count how many different classes of ships were launched.
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col :  | country | builder | location | ship | class / type row 1 : 6 march | united states | john roach and son | chester, pennsylvania | city of rio de janeiro | passenger ship row 2 : 13 may | germany | kaiserliche werft wilhelmshaven | wilhelmshaven | bayern | sachsen-class ironclad row 3 : 13 june | united kingdom | royal dockyard | devonport, devon | pegasus | doterel-class sloop row 4 : 31 august | united kingdom | royal dockyard | sheerness | gannet | doterel-class sloop row 5 : 23 october | norway | karljohansverns verft | horten | nor | vale-class gunboat row 6 : 1 november | norway | karljohansverns verft | horten | brage | vale-class gunboat row 7 : 9 november | germany | a. g. vulcan | stettin | württemberg | sachsen-class ironclad
count how many different classes of ships were launched.
Country Builder Location Ship Class / type
6 March United States John Roach and Son Chester, Pennsylvania City of Rio de Janeiro Passenger ship
13 May Germany Kaiserliche Werft Wilhelmshaven Wilhelmshaven Bayern Sachsen-class ironclad
13 June United Kingdom Royal Dockyard Devonport, Devon Pegasus Doterel-class sloop
31 August United Kingdom Royal Dockyard Sheerness Gannet Doterel-class sloop
23 October Norway Karljohansverns Verft Horten Nor Vale-class gunboat
1 November Norway Karljohansverns Verft Horten Brage Vale-class gunboat
9 November Germany A. G. Vulcan Stettin Württemberg Sachsen-class ironclad
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