Okay, I’ve broken it down a bit, for example and ideas mainly. I’ve commented on more than just the description, but take from it whatever you like. I hope some of it is helpful.

There could be no restless slumber for Isaac Weiscorft

At this point we do not need to know his surname, and the flow is better without. Remember, first page, tight, to the point, waste no words. And think about making one this one sentence. It's a more powerful start.

for His [something, long-dead, missing, long-ago] lover’s raven [something dark that reflects her character, unless she's a bird raven tells us no more than black – pitiless, soulful] black eyes plagued him. always

Always is word you can sometimes happily leave out. If they plague him, they plague him. We take it as read.

He awoke in a sweat to a mad cacophony of sound.

Now you had some comment regards the cacophony. You have originally suggested it is the memory of her eyes that stops him from sleeping, or at least sleeping well. See how if you add in some info where I've put brackets could indicate a bit more of the why? But hold on, becasue we are getting mixed messages by mentioning the noise. Is he waking from the noise, or the memory? And is the noise, normal? And why is he sweating? Is it hot? Where they very intimate memoriesthat made his heart rate?

The crack of steel mixed with various wind instruments which made the very air itself seem to rebel and strain under the weight of the sound.

You are trying to show here but end up telling. And is the ship breaking apart, because you really don't want steel to crack, as far as I am aware. BUT it’s a good placeholder for something more pretty you can change later, because you clearly say the kind of sound you want. I'd mark it to come back and work on it.

Cursing this infernal ship, he crawled out of bed struggling to gather his bearings while adjusting to the [some sort of rocking. Then you can get rid of the repetition of ship] rocking of the ship.

Otherwise, good sentence.

Looking at himself in the mirror,

This is where you got into trouble with other commenters. Let's think about it. What's he doing. Is he sitting, sitting where? On a cramped bunk? There could well be a mirror. He could catch a glimpse of it, (the mirror, not himself, but refuse to look, knowing how much his tidy, gentlemanly looks have deteriorated. And did you notice how many times you say raven in this passage?

So think about what kind of man he is and how a short passage about what he looks like, can show us his character and how reluctant he is to leave his rom.

As it slipped again off shelf, again, Isaac grabbed the polished steel he’d been given for grooming. Sliding it under his meagre pillow he refused to even check the progress of the scruff he couldn't call a beard. Back in blah blah home town, he often had cause to regard his fine looks and enjoyed appling the latest in lotions and potions. He'd scrape his chin as smooth as he, or his barber could muster, happy to revell in the constant compliments on his fine Weiscorft cheekbones. He had happily been a very vain man.

Here on this blah blah ship, it was pointless to even run a comb through his hair. He used to deliberately shine it with perfumed oil, leaving it short and chic, shining like a raven’s folded wing. In his new position as blah blah, it still shone, but naturally, through lack of regular washing. And as he couldn’t bear to pull it back in such an old fashioned style tied with a leather, he hacked at it with his razor, dulling the blade, which contributed to the patchiness of his beard. The only blessing he could find from his horrible lack of sophistication, was that his mother did not have to see him. He knew she would never recover, if she even recognised him.

See what I did there? Now it may not fit details of your story, and needs work, but we know he has black hair, we know he has fine cheekbones, we know he used to enjoy looking smart and now looks shocking. If we also know he should be sleeping and a reason he might not want to leave his bunk yet, it makes sense he would sit and mull over his situation. But he never once looked in that mirror.

I hope this points you in the right direction regarding physical description. :)