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  #3381  
Old 01-27-2014
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by Dean101 View Post
I'm not sure if I completely understand this concept. This is how I'm visualizing it;

Up to a point and depending on the location, weight (displacement) increases stability. At a certain point it starts to negatively affect stability. If I load an already heavy displacement boat (such as Brent's) with the additional weight of cruising gear and equipment and assuming I try to keep heavy items low and light items high wherever possible, I may raise the displacement to a point that it negatively affects stability. If I load a light displacement boat of similar hull dimensions with the same weight and load distribution, I am in essence only increasing displacement and therefore stability. It takes more weight to reach the point of negative impact.

In other words; Assuming two hulls built with the same shape, length, bean, etc, one heavy because it is built from steel and one light and built from cored fiberglass or whatever. The heavier hull has less tolerance to weight because its own weight is closer to the point where the entire boat will just sink, like piling rocks on a flat board until it sinks in a pond. The light boat can accept more weight before reaching that point.

Is that basically what Bob was talking about?
No. He certainly can explain better but he was talking about two boats with the same displacement, an heavy one and a light one and that means that the light one to have the same displacement has to be considerably bigger.

Regarding two boats of the same length and beam, one heavy and other lighter, assuming that both are well designed it does not work the same way.

The heavier one will have a lot more ballast (assuming that both have similar keels and the same ballast ratio) and if you are correct in saying that the lighter boat can take more weight without sinking it is also true that the same weight will have a bigger influence in raising the boat CG making it more unstable at considerable angles of heel diminishing in much the AVS.

In short, the load will represent a much bigger proportion regarding the ballast of the lighter boat than to the ballast of the heavier one. If the load is excessive, even if properly stored it will only increase stability at smaller angles of heel making the boat dangerous if by any reason it heels considerably.

That's why each NA gives for each boat a max load one that will allow it to have a non dangerous AVS.

Regards

Paulo
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  #3382  
Old 01-27-2014
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by Jeff_H View Post
The discussion with Brent last week about the impact of having a sealed steel mast vs a flooded aluminum spar left me a bit curious. I do not know what size tubing Brent uses for masts, so I made an assumption and out of curiousity, I looked up the weight of a 6" diameter standard weight steel tube and the volume of air that would be trapped within it. A 6" diameter standard weight steel round tube weights 18.97 lbs per foot. The trapped air in it would provide 11.4 lbs of flotation. That amounts to an after floatation mast weight of 7.57 lbs per foot. In other words, even with the floatation from the trapped air, inverted, the submerged mast will still weigh 7.57 lbs more than its floatation.

I compared that to an aluminum mast section with a similar E*I and Fb*S. That mast weighs 5.9 lbs per foot. In other words, lighter than the weight of the steel mast even with the buoyancy from the trapped air.

On the other hand, I am not clear in my own mind on how to treat the water within the mast. The aluminum mast would hold approximately 12.3 lbs of water per foot. That would take the combined weight to 18.2 lbs clearly heavier than the buoyed steel mast. But arguably as the mast surfaces, that water can excape as quickly as it comes in.

What is clear is that with a mast that weighs 18.97 lbs vs a 5.9 lb mast, you will end up either a lot more prone to capsize or with a whole lot more ballast.

Jeff
We use a 6 inch tube with a wall thickness of 11 gauge, roughly a third the weight of the pipe your calculations are based on.
Shows how jumping to confusions can give a grossly distorted picture
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  #3383  
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by PCP View Post
Yes, that number regards the AVS.

The ISAF rules for category 0 demand more if the boat is not certified by ISO 12217-2 (RCD):

Either AVS in ORC Rating System of not less than 120 or a minimum STIX value of 32 and AVS not less than 130 - 0.002*m (Where “m”
is the mass of the boat in the minimum operating condition as defined by ISO
12217-2.)

But this are minimum standards and the AVS is only a part of the story. Weight and size of the boat has a huge influence on the overall boat stability. If the weight of Brent's boats are a positive factor in their overall stability, the size (that also relates with weight) is on a kind of limit zone when you call it a boat for sailing in high latitudes.

Let's say that for a 36ft Brent's boat (if not overcharged) has a better stability than most 36ft, specially considering mass production ones (due to his bigger weight).

Brent has the idea that his boat has a big loading capacity and if someone takes that to the letter and overcharge the boat, the stability can be compromised (on his boat or in any boat). In fact, as Bob had already explained, a good well designed modern light boat with the same weight of Brent's boat (a bigger boat) will not only have a bigger overall stability as it can carry a bigger load.

