Hydrographic surveying — fixing soundings by “range and one angle” In the “range and one angle” method of locating a sounding, where does the surveyor take the angle measurement while the range line is maintained by shore marks?

Introduction / Context:
Hydrographic surveys require accurate horizontal positioning of depth measurements (soundings). One practical method is to keep the boat on a pre-set range (transit) defined by two shore marks and take a single angular observation to fix the position along that line.

Given Data / Assumptions:

• A shore transit (range) is visible to the boat crew.
• One additional observation (an angle) is made to a third conspicuous point.
• No electronic positioning is assumed.

Concept / Approach:

The “range” ensures the boat lies on a known straight line. Taking one angle at the boat to a third shore mark provides a second locus that intersects the range at the boat’s instantaneous position, fixing the sounding efficiently without two-shore observer teams.

Step-by-Step Solution:

Verification / Alternative check:

Alternative classical methods are “two angles from the shore” and “two angles from the boat.” “Range and one angle” specifically implies the angle instrument is on the boat while the range is provided from shore alignment.

Why Other Options Are Wrong:

• Shore-only angles require a different method (“two angles from shore”).
• “Either place” is imprecise and defeats the named method’s economy.
• Angles are essential; otherwise a single range cannot give longitudinal position.

Common Pitfalls:

• Letting the boat drift off the range while taking the angle.
• Poor selection of the third point leading to bad intersection geometry.

Final Answer:

On the boat.