would you use 5086 or 6061t6

im currently going thru the steps of having a designer work me up a 30 -32poker run style boat..it`ll be my 3rd build but my first serious attempt at making it a business..i understand the trade off qualities of building with either alloy but it just smacked me in the face that these boats don't normally stay in the water for much more than a day at a time.. as far as I can see in my limited experience with good insulating qualities in regard to dis similar metals & a marine quality paintjob (awlgrip or better) it doesn't seem that paying the expodential hike in cost for the 5086 alloy would be a must for this kind of boat...any opinions ...or better yet..any FACTS as to why I shouldn't use the 60 series ?

 

would you use 5086 or 6061

building a 30-32`poker run style boat & had the thought that this style of boat rarely sees more than a full day in the water is 5086 necessary...this will be my 3rd build & my experience is limited to those 2 before it ..I understand insulating against electrolysis in regard to dissimilar metals & I had the thought that between that & a marine quality paintjob (awlgrip or better) galvanic corrosion may not be such a problem with a boat that doesn't stay in the water for long periods of time ..any reason to NOT use 60 series through out the whole build for this kind of boat ?? I ask because of the humoungus difference in price between the 2 alloys

 

p..00

All hull plating, especially plating that is below the waterline must be 5000 series. I always use 5083, but it seems in the US the preference is 5086, not sure why?

6000 series is highly prone to increased corrosion. The preferred choice is 6082, but again, in the US the preference appears to be 6061 (Aerospace alloy). 6061 has 3 times as much copper as 6082, so it is also not recommend. But even the 6082 is not wholly immune from such.

The 2 main issues are
1) strength
2) fatigue

1) 5083 does not lose is strength from the O/H111 (annealed temper) when welded; that being ~125MPa. If you go for a higher strain hardened alloy such as H116 then of course the HAZ will reduce the strength back down to that of O/H111 temper, circa 125MPa.

If you elect the 6082/61, when welded the strength reduces from 220-240MPa down to 110MPa, a massive reduction. Thus if you're trying to save weight and want longevity, its a very very poor choice for hull material. Since you would have to increase the scantlings to gain back what you have lost. In other words, increase in weight, and thus cost!

2) Fatigue 6000 series more prone to fatigue than 5000 series. Aluminium is a poor fatigue performer since it has no 'limit' as such like steel. But 6000 series is inferior to 5000 series.



That's it in a nut shell.

There was a good article about aluminium and fabrication in Proboat last year.

 

I've heard theres a difference in alloys that can get confusing when americans & Europeans speak on the subject of aluminum alloys..is it possible that h111 is equivalent to h116 or is it more likely that im just not familiar to h111 ? also is it acceptable to weld 6061 to the 5086 ABOVE the waterline (using 5086 h111 or h116 below the waterline).. after your answer my guess is that a 50 series plate should be used throught the shell plate entirely, ?..on a similar note i spoke with PAR today via telephone for a good bit & he spoke very highly of you, so thank you for the reference

 

i just saw the charts you sent ...it looks like the 50 series is the better choice throught ...including as use for scantlings & or any other structural members as well

 

this would raise the question of which filler wire to use when welding ..I believe the standard wire used in mig & tig operations is 4040 is this acceptable ,or should I find & use a specialty wire for weld wire (mig) & or filler rod(tig)

 

No, these are tempers. See below extracts from LR and DNV rules for an easier explanation, since the temper defines the yield/proof stress of the material above that of the initial annealed temper.

Yes it is. But not really recommend as it gets a bit messy especially on small boats. On larger boats, I have done so myself, but these are in the 30-60m range and far from the waterline.

Correct, especially on small boats. I would opt for 5083-O/H111. 5083 is the industry standard has a better yield strength and the O/H111 temper makes for much easier fabrication/rolling.

 

No..!!!!!!!

If you're welding just 5000 series alone (5083-O/H111), and nothing else, then i would recommend 5356. If you are also welding to 6000 series internally such as 6082-T6 (i.e extrusions for scantlings/stiffeners) then I would use 5183 filler wire.

