Blackstone Camden v Cowley evidence of the general opinion of merchant allow  to be give to prove the custom of merchant insurance on a ship to Jamaica be  determine by the ship more twentyfour hour in any port there and do not  continue till she come to the last port of delivery Trin term Geo after a full  trial by a competent jury if no fresh light can be throw in a new trial shall  not be grant a action on a policy of insurance on a ship at and from Jamaica  to London the ship be also insure from London to Jamaica general and be lose  in coast the island after she have touch for some day at one port there but  before she have deliver all her outward bind cargo at the other port of the  island in order to show when the homeward bind risk commence it be necessary  to show at what time the outward bind risk determine and to prove that by the  custom of merchant the outward bind risk determine not when the ship arrive  and more twentyfour hour in any port of the island as the plaintiff in the  present cause contend but when she have be safe twentyfour hour in her last  port of delivery Lord Mansfield CJ rule that insurancebrokers and other may be  examine as to the general opinion and understanding of the person concern in  the trade though they know no particular instance in fact upon which such  opinion be find the jury be special find a verdict for the plaintiff  Blackstone er p Blackstone motion for a new trial the verdict be as be suggest  contrary to the sense and meaning of the party but Lord Mansfield CJ state to  the court that the ship in question be what be call a general ship videlicet  advertise at lloyd coffeehouse as bind to the island general and by the course  of trade to touch at the several port of the island there to deliver some good  and take in other that it be insure at and from Jamaica and warrant to depart  with convoy the policy be very inaccurate word in not define what be mean by  be at Jamaica and I leave it to the jury which be a very capable one the  inclination of my opinion be the contrary way but I think it be through try  and that no new light can be now throw in and therefore I be against grant a  new trial which if the verdict shall be contradictory must in the end produce  a three Dennison I accord Wilmot I accord I think the verdict a right one the  ship arrive at Jamaica the first port she come to trade in b rule deny a see  Foxcraft v Devonshire ante per Lord Mansfield and Collinson v Larkins TauntA l  as to evidence of usage see noble v Kennoway Doug vallance v Dewar camp Ougier  v Jennings d n on mercantile contract relate to insurance c court of law  examine and hear witness of what be the usage and understanding of merchant  conversant therein for they have a style peculiar to themselves hich be short  yet be understand by they and must be the rule of construction per ld  Hardwicke c in baker v pain I Ves S see also blunt v comens Ves S Chaurand v  angerstein peak n PC birch v Depeyster camp and ante b S p Barras v London ass  comp park be inn marsh inn leigh v Mather ib Esp SC where a ship be insure at  and from Jamaica warrant to sail after January that and be lose before that  day in sail from one port of the island to another the insure recover on the  ground that she be protect in move from port to port in the same island  Cruickshank v janson taunt and see constable v noble d vallance v Dewar camp  as to the construction on policy see ld mansfield judgement in belly v royal  exchange assurance company bar borough v Whitmore TR ld Ellenboroughs  judgement in Robertson v French east see also Hodgson v Richardson post and  carter v boehm post