metals,steels

[Redsky]

iv heard a lot about corten
what about 1095 or 5160 alloy?iv heard a36 mentioned
any suggestions aprecated. espically on 5160 spring i can probably get 1/4"x12"x22' strips

[jehardiman]

One does not use high carbon steel for hulls because of increased fabrication and maintainence cost as well as the materials propensity for brittle fracture.

[Redsky]

what about A-36 then i can get hot roll sheet in that fairly easily....though i have a hard time seeing how annealed fine graine 5160 spring steel isent good enough with modern epoxy paints....if it was hard or even half hard i could understand the brittleness issue though the most commen use for it is heavy duty truck leaf springs in a tempered state.
and what about thickness ?
if some special spec steel is needed, who supplys it.

[jehardiman]

You should see the thread "Steel Speds?" http://boatdesign.net/forums/showthread.php?t=12059

In the US, normal "ordinary strength" (OS or generic "A36") steel is generaly spec'ed American Bureau of Shipping (ABS) Grade A (ABS/A) or B (ABS/B) which goes down to 3/16" thickness, however this material cannot be used in certian structural components. For normal "world wide" applications where there will be a classification society inspection, I (when building in the US) would spec ABS high strength fine grain killed plate such as ABS/DH32 and ABS/EH32, or ABS/DH36 and ABS/EH36. These steel have significantly better impact properties and toughness. <<snip>> I would spec ABS/EH32, OS steels only have good impact down to ~ 10F.

For 5160 it's not the base material, though high carbon steels have problems in a marine environment, it's the welding. See this page: http://www.suppliersonline.com/prope...60.asp#General

[Redsky]

oh.. well i wasent planning on welding it i was thinking of lapstrake planking with 5160...and pulling a real ancient anti corrosion treatment,,,after punching the fastener holes ,,wirebrush and bronze it useing a rosebud torch and hot silicon bronze the romans used to bronze swordsblades...and carmakers used and still do in street rod building ,lead smoothing...so why not hot apply bronze to steel sheet?, and i did read that thread but im not shure where i would find dh and eh steel my usuall steel page that i look at http://www.admiralsteel.com/

[jehardiman]

You need to go to a plate supplier. Usually, the same steel used to make A36 will conform to ABS also, you just have to buy the certification, as the scrap mix varies day by day. Try Pacific Steel or Oregon Steel if you are in the NW.

[Redsky]

thanks.....and out of curiosity your mentioned 3/16's should be ok for up to what boat size? 30'?

[jehardiman]

Originally Posted by Redsky

thanks.....and out of curiosity your mentioned 3/16's should be ok for up to what boat size? 30'?

I mentioned that because it is the thinnest plate normally spec'ed for shipbuilding, everything thinner is sheet and generally not subject to inspection.

The thickness of the hull plating on a vessel is dependent on the structural design and framing method. You can build large vessels with 3/16 skin plating. The some of the largest ships built, ULCC's around 500,000 tons, only have skin plating a 1/2 inch thick due to the framing design used.

[Redsky]

ok thanks i suspected frameing had a lot to do with it couple of lighter boats 30' ish i think id like to build in steel one i saw on here today..the other iv been looking at in boat trader the original is a composit job but personally i prefer either metal or wood by itself.

[Redsky]

Out of curiosity what the best version of Titainium for marine use?

[jehardiman]

Originally Posted by Redsky

Out of curiosity what the best version of Titainium for marine use?

Of course, in the marine fields, there is never a best. Each specific application has a specific material the best suits those requirements.

In general, for piece parts, Ti-6Al-4V is used because of cost and availability (marine use of Ti is very low compared to Aerospace and chemical). Ti-6-4 was designed for forging/machineing and has some welding, stress corrosion cracking, and cold work problems that limits some applications. For other applications, such as large welded structures, other types are used such as Ti 5Al-1V-1Zr-1Mo

Also remember that with a stiffness about 1/3 that of steel or Al, trying to use Ti in some applications will result in a structure heavier than a comparable steel or aluminum one. Finally, it will corrode anything (except maybe CF, which will eat the Ti) it is attached to while in seawater.

Edit to add You need to spec Ti-6-4 as "ELI" (Extra Low Interstitial Alloy Content) to get the best marine corrosion and welding properties.

[Redsky]

ok i get the picture..dont build a ti boat unless its ALL ti due to the corrosion factor,, im not real fond of aluminum because of what the factories around here did back in 2001 laid everyone off and sold their contracted energy needs back to the grid

[Redsky]

another question iv see a subtance used to preserve steel agianst rust dyes it like grey/black they called it Navel jelly i think,,, thinking about fasteners has brought me back to rivits agian and maby rod for rivits from exactly same material as hull skin wouldent make good rivits...... http://www.mcmaster.com/ part # 8791k126 <alloy 625> instead?

[jehardiman]

That dark black/grey/green stuff is called phosphate coating, I personally wouldn't use it (hydroscopic), but Google it up and read for yourself.

And using Inconel 625 is a waste. Just use mild steel, no need to create a corrosion cell under the rivet head.

[MikeJohns]

Originally Posted by Redsky

.........a a real ancient anti corrosion treatment.................. bronze it useing a rosebud torch and hot silicon bronze.....so why not hot apply bronze to steel sheet?,

Redsky

Sounds novel but I suspect it is a trap, you will create accelerated corrosion pits since you now guarantee a galvanic cell at every scratch crack and dent in which the structure will sacrifice to the coating. Far better that the coating sacrifices to the structure.

Eopxy is pretty good tough paint, easy to apply and can last for decades. If the anodes are maintained even bare steel under the water is not corroded but accumulates metal salt deposits. Above the water and inside coat with zinc........... not bronze please.