Pros and cons of steel sailboats - Page 273 - SailNet Community
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post #2721 of 5317 Old 12-07-2013
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Re: Pros and cons of steel sailboats

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Originally Posted by outbound View Post
Thanks Guys- Enjoyed the discussion of Al my last post precipitated which encourages me to try again.
I truly, truly love my boat so please don't take this the wrong way. If I had no financial restrictions I would build a one off utilizing modern wood epoxy techniques. With advancement in fabric technologies and available of woods from around the world I would have hull construction derived from an outline offered around 10 years ago in Wooden Boat.
The inner core would be edge nailed strip plank using plastic or bronze nails and a low density wood. This would be coated with double diagonals of appropriate fabric. Then a layer of hard wood laminates appropriate to vector analysis of forces applied. Then on the outside lay up of puncture and abrasion resistant fabric. The design would incorporate integral epoxy coated tanks centrally and water tight bulk heads fore and aft( just forward of rudder(s) posts). Through hulls would all be stand pipes or in sea chests.
At present the military have utilized fabrics as armor. Wood for weight remains an excellent construction material both in terms of strength, acoustic/thermal properties and lack of restriction in developing complex shapes.
Given there are so many sailors with much, much greater resources than I can anyone offer an explanation why we don't get a chance to drool over such boats.
Wood is the most complex, weakest, and least forgiving boat building material
ever used, with the greatest number of liabilities. As Frank Freddette, an old sealing schooner designer, once told me "It doesn't make much sense to build a boat out of wood anymore. There are so much better materials available today."

Brent Swain, Boat designer, Builder, and author of "Origami Metal Boatbuilding"
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post #2722 of 5317 Old 12-07-2013
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Re: Pros and cons of steel sailboats

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If the builder converts 3/16 steel plate to 1/4 alloy that’s only an increase of 1.3 times which will be a little weaker than steel but not alarmingly so.

Talking common boatbuilding materials. Alloy needs to be 1.4 times thicker that steel to have the same resistance to buckling. Stiffness scales linearly to Youngs modulus and by the cube of the material thickness. Young modulus or stiffness (desigated E in GPa) of most boat building alloys is around 70 and steel is 200. so for the same thickness alloy is only 35% as stiff (for 30% of the weight). If we take the cube root of (1 / 0.35) we get 1.42 as the required thickness increase. Or one half the weight of the equivalent structural material for the hull for 1.4 times the volume of material.

Alloy makes sense for lightweight boats and can be further lightened and made stronger by adding framing since deflection also goes by the cube of the span. So halving the span reduces deflection by a factor of 8. That’s why with alloy you juggle the skin and framing to find a good balance of strength and weight.

But novel alloy structures also need a careful analysis to ensure that not only material stress is within fatigue and buckling limits, but weld stresses are below the fatigue stress allowances. Alloy should also be professionally welded. It’s the worst material for the home builder to attempt to build in and it’s very easy to produce nice looking welds which have no penetration and can fail easily.

But I think you’d be daft to build an alloy Brent boat, you’d never recoup the material costs in resale. You’d buy a used Brentboat for less than the alloy cost.

It would be much more sensible to opt for a better designer and build compliant to ISO or some class scantlings. At least they catch the design pitfalls which can be numerous. With alloy the devil really is in the detail. You would also have a much better cost to strength ratio.

You find that most common materials have quite similar stiffness to density figures or what’s called ‘Specific Modulus’ Lighter materials have the benefit of being able to increase stiffness with thickness at a much greater rate than they increase total mass. But lot of boats don’t benefit much from a lighter hull construction particularly if they are a heavier type of vessel by design. Alloy does corrode less but a hot zinc or aluminium sprayed steel hull (internal deck and even topsides) comes close in durability if you can afford it.
By span do you mean span between all supports, such as the distance between chines and decks, lonigitudinals , etc , which have far more rigidity than frames ?
How much credit do you give to the huge increases in stiffness given by shape, which adds far more stiffness than mere transverse frames?
Miss any one of these factors in your calculations, and all they become irrelevant

Brent Swain, Boat designer, Builder, and author of "Origami Metal Boatbuilding"
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post #2723 of 5317 Old 12-07-2013
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Re: Pros and cons of steel sailboats

Frank the cannibal?
He was an awful designer. His sterns were really weird.
I never met him. I just heard the cannibal stories. He was probably a real nice guy.

I have to go along with Paulo on the helm balance issue. I've done three very light, wide stern boats, the two FlyTiger models and the one off ICON. All are very well balanced. As Paulo says two fingers, lightly on the wheel is all it takes to drive ICON. ( Don't forget the FT10 won its class in the the Wirth-Monroe race in Florida on Thursday. Yahooo!)

