Aluminum small hull design

[FlyingDClay]

Maybe this is a bit technical but I'm guessing there might be some mechanical engineers/designers or naval architects here.

My old mid-70s Alumacraft fishing boat had transverse hull stiffeners. My 1950s Flying D has longitudinal stiffeners.

In a light aluminum fishing boat/runabout is there anything significant regarding hull strength or stiffness when comparing transverse vs. longitudinal bracing?

 

[gm280]

Usually the creases in the length of the aluminum hull to form the "V's" and steps accounts for the "stiffeners" and offer that longitudinal strength. If the hull were built flat with out any creases, I think the hull would be very flimsy in that direction. Since there are no creases transversely, they add in the bulkhead to offer that support. Amazing how just one rig changes a piece of flimsy aluminum to stiffer capabilities. I used a metal roller on such a flat piece of aluminum, and it instantly became remarkably stiffer with just one rig rolled into it.

 

[ahicks]

I would add that the hull size and shape may determine what needs to be done to maintain stiffness. A canoe for instance isn't going to need much longitudinal help. Just transverse will work there.

A Jon boat though, is going to need both longitudinal and transverse help to keep the bottom from "oil canning". Longitudinal creases and ribs pretty much required here.

 

[Lowlysubaruguy]

Another thing that occurs when metal is bent or forced into a different shape such as the ribs pressed into aluminum hulls is work hardening of the material which ads almost as much strength as the rib itself.

 

[Texasmark]

I don't meet your background criteria but I had 2 Alumacraft boats under 16'. I think high tensile aluminum, like 5052 T6 as an example is inherently rigid. Next their cast chines, keel, and connecting bow and transom caps, when coupled to the transverse ribs and rounded chines (providing bending and flexing resistance as compared to a crimped hard chine), in themselves form a pretty rigid frame.

Of all the aluminum boats build back in the 60's give or take in my early years of boating, the Alumacraft hull was my favorite for that reason. When you can put a remote control operators station in front of the rear seat with a 33 hp Johnhy on a 14' boat and have nothing but a "unibody", no yawing, twisting, rattling, this and that, their system proves itself......as I witnessed with a friend of mine.
Lacking the internet and all we have today, I "Lusted in my Heart" (Jimmy Carter) for a 16' with a Johnson/Rude 50 hp Looper and none (used so I could afford it) could be found at the time.....wanting a bigger boat for bigger waters.

On Johns, as stated, the contour of the stamped aluminum bottom and sides (V shapes) supplies the longitudinal strength with no additional weight...to speak of.

 

[Texasmark]

Here are some pictures of a Duracraft which, in the time, was very similar to Alumacraft construction. You get the high tensile aluminum and it resists bending up to it's stress limit (work hardened joint, if hard enough fractures on the 2nd or 3rd iteration)....where it starts to molecular separate, unlike soft rolled aluminum (aluminum foil in your kitchen) that just crumbles and can be smoothed back out by hand. The boat builders deliberately use this trait in their light weight hull design.

As mentioned, the bow and stern cast caps and the extruded aluminum splash rail along the "soft chine area", gunwale and keel aid in the support.

1962 Duracraft 14’ V Bottom Boat - boats - by owner - marine sale

1962 V Bottom boat for sale. It is an Evinrude-type blue and white color. Good condition - we’re moving and can’t take with us. Has two chairs and seat in the middle. Comes with 40 lbs thrust Endura...

littlerock.craigslist.org

 

[FlyingDClay]

Thanks all for your insights and sharing your knowledge and experience. I've learned a lot.