The sea is not crossed by rafts. دَأْمَاءُ لاَ يُقْطَعُ بِالأرْمَاثِ.

he sea is called "da'maa," and a raft is made of wood joined together and used for fishing or other purposes.
This proverb is used to describe a great undertaking that can only be accomplished by someone with the necessary helpers and equipment.
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The Arabic proverb "Da'maa' la yuqta'u bil-armaath" means that a momentous matter or a great task cannot be accomplished with weak or insufficient means, but rather requires appropriate resources and support.
The closest English proverbs to this meaning are:
Don't bring a knife to a gunfight.
— That is, don't tackle a great task with unsuitable means.
You can't cross the ocean in a canoe.
— Very close to the image of the Arabic proverb, though not a well-known saying.
Great tasks require great means.
Horses for courses.
— For every situation, there is what suits it.
— That is, every task has its tools and people.
A big job requires big tools.
— A common expression, though not a traditional proverb.
The best and most common English equivalent in meaning is:
Don't bring a knife to a gunfight.
However, if the intention is to maintain the image of the sea and crossing, the closest expression is:
You can't cross the ocean in a canoe.
That is: Don't tackle great tasks with flimsy means or with helpers who are incapable of handling them.
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الدأماء: البحر، والرِّمْث: خَشَبات يُضم بعضُها إلى بعض ثم تركب في البحر للصيد وغيره.
يضرب في الأمر العظيم الذي لا يركبه إلا مَنْ له أعوان وعُدَدٌ تليق به.