Regards

Paulo
I see very little storage space above the waterline on most cruising boats. All weight stored below the centre of buoyancy is ballast albeit, less effective than ballast at the bottom of the keel, but never the less, adding to self righting ability in the event of a rollover, as long as it stays in its lockers. All my storage can be locked in, in ways that it wouldn't come out in a rollover . When my boats have been cruising for decades, from Cape Horn to the Aleutians, and several circumnavigations, with zero stability problems, its a bit of a stretch to claim that they will suddenly start to have stability problems, by decree, from those who have absolutely zero experience on any of my boats , and minimal cruising experience, or steel boat cruising experience of any kind.
Silas Crosby has come up about 6 inches since Steve emptied her out , at 1150 lbs per inch immersion! He said the storm he encountered off the Aleutians was far more sever than anything he experienced in the Southern Ocean. Had he had any serious stability problems, he would have definitely experienced them there, if not far sooner.

Last edited by Brent Swain; 01-28-2014 at 07:26 PM.
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  #3384  
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Re: Pros and cons of steel sailboats

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Originally Posted by outbound View Post
Still its too bad in a way the concept of bilge keels hasn't been more aggressively pursued in recent years. To my simple understanding if you had twin bulbed keels you might get very reasonable stability without major draft and ability to careen while being upright in a large tidal zone much like the British do.
With twin keels, your stability is roughly the same as with a single keel with same draft, the depth of the ballast being the same. With the keel being the centre around which a boat rolls, having two such centres in a twin keeler drastically reduces rolling. The ability to dry out for maintenance, while drastically increasing the odds of having a cleaner bottom for more of the time, is not the only advantage of twin keels. Many places where I have been anchoring for decades are not useable by boats which cant dry out ,and the deep water alternatives are not all that attractive. That is one of the reasons I have benable to avoid moorage fees. My uncle, who cruises Queensland, said that entire coast is mostly open ocean with only really protected water being river mouths ,available only to boats which can dry out, and have less than 5 ft draft. If you cant dry out and have over 5 ft draft there, you are rolling in an ocean swell. A couple who did a circumnavigation on one of my 36 footers ( Island Breeze) said that is the case not only there, but in many cruising areas w around the world.
Steve said being able to dry out on Silas Crosby was a huge advantage in the Straits of Magellan enabling him to sleep soundly, while the ingle keeler skippers were awake all night, worrying about dragging anchor. No way two keels hard aground are going to drag .

Such practical considerations , simply don't show up in mathematical calculations and those who only understand that which can be expressed in numbers, don't have a hope in heel of comprehending such practical considerations, especially if, like Bob and Smack, they have no hands on experience ( which makes them a poor source of advice on any practical considerations of yacht design.
On BD.net anyone supporting my arguments, including several Coast Guard members were automatically accused of being me.
Naturally ,anyone bringing attention to practical maters are automatically, defensively attacked by those who are weak in comprehending practical matters due to lack of experience in actually trying to use what they advocate .Fortunately, they are not the only ones reading my posts, just the loudest , trying maintain their illusion of relevance. I often get private emails asking for info which they didn't want to ask on the forums , for fear of getting ridiculed for not buying the "Just throw money at me and I will solve it." type of response.
I am happy to give them low cost, simple solutions , which would get shouted down, by jeering adolescence, on the forums.

Last edited by Brent Swain; 01-27-2014 at 06:28 PM.
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  #3385  
Old 01-27-2014
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Re: Pros and cons of steel sailboats

Ballast,even depleted uranium, takes up volume. One would think for the same draft and weight of ballast by utilizing twin keels you could get that weight lower improving righting arm. Would someone other than BS confirm this thinking please . Apparently BS missed out on HS physics as well as NA school but this seems apparent to me. Only way single keel could get same CG would be to employ a bulb or increase chord or use winglets.
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  #3386  
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by bobperry View Post
Out:
We need Paulo on this. He has posted several new European models that have modern fin and bulb tandem keels. They look quite good. But there is little to gain from having two crude, low aspect ratio BS keels other than the ability to have the boat stand on it's "feet" when the tide goes out.
Picture your anchor rode getting hooked up on the back of those fancy fin and bulb keels . Then imagine the wind coming up in the night, leaving you on a lee shore, beam to wind and sea, with no chance of getting your anchor rode free from the windward keel. That is what happens when your twin keels are designed by numbers crunchers, with no hands on experience . Such practical considerations simply don't show up in the numbers game, and people who don't have hands on experience simply cant grasp the concept of anything not being a mathematical question. It can take a model to design twin keels which wont foul their anchor rodes in such a way. Most "High Tech "twin keels are a disaster waiting to happen in this regard. Warning people of the screwup advice from people like Bob and Smack, who have no steel, or twin keels, or long term cruising experience, is what keeps me posting.
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  #3387  
Old 01-27-2014
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Re: Pros and cons of steel sailboats

That's a crock!
" I see very little storage space above the centre of buoyancy on most cruising boats"
What a ridiculous statement!

