The law of property on the Island differs (and in the past even more so) in many significant aspects from that of England. Until the abolition, in 1911, of the Lord's Rent, all landowners were legally tenants of the Lord of Man, paying both rent and fines (i.e. a tax) on transfer (alienation). Under the 1702 Act of Settlement any alienation of the tenancy either by sale or mortgage needed to be recorded in the Rolls Office - the officially recorded (or enrolled) deed, agreement etc thus gave official title to the land. Hence unlike England all deeds were centralised from that date allowing a much more convenient search than for the more widely dispersed deeds in England. Prior to this Act it was a voluntary act of the parties to record such transfers in the Court Records.
The various indices for these deeds (+ mortgages) are described elsewhere - many deeds have been trabscribed with some 5000+ plus summaries of pre 1847 deeds available on the CD Rom.
N.W. Alcock Old Title Deeds. A guide for Local and Family Historians Chichester:Phillimore 1986 (ISBN 0-85033-593-0) - gives a good introduction though covers only English law.