What does it mean ?

[alecsandros]

"Spotting Rules at Long Range. (C.B. 3001/37, page 25, paragraph 31.)

28. Nelson and Rodney have found the use of triple broadsides instead of rapid at ranges above 12,000 satisfactory, but while this procedure should continue for trial it is not yet desired to standardise it.

It is possible that better results may be obtained by some other procedure, such as rapid broadsides, while hitting, and reverting to triple broadsides with controlled fire for regaining."

what does "triple broadsides" and "rapid" refer to.. ?

[lwd]

This is just a guess (however guessing wrong seems to generate very fast corrections so ...):
Triple broadsides likely refers to fireing 3 sets of broadsides with either 1 gun per turret (most likely I'm guessing) or with each turret.
Rapid may have been fireing as fast as possible. Which may result in something simliar to the latter case above but not as deliberate.

[tommy303]

I believe triple broadsides referred to the practice, once range was found and salvo MPI was centered on the target, to fire 3 broadsides and then readjust for any apparent movement of the target away from the predicted MPI. Then three more would be fired and adjustments once again made. In rapid broadsides, the target was fired on continually and adjustments made salvo to salvo. At lower ranges this would tend to work well as broadsides arrived before the next could be fired, but at longer ranges this was more difficult as it was possible to fire at least one broadside while another was still in the air, i.e., before the previous broadside could be spotted and corrections applied.

[Karl Heidenreich]

Maybe someone was drunk...