Thermophysical characteristics of liquid boiling under low pressure and in vacuum in ship desalting installations are characterized by substantial features. First of all, a physical picture of forming steam bubbles on the heat surface, its geometric dimensions is revealed. The results obtained on single tubes for such regimen of steam generation offered calculative dependences for projecting evaporators working at low pressure. However, they do not take into account the complexity of generating steam phase in passages of tube bunches occurring in constructions of real evaporation installations. To heat exchange equations, correcting coefficients are brought in for a calculation of process differences on single tube and a tube bunch. Experimental data show that physics of boiling process on tube bunches greatly differs from the picture observed for single heat surface as a rising phenomena of circulation in a frame of a heat exchanger and interaction of now locally along the tube introduce marked peculiarities in heat exchange. Effective values of heat transfer at boiling on the tube bunches may be attained provided distribution of temperature field in two-phased medium and on the heat surface is known. Experimental data and the equations of hydrodynamic and heat transfer for seawater boiling under vacuum on the tube bunches is reported.