This is the biggest boom that could be set up there, without closing the resturant next door, 35m of 3in hose 20 mm stone.

Nice Job.

(as 20mm stone only gives a factor of ~x3.75 in a 75mm pipeline, and min factor of at least 5x (stone size) is required for safe operation) what do you do if you plug the 3" line under water?

I think the 5x stone size has gone due to better mix designs. We have pumpers using 8 to 10 lengths of 75 mm x 10 metre hoses at any one time with 20 mm stone. This gets down to some pumpers used a 3x  stone size.

Being an underwater mix, it was possible 32 mpa or more high cement mix with reduced stone content.

Thanks digger,yes we use 20mm stone all the time with 3in hose, so much easyer