The Nantucket whale-men being extremely well acquainted with the Gulph Stream, its course, strength, and extent, by their constant practice of whaling on the edges of it, from their island quite down to the Bahamas, this draft of that stream was obtained from one of them, Captain Folges, and caused to be engraved on the old chart in London, for the benefit of navigators, by
B. FRANKLIN.
Note, The Nantucket captains who are acquainted with this stream, make their voyages from England to Boston in as short a time generally as others take in going from Boston to England, viz. from twenty to thirty days.
A stranger may know when he is in the Gulph Stream, by the warmth of the water, which is much greater than that of the water on each side of it. If then he is bound to the westward, he should cross the stream to get out of it as soon as possible.
B. FRANKLIN.
[Observations of the Warmth of the Sea-water, &c. by Fahrenheit's Thermometer, in crossing the Gulph Stream; with other Remarks made on board the Pennsylvania Packet, Capt. Osborne, bound from London to Philadelphia, in April and May, 1775.]
| Date | Hour | Temp. of Air. | Temp. of Wat. | Wind | Course | Distance | Latitude N. | Longitude W. | Remarks |
| April 10 | 62 | ||||||||
| 11 | 61 | ||||||||
| 12 | 64 | ||||||||
| 13 | 65 | ||||||||
| 14 | 65 | ° ′ | ° ′ | ||||||
| 26 | 60 | 70 | 37 39 | 60 38 | Much gulph weed; saw a whale. | ||||
| 27 | 60 | 70 | SSE | WbS | 37 13 | 62 29 | Colour of water changed. | ||
| 28 | 8 A.M. | 70 | 64 | SW | WNW | 37 48 | 64 35 | No gulph weed. | |
| — | 6 P.M. | 67 | 60 | 34 | Sounded, no bottom. | ||||
| 29 | 8 A.M. | 63 | 71 | N | W | 44 | 37 26 | 66 0 | Much light in the water last night. |
| — | 5 P.M. | 65 | 72 | NE | 57 | Water again of the usual deep sea colour, little or no light in it at night. | |||
| — | 11 dit. | 66 | 66 | NWbN | WbS | 57 | |||
| 30 | 8 A.M. | 64 | 70 | NE | WbN | 69 | |||
| — | 12 | 62 | 70 | EbS | 24 | 37 20 | 68 53 | Frequent gulph weed, water continues of sea colour, little light. | |
| — | 6 P.M. | 64 | 72 | ESE | WbN | 43 | |||
| — | 10 dit. | 65 | 65 | S | 25 | Much light. | |||
| May 1 | 7 A.M. | 68 | 63 | 60 | Much light all last night. | ||||
| — | 12 | 65 | 56 | SSW | WNW | 44 | 38 13 | 72 23 | Colour of water changed. |
| — | 4 P.M. | 64 | 56 | WbN | 21 | ||||
| — | 10 dit. | 64 | 57 | SW | WNW | 31 | Much light. | ||
| 2 | 8 A.M. | 62 | 53 | 18 | 38 43 | 74 3 | Much light. Thunder-gust. | ||
| — | 12 | 60 | 53 | WSW | NW | 18 | |||
| — | 6 P.M. | 64 | 55 | NW | WSW | 15 | |||
| — | 10 | 65 | 55 | NbW | WbN | 10 | |||
| 3 | 7 A.M. | 62 | 54 | 30 | 38 30 | 75 0 |