Steel single-chine fatigue

[TCopp]

I've searched this forum and could not find an answer to my question. So here it is:
Is a steel single-chine sailboat exposed to more weld fatigue than a multi or radius chine since it has more wetted surface?
I've read that it is better to have less welds. Therefore I would assume a single-chine would have less welds and less weld issues. But would a single-chine design be exposed to more stress than another design.

[timgoz]

TCopp,

I am not an NA, but with either a single-chine or multi-chine, properly built steel boat, weld fatigue should not be an issue. Many welds approach 100% strength & all welds should be more than adequate strength wise.

TGoz

[MikeJohns]

Originally Posted by TCopp

Is a steel single-chine sailboat exposed to more weld fatigue than a multi or radius chine since it has more wetted surface?
I've read that it is better to have less welds. Therefore I would assume a single-chine would have less welds and less weld issues. But would a single-chine design be exposed to more stress than another design.

TCopp.

No extra induced stress. often lower if there are chine bars, and the wetted surface area is a bit nebulous too. There is not much in it these days a lot of so called round sections are pretty flat too and the chine boat generally tends to be a bit stiffer and has better roll damping.
A chine hull tends to damp the rolling out better too. But we always come back to the disclaimer "depends on the design"

Good luck

[rdickins]

Actually there is an induced stress or stresses along the weld. As the weld material cools the metal contracts creating an internal stress long the weld. The induced stress is the reason steel structures will often crack along a weld seem. Also there can be a change in the hardness of the steel next to the weld as it is heated and cooled. All of these thing can negatively effect the fatigue life near the weld seem. That said the real question would be what loads are going to be experienced in the area near the weld. For the most part because of certain conditions such as impact loads are much higher then the cyclical loads that would result in fatigue failure the structure is overbuilt with respect to the fatigue failure. At least that is my understanding of why fatigue is not much of an issue on the hull of most smaller vessels.

[MikeJohns]

R Dickins

Thats the same for round or chine, but these days with modern welding gear and properly prepared seams and correct welding sequence the shrinkage is minimal and the resulting strain is distributed. You can anneal the weld too. Steel plate has traditionally been applied far thicker than required to give corrosion allowance. Fatigue generally becomes a non issue in steel boats .

The more care you apply with steel the stronger the result. Weld schedules are written with all this in mind too. More of a problem is weld embrittlement from impurities and also over-welding with large pools that cool slowly allowing the resultant "crystal " growth in the weld zones. Multi run welds tend to self anneal. But even steel boats built terribly by incompetent fools have surprisingly few problems. The best home built material by a country mile.

Cheers

[timgoz]

Right on Mike.