Perhaps if I may say in a gentle manner, just to clear the waters, that you should also check that the owner doesn't assume that you might cough up for the excess if something happened.
You know not something that you might do, say the local garbage collector backed his truck into you while you were lifting off it could bring water to your eyes. Not the crash, that's easy a few beers in the pub gets the heart settled, I mean paying for the excess.
The amount of excess is dependant on the premium also and it may vary, over here anyway, its say between 5% to say 15% of hull value. Just be sure of your arrangements first is what I am suggesting. It's a terrible way to ruin a friendship if you're not careful.