Need scantling for 17m motor yacht in ISO SCT or Hullscant will pay for it

Generally any structural member that has an included angle of 150 degrees or more the knuckle of that joint is not considered as a "support". Thus if you image the angle to be 90 degree, its simple it is a corner joint. If the angle is 180 degree it is a flat/horizontal 'joint'. Thus somewhere the 90 degree joint (if the angle in continuously increased) is no longer the effective support, which of course effects the span. The cut-off is at 150 degree. Less and you're ok..over, and its a full span joint.

It looks like those are 2 chine lines. If so, that would explain it.

 

Thanks AH. Seems it is a detailed explanation of the plating knuckle/joint as it transition from midship to fwd position as illustrated by LR.

 

Linda- In illustration num. 90, what is the lowest deadrise angle? It seems it does not qualify as a natural stiffeners.

ISO does not discuss keel plate or keel reinforcement. If it should be treated as a "natural stiffener", if it qualifies. As a general rule, the keel should be 1.5X than the bottom thickness. Same rule applies to chine to make it "strong and stiff enough to be considered as proper stiffeners".

 

Keel plate reinforcement as per LR rule.

 

AH- just one more clarification to see if I understand the key points right.

1. Between 130 and 150 degrees is a natural stiffener and thickness is left as such. No reinforcement necessary,

2. Below 130 it is a joint and should be reinforced.

3. Above 150 degree, it is a depth of curvature, not a "natural", and the span/spacing is increased.

 

Re

It has nice&deep groove, not much less than pilot boat,
What I was thinking just use it instead one of the longitudilans,

 

Re

Its more like this,
Pink line is mold connection hull to side

Thanks 3 green side longitudinals, and "natural" stiffener would be middle green.
This is rough, have o decide for connection type of hull and deck.

 

Looks good Linda.

Normally, the bottom shell thickness extends past the waterline and goes up over the bow where the area of slamming is. This is more or less defined by the chine.

It is a good idea to have the longitudinals follow the chine line and divide the panels evenly until it becomes impractical to do so. The goal is to have the longitudinals meet at the stem.

 

Unsure what you mean in no.1. When you refer to "reinforcement" are you referring to the primary or secondary member?

 

AH
I was sort of condensing the rule in order to have key points for memorization. ISO states:
"The above analysis is only valid if the “natural” stiffeners (round bilges, hard chines, etc.) are strong and stiff
enough to be considered as proper stiffeners. This means that they shall fulfil the requirements of Clause 11
for stiffeners. The length of these natural stiffeners is their unsupported length between members such as
bulkheads, floors and frames. As they are often curved, the factor kC is usually helpful. The pressure limitation
of 8.4 may also apply.
Chines with 130° " : " 150° are generally considered to fulfil the above requirements."

So will assume that "natural stiffeners" does not have to be reinforced with additional members or doubling of plating. Correct?

 

You need to separate a stiffer from its own strength requirements.

For example.

Lets say you elect to use a chine as a "natural" stiffener. And lets say the chine has an angle of 110 degrees. So it is nearly a right angle, but not quite. Thus the spacing of a longt. structural member from this 'chine' is the spacing of that stiffer under review. So if the stiffener is 200mm from the chine, and all other stiffeners are 200mm from that stiffener, we can clearly state the stiffener spacing is 200mm.

So, for the outer most stiffener, the spanwise support is from half way between it and the second stiffener, i.e. 100mm, (call this A) and then half way between it and the 'chine' (call this B), i.e 100mm. It is still the 200mm spacing. BUT...and this starts to address the other point. The support at A is the second stiffener, the support at B is the 'chine'. But if the chine, despite it being considered a natural stiffener, simply owing to its included angle, is just a thin sheet of paper on the other surface that is at 110degrees, how much "structural" support does it offer the stiffener? Now consider instead of a thin sheet of paper, the surface is 10mm thick steel.

Clearly the thin sheet or paper offers very little strength owing to its own stiffness being very low and coupled to it, the shear path that is also required to transfer the load it is supporting at B, that comes from the load applied to the long.t stiffener it is supporting. Whereas if the support surface is a sheet of 10mm thick steel, even by simple inspection this is clearly significantly superior and has adequate shear strength.

If we now consider another scenario.

If there is a transverse frame as in your fig.3.1.4e above, The chine, again being say 110degrees. The span of the transverse frame would be from the keel to the chine. The chine must be able to support the frame, therefore it must be able to absorb the shear load and any bending moment imparted to it from the frame. Thus the chine must have the strength to carry the loads in shear and stiff enough to prevent successive rotation owing to the loads from the frame which it supports. The stiffness, is directly related to its properties, i.e shape and materials. If the chine is carrying say 5 frames, there are 5 lots of shear to support and all the rotations too. Thus the span, of the chine is from WTB to WTB, supporting 5 applied loads along its length and so the chine must act like its own structural member, like any girder or beam that supports secondary stiffening attached to it.

Then if the angle is of course greater than 150degrees, the span of the transverse frame is from keel to deck.

Does this help?

 

Thanks AH for the lengthy explanation. It is very clear now what I was trying to figure out in post #89, the strength of a bilge radius or an acute bend.

This fulfills the ISO conditional statement "The above analysis is only valid if the “natural” stiffeners (round bilges, hard chines, etc.) are strong and stiff
enough,,,,"

 

re

I found this.

Ad Hoc, yes 2 chines, I found they say 2 chines, gave them short transverse stiffener span too.

 

Linda- In this patrol boat image, something seems to be lost in translation. It is neither a transverse framing nor longitudinally framed design.

The definition of the terms seems not to apply and I wonder how the calculations did fare. Attached snippet from the attachment you posted.

 

Seems odd that they laminate with mat only. Also, the fillets have a very small radius.