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Old 19-06-2010, 13:49   #196
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Seems like just the kind of logic that leads to the missinformation. Do you think designing and building a 100 ton ship is similar to a relatively small yacht? Do you think strength is in and of itself the determining factor in ship construction? The information is out there. Take a look.

Anyway, heres a good example of the wonderful strength of steel. Center mass T-bone with a tanker. Increadible! It sailed quite a distance but probably with a little less effiiency.

(If you understand aluminum vs steel you can see the increadible plasticity of steel here. Aluminum wouldn't
have "yielded"..would have bounced.)


Yes people generally say that aluminium is four times stronger than steel pound for pound but most boat made of aluminium are made lighter than their steel twin would be, the hull plate is thicker than steel but still not usually built to the same weight. In my experience with aluminium often it fails at the welds, which is why there are some designs that work better for aluminium or at least that boats are put together slightly differently when built of these different materials, I find working with steel to be less counter intuitive than building out of aluminium, just because of the weld induced stresses. Steel is the more basic and fool proof of the two, easy to over build, cheap, and strong, I'll stick with steel.
Also maybe not necessarily with a hull, but something I take into consideration when ever debating building something out of steel or aluminium is the amount of abuse it going to take. For example, my spreaders, I built them out of 1" stainless pipe rather than going for aluminium pipe cause I know, if you give aluminium pipe a good bang with something you can put a good dent into it and aluminium pipe with a dent in it has close to no compressive strength. The stainless pipe, I know won't dent so easily and even if it were dented it'll still be stronger and I could potentially un-dent it and know there wouldn't be any major stress concerns.
And they are starting to build some larger vessels these days out of aluminium, go fast ferries is what I'm thinking about, good reliable aluminium welding is a pretty new thing, as is it's smelting really, whereas steel/iron has been around in the boat world for a century or more. Neither of these have really played a large part in the small boat building world for very long though and 300 ton tanker design/building is a little different than the under 50 foot crowd.

I love that boat (gringo), apparently they just kept on sailing till they got back to the states
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Old 19-06-2010, 14:40   #197
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Steel is and has been the most used material in ship building as it can accept more variation in construction quality and still function adequately. Aluminum has been the elite choice of materials mainly for its lower weight and similar to steel strength. But aluminum accepts less error in construction techniques before the boat is risque. So in my mind aluminum is the "designer's choice" for high end boats constructed by the best of the builders and techniques. Steel is the "people's choice" and us common folk/welders can achieve success working with it.
- - I would build a steel boat myself but no way would I attempt to do it in aluminum.
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Old 19-06-2010, 15:56   #198
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If you buy or have built, an aluminium boat the quality of the welders/ boatbuilders is the first thing you should verify. steel can be easily homebuilt but, aluminium needs experienced qualified welders.

As some people have pointed out, even if professionally done, the welds in aluminium are slightly weaker than the strength of aluminium itself. This is well known and aliminium boats are designed assuming the weaker strength of the welded material for their calculations. This has the advantage that much of the structure is actually stronger than the designer assumes.

“Strength” is a poor term when discussing boat structures. The big difference between metal and GRP is their “plastic” range. If we take 2 equally strong boats one metal the other GRP. The designers have chosen to make these structure equally “strong”(metal boats are more likely to be overbuilt, but lets assume they are the same), so it will not be damaged by everyday bumps with say a pier when docking, but if these 2 boats exceed their design strength when say hitting a container at full sailing speed,
Both boats will be damaged once they exceed their design parameters, but the brittle GRP structure fractures loosing its watertight integrity and sinks. The metal boat will be damaged, but is much more likely to retain its watertight integrity, keeping the occupants safe.
To design a GRP structure with the same resistance to puncture as a metal boat is not practical without heavy and very exotic laminate.

.
Discussion on the minor difference between the “strength” of aluminium and steel boats obscures the fact that their is a enormous difference between the puncture resistance of metal and GRP boats.


Tragedies like the loss of Airwego (and my heart goes out to them I hope they get back on the water soon) are much less likely with a metal boat.
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Old 19-06-2010, 16:17   #199
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Since this thread is about Steel (metal) boats and not about FRG I don't get into discussions of FRG impact resistance which is basically non-existent when compared to metal. However FRG hulls can be designed to mitigate such problems being boat threatening. Water-tight compartments, collision protective water-tight compartments, etc. can all be designed into FRG boats.
- - But again we are discussing Steel boats where impact resistance is because of the material superior to all other hull choices. However, Steel/metal boats are definitely inferior when corrosion is up for discussion in comparing hull materials. So you pick your priorities and financial resources and then decide whether steel is for you or not.
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Old 19-06-2010, 18:12   #200
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Oh my, here I go about to make everyone angry at me again. The short of it is, I don't agree. Steel has a bad rep. People who don't know much if anything about boats, think of steel boats as rust buckets that are way too heavy and very slow. We know those things are not true, or only part truths at best, but John Q Public doesn't. Aluminum is seen as having all the advantages of steel with none of the disadvantages. After all, it doesn't rust! It's also lighter, and as you heard here, "stronger," so what's not to like by the ignorant.

