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Old 17-06-2010, 17:45   #166
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Gordy,
aluminum requires alot of heat (because it conducts) and so you have to move faster or you end up with a hole and a puddle. Also you are working with thicker material, ussually twice as thick, and distortion isn't the problem that it is with thin steel. With steel your welds are short to keep the expansion to a minimum and you move away to another spot to let the first spot cool and contract. Then back and chip and prep fpr the next few inches and on and on. With thicker aluminum that doesn't distort (as much) with the heat you can get down to it and you are moving faster anyway. Then there are other time saving advantages to aluminum. Cutting is done to the line with a saw instead of a torch and plasma which both require grinding to the line (which has been burned away and has to be re set). And a big one is finnish prep. With steel it is blast, prime, paint and paint and paint and paint some more inside and out. With aluminum there is no need except outside below the waterline. It is said that if you are having a boat built and paying for labor it is possible to pay for the additional costs of the aluminum in the labor saved in welding and paint if you choose to go bare aluminum except the deck (where you would burn your toes off if unpainted in the tropics) and the underside. With the cost of aluminum down nowadays (China is producing great quantities and even US aluminum is down to compete) it is probably very true. When I recently priced out the ordered aluminum that goes into a Gazelle it was 6000# at $2.50 (average between 6061 framing and 5083 plating) and came in about the cost of corten and mild at 10000 # ordered material. The addition of wire and gas is real and substantial but if you are using mig for steel it's proportionally similar (another good reason for stick with steel. Cheaper than wire and gas but a little more labor intensive.)
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Old 18-06-2010, 05:38   #167
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Excellent answer Conrad.
Thanks for the clear, concise, & yet complete explanation.
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Old 18-06-2010, 12:12   #168
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Why “less with aluminum”?
Aluminium Welding is fast really fast, once you get the pound gun setup nice for the thickness of metal that you're going to be welding, you will start running welds about as fast as you can pull that thing across the seam, there are two things that I found hard to get the hang of with aluminium welding. One is getting the machine setup right, which is really important so as not to induce any extra weak points in the metal and takes some skill. The other is getting used to moving that fast along the to-be-welded area with out diverging off to the side away from where I wanted the weld to be, I imagine this gets easier with practice, as does the first problem.
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Old 18-06-2010, 12:17   #169
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Why “less with aluminum”?
and of course the cutting and fitting is faster and easier as is the grinding afterward, especially since generally you do very little of it since you want to leave extra weld metal with aluminium more than you do with steel.
Aluminum welds are weaker than the surrounding metal, steel welds are stronger than surrounding metal.
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Old 18-06-2010, 12:39   #170
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Much better answer than mine Gordy.

One guy I know said this about his aluminium boat (also origami style) : It's just like a wood boat but with out the maintenance, but if a wave picks you up and drops you on a rock it'll pop open like a tin can, with steel you might have a better chance. He spends most of his time on the north BC coast where there are plenty of rocks, boat seems fine.

So basically aluminium is light, and strong, though not as strong as steel, could probably be built for the same cost once you consider the saving on work and paint. They will always sail better since the weight will be centered lower in the boat.
The only downsides that I can see is that they are less strong than steel(though no worse than wood or glass) and more difficult to work on in remote areas of the world so unless you carry you're own equipment to weld it with you, aluminium is less ideal for a cruising boat.

I was going to pick up an alternator from the scrap yard to turn into a welder on my boat but didn't get around to it, but I have used the welder that Brent Swain has on his boat, I figured that it would work but would be a little hokey, but it's one of the smoothest welders I've ever used the rod just melts itself into the work. With AC welders the rod sort of "bounces" as you feed it into the puddel a little it's hard to explain but that sort of goes away with DC welders and the rod feeds in much smoother. I'm told this has to do with the frequency that the welder is running at, with 220v DC buzzboxes they run at 60 hz (I guessing here) where as the alternator welders run at some really high pulsed DC frequency. I think of it as instead of the rod melting into the puddle a little bit 60 times a second the rod is now melting an even smaller amount but 800 times a seconds or whatever the alternator runs at.
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Old 18-06-2010, 13:17   #171
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... The only downsides that I can see is that they are less strong than steel (though no worse than wood or glass) and more difficult to work on in remote areas of the world so unless you carry you're own equipment to weld it with you, aluminium is less ideal for a cruising boat...
Can't any material can be built (more or less) as strong as another?

Can't any metal boat be repaired (at least temporarily) with Fibreglass (patching) materials & techniques?
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Old 18-06-2010, 13:26   #172
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WOW some excellent posts. I am not bad mouthing Oyster boats. All I said is in the last few years at least two (that I know of) have sunk when they struck objects in the water while they were in deep ocean. I used those incidences not to diminish Oyster's, as they are some of the best made glass boats around. My point was any glass boat, even the best built one (like Oyster) does not do well when it collides with objects floating in the ocean; and once struck, they sink quickly. Lesser made boats than Oyster's would have sunk even quicker, and that was my point. My personal belief is that steel boats are the safest boats on the sea, followed by aluminum boats. Certainly Oyster's are well made and perhaps to some better looking. Still, to me, I'll stick with steel.

Excellent comments on aluminum welding. It is easier to work with, welds and cuts much faster and does not need expensive painting schemes. It is not as strong as steel but it's lighter.

