Vessel now identified with the expert help of Manfred.

It is the Brazilian Navy's hydrographic ship 'Almirante Saldanha H10'.
She was originally built as a nautical training ship for the Brazilian Navy; as a 4 masted schooner (with 19 sails) & one diesel auxiliary engine of 1,400 hp, coupled to 1 shaft with a four-bladed propeller. N.B. as a training ship she held the pennant 'U 10'.
Later, when converted to a hydrographic surveying vessel, did she take the 'H 10' pennant number.

Keel laid on 11/06/1933, launched on 19/12/1933, and commissioned into the Marinha do Brasil (Brazilian Navy) on 11/06/1934, by Vickers Armstrong Ltd., Barrow-in-Furness, England (688)
3,3,25 tons loaded displacement, AS:
'Almirante Saldanha'.

In 1956/57 the vessel was partly converted into a Hydrographic research ship, with an oceanographic laboratory being installed in the former Marine Guards' starboard quarters, and a 5,000 meter echo-sounding machine, in place of the old torpedo launch tube platform, which had been removed.
The ship retained its name and most of its external appearance.

Between 1962 & December 1964 the ship was remodeled at the Rio de Janeiro Navy Arsenal, being converted from a School Ship, to carry out Oceanographic surveying and research. The remodeling included the installation of marine biology, chemistry, meteorology, radioactivity, geology and ichthyology laboratories, as well as six winches for oceanographic operations, three echo sounders and a sonar for detecting schools of fish.

06/08/1990, the ship paid off after 56 years of service; it had sailed 694,972 miles, spent 4,738.5 days at sea, with an average of 85 days at sea per year, and after modifications, it reached an average of 105 days at sea per year, carrying out 8,150 stations and 135 oceanographic commissions.

Further data on the ship, from the Marinha do Brazil's website ( in Portuguese ) can be found here:
https://www.naval.com.br/ngb/A/A044/A044.htm

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For identification purposes only - I will remove the photo after the vessel has been identified.

Circa 1966, believed to be the island of snakes, Ilha das Cobras (Island of snakes) Brazilian Naval base, with Sugarloaf mountain in the left background.

Any suggestions please?

The white-hulled ship to the left has, what appears to be, a dramatically sloping (aft-wards) yellow funnel amidships, and many portholes/accommodation, so I suspect it is a Naval training ship, or even a Naval hydrographic ship?

Scanned from a slide.
From the collection of the late Niels Anker Larsen, former Danish Merchant Navy Radio Officer.