Technically, there is no contract without compensation. Although a 10% offer deposit seems exorbitant, some sort of good faith deposit is required in order for the offer to become an enforce-able contract.
I would suggest that you write a check large enough so that the seller knows you are serious with the balance of the 10% to be put in escrow upon acceptance of your offer by the seller. Offer should be made subject to personal inspection, mechanical and structural survey, and sea trial. Others above have suggested timelines for response and performance as well.
Best of luck. I hope your offer turns into a purchase.