When is an 8,500-square-foot Bridgehampton mansion not quite enough? When you’re Miami hotelier and developer Don Peebles. The megasuccessful Obama fund-raiser (nearly $300,000 last week) just bought a four-bedroom cottage near the Sag Harbor Yacht Club, five minutes from the bigger place he already owns, for just under $2 million. Why? Because the main house, which he purchased in 2005 for around $7 million, isn’t on the water. The secondary house will serve as a “beach and boating cabana,” says his broker, Prudential Douglas Elliman’s Lori Barbaria. “It’s on the most spectacular beach in Sag Harbor.” Peebles himself puts it this way: “Katrina and I love our Bridgehampton estate and the expanse of the grounds, but we are not on the water, which our kids love. The Sag Harbor purchase, which is only five minutes from the Bridgehampton place, gives us a beach house, as it’s directly on the Shelter Island Sound. It also provides us with a third guest house (our estate has two guest houses on it). We’re excited that this combination of homes will be the perfect summer experience for our family.”