A jet drive is not a propeller drive
Here's how a jet drive works. Water comes in through a grate under the hull. An impeller in a tight-fitting housing speeds it up, and it blasts out through a steering nozzle at the back. No prop turning in open water. No gearbox in a lower unit, no skeg hanging below the hull. You steer by aiming that jet, and that's why a PWC only steers under power. Let off the throttle and there's no thrust to steer with. The machine just keeps going.
So the service work is a whole different job. No gearcase oil and no prop to reshape, but there's a pump to inspect, a driveshaft with a bearing and a seal behind the impeller, and a jet housing that has to stay clear to work at all. Damage looks different too. Touch bottom in a prop boat and you bend a blade you can see. On a jet drive, it feeds sand and gravel straight through the impeller and the wear ring, where you can't.
The impeller and the wear ring
The impeller spins inside a wear ring, and there's a tiny gap, by design, between the blade tips and that ring. Keep the gap tight and the pump's efficient — water gets driven out the nozzle instead of sneaking back past the blades. But sand, gravel and weed going through carve grooves into the softer ring and nick the blades' leading edges. Bit by bit the gap opens, and you lose thrust without the thing ever feeling broken.
Once you know the symptoms, they're easy to spot. The engine revs to its usual ceiling, but the ski won't hit the speed it used to. Acceleration out of the hole goes soft. It cavitates under hard throttle. Owners often start chasing the engine right about then, and get nowhere. We measure the blade-to-ring clearance first, because a worn ring is a common and fairly contained repair, and there's no sense tuning an engine around it.
The intake grate, weed and debris
Everything the pump takes in goes past the intake grate first. Weed, fishing line, a plastic bag, a length of rope: any of it can wrap the driveshaft behind the impeller. Line's the worst, because it works into the driveshaft seal, cuts it, and lets water into the bearing. Sand picked up in shallow water goes right through the wear ring and does its damage on the way. You won't see any of this from the seat.
On Lake Winnipesaukee, it's the shallow weedy coves and the sandy shallows near shore where intakes pick this stuff up. Idling through weed will do it. So will riding into a foot of water to load onto a trailer. Ski suddenly loses its push? Kill it. Don't try to power through — that's exactly when whatever's wrapped around the shaft gets pulled tighter. We clear the pump, check the seal and look the shaft over for scoring.
Flushing, oil and spark plugs
Flush after every outing. Seriously, every one. It's the habit that keeps these machines alive, fresh water or not. The lake sends in bits of weed, sand and silt, they settle into the cooling passages and the exhaust, and they sit there holding moisture against the metal for months. Follow the machine's own flushing steps, in order — on most, the engine runs with the hose hooked up, and it has to be shut down in a set sequence or water backs up into the exhaust.
These are small, high-revving engines that work hard for their size. The routine work is oil changes and spark plugs, done to the engine's own service schedule, not some number off a chart. Plugs fouled by long idling and short runs are a common cause of a hard start or a rough one, and they're quick to rule out first. Watch the fuel too. Pump gas runs up to ten percent ethanol, which draws in water and does a part-full tank no favors.
Winterizing and storage
On a PWC, the freeze risk is the water left sitting in the pump, the cooling passages and the exhaust after the last ride of the year. It won't all drain out on its own. Whatever's left in there when it gets cold turns to ice, swells, and cracks whatever's holding it — on these machines, an exhaust part or a cooling passage. Winterizing gets that water out, treats and stabilizes the fuel, and protects the engine's insides the way the manufacturer says to.
Here, that risk is real, not theoretical like it might be farther south. Ice-out on this lake was declared on April 13 in 2026, and the record kept since 1888 runs from March 17 at the earliest to May 12 at the latest. A ski left in an unheated garage or under a cover sits through months well below freezing before any of that. The battery comes out, gets charged, and gets stored somewhere it won't freeze dead and fail in spring.