Possible Clues:

• Suffering an attack like being on a yacht
• A beast with some complaint making a charge
• One may be having an attack of this while out in a yacht (9)
• One might be getting an attack of this while on the yacht
• While on the yacht it's silly to be sick
• There's something by way of yachting that makes 17 across sick
• Silly to be sick while on the yacht
• Silly to be having an attack while you're out in the yacht
• Like being on 17 across and getting sick of it
• Silly to get sick while in the yacht