It is not clear to me why in the translation of

Phaeselus ille quem videtis, hospites,

ait fuisse navium celerrimus,

neque ullius natantis impetum trabis

nequisse praeterire, sive palmulis

opus foret volare sive linteo.

One could not translate celerrimus as a a noun, i.e. Phaeselus, whom you guests all saw, said that the quickest of the ships...

If I do this the rest of the sentence works out gramatically:

the quickest of the ships,

neither of any (value) swimming by the trunk, nor was it passing using the paddles through the linen as it would have wanted to.

Is there some rule against this?

It is not clear to me why in the translation of

Phaeselus ille quem videtis, hospites,
ait fuisse navium celerrimus,
neque ullius natantis impetum trabis
nequisse praeterire, sive palmulis
opus foret volare sive linteo.

One could not translate celerrimus as a a noun, i.e. Phaeselus, whom you guests all saw, said that the quickest of the ships...

If I do this the rest of the sentence works out grammatically:

Phaeselus, whom you guests all saw, said that the quickest of the ships
neither of any (value) swimming by the trunk, nor was it passing using the paddles through the linen as it would have wanted to.

Is there some rule against this?

It is not clear to me why in the translation of

Phaeselus ille quem videtis, hospites,

ait fuisse navium celerrimus,

neque ullius natantis impetum trabis

nequisse praeterire, sive palmulis

opus foret volare sive linteo.

One could not translate celerrimus as a a noun, i.e. Phaeselus, whom you guests all saw, said that the quickest of the ships...

If I do this the rest of the sentence works out gramatically:

the quickest ships,

neither of any (value) swimming by the trunk, nor was it passing using the paddles through the linen as it would have wanted to.

Is there some rule against this?

It is not clear to me why in the translation of

Phaeselus ille quem videtis, hospites,

ait fuisse navium celerrimus,

neque ullius natantis impetum trabis

nequisse praeterire, sive palmulis

opus foret volare sive linteo.

One could not translate celerrimus as a a noun, i.e. Phaeselus, whom you guests all saw, said that the quickest of the ships...

If I do this the rest of the sentence works out gramatically:

the quickest of the ships,

neither of any (value) swimming by the trunk, nor was it passing using the paddles through the linen as it would have wanted to.

Is there some rule against this?