urgent calculation

Hi there,

I´m trying to calculate the dynamic forces on a sunroof/radarmast m=1.5t (a heavy one) caused by rolling and pitching of the boat. It´a 26m motoryacht.
My target is to calculate the pillars for that roof. It is build like a very big table.

Thanx

Max

 

Since this IS how I earn a living, I will ask if you want to pay me first. (if so, read no further - send cheque ;-))
But, if you don't, here are some hints to get started. You have to think of the rolling period of the boat (with 1.5 tonnes of sunroof up top), and then you can calculate the acceleration using simple harmonic motion formulae. This will give you a "lateral" load on the legs (acceleration times mass) which can then have a factor of safety applied (2.5 doesn't sound too high), and the design can be started using bending strength of the leg tubing.
Also bear in mind that if this boat is going to out in any wind (it doesn't matter how fgast the boat can go) then you need to design for that as well. Loads are cumulative in design, not subtractive. ;-)
Steve

 

ABS guidlines of 15deg double amplitude roll in 10seconds is a good starting point.

 

Thanks for your help,
i calculated the roof for a very quick period of douple amplitude of 12 sec / 60 ° because i think that the highest forces will be in this construction when the boat got a big wave from the side. So I took safty faxtor of 3 on this calculation and a factor of 4.5 for the case that the boat slams into a wave coming from the front.

And again thanx for your help.

Max