If you have belt dusting something is wrong. You are pulling too much power with the belt or it is slipping due to tension or incorrect V fit. Also if concern is having two pullies of different V. Alternators and engines can have different manufacturers so there is no guarintee that they will match. This would make it impossable to get the right belt in all cases.
In my case I have a single pulley and a PO installed 150 amp alternator and until I "de-rated" the alternator via the regulator it would go through a belt in a few engine hours. Now that I have a 50 amp (regulator driven) the belt is much happier and it has lasted two seasons. I do not notice any indication of the batteries not getting charged but I have only had one week long cruise during that time. The batts seemed to get enough charge with normal engine use and only required 1 half hour "charging session" after an extended stay and long sailing day without the engine.
In my case I have a single pulley and a PO installed 150 amp alternator and until I "de-rated" the alternator via the regulator it would go through a belt in a few engine hours. Now that I have a 50 amp (regulator driven) the belt is much happier and it has lasted two seasons. I do not notice any indication of the batteries not getting charged but I have only had one week long cruise during that time. The batts seemed to get enough charge with normal engine use and only required 1 half hour "charging session" after an extended stay and long sailing day without the engine.
