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Wandering around a boat show
If you want to go further afield in your boat, or want to take more people along, upsizing indeed transforms your time on the water. So let's look realistically into the ways that size really does matter as well as the benefits and challenges of a jump up the size ladder.
Space = Stuff
On a powerboat, going up from a 25 footer to a 35-footer, the length increases by 40 percent, but the "cubic" living space increases by at least 50 percent, and your storage space increases by even more. On a sailboat, going from 25 feet to 35 feet, length increases by 40 percent, but interior volume almost doubles. This means you'll have room for the guests or grandkids — more cabins, more heads, more room around the salon table, more cockpit space — and for all their stuff. You'll be able to carry more water toys, more fishing or diving gear, more computers and cameras, and more water, fuel, and food. That last translates into being able to go farther between grocery stores, pumpouts, and fuel docks, which means more boating fun on your weekend getaways, and taking along more people with whom to share it.
Powerboats
Stability = Comfort & Safety
Proportion is a beautiful thing, but the smaller the boat, the harder that is to achieve. To have much usable volume on a small monohull boat, it has to be wide. But a wide boat doesn't move through the water as efficiently. The "length-to-beam ratio" is used as a measure to compare hulls; a 20-foot runabout with an 8-foot beam has a length-to-beam ratio of 2.5. Going from a ratio of 2.5 to 3.5 (think of a 28-foot boat with an 8-foot beam) increases stability; makes the boat easier to handle, making it more comfortable to run at speed for long distances; and makes it more capable when dealing with chop or waves, translating into less seasickness, less pounding, and more fun. But you'd have to reduce the beam to six feet on a 20-foot runabout to get to a length-to-beam ratio of 3.5. A longer boat can have a wider beam without hurting performance. The same is true on monohull sailboats — smaller sailboats tend to be very narrow; otherwise they wouldn't sail well. The sweet spot on the length-to-beam ratio for a monohull is somewhere between 3 and 4, translating into about a 10-foot beam for a 35-foot boat.
Sailboats
Speed = Distance
On a displacement hull, which includes trawlers and most sailboats, the boat's speed is limited by the length of its waterline, so length translates into additional speed in a mathematically precise way (hull speed = 1.34 times the square root of waterline length). When my husband Evans and I went from a 37- to a 47-foot sailboat, our theoretical hull speed increased from 7.3 to 8.4 knots. We thought that extra knot would make a huge difference on offshore passages, but in fact it made much more of a difference during coastal cruising. In a leisurely half-day of sailing, we could go 35 miles instead of 25. Over the course of a week's cruise (three days out, three days back), we could go 30 miles further, opening up anchorages we'd never explored before. Length also translates into distance on planing hulls, though not in the same way. Most planing hulls are comfortable somewhere between 25 and 35 knots, but the increased comfort level means you'll be willing to go for much longer than on a smaller powerboat. On a 35-foot boat with a flybridge or protected watch-keeping station, you'd enjoy an hour's run just to eat dinner at your favorite restaurant. That might not be the case in a 25-foot runabout. And on the 35-footer, you could take a half-dozen of your best friends along and everyone would be comfortable.
Size = Cost
A bigger boat costs more than a smaller one, and costs increase disproportionately with length. Slips and haulouts are charged by the foot, and other costs go up with surface area, volume, or displacement, and increase even faster — bottom paint, canvas, anchors, line, chain, and fenders, to name a few. When Evans and I went from a 37-foot sailboat to a 47 foot one, the 30-percent length increase doubled our costs of owning and running the boat.
How much will it cost you to go up in size? The absolute dollar amount varies, depending on the boat's age, how much fancy equipment it has aboard, and how you use your boat. A bigger, more complex boat may mean you can no longer do the routine maintenance yourself. Ownership costs jump when you start paying professionals. One rule of thumb from industry experts is to assume you will need to put in about 10 percent of the acquisition cost each year in maintenance to keep up with depreciation. That means 10 percent of the total purchase price of a new boat. For a used boat, it means 10 percent of the TOTAL of the purchase price PLUS the cost of any new systems you invested in to bring that used boat up to speed. So, you'll pay for those extra feet — but you'll be able to go farther, in more comfort, and take more people along for the ride. If your boating family has expanded, or if you're getting tired of the same old cruising ground, those extra feet add a whole new dimension to your boating life.