 

my common sense ...& by that I mean YOUR engineering knowledge.. is telling me to just use 5083 h111 through out the boat ,scantlings , stiffeners, shell plate & all & use 5356 filler wire , with the thought that its a 30 `32` boat & not a battleship that requires a fleet of 18 wheeler trucks to deliver the material,so my savings aren't worth sacrificing any strength or fatiguing properties as the dollar amount is VERY low (comparatively)

 

It is perfectly acceptable to sue 6082-T6 for the long.ts/stringers inside the hull. This is common practice. Since using 5083 either cut from plate or extrusion for your stringers shall be a bit more expensive. But that is your choice. An all 5000 series hull & long.ts is superior, but very few actually are like this. Since the stiffeners are generally extrusions in the 6000 series, which are cheaper and readily available.

 

if all or most of my longitudinals will have some curve to meet the shape of the hull they`ll be cut from plate..& again ,im no engineer but I would imagine they should be the same thickness as the hull & being probably the single biggest strength producing member of the boat I think I may opt to make the longitudinals from 5083 h111 & any extruded shapes for bracing or stiffeners from 6082 t6 as im not sure these shapes even exist in 50 series aluminum ,,,should I use 5183 filler wire over ALL or 5356 on the shell plate & 5183 where the separate alloys meet

 

Now you're getting into 2 different fields.

1) Design...the scantlings will depend upon your SOR. The plate thickness and the long.t thickness and stiffness is wholly dictated by the SOR....the main ones being top speed, draft, dead-rise angle and of course its displacement. The structure is, what it is....which leads into

2) fabrication. Bulb bars, FB's or whatever are easily bent to conform to the shape of the hull there are many different types of machines for rolling/bending/forming sectional shapes depending upon the size of radius/roll and section shape.

If you're unsure about #2, then i would suggest you seek assistance from someone locally that has built before. You may be able to use their machines, on hire, rather than buying them. It is a straight forward procedure, but does require skills to get the correct shape and not crack/over strain the alloy section.

 

im a small time fabricator & I own most of the equiptment used for bending, I`ve used charts before to bend aluminum ..these charts usually tell me what alloy can be bent over a given radius before it cracks ,but these charts usually refer to sheet goods being bent along its face or an extrusion being bent over a radius , .. the shapes of the scantlings (if bent) I imagine would be flat bar (as they usually are cut from sheet or plate goods in my experience) , the flat bar would bent the "hard way" ( say 1/4" x 2" bent over the 1/4" face ) & would usually be long easy continual elliptical shape to conform to the hull, is it sensible to think that if I use a chart for my specific alloy being bent that I would use 2"as my reference size & just not superceed the max bend radius ,or do those charts go out the window with elliptical shapes ? it seems that a cut scantling plan would be superior so to not load any stresses into the metal that the designer didn't calculate into the part, if bent it would have to be done on a ring roller & worked repeatedly ,if im not mistaken the h tempers do "work" harden

 

hmmm..sounds like you haven't bent angle bars, bulb bars or FB's before using an Ekold machine or similar? It is a bit different from rolling/bending sheets of plating. See here:-

http://www.eckold.co.uk/
http://www.youtube.com/watch?v=01RnS6G6t30

If you're unsure, I would suggest finding a local builder familiar with such procedures otherwise you may do more harm than good and waste too much bulb bar/FB in creating the desired shape you need.

 

you're right ...I don't have MUCH experience with that kind of bending I actually own a very small manual version of a piece of equipment similar to this but it will only bend up to 18 ga. steel...it will shrink & stretch & I`ve used it to reproduce patch pieces in autobody repair but have no experience on bigger material or aluminum with it & only very little experience with it on thin steel,so I think I`ll take your advice on that one & hire it out if that turns out to be the way to go...I think its great to have that as an option now ,..I could cut the nested scantlings out of thin steel with my cnc plasma cutter & hand those over to the bender for use as templates , the thought arose originally because I think flat bar is cheaper than sheet & or plate & in 60 series definetly available...that is an outstandingly impressive machine