Inflatable Boat Motors: Getting the Fit Right on a RIB or Tender

An inflatable or RIB tender behaves differently on the water than a rigid hull boat of the same length, and that changes what you should actually look for in an engine. Soft-bottom inflatables in particular are sensitive to weight in the stern in a way fiberglass boats aren’t, and the low transom height most inflatables have rules out a chunk of the outboard market before you even get to horsepower. Inflatable boat motors are their own category for good reason.

We rig tenders and small RIBs for sailors, charter operators, and weekend boaters constantly, and the questions are pretty consistent regardless of who’s asking.

Weight matters more here than on a rigid hull

A heavy outboard on a soft-bottom inflatable pushes the stern down further than the same motor would on a rigid fiberglass hull, because the inflatable’s buoyancy is distributed differently and the floor flexes rather than staying rigid. That extra squat at the back affects how the boat planes and how much it porpoises at certain speeds. This is the single biggest reason to stay toward the lighter end of whatever horsepower range your inflatable is rated for, rather than maxing it out just because the transom plate allows it.

Short shaft is almost always the right call

Inflatable transoms sit lower in the water than rigid hull transoms of similar length, so short shaft (roughly 15 inches) is the standard fit for the vast majority of inflatable boats and RIBs under about 12 feet. Long shaft motors are really only needed on larger RIBs with a deeper hull section forward of the transom. Check your specific manufacturer’s spec sheet, but when in doubt, short shaft is the safer assumption for inflatables.

Reinforced transoms and motor mounts

Inflatable transoms take a lot of stress from engine vibration and torque, which is why most quality inflatables have a reinforced transom panel, sometimes with an aluminum or marine-ply backing plate behind the PVC or Hypalon skin. If you’re mounting a motor heavier than what the boat originally shipped with, it’s worth confirming the transom reinforcement is rated for it — a transom that flexes under load wears out a lot faster and can eventually crack.

Two-stroke, four-stroke, or electric for inflatables

The same trade-off that applies to portable motors generally applies here, with an inflatable-specific wrinkle: fuel and oil spills are harder to clean out of the textured non-skid floor and tube seams than off a fiberglass deck. A four-stroke avoids the oil-mixed-with-fuel handling entirely, which a lot of inflatable owners appreciate even at the cost of a bit more weight.

Electric motors solve this even more completely. The Torqeedo Ultralight and Travel series are popular specifically on inflatables and RIB tenders because there’s no fuel smell in a small open boat, no spill risk, and the lighter units weigh in around the same range as a small gas motor. For short trips to shore or quiet anchorage cruising, it’s a genuinely good fit for this boat type.

Saltwater and roll-up inflatables

If your inflatable is the roll-up, store-it-in-a-bag type rather than a rigid-hull RIB, pay extra attention to flushing and rinsing the motor after saltwater use, since these boats often get stored in less ventilated spaces than a RIB left rigged on davits or a trailer. Salt residue left on a motor that’s about to sit in a bag in a locker for weeks accelerates corrosion more than the same residue on a motor that airs out on a mooring.

Matching horsepower to your specific inflatable

Most inflatables and RIBs under 9 feet are rated for somewhere between 3.5 and 6 horsepower. Boats in the 9 to 11 foot range commonly run 6 to 15 horsepower, and larger RIBs from 12 feet up can often take 20 horsepower or more. We carry options across that whole range, including small short-shaft motors like this Suzuki 2.5 HP, the Tohatsu 6 HP for slightly larger tubes, and the Tohatsu 20 HP class for larger tenders.

A few common questions

Can any outboard go on an inflatable boat?
No — stick to the horsepower rating on the manufacturer’s plate, and lean toward shaft length and weight recommendations specific to inflatables rather than general outboard buying advice.

Is an electric motor powerful enough for a RIB tender?
For short trips between anchorage and shore, yes, electric motors in the right size class handle this well. For longer runs or carrying heavier loads regularly, gas still has the edge in range and sustained power.

How do I know if my inflatable needs short or long shaft?
Check the manufacturer’s spec sheet for your specific model. As a general rule, inflatables and RIBs under about 12 feet use short shaft; longer or deeper-hulled RIBs may call for long shaft.

Quick specs at a glance

For a rundown of the safety equipment that applies to small craft including inflatables and RIBs, Discover Boating’s guide to U.S. Coast Guard requirements is a clear, non-technical summary worth reading before your first trip out.

Where to Find Inflatable Boat Motors That Actually Fit

We stock inflatable boat motors across the short-shaft, low-weight range that fits tenders and RIBs specifically, in both gas and electric. Tell us your inflatable’s length, tube diameter, and rated horsepower and we’ll point you to options that actually fit rather than just technically bolt on. For the engines built for bigger fishing boats, see our fishing boat motors guide, and for one-person-portable options, our portable outboard motors guide covers similar ground from a different angle.