The most common and most likely answer to this crossword clue is the 10 letter word FIBREGLASS
I've seen this crossword clue in Financial Times
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More clues leading to the result FIBREGLASS
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The straight part
We know that "boat material" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case boat material = fibreglass.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FIBREGLASS mean?
FIBREGLASS noun- Silica based glass extruded into fibers that possess a length at least 1000 times greater than their width.
- Ellipsis of fibreglass wool
- A composite material made from fine fibres of spun glass held together with resin.
- To apply fibreglass to.