Various longitudinal stringer routing methods on aluminium vessel

[Joonatan]

Hey guys,

There is different ways to route longitudinal stringers in aluminium (or steel) vessel. One method is so that they do not have any curvature inward towards the keel line (port side in the pictures). Another method is so that the stringers would turn toward the keel line of the boat (SB side in the pictures).

Is it preferred that stringer route would turn towards the center line (keel line) when the stringer is getting closer to the bow? Or would it be okey to do it so that the stringer would not turn toward the centerline? If this is not preferred could you please explain why?

In all these scenarios the longitudinal stringer would be normal to the bottom surface.

Btw. the pictures are just simple examples to explain my point.

 

[BoatBuildLog]

Interesting comparison. Are you planning to build this design yourself once you settle on the stringer layout ?

 

[Joonatan]

Not planing to build this design. But I am curious about this subject and in the future to be able to determine the best way to route the longitudinal stringers.

 

[baeckmo]

The longitudinals are supported by transverse stuctural members and the beam must have minimal bending in the plane of the surface, between the supports. Imagine a bridge between two points; if it has a curvature in the horizontal plane, it is getting an additional twisting loading on top of the bending moment in its vertical sections.

So, neither of your examples seems to suit the SOR, both have too much beam curvature (ie too small local radii) in the plane of the surface. Personally, I often use a set of diagonals to find suitable distribution of long:s, but I guess that is where the constructor's individual experience kicks in.

Your images seem to show external longitudinals, as often used for spray-rails. There you have the additional requirement of placement for hydrodynamic efficiency, and again the best shapes tend to be linked to diagonals. The "buttock-based" shape often results in too high angle-of-attack of the fw part of the rails, causing heavy spray into the air and actually decelerating the boat when hitting a wave.

 

[BoatBuildLog]

Not planing to build this design. But I am curious about this subject and in the future to be able to determine the best way to route the longitudinal stringers.

Got it, that makes sense. its one of those details that seems simple until you start thinking about load paths and how everything comes together near the bow.