Three mechanics explain nearly every surprise on a dockage invoice. The first is that you are almost never billed on your boat’s actual length. Marinas bill on slip length or length overall, whichever is greater. A 44-foot catamaran assigned to a 50-foot slip pays for 50 feet, every month, for as long as the contract runs — and if your LOA includes a bow pulpit, davits and a dinghy hanging off the stern, the marina will measure that too. Ask which figure a quote is based on before you compare it with another marina’s.

The second is that the per-foot rate climbs with size instead of falling. Buyers routinely assume a volume discount that does not exist. The published municipal rates are the clearest illustration: the City of Newport Beach publishes its Balboa Yacht Basin slip rates at $53.34 per foot per month for a 40-foot slip, $59.03 for a 50-foot slip and $74.20 for a 75-foot slip. Going from 40 to 75 feet nearly doubles the rate per foot and more than triples the monthly bill.

The third is seasonality, which in the Caribbean cuts the opposite way to the US. Northern marinas price high in summer and dump rates in winter. Caribbean marinas price high from December to April and soften through hurricane season, when many owners haul out or move south of the insurance box anyway. If you are weighing where to keep a boat you are buying, that seasonal shape matters as much as the headline rate, and it feeds directly into the annual cost of owning a yacht in the Caribbean. An older boat holding down an expensive slip is usually the moment owners price what a repower costs against simply moving on to a newer hull.

This is the number nobody publishes and every multihull owner discovers at the invoice. A catamaran occupies roughly twice the water surface of a monohull of the same length, and marinas price the water, not the boat. The common structures are a flat 1.5× multiplier on the monohull per-foot rate, a beam surcharge billed per foot of beam above a threshold, or assignment to an end tie or T-head that is priced as a larger slip than your length would otherwise buy.

A 45-foot cruising catamaran with 24 feet of beam can easily pay what a 65-foot monohull pays, and in some marinas will simply be told there is no berth — finger piers in older harbours are spaced for monohulls and physically cannot take the beam. When you are comparing yachts for sale in the Caribbean and a multihull is on the list, get a written dockage quote for that specific beam at the marina you intend to use before the offer, not after. It is a larger annual line than most buyers model, and it is the single biggest gap between a monohull budget and a multihull one.

Two cautions about reading that table. First, transient rates multiplied by thirty are not a monthly rate; every marina that offers both discounts the monthly figure heavily, often by half or more, and a seasonal or annual contract discounts it further. Nanny Cay in Tortola publishes nightly dockage at $1.25 to $1.50 per foot, which is the structure the whole territory uses — but nobody keeping a boat there pays that rate for a year.

Second, availability moves price more than any published card. In a market where every slip is spoken for and the waiting list runs years, the real cost of dockage includes what you pay to be somewhere else while you wait.

The per-foot rate buys you the water and the cleats. Nearly everything else is metered, surcharged or extra, and on a full-time berth these items routinely add 10 to 25 percent to the invoice. The items below are the ones that appear most often and surprise owners most reliably — they are also the difference between a dockage estimate and real liveaboard running costs.

For most Caribbean owners the honest answer is a mix. A slip buys convenience: step-ashore access, shore power, water, security and somewhere to run a contractor’s extension lead. A mooring ball buys cheap, safe swinging room and costs a dinghy ride. Dry storage — hauled and stood in a yard — is the cheapest of the three per month and the right answer for a boat that is not being used, particularly through storm season, when many insurers price the difference for you.

The pattern that works for cruising boats is moorings or anchoring while in use, a slip booked for maintenance periods and provisioning, and a haul-out for the off-season. The pattern that does not work is paying for a premium slip twelve months a year for a boat that is aboard it for three.

Dockage is usually the second-largest annual line after insurance, and unlike maintenance it is entirely predictable — which makes it the easiest place to be honest with yourself before you buy. Take the actual LOA including pulpit and davits, round up to the slip size the marina will assign, apply the multihull multiplier if it applies, multiply by twelve, then add 15 percent for metered services and fees.

Do that arithmetic before an offer rather than after, alongside pre-purchase survey costs and insurance, and the ownership budget stops being a guess. A boat that fits your cruising plan but not the berth you can actually get in your home harbour is a problem you want to find during the search, not during the closing.