Some marina's would allow that, but if your travelling light why not d/i/y. I do all my small stuff in the sink with a homemade Rubbing board, Pre rinse in the river to get most of the soap out then a final rinse in the sink. If your hiring a trad style boat all the better, rig up a little washing line with a bit of string above the engine,'' clothe pegs are cheap and useful for other things too, like when you visit a sanitory station to empty the toilet or pump out, just pop one on your nose and hold your breath'' things will dry quickly there above the engine. If a cruiser stern boat rig up a couple of washing line front and back. Scrubbing boards can be bought cheap online or in oil shops here. The macho gueezers that won't relinquish the helm for er-indoors to have a go are easily identified, they almost always stand bolt upright, chin in the air like an admiral of the fleet, wear Breton or Captains hats and frequently bellow out orders and instructions to er- indoors at the front, sometimes by megaphone. The only time that Macho captain is likely to let er-indoors have a go at the helm is when he in quiet panic has made a huge boob himself, and big danger is iminent like he's headed the boat straight at a weir by mistake,bellows for her to come and have a go at the tiller, when disaster strikes, grabs the tiller back from her and blames her for the terrible results, Hope you have a tremendous and great holiday.