Forces in fittings

[Ulyxeus]

Hello,

I would like to calculate the forces and tensions into sheets and halyards in order to dimension fittings (cleats, clutches, winches ...).
Is there any formula I could use ?

I only know this formula : F = pressure in sail = 1/2.ρ.S.V^2.C
ρ = density of air (1.29 kg/m3)
S = Sail area (m2)
V = Wind Velocity (m/s)
C = aerodynamic coef. (about 0.9)

Can I assume the tension into the halyard is F/2 ?

Thank you very much.

Hi Ogrim! nice to read of you. I'm new of the forum, and i'm finding load info for changing my deck fittings.
In your formula, you put F (= in-sail pressure) = 1/2 *p....etc. Later, you say that The tension in halyard is F/2. That would mean the formula for halyard tension can be written as : HT= 1/2*(1/2*p...etc)
I'm in doubt because of the two times the reduction coefficient 1/2 (= 0,5) is used.
Is this correct , or ...?
I appreciate very much all your reply on this.

 

[TANSL]

Maybe this file can help you.

 

[Ulyxeus]

Maybe this file can help you.

Thanks indeed! I understand that calculating the halyard load is more a matter of safety confidence rather than of maths. And this affects also calculating blocks and shackles loads .. :-( .
Regards.

 

[Ulyxeus]

Maybe this file can help you.

I have received form a friend in Italy - a young Italian rigging engineer, Raffaele Fredella ('u- can see him in FB ) - the file below!: he said it's the only recent article that Deal with the calculation of forces on each and every area of sails starting from force equilibrium to the max righting moment a sailboat can set; it's a paper of the German sail registrar, and is widely used form a lot of nautic engineers to parameterise their own calculation tools. Hope you too can find it reliable and useful
https://www.google.it/url?sa=t&source=web&rct=j...

 

[TANSL]

@Ulyxeus, thanks for that document.
DNVGL is a classification society, as you know without a doubt, and CSs always have regulations that allow the calculation of most boat items. The problem is that they can be difficult to apply and that they are usually much more demanding, for small boats, than other standards.
That said, in my opinion, DNVGL is one of the best CSs.

 

[Ulyxeus]

TANSL, Yes you are right : they are very difficult to apply, but you have to know at least their rationale to act responsibly for your sailboat. That said, sorry I'am an amateur for such a calculations, not a professional . So I do not dare giving any evaluation for the paper I posted, but only sharing information for shake of better knowledgement of all members interested in such a issue.

 

[TANSL]

I agree with you. Although I have not studied the DNVGL regulations, I am sure that it is technically irreproachable. All the documents of the CS are of great technical height.
However, when a ship does not need to obtain the classification of a CS, it can be very burdensome to try to comply with their regulations. That is why there are many other, simpler rules, that apply to small boats or pleasure craft. A norm very applied in yachts is that of the NBS that, among other things, describes a procedure to calculate the rigging of sailing boats (one of the softwares developed by me uses precisely these procedures). Another standard that, for example, is mandatory to obtain the CE mark on recreational boats, is ISO 12215. It refers to the scantling of small boats and is more manageable than those of the CS.
It is not normal, imo, although it may be the case, that a recreational craft designer knows the rules of the CS in depth.

 

[Ulyxeus]

It is not normal, imo, although it may be the case, that a recreational craft designer knows the rules of the CS in depth.

imo, the more one knows , the better is for every field of human activity. Problems arise only from misuse or misunderstanding of the knolwedge.
Thank you indeed for your attention.

 

[TANSL]

The fields of knowledge are so vast, even if we limit ourselves only to the design of small boats, that one has to learn to select what is not worth learning. In our times, fortunately, it is preferable to hire a specialist for each subject, instead of trying to learn more things that fit in your head. But, of course, a minimum general culture is necessary to understand what the specialist says.
@Ulyxeus, a pleasure to talk with you.