Type of Aluminum

[Scott Lipp]

I am in the process of having a 18 ft long 6 ft wide bottom Aluminum Jet sled built. It will be a very heavy boat (Yamaha 150 HPDI, Yamaha T8, minkota 101 electric, 4 batteries,ect). My last boat was built out of 6061. I realise the main materials used now are 5052, 5083,and 5086. I have found information on these materials but with all the diffrent types 5052H34,5083H112, ect, What is the best for sides of the boat verse bottom of the boat? I would like to have very good impact strenght for the sides and bottom. Also were should the majority of the heavy items (Batteries and gas tank) be located in regards to front to back placement in the boat. Any ideas would be appreciated.

Thank you

[Karsten]

The number after the H refers to the heat treatment process the aluminium went through in order to increase it's strength. Unfortunately if you weld aluminium you reverse this process and the material around the weld will be in the weak annealed form. In order to get the original material properties back you would have to heat treat the whole boat after it has been welded.

Since the welds are usually in highly stressed areas around joints the annealed properties drive the design properties. I would therefore look for an aluminium with good annealed properties and look at the heat treated properties like something you might get in areas where you don't really need it. Obviously it also depends on the detailed design. If you use extruded stringers and weld them to the hull you might be able to claim the "good" properties for the stringer capping flange if you don't weld anything else to it.

[stonebreaker]

Tracker Boats use .125" 5052 aluminum for their boats.

[stonebreaker]

Just as an interesting aside, I noticed the Tracker aluminum bass boats are about 600 pounds lighter than the company's fiberglass versions. I never realized fiberglass was that heavy.

[marshmat]

It's not uncommon for an aluminum hull to weigh in at a lot less than a comparable glass hull. Aluminum can take a lot more flexing than fibreglass, which has to be very thick and rigid or else it will gradually delaminate from fatigue. Rivetted-aluminum hulls are generally designed so that the skin flexes to absorb the impact of waves (or rocks!). Aluminum's properties, and this ability to flex, allow the skin to be much thinner than is needed for a safe fibreglass skin.

[RANCHI OTTO]

I use 5083 and 5086 for plates and 6005 & 6060 for profiles.

[RANCHI OTTO]

This is a diagram based on constructed GRP and aluminum boats (red points).

Between 14 and 20 m, the weight of deck + hull is abt. the same but higher than the indicated one from the author.

GRP for craft with a length in excess of 25 m comes closer to the steel weight.

The structure of my boats have been calculated and approuved by Bureau Veritas and sometimes by LLoyd's Register.

The speeds for all boats were in excess of 40 knots.

[Thunderhead19]

5086 is harder than 5052, and though it doesn't bend well, it makes a better, more damage resistant hull bottom and sides. 5086 works well for the items that need bending. 50xx plate is decent for marine application due to the minimal copper content. This takes away some strength and rigidity, but provides excellent corrosion resistance. In addition to reduced strength from the lack of copper, it makes these alloys virtually un-heat treatable. The upshot of this is that welding 50xx series has less of a negative effect on strength than it does on 60xx series.

[stonebreaker]

Originally Posted by Thunderhead19

5086 is harder than 5052, and though it doesn't bend well, it makes a better, more damage resistant hull bottom and sides. 5086 works well for the items that need bending. 50xx plate is decent for marine application due to the minimal copper content. This takes away some strength and rigidity, but provides excellent corrosion resistance. In addition to reduced strength from the lack of copper, it makes these alloys virtually un-heat treatable. The upshot of this is that welding 50xx series has less of a negative effect on strength than it does on 60xx series.

Did you mean that 5052 works better for items that need bending?

[Thunderhead19]

Aww...yeah! 5052

(lousy brain, not even worth the 5.50 I paid for it)

[stonebreaker]

So what is the relative ease of welding 5052 vs. 5086? Any idea on the relative merits of tig vs mig?

[Thunderhead19]

Personally, I don't thing you'll be able to tell the difference. Tig is time consuming and requires a practiced touch, fiddley and very pretty. Mig is fast, reliable and you can get going with very little practice. Mig doesn't have to look shabby either.