, EVER!!

So, in terms of its intact stability, the designer can easily issue a statement regarding the design; for home builders; based purely upon the hull form (even if roughly, since no 2 hulls will be 100% exact, but close enough for stability). It is something we are required to do when we issue stability books for Flag compliance.

The stability book (yes notice I say Book, as it is ends up being a thick book), should have all the hydrostatics, cross curves of stability etc etc. All the usual stuff one would expect any competent professional designer to provide with their design.

One part of the booklet, has “Loading”, and linked to this is the “Max KG”.

What this is, a simple KG curve of the vessel with a range of displacements and the KG at that displacement. The KG is the maximum it can be before the vessel is considered unsafe. Here is one for a vessel I did last year, as an example:



In the booklet, you then provide a simple example of how to calculate the KG and compare the result on the Max KG curve. I performed one with a cargo carrying load of 20 tonne, as shown.

So, what the owner does, or rather in this home build case, can do, is work out, by a proper detailed weight and centres spreadsheet establish with the equipment they are buying and where they wish to locate the item, what the final KG (or VCG) will be. This simple study could save a lot of time and hassle, and probably your life too.

Once the vessel is launched, you incline her, then you know for sure where the KG is and the displacement, and thus, is she safe or unsafe and how much you can alter the KG before she does become unsafe.

So, for a home build, you can do whatever you like, place whatever you like where you like, but, in the full knowledge of what is or is not safe to do.

Does BS provide such data for the home builder to reassure them about the stability and safety of their home build, no….so, do you consider that behaviour of a designer of his boat to be safe or unsafe?

 

I didn't get a set of data from Tom for the design I'm building either so I'm not sure if small boat designers do this. My build is to a 1964 design however.

My problem with the BS boats is actually the BS claims which when examined turn out to be crap or based on a single example somewhere under uncontrolled conditions. The initial stability curve as posted here by junk2lee being a classic example. It's been debunked comprehensively and what happens? The designer keeps right on trying to defend the indefensible and introducing various red herrings and extraneous factors.

I have the same question as tazmann: are those BS 36 hulls, if built reasonably close to the plan, going to have sufficient stability to be safe for crossing oceans? OK they don't meet the ISO standard, I suspect my Witch design might not either, but a lot of Witches (and their bigger/smaller sisters) have been built and a few of them have been used in a circumnavigation.

I know it's a judgement call but still, it does seem that one can cross oceans in a BS 36 and have a reasonable expectation of getting to the other side alive.

PDW

 

PDW

The stability of any vessel is governed by the relationship between the CoG and the CoB. If you don’t know this, how can one asses the stability?

Perhaps those small boat designers do not know how to do this, because if they do, why “keep” this data to themselves?...it is an important aspect of the vessels safety even more so for a home build. Since as I pointed out, if you need to know what will influence the stability of your home build. Using a small light diesel genny is going to make a difference compared to using one that is say twice the size and weight, or using a very heavy heavy anchor, or a mast that is twice the weight of one recommended etc etc….without guidance and the effects of such changes, how do you what this effect is?

My best mate is a yacht designer. He would never consider designing a yacht without a stability review. It is part of any process of designing a boat, any boat. Does it float, does it float upright etc..can only be answered by reviewing the design.

This is not to say home builds or any build per se is unsafe.

That is why, quiet rightly, you are getting (as you have stated) Mike to perform an inclining of your home build.

But the question is, why are you doing this?...the answer to that question, answers the whole MO of the thread.

 

It was a two-way trip ... and no freighter or tug to yard her in a single pull .She was dragged out by hand with come-alongs....not the work of a single high tide.The solid wood mast was cracked across-a horizontal fracture from the pounding as she was slowly in transit seaward .

If this was your boat,wouldn't you be proud that she showed little damage?

 

I would suggest that you do not leave it until launch
Getting a weight from load cells near completion will ensure you have your paint in the right place and also it is a good idea to (if your structure ) is strong enough, to find her point of balence for and aft,
make sense?

 

I don't have the data to hand, it may be there in the pile of plans somewhere. I bought them in 2003, went through them back then and since I started the actual build have really only bothered with the construction plan & the lines/offsets. I assume that Tom does have the data. He certainly does know the VCOG etc as possible changes which affect this have been discussed (like people who substitute steel cabin tops for marine ply, and install sloop rigs on hulls designed for low aspect rigs).

I have been careful to build as closely as possible to the design and to consult before making any substitutions of material, ballast etc. There have been a lot of these built and they keep coming up for sale. Some are over 40 years old & still sailing. Mine will be built very closely to the designer's spec.

Why am I building a design without having all the numbers on hand? It never occurred to me to ask for them, in fact. I'm still not too fussed over it all for what I'm building. I'm certainly interested but the design works. Tom can tell me why and what effect making various changes has. If I asked him for all the data, I expect I'd get it.

If I was building an ice breaker or similar as the first hull of a class I'd be more concerned. Building hull number 150-odd of a 40+ year old design, no. We'll get some numbers from the finished build.

As I've almost finished all the steel work now if I had the load cells I could jack the hull up a bit and get the hull weight sans interior, engines, tanks & rig.

I'm open to suggestions on this but realistically, I can't see that it's a big issue in my case.

PDW

 

Yeah. Structure is strong enough, for sure. The keel is a full length box section with a 200x40 flat bar bottom shoe. It's only sitting on its steel cradle in 2 places.

Got to find someone with the load cells etc...

 

ok leave her in cradle, then lift her and put a smallish round bar under the sole, this is the way, costs nothing, you can see how she balances