Any crane experts on here?

[Daydream believer]

I find myself in total agreement with what you have stated (especially the last sentence!).

As my proposed crane can rotate about a vertical axis, the risk of the mast falling at an angle is diminished.

The tests we performed with the original boom were with ~300kg. That was with the boom horizontal which is a worst case. With the boom near vertical, the test is less onerous.

Useful input.

You may have missed the point a little. If the mast did slip & fall on the OPPOSITE side of the boat whilst still attached to the jib. It will have the effect of pulling the crane outwards. I found in my test that it took significantly less weight to cause the wheels on the opposite side of our gantry to lift off the ground, when I started to swing the weight thus.. To explain this a bit clearer, imagine the jib set at its max reach, with the weight near the ground . Then looking from above swing the weight in a circular motion. At some point the weight will swing beyond the reach of the jib. That creates the effect that I felt might come about in an accident. Hence I took steps to re create it & measure the weights.
The exercise also took into consideration side loads on the jib to test twisting which happens when the weights are swinging right angles to the jib.
I think that if I had to stand in front of a coroner & explain what I did I think that he would consider that as a sailing club we had taken due care & consideration

 

[Daydream believer]

deleted

 

[Graham_Wright]

You may have missed the point a little. If the mast did slip & fall on the OPPOSITE side of the boat whilst still attached to the jib. It will have the effect of pulling the crane outwards. I found in my test that it took significantly less weight to cause the wheels on the opposite side of our gantry to lift off the ground, when I started to swing the weight thus.. To explain this a bit clearer, imagine the jib set at its max reach, with the weight near the ground . Then looking from above swing the weight in a circular motion. At some point the weight will swing beyond the reach of the jib. That creates the effect that I felt might come about in an accident. Hence I took steps to re create it & measure the weights.
The exercise also took into consideration side loads on the jib to test twisting which happens when the weights are swinging right angles to the jib.
I think that if I had to stand in front of a coroner & explain what I did I think that he would consider that as a sailing club we had taken due care & consideration

Yes, I understand.

Out hoist had a lifting capacity of 35 tonnes and is unlikely to fall over! That said, the point remains that any sideways pull will swivel the crane base..

 

[Graham_Wright]

View attachment 123436
I designed this for our sailing club. I am a chartered civil engineer with a lot of experience of steel structures. We had it tested by a reputable crane testing company; they did all the legally required overload tests and gave us a certificate for a SWL of 300kg.
The boom (part 03) is 7. 8m long 100m diameter and 6mm wall thickness. In the horizontal position the boom has an unfactored compressive capacity of 27kN. If it was 60mm diameter with 6mm wall thickness the compressive capacity would be zero at that length due to self weight bending. At 6m long the capacity of the 60mm diameter tube would be 8kN and at 5m long it would be 13kN. One important point is that the end fittings are carefully detailed to ensure that the forces are applied along the centreline of the tube. Your sketch seems to indicate that the loads may be applied eccentrically which will reduce the compressive capacity.

- Technical enough?

I sought an expert. It seems I have found one!

That is exactly what I was hoping for and I will present it to my mentor at the club.

One important point I missed is the eccentricity of the end fitting. The original fit did indeed apply the pull along the axis of the tube picking up on the pivot pin for the lifting wire sheave. That would certainly have exacerbated the bending problem.

Thanks a lot.