The center of bouyancy of any "normal" sailboat is below the DWL It has to be.
I checked quickly two of my moderate designs. One had a VCB of -.92' and the other a VCB of -.94'. So, let's round it off and say for a 40' to 50' boat the VCB will be about 1' below the DWL. Think about that. There is really not much boat left below that. It's a wedge. How the hell can most of your stowage be below the VCB? Essentially we are talking about the bilge. You can get some tankage in the bilge and that's a good way to lower the VCG. But given the VCG of a "normal" cruising boat is usually around the DWL or slightly above and this bilge weight is not very effective at lowering the VCG. There is just not enough arm to the moment. Fifty gallons of fuel weighs 362 lbs.. Sure it helps lower the VCG but by very much. Generally gear will, propbably not have the weight of fuel so even if you do pack your bilge with stowage material you will still not lower the VCG appreciably.

Brent talks about "lockers". Are these bilge lockers? Again he is wrong. In a normal cruising boat almost all the good stowage volume is above the DWL. That's where the available volume is. Once you get below the DWL there is simply not enough boat left for it to be where you stow the bulk of your gear.

I never suggested BS boats had a stability problem. Don't put me in that camp. Given their weight and general shape I think they would have reasonable LPS. Certainly not the 175 degs that BS claims. That is just plain silly. But I can see a LPS for the BS 36 around 130 degs maybe as high as 135 degs, maybe. (I prefer LPS, limit of positive stability.)

I don't have a problem with the reality of the stability of BS boats. I have a problem with BS's efforts to discuss stability at all. The boats are ok. He's very confused and ignorant on the subject.

If I was going to pick on the stability of a BS 36'er I'd estimate that their initial stability, that is their Rm's through the first 20 degrees is very low. Without lead ballast and steel construction the VCG of the boat will be high to begin with and given their high deadrise shape and moderate beam you have a recipe for an initially tender boat. This is not theory or opinion. This is just physics and naval architecture. This does two things: It makes the boats very tender initially. This makes for a boat that is not much fun to sail as you have to reduce sail quickly when you get some breeze. The boat is always on it's ear. But the good news is that with low initial stability you get a nice comfy ride. You'll roll but you'll roll slowly. This is a good trait foir an offshore boat so long as you don't mind a tender boat. For most of us who are not intendind any long offshore passages the initially stiff boaty will certainly be a faster boat that can carry it's sail well and not require reefing until you have more than 20 TWS. Face it, people like stiff boats.



This photo must rip your heart out Brent or should I call you "Jack"?
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  #3388  
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Re: Pros and cons of steel sailboats

When Patrick Bray had one of his earlier twin keelers featured in Pacfic Yachtring, one which would have a major problem with anchor rodes fouling them, I phoned him up, and described the problem of anchor rodes fouling one, which resulted in the shape of the keels he now designs. It also allows a much stronger attachement to the hull, via much longer chord
I started out with asymmetrical keels. They didn't sail any better than symetrical ones.
Deridders on Magic dragon found a huge performance improvement ,when they went from asymmetrical to symmetrical. There is a Ted Brewer design in the harbour here, with asymmetrical twin keels. I'm told she is as slow as a bureaucrat's brain.
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  #3389  
Old 01-27-2014
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by Dean101 View Post
I'm not sure if I completely understand this concept. This is how I'm visualizing it;

Up to a point and depending on the location, weight (displacement) increases stability. At a certain point it starts to negatively affect stability. If I load an already heavy displacement boat (such as Brent's) with the additional weight of cruising gear and equipment and assuming I try to keep heavy items low and light items high wherever possible, I may raise the displacement to a point that it negatively affects stability. If I load a light displacement boat of similar hull dimensions with the same weight and load distribution, I am in essence only increasing displacement and therefore stability. It takes more weight to reach the point of negative impact.

In other words; Assuming two hulls built with the same shape, length, bean, etc, one heavy because it is built from steel and one light and built from cored fiberglass or whatever. The heavier hull has less tolerance to weight because its own weight is closer to the point where the entire boat will just sink, like piling rocks on a flat board until it sinks in a pond. The light boat can accept more weight before reaching that point.

Is that basically what Bob was talking about?
The only factor which affects how a boat will sink from adding weight (stores, gear etc.) is the Pounds Per Inch Immersion. It is dependent on the waterplane area, not the displacement of the boat. A heavy steel boat and a lightweight cored boat, each with 1500 Lbs per inch immersion will both sink at the same rate from additional weight being added.
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  #3390  
Old 01-27-2014
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Re: Pros and cons of steel sailboats

Well I had a very nice morning. We launched the Sliver project boat FRANCIS LEE. There are still some odds and ends to take care of including getting our new sails but we are almost ready to go. The cove stripe will go on now. I can't wait to see that.

As you can see we are still floating high and on the designed lines. That's always good. Boats gain weight over time so you like to be light at launch.

My client is very happy. I am happy.

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