Originally Posted by AusCan
A 3/4" diameter hose will always have less pressure drop than a 5/8" hose over a given length and flow rate. ..............
Yep, similar to having less resistance with a larger wire size.
As far as washing a boat, I don't think you will notice any difference with a slightly larger hose diameter. What you will notice is, the pressure and volume available to you drops as others are washing their boats on the same dock. Your best pressure will be if nobody else is washing their boat.
If you really want pressure, buy a pressure washer. Buy the smallest you can find and be very careful with it. You can easily remove tape stripes or blow out window screens. Practice on something cheaper than your boat first.
The problem I have with hoses is, the dry stack customers think the hoses belong to the marina so if there's no hose where they dock, they walk until they find one (mine) and move it to their dock. I finally had to strap mine down to the dock with conduit holders.