Take any one of those wide ( L/B's below 3.4), lght (D/L's below 130) flat bottomed boats and heel it over 20 degrees. They roll bow down but the keel gets a nice angle of attack and the water sees a long, sliver of a boat. It's a very easy shape to balance. If these boats all had bad helms they would have corrected it by now. Similar hulls and similar frac rigs with similar keels and similar rudders they have to be able to figure it out and I'm certain they have. You can't win races in a poorly balanced boat. These boats didn't pop up over night as an experiment. They have evolved.

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Last edited by bobperry; 12-07-2013 at 08:26 PM.
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post #2724 of 5317 Old 12-07-2013
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Re: Pros and cons of steel sailboats

Frank Freddetts designs like Pathfinder and Longfin reflect the west coast troller stern.Form tends to follow function (Sullivan) This is an example of design evolving to fill a need. Some sailors think their needs evolve as designers pull up pretty or faster as the only criteria for excellence. Others may be impressed with a sturdy counter to shuck oysters. Those probably balance affordability and practical comfort with NEW and modern. If you are just a dreamer, dream on. (Frank used to sit on my cap rail and talk about the old days)
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post #2725 of 5317 Old 12-08-2013
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Re: Pros and cons of steel sailboats

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Frank the cannibal?

I never met him. I just heard the cannibal stories. He was probably a real nice guy.
WELL? You can't just leave it at that. The rest of us haven't heard the stories.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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Re: Pros and cons of steel sailboats

Surprised by Brent 's comment about wood. Maybe he was talking about plank on frame.seem to recall boats up to 100' being done in cold molded. Went up to Covey island and saw some of the gorgeous designs they were putting out in strip plank. Brent may want to investigate modern wood construction. Like Paulo points out real advances in construction techniques have occurred. Don't see much resorcinol now a days.
Paulo you make a very good point. Production yards must built for the masses,must create buzz their boats is the new and improved version or go out of business. Bene is the largest yard in the world. They make a fine product and enjoy the cost effiencies that come with large production runs. They and Hanse, Catalina, or even Hunter have this advantage. The issue of keeping costs down, of designing to keep construction time down, of designs to create a boat that will look good in the shows also apply. But I think it's a wonderful thing Bob is still able to design and sell his designs. That two French seat of their pants sailors can design and actual build the Boreal. In short there remains and hopefully will always remain a non "for the masses" market.
For myself ( and now >55 others) I know I 'd rather be on my boat when off the shelf than any of the "off the shelf" production boats. As I said before " different strokes for different folks". There is no right or wrong on this.
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Re: Pros and cons of steel sailboats

Given the wide variety of construction techniques the modern "wooden" boat builder uses it seems rather naive to condemn all wood boats as if they are all equal. There are some really beautiful wooden boats being built today in Maine and in the UK. These are true works of art and wonderful boats. I don't think anyone involved with these efforts sees any of these boats as inferior in any way.

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Re: Pros and cons of steel sailboats

I am not surprised by Brent's comments on wood seeing that they came from Brent.

But as Bob noted above there is a very wide range of species and construction methods that employ wood. Any boat is only as good as it's design, engineering, and build quality. In a broad sense, choosing the right species and construction methods, wood can be one of the strongest for its weight, lowest maintenance, least expensive, and most durable materials that is out there. In my mind , wood would probably be my first choice for a "one off" design. Depending on your environmental ethics, it is also a material that is a bio-renewable resource, which personally appeals to me.

But not all wooden boats are the same, and given a poor design , wood species and building details then wood could be one of the heaviest, least durable, high maintenance materials that are out there.

Given the wider range of good to bad construction that is possible, Brent is not 100% wrong.
But obviously, he and I would disagree on his blanket statement decrying wood.

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Re: Pros and cons of steel sailboats

Epoxy cold mould would be my choice for a custom boat.

Varnished of course.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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post #2730 of 5317 Old 12-08-2013
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by Brent Swain View Post
What amore competitive market has given them is a powerful incentive to cut costs ,then make up bogus technical arguments to justify under building things.
For the more common type of cruisers, I mean plyvalent cruisers the offer can come from 20 boat builders or more. Sailors do not chose the least expensive:

What people look is the best deal for the money. That includes price, boat quality and finish, interior space, boat performance and a suitability to their sailing and life style that includes cruising style.

Brands like Arcona, X yachts or Halberg-Rassy would have bankrupted long ago and nobody would be buying the Beneteau Sense that is way more expensive than the Beneteau Oceanis series. That would be good for Varianta that would be by far the most sold boat. That's not the case by far, very far

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Last edited by PCP; 12-08-2013 at 08:08 PM.
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