Explanation

Blank (i)

copper-sheathed hulls proved far more (i) _______ than iron-fastened counterparts

We need a word that reflects overall advantage or economic benefit.

A. precarious = unstable negative, wrong
B. lucrative = profitable fits perfectly
C. adaptable = flexible not the focus

B. lucrative

Blank (ii)

whereas copper sheathing (ii) _______

This contrasts with iron being locally sourced, so copper is likely harder to obtain/more restricted.

D. demanded imported materials obtainable only through a single European monopoly fits contrast perfectly
E. catalyzed the development of novel metallurgical techniques this is irrelevant
F. entailed burdensome maintenance schedules this shifts topic (maintenance, not sourcing)

(ii) = D

Blank (iii)

the considerable outlay they demanded was, in the final accounting, amply _______

We need something meaning the cost was justified or paid back.

G. a drain on = negative cost burden this is wrong
H. a supplement to = unrelated meaning
I. recouped by = recovered/justified this perfect fit

(iii) = I

Answer: B,D,I