Outboard in the Water: Tilted Up or Down? 

The decision of whether to leave your outboard tilted up or down while your boat is sitting in the water might not seem like a big deal, but the wrong choice can lead to big problems. 

Either choice has its pros and cons, but here are some reasons for leaving your boat's outboard motor tilted up or down. 

Why Leave an Outboard Tilted Up

There are three main reasons for tilting your outboard up and out of the water: marine growth, galvanic corrosion and electrolysis.

Marine Growth

Marine growth is the buildup of marine lifeforms such as barnacles, algae and seaweed that attach to and grow across any part of your boat that’s submerged in the water. This growth blocks cooling inlets and exhaust ports; spoils the profile and efficiency of the propeller; and ruins the outboard’s hydrodynamics and causes drag in the water. Marine growth happens faster in warmer waters and is usually more prolific in salt water, although some freshwater areas are prone to fast development of marine growth.

Galvanic Corrosion

Galvanic corrosion is a process in which one type of metal begins to corrode when in contact with another type of metal via an electrolyte. In the case of your outboard, the metals are most of the parts in the powerhead and gearcase, and the electrolyte is the water. Galvanic corrosion happens much faster in salt water (a stronger electrolyte), but also occurs in fresh water.

Anodes or zincs protect outboards from galvanic corrosion. 

Electrolysis

Electrolysis is a chemical reaction caused by the introduction of an electrical current. As the current passes through a metal, it causes it to lose electrons and decompose.

In the case of your outboard, the electrical current could be a stray from the boat’s electrical system or an improperly connected shore power cable, and the metal is any of the parts in the powerhead and gearcase.

Why Leave an Outboard Tilted Down

The two most insistent reasons to leave your outboard tilted down in the water are to prevent accidental damage and theft.

When it comes to damage, the chances of an outboard accidentally being hit are much higher if the outboard is pointed up and away from the transom. A hit from passing boats or contact with a dock piling can easily snap a propeller blade, bend the prop shaft or damage the gearcase. Tilting the outboard down reduces its vulnerability to accidents.

As for the theft part of it, a nice shiny propeller exposed by an up-tilted outboard makes a tempting target for a thief. Propellers are easy to remove and can be expensive to replace, so keeping it submerged makes it much more of a challenge to a would-be thief.

When to Leave an Outboard Tilted Up

There are more pros to trimming up your outboard when the boat is left in the water, and they’re far more compelling than the pros of leaving it tilted down. 

For example, tilting the motor down may prevent the propeller from getting stolen, but if it results in the entire lower unit corroding and needing repairs, it’ll cost you a lot more than what the actual prop theft would. It’s best to tilt your outboard up when leaving your boat in the water to prevent marine growth from forming and from corrosion eating away at its metal parts. That being said, there are some instances when you may prefer tilting your outboard down.

When to Leave an Outboard Tilted Down

If you plan to use your boat again the following day after mooring it, you can leave the motor tilted down. 

The hours between dusk and dawn probably won’t be enough for any significant marine growth to occur, and provided your outboard’s anodes are in good shape, the unit should be protected from corrosion and electrolysis. If you live in a cooler climate and leave your boat in fresh water, the chances of marine growth will be a lot less, or the growth will be slower. Leaving the motor trimmed down in the water in these conditions for a week or two may not lead to any significant marine growth buildup. 

If you leave your outboard tilted down for a period of time, raise and inspect it at least weekly, clean and flush it (marine growth can and will occur inside the cooling system) and replace any anodes that have deteriorated.