FRG is popular for one major reason: Make a mold, churn out 1,000 boats with minimal effort. It's far less labor intensive than the one off metal boats or wood boats. I guess you can argue that the cold molded boats could be kinda mass produced off a mold, but the process is too labor intensive to be competitive. FRG has few if any other redeeming qualities. We all know, or should know, what happens when you strike objects in the water in a FRG boat....you sink. They don't do well when whales ram them either. Still, they can be more or less mass produced, even to the interiors, so they are the most cost effective way to make a boat.

Early on, the public got snookered into believing FRG boats were "maintenance free" and many still believe that. I mean, after all, they don't rust, right? Everyone has them, so they must be good, heard mentality. Then there are us few, us precious few who don't blindly hang with the heard! Good on us!!

Regards,

Thomas
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Old 19-06-2010, 18:15   #201
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Determining factor ... hmmm ... le me think ... watertightness perhaps?

Strength is a major factor, big ship or small ship. Off course, things are not scalable, but they are accountable.

b.
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Old 19-06-2010, 18:52   #202
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And if steel has bad rep it is only because there are so many amateurishly built steel boats around. Let's go get ourselves at a properly built Koopmans and hello.

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Old 19-06-2010, 18:56   #203
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yep, that's true. Like the guy in Pt. Angels who named his beautiful John Simpson designed boat, "Rusty Nail" then let her sit in the water for 5 years untouched! There should be a special place in hell for folks like that!

Thomas
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Old 19-06-2010, 20:09   #204
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Salty monkey's enjoyed his first MIG weld intensive class today! WHOOHOO!

Enlightening. But takes a lot more skill than he imagined.Blew out a tip. Hard to get off the splatter - too fast on the ovals and the half-moons, and too slow on the draw. Had a picture to share but I cannot upload due to size.

...and empowering!
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Old 20-06-2010, 10:01   #205
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Yep. Learning skills that may look easy is an eye opener. I learned sailmaking for 18 months. Before taking it up I knew it was difficult. Now I know I was right. But I loved my time in the loft as much as I loved my earlier office job (doh, I probably liked the loft job more!)

All well done boat work - sails, wood, welding, lamination to name but few is in fact a time consuming process (to execute, and to learn).

Which partly explains why the modern pop-out mass market boat, assembled by briefly trained but otherwise ignorant workforce are less than perfect tolls for any serious cruiser.

b.
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Old 20-06-2010, 10:53   #206
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If you buy or have built, an aluminium boat the quality of the welders/ boatbuilders is the first thing you should verify. steel can be easily homebuilt but, aluminium needs experienced qualified welders.
Yes, we looked at a nice aluminum boat, went so far as to have an accepted offer and to do a survey, at which time we backed out.

The night before the survey the owner got talking about the build process. He had the boat welded up on the cheap by guys when they were out of work. At least 5 different outfits by his telling. When the surveyor got into the boat he immediately found "issues." While some of the welding was wonderful, much of it looked like something I would do.

Also, there was no consistency on the amount of welding done, some floors would be welded nearly 100%, others no more than 25%.

To simulate a rounded hull below the water line they had plated her not with the sheets running lengthwise, but running up and down. So there was a weld every 24" to 19".

When we hauled the boat we found that they had not ground off the welds on the outside at all. Some were standing proud a good 1/4" so it made for a very rough bottom.

After consideration for a couple of days we pulled out of the deal. That ended up costing us probably $7K when you factor in the survey, the trip, lost time for work, car rental, hotels, etc.

Had she been welded up decently she would have been a hell of a boat.
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Old 20-06-2010, 18:04   #207
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Second and last day today - finally got some decent welds. Dragging in front of me - left to right with head slightly to left allowed me to check the puddle, distance and speed better. Also allowed me to relax more and slooooow down.

Man, what a feeling. Every boater should go through this.
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Old 21-06-2010, 12:00   #208
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Man, what a feeling. Every boater should go through this.

I agree, you start turning out your own gear that's stronger and more reliable and doesn't break your bank account and you'll never go back.
While building my boat I went to the scrap yard way more than any chandeliers, it's the way to go.
Salty while you're in class why don't you see if they'll let you build an anchor or two just go down to a marina and take some measurements, make a pattern off a nice size rocna or manson or even a delta the first two seem like the easiest to make though for the manson one would need to find a piece of large diameter pipe for the flukes, the rocna looks like it's the easiest. Use either AR plate, T1 or QT100 for the shanks and mild steel for the flukes , I'd use 7018 rod or some high strength wire for welding the high tensile steel. You could even make the shanks removable like the Raya anchor, could make a nice big storm anchor that way.
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Old 21-06-2010, 13:18   #209
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Great idea haiden. Unfortunately, this class was only the weekend. Going to take the TIG later in the summer.

But really, would like to make myself a Manson like anchor. great idea.
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Old 21-06-2010, 13:34   #210
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Yep, it's doable, but if Manson or Rocna ever got word you might find yourself on the wrong end of a nasty patent infringement suit. Then again, if you didn't advertise what you were doing, how would they get the word?

Regards,

Thomas
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