My last Fireball had a Cumulus. But many newer for sale have Alto. 
Please could you advise whether an Alto would be suitable for a 10 stone helm with a 10 stone crew or a 12 stone crew.

Hi George,
I sail with both masts with your weight I uses a Cumulus mast.
There are more tuning guide for Cumulus easy mast to tune up.
The is Alto is a quick mast I crew my own fireball I am 14stone(90 kgs) and Hannah Showell is my helm is 9stone (58kgs).
Tim Rush fitted the Alto mast in to my fireball (14430 Jango Fett) using Martin Lewis rig setting.
We had a 6th place at Sligo Worlds on the 1st day using Norths T 10  main sail.
I did have to buy a good second Norths T 10 main sail to use for high wind sailing to keep the new good one for Championship sailing.
I think both masts are quick more top sailor are using the Alto but hard mast tune.
You cannot use you old P&B Cumulus cut main sail ref pre-bend on an Alto but you can the North T 10 main on both mast.
I hope this helps.
Bazza Smith (14889 Millennium Falcon)  

 

   

George,

With your weight I would recommend the Cumulus.  The Alto probably needs a little more weight.

Regards,

Vyv

Would agree with Vyv.

The Alto is a stiffer section for the larger crew. 
The Cumulus is more bendy and suitable a smaller crew.
Championships have been won using both sections in the recent past, depending on crew weight and prevailing wind conditions.

Definitely go for the Cumulus.
See you on the water.