Hydraulic Autopilot Pump Flow: Sizing in GPM

What pump flow means on a hydraulic autopilot listing

The hydraulic pump is the part of an autopilot that moves hydraulic fluid from the helm to the steering cylinder, which turns the rudder. The output of that pump is a flow rate, usually described in gallons per minute (GPM) in general terms, or as the volume of fluid the pump can move for a given steering system.

On a listing, you rarely see a GPM number. Makers name a pump by the steering system it is built for, for example a steering cylinder volume range in cubic centimeters (cc) or cubic inches (in³). The maker's page for the drive unit states that range, and the listing carries the same name. That is why this article compares pumps on stated details rather than on flow figures the catalog does not give.

How the steering cylinder decides the flow you need

The steering cylinder holds a certain amount of fluid for the rudder to travel from lock to lock. The pump must move enough fluid to fill the cylinder within the time you expect the rudder to respond. If the pump flow is too low for the cylinder, the rudder turns slowly and the autopilot feels sluggish. If the flow is too high, the rudder can move too quickly and steering gets twitchy.

That is why a pump is stated for a steering system range, not for one exact number. Raymarine's drive unit page, for example, lists its Type 0.5 hydraulic pump for steering systems of 50 to 110 cc, the Type 1 for 80 to 230 cc, the Type 2 for 230 to 350 cc, and the Type 3 for 350 to 500 cc. Those ranges are the stated details a buyer compares.

What flow does to rudder speed

Rudder speed is the consequence of flow. A higher flow rate moves the rudder faster, and a lower flow rate moves it slower. The right speed depends on the boat's steering characteristics and on how quickly you want the autopilot to correct the heading.

No listing can tell you how a pump will behave on your boat. The stated range tells you which steering systems the maker built the pump for; the rest is a question for a dealer or a qualified installer, and for the maker's manual.

Reading the manufacturer's stated ranges

When you read a hydraulic autopilot listing, the pump name or the pack name often carries the pump type. Raymarine packs, such as the EV-100 Power Pilot, EV-150 Power Pilot and EV-200 Power Pilot, are named for the powerboat steering systems they suit, and the drive unit page shows which pump type each uses.

Furuno uses pump codes in some pack titles, such as PUMPOCT10-12 and PUMPOCT16-12 for the NavPilot 300 and 711C packs. Those codes name the pump in the box. The maker's page is the source for what each code covers.

• Type 0.5: 50 to 110 cc (3.1 to 6.7 in³)
• Type 1: 80 to 230 cc (4.9 to 14.0 in³)
• Type 2: 230 to 350 cc (14 to 21 in³)
• Type 3: 350 to 500 cc (21.0 to 30.5 in³)

Questions to ask before you settle on a pump

Before you order, you need a few answers about your boat. The pump is the part that has to physically match the steering, so it deserves the same attention as the control head or the course computer.

Ask these questions and check the maker's page for the drive unit before you compare packs.

• What is the steering cylinder volume on your boat?
• Does the maker's page list a pump range that covers it?
• Is your steering hydraulic, and does the listing name a pump type for it?
• Do you want the pump in a complete pack, or do you plan a core pack with an existing drive?
• Who will confirm the pump size: a dealer or a qualified installer?

Who should pay attention to pump flow

Anyone choosing a hydraulic autopilot, whether for a powerboat with hydraulic steering or a sailboat with hydraulic steering, should pay attention to the pump range. It matters most to buyers who keep an existing drive and buy a core pack, because the pump is the part they already have or the part they replace.

If you are buying a complete pack, the pump is in the box, so the pack title or the maker's page for that pack tells you which steering systems it suits. See the best hydraulic autopilots guide for listed picks, and the core pack guide if you plan to keep your current pump. For the whole system in one order, the complete pack guide is the place to start, and the control head guide helps if you want a head in the box as well.

What to pick for your situation

Questions

What does GPM mean on a hydraulic autopilot?

Gallons per minute is a general way to describe pump output. Listings more often state the steering system volume range the pump is made for, so use the maker's page as the source for what each pump covers.

How do I know what pump flow my boat needs?

You need your steering cylinder's volume and the maker's stated range. A dealer or a qualified installer can confirm which pump type suits your boat.

Is a faster pump always better?

No. The pump must match the cylinder volume. Too fast can make the rudder twitchy, and too slow makes the steering sluggish. The stated range is the guide.

What if my steering system size is not in the listing?

Check the maker's page for the drive unit or pump. If the listing omits the size, ask the seller or a dealer before you order.

Can I use the same pump on a sailboat and a powerboat?

The pump is matched to the steering system volume, not to sail or power as such, but the boat's steering characteristics still matter. Confirm the range with the maker.