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  #3341  
Old 01-25-2014
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Re: Pros and cons of steel sailboats

Looking at the Al boat made me recall article in a trade journal in which the owner of Waterline discussed paint. He commented on how hard it is to keep paint on Al c/w Fe. I see even many top end Al hulls ( K+M, Boreal, Kanter) boats are left bare. ? Why won't Al hold paint? ?Are there new paint systems for Al?
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Re: Pros and cons of steel sailboats

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Originally Posted by PCP View Post
Why do you say this? It is true that stability curve makes no sense but a value of about 130º or even superior for an AVS is pretty good, the hull design has nothing new or interesting but it seems adequate to me and the boats are heavy contributing for the overall stability. Besides they sailed extensively offshore with a good proven record regarding seaworthiness.

So, why do you find them dangerously unstable?

Regards

Paulo
Paulo
I see you point, if Brent's boat's have an APS of 130 degrees, then they are reasonably stable . But I think that this APS is still to be proven. In order to accurately model the righting moments curve, you need to know the position of the vertical center of gravity. That is most easily obtained through a simple inclination test. In the absence of a known VCG the APS claimed is merely a conjecture.

In the preliminary design stage, for simple rough validation, from experience most knowledgable and experienced yacht designers can guess at the VCG's for a design type they have worked on with some frequency. I would think that the Brent boats have a number of unusual design features which would make a seat of the pants estimate difficult. For example, on the positive side Brent claims that his masts and pilot houses are air tight. And there is the boats moderate beam. That would help with stability at large heel angles. On the negative side, there are the heavy weights of a steel deck and deckhouse, a steel mast, and low density ballast.

Without modeling the buoyancy of the pilot house and mast, and without an actual VCG, it's hard to know how these contradictory factors resolve themselves, and therefore any claims regarding the APS is purely unsubstantiated speculation.

Jeff
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  #3343  
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by Jeff_H View Post
Paulo
I see you point, if Brent's boat's have an APS of 130 degrees, then they are reasonably stable . But I think that this APS is still to be proven. In order to accurately model the righting moments curve, you need to know the position of the vertical center of gravity. That is most easily obtained through a simple inclination test. In the absence of a known VCG the APS claimed is merely a conjecture.

In the preliminary design stage, for simple rough validation, from experience most knowledgable and experienced yacht designers can guess at the VCG's for a design type they have worked on with some frequency. I would think that the Brent boats have a number of unusual design features which would make a seat of the pants estimate difficult. For example, on the positive side Brent claims that his masts and pilot houses are air tight. And there is the boats moderate beam. That would help with stability at large heel angles. On the negative side, there are the heavy weights of a steel deck and deckhouse, a steel mast, and low density ballast.

Without modeling the buoyancy of the pilot house and mast, and without an actual VCG, it's hard to know how these contradictory factors resolve themselves, and therefore any claims regarding the APS is purely unsubstantiated speculation.

Jeff
Tad Roberts had a good look at it and found a number superior to 130º for the AVS:

Quote:
Originally Posted by MikeJohns View Post
..
Tad says 131 degrees based on the lines you provide and his most thorough estimate of weights and moments which he gave you for free to comment on and modify if required.
That was his final figure, anything else was preliminary and was altered as the study progressed and that included a 3d computer model of the hull.

..disproves Tad Roberts best estimate of the center of gravity from his weights and moments study, then you should only quote 131 degrees. To tell anyone anything else is misrepresentation. Especially now it’s been explained to you clearly several times.
...
Bob Perry guessed something similar and looking at the design and numbers I would say that the boat has at least an AVS of 120º that for an heavy steel boat is already a very acceptable number that is common in many designs of this type.

As I said everything seems "normal" on the BS 36ft design even if pretty conservative and even out dated. Bob expressed already a similar opinion.

I cannot understand how someone can say that design is: "dangerously unstable"

He says that based in what?

Regards

Paulo
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  #3344  
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Re: Pros and cons of steel sailboats

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Originally Posted by outbound View Post
Looking at the Al boat made me recall article in a trade journal in which the owner of Waterline discussed paint. He commented on how hard it is to keep paint on Al c/w Fe. I see even many top end Al hulls ( K+M, Boreal, Kanter) boats are left bare. ? Why won't Al hold paint? ?Are there new paint systems for Al?
Most metalls are "difficult" to paint, ie they are not like wood or GRP. Most metals should be treated with something prior to painting. This treatment is crucial as it makes the paint get a better grip. Similar, control of environmental conditions (as humidity, temp) is important prior and durng painting and while the paint dry.
Al is in principle not different from other metals, but care has to be taken as it is easy that some moisture creeps in, resulting in some corrosion followed by paint lifting.
Most airplanes are made of Al. Most of these are painted, parts or in full. Studying airplanes, which I have had my share of, the paints seems to stick on in spite of very high temp diffs, abrashion with dust in relative high speed and so on.