The painting scheme I outlined is how I would paint any steel boat I might build. I like the Delta Db and Delta T products. That's not to say there aren't better products out there, there may be. I've used these and they have worked well for me. My radius chine Roberts was rather flat on the bottom. When she is beating into the chop and falls off a wave the hull tends to "ring" due to her design. The Delta Db will lesson that ringing. The multiple layers of coatings are in my view necessary to protect the steel for all the reason mentioned about coatings earlier. I think it's hard to use too much paint on a steel boat. Some people don't think foaming the interior of the boat before adding the joinery is necessary. I don't agree with that philosophy at all. To me, it's mandatory. Just my personal opinion for sure. You probably have your own.

As to Brent Swain's advice to coat the foam with some flat latex house paint, what can I say? He says it works. I've never tested it, but I believe Brent to be an honorable man with a wealth of experience on all things steel boats, so I tend to believe him. Whether you do or not is up to you. I think it might be interesting to set up a test of his theory. I think I just might try that if I ever have the facility to do it. I'm sure it would be an interesting test.

As for stick vs wire feed. I've done a lot of welding with both, I feel it's more a personal preference thing. I do know most stick welding is done with 220V machines. I have limited experience with 110V machines and my experience with them was not a good one, so I'll stay with the 220V boxes. Miller vs Lincoln vs Hobart vs made in China no name? I've used Miller extensively, they make excellent welding machines. I've used Lincoln not as much, but I think their machines are every bit as good and perhaps even a little better than Miller. I've not used Hobarts, so I can't comment. I generally avoid things made in China if I can.

Regards,

Thomas
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Old 18-06-2010, 13:36   #173
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Gord I'm not an engineer, but I know that the simple answer to your question is yes kind of. Paper is easily torn and penetrated, but if you stack enough sheets of paper together they will stop a bullet! So, I think you could make a boat out of paper that would be very difficult to damage when it ran into a rock, but the sides would be several feet thick, so it's not practical. Ditto any material. A relatively thin sheet of steel has more impact resistance than a much thicker sheet of FRG. I'm sure some of the engineers here are far more qualified than I to quote the stats of the different materials.

Yes, you could patch up a steel hull with fiberglass, but why would you want to? The patch would not be nearly as strong as the surrounding metal. It would be more expensive than using steel and would take a lot more time. Welding machines are common in most parts of the world. Brent's alternator based welding machine can be carried on board to cover you in those very remote places where welding machines aren't available.

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Old 18-06-2010, 13:50   #174
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Yes, and I could make the statistical claim that you don't see that many steel boats sinking because there aren't as many out there!

It's a fallacy to think that a steel boat is a "jesus" material. There are just as many wrecks with steel boats on reefs as there are fiberglass. I might add the hull shape has a good chance at salvation on any boat.

Read carefully:

"Can't any metal boat be repaired (at least temporarily) with Fibreglass (patching) materials & techniques?"

the key word is "temporarily" in such instances I would advise might be when you are not in a port of call or even in a port at all...

So Yacht66 what boat to you have? I'd be curious.
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Old 18-06-2010, 13:52   #175
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Can't any material can be built (more or less) as strong as another?

Can't any metal boat be repaired (at least temporarily) with Fibreglass (patching) materials & techniques?
I guess you COULD do either of those things but I would say that is hardly ideal.
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Old 18-06-2010, 14:08   #176
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Roberts 65, steel, twin engine cutter rigged. I haven't done a survey, but I think it would be interesting to see the numbers. My hypothesis would still be fewer of those sunken boats would be steel than glass or wood. It would certainly be interesting exercise though. No one is claiming steel to be a "Jesus" material. It is a good material and many of us believe it's superior to glass and plastic, but of course, you're welcome to believe what you will. I do know there are many pictures out there of steel boats sitting on rocks without significant damage and sailing on. I'm not familiar with many glass or plastic boats doing so, which is not to say they haven't, you just don't hear much about them if they do (emphasis on IF). I'll still stick with steel. Bernard Moitessier's steel boat Joshua did pretty well during the hurricane in Cabo while all the fiberglass boats did not.

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Old 18-06-2010, 14:21   #177
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..Bernard Moitessier's steel boat Joshua did pretty well during the hurricane in Cabo while all the fiberglass boats did not...
Sure is, and he eventually sold it for $5.00 as scrap.
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Old 18-06-2010, 14:29   #178
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I heard he gave her away, but in any case the recipients of his largeness pumped the water out of her and cleaned out the sand, then re-floated her and sailed away! She's still in use, currently based in France the last I heard! Whether they paid $5 or got her for free, they got a hell of a deal!

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Old 18-06-2010, 14:55   #179
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Twin engines on a sailboat. I like that. wish we could put twins on a small. always have a backup.
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Old 18-06-2010, 15:24   #180
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It was that way when I bought it, but I've come to really appreciate the advantage of twins, particularly in a boat this size. My twin engines eliminate the need for bow or stern thrusters yet make the boat highly maneuverable in tight spaces. Because the props are counter rotating, I have no issues with stern walk. She's able to back in a straight line for as long as I care to go backwards. I love them. Most diesel engine failures at sea are fuel related, so I'm careful to keep my port and starboard fuel tanks separate. I'm not sure it would be worth the extra expense and hassle in a 36' boat like you aspire to, but in boats over 50+ feet LWL I think it makes a lot of sense.

Thomas
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