Seams crossing longitudinals

[Arvy]

Hi all,

I somewhere read that one should try not to cross seams and longitudinals. But I find it extremely difficult to create a set of stringers (longitudinals) that don't cross any seams.

How much of a problem is it that they do cross? It is for a 40ft steel build sailing yacht.

Thanks for your replies and insights in this matter.

ps. can anyone point me to a good book about metal boat building?

Grtz,
Arvy

[MikeJohns]

When joints are running in the same direction you put butt-joints in plating a minimum of around 50mm away from longitudinals and frames preferably more.
Right angled crossings of butt joints to framing is unavoidable and this is standard procedure on all framed metal vessels.

"Steelaway" (I think my Smith) is probably the best material for the novice to read for a start.

[Brent Swain]

This is total ********. There is absolutely no problem with seams over longitudinals, as long as the seam over the longitudinal is V'd or gouged for full weld penetration.
Extra, short longitudinals across the seam are a good way to keep the seam fair.
Brent

[MikeJohns]

Brent

The idea is to avoid a hard spot (stress concentration) in the plating directly on the weld.

Just to make sure we are talking of the same thing; the recommended offset is for a welded joint running parallel to the stringer or transverse , there is no problem with the stringer or frame crossing the welded seam.

In theory a 'perfect' weld could be made anywhere in a steel structure without any problem. However the weld zone does not match the parent metal and is prone to stress risers and locked in stresses within the weld itself. It is also more brittle and more prone to fatigue.

Good practice also allows for some tolerance in the welders ability.

It pays to look at the type and size of the vessel being designed too as global loads carried in a stiffened shell can be considerably higher in a larger vessel.

Many of these sorts of guidelines have not originated from theoretical design but from observed failures.

[Brent Swain]

You definitly want lots of stringers crossing a seam to keep it fair and stop it from ridging.
The only way I was able to keep transverse seams fair on a flush deck or cabin top, given the camber, was to locate a strong beam directly under the seam to stop it from shrinking longitudinally and pulling the seam down between beams.
Brent