把握不大 meaning in English

be not quite sure

I am uncertain about grammar and some idioms
我对语法及一些习语把握不大。
They have the opportunity to stop and look at anything they see , but may be careful about spending money , as they are not sure how much they will need for travelling around
他们有机会停下欣赏所见到的景物，但通常消费很理智，原因是对旅行的费用把握不大。
Indeed , it was not much in my thoughts , that we could be able to recover the ship ; but my view was that if they went away without the boat , i did not much question to make her fit again , to carry us away to the leeward islands , and call upon our friends , the spaniards , in my way , for i had them still in my thoughts
说实话，我认为收复大船的把握不大。我的看法是，只要他们不把那只小船弄走，我们就可以把它重新修好。那样，我们就可乘它去利华德群岛，顺便把那些西班牙朋友也可带走。