question one=can my 401k contributions be dedductible on my tax return
question two= is my boat qualifiy as a second home it does have (living quarters,bathroom ,kitchen) , and can I deduct interest paid

Question 1 - your 401(k) contributions are already deducted from income in the sense that your contributions are pre-tax and hence NOT included in your income for tax purposes. When you receive your W2 form at the end of the year the amount reported as income does not include the money you put into your 401(k) plan. So - no, you cannot take a second deduction for your 401(k) contributions.

Question 2: Yes, IF the boat has sleeping, cooking and toilet facilities, and if the loan against it is secured by the property (i.e. if you default the bank takes the boat) then it can qualify as a second home.