/J
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by outbound View Post
Looking at the Al boat made me recall article in a trade journal in which the owner of Waterline discussed paint. He commented on how hard it is to keep paint on Al c/w Fe. I see even many top end Al hulls ( K+M, Boreal, Kanter) boats are left bare. ? Why won't Al hold paint? ?Are there new paint systems for Al?
It is clear that we can paint aluminum looking at the reference to airplanes and the harsh conditions the paint has to endure Low temperature at altitude high temperature on the tarmac and high speed dust abrasion. The temps change rapidly on takeoff and landing.
Next up Ford will have an all Aluminum F-150 for 2015 ? My guess is it will be painted. I am sure they will have some paint issues. This will bring about more research and this will slowly make its way out to the public. Then behold we will have new paint systems.
Good day, Lou
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by PCP View Post
Tad Roberts had a good look at it and found a number superior to 130º for the AVS

I cannot understand how someone can say that design is: "dangerously unstable"

He says that based in what?

Regards

Paulo
I agree that an AVS OF 130 would not be considered 'dangerously unstable' but I think that the point about Tad Robert's calculation of the AVS was that Tad did not have an accurate VCG and so the number is at best an approximation, and at worst totally bogus.

Jeff
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Re: Pros and cons of steel sailboats

I'm with Paulo on this. If BS boats have a LPS of 125 degs then I would not call them "dangerously unstable"". I think with their single chine, high deadrise shape coupled with modest beam they will suffer for initial stability but I'd stick with my 125 to 130 degs estimate for LPS. But there is a caveat.

I'd love to know what a steel, welded mast weighs. I suspect it is at least double that of an alu stick. That can dramatically raise the VCG.

I was working on a 56'er. I came in one Monday morning and looked at the weight study file. The VCG was abnormally high. I knew something had gone wrong so I began going over the numbers. When I got to the rig section of the weight study I noticed that I had input the weight of the mast twice by accident. It was one of those mistakes that becomes a very usefull lesson.

What I am getting at is that if a BS boat has a welded steel mast the VCG could be 6" above the DWL and that would have a huge effect on stability. I really don't know BS boats very well, only from what I see in th pics posted. BS is extremely reluctant top post his "design" work. But from what I see, if the boat has an alu mast, say the 36'er, I'd guess VCG to be 1" above the DWL maybe 2". I agree with Jeff. Hard to wax on about stability without an accurate VCG.

Obviously we can't ask BS because I know better then to believe anything he posts. I think I would trust Tad's work on this. He put some time in on it and he knows naval architecture.
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  #3348  
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by bobperry View Post
I'm with Paulo on this. If BS boats have a LPS of 125 degs then I would not call them "dangerously unstable"". I think with their single chine, high deadrise shape coupled with modest beam they will suffer for initial stability but I'd stick with my 125 to 130 degs estimate for LPS. But there is a caveat.

I'd love to know what a steel, welded mast weighs. I suspect it is at least double that of an alu stick. That can dramatically raise the VCG.

I was working on a 56'er. I came in one Monday morning and looked at the weight study file. The VCG was abnormally high. I knew something had gone wrong so I began going over the numbers. When I got to the rig section of the weight study I noticed that I had input the weight of the mast twice by accident. It was one of those mistakes that becomes a very usefull lesson.

What I am getting at is that if a BS boat has a welded steel mast the VCG could be 6" above the DWL and that would have a huge effect on stability. I really don't know BS boats very well, only from what I see in th pics posted. BS is extremely reluctant top post his "design" work. But from what I see, if the boat has an alu mast, say the 36'er, I'd guess VCG to be 1" above the DWL maybe 2". I agree with Jeff. Hard to wax on about stability without an accurate VCG.

Obviously we can't ask BS because I know better then to believe anything he posts. I think I would trust Tad's work on this. He put some time in on it and he knows naval architecture.
You know what's really scary about all this? I barely understand what you guys are saying - and I'm an ex-architect. You guys, and the guys on BDnet, are experts on this stuff...and you're concerned.

Now, take a look at BS's target market. These are people that, for the most part, have no idea what VCG or AVS or even LWS means. They are, by his own description, "cruiser wannabes".

All they have is trust that Brent is an honest expert who has fully addressed all of these factors in his calculations...when it appears he doesn't even know what many of them mean.

That is scary. When a guy tells you he's an expert yacht designer - you kind of need to believe he's telling you the truth.

If I were a cruiser wannabe, and I came across these concerns from real experts, I'd be wondering if the trust I'm about to place in the vague BS drawings I'm about to spend hundreds of dollars for - then the several years and many tens-of-thousandes of dollars I'm about to throw into BUILDING THAT HUNK OF STEEL MYSELF AS AN AMATEUR!!! - might be a bit misplaced.

I think potential death by Fukushima Debris is a much, much better bet.
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  #3349  
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Re: Pros and cons of steel sailboats

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Next up Ford will have an all Aluminum F-150 for 2015 ? My guess is it will be painted. I am sure they will have some paint issues. This will bring about more research and this will slowly make its way out to the public. Then behold we will have new paint systems.
Good day, Lou
Maybe the information is already there - in the bicycle industry. About twenty five tears ago when the aluminum bicycles were making their first big splash on in the US market, paint was a major problem. Between flexing and inevitable scraping and scratching, sweat would find its way between metal and paint and soon large patches of paint would flake away exposing a fine coat of aluminum oxide. Today's paint jobs are much better and the best (for adherence) were an epoxy powder coating process. Also, for bonded frames anodization worked pretty well. I wonder what they are doing today as even cheap discount store bicycles are made from welded aluminum frames.
John
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Re: Pros and cons of steel sailboats

Good point, John They have been painting bikes for years !
Good day , Lou
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