Caclulating hull strength WRT chain plates

[DuncanC]

Hi and thanks for reading.

I want to attach a pair of chain plates to the back of my yacht. They would provide a fastening point for a series/Jordan drogue.

Working out the loads that the drogue makes is done for you by Mr Jordan, calculating shear strength of bolts and the breaking strength of the fastening point in the chain plate are also pretty easy.

The thing I can't seem to find out is how to calculate the strength of the hull where the chain plate is fastened.

The hull will need at least x bolts tightened to torque y distributed in some way. So how is this worked out?

I tried considering the compression strength of the hull material and then guessing an area of each bolt that is in contact and comparing that against the max possible load. But.. how much of a bolt is actually in contact? In a perfect hole then half the circumference would be in contact - but that isn't going to happen in real life!

There is also the challenge of working out the spacing of the bolts.

NB: I have also read that actually the chain plates are bonded to the hull via the friction created by the pressure from the bolts...? Any knowledge on that would great.

Thanks again for reading.

[HappyMdRSailor]

Originally Posted by DuncanC

Hi and thanks for reading.

I want to attach a pair of chain plates to the back of my yacht. They would provide a fastening point for a series/Jordan drogue.

Working out the loads that the drogue makes is done for you by Mr Jordan, calculating shear strength of bolts and the breaking strength of the fastening point in the chain plate are also pretty easy.

The thing I can't seem to find out is how to calculate the strength of the hull where the chain plate is fastened.

The hull will need at least x bolts tightened to torque y distributed in some way. So how is this worked out?

I tried considering the compression strength of the hull material and then guessing an area of each bolt that is in contact and comparing that against the max possible load. But.. how much of a bolt is actually in contact? In a perfect hole then half the circumference would be in contact - but that isn't going to happen in real life!

There is also the challenge of working out the spacing of the bolts.

NB: I have also read that actually the chain plates are bonded to the hull via the friction created by the pressure from the bolts...? Any knowledge on that would great.

Thanks again for reading.

Make a diagram of what you are thinking.... This should be easy to calculate...

[DuncanC]

I have attached a quick pencil sketch of the 'suggested' way of doing this.

But basically it is just an exterior chain plate.