Overview

Mercruiser’s answer to the Volvo Duo-Prop, the Bravo III features twin counter-rotating propellers in an aluminum outdrive. Bravo III’s are found on applications ranging from 190HP to 525HP with the new Bravo IIIXR. For single-engine boats, twin prop drives are generally the standard over 260HP to improve handling and low-mid range performance.

Principle advantages of the Bravo III vs single-prop drives:

Straighter tracking due to counter-rotating propellers

Better coupling of engine power to water for a given propeller diameter

Improved acceleration at low RPM’s

Smoother clutch and general operation (vs the Mercury Alpha drive)

Disadvantages:

Weight, Cost, Complexity - almost twice the weight as the Alpha, expensive SS prop set, complex gearing

Lower top end due to increased prop drag at high speed vs. single prop

Propensity for galvanic corrosion

Basic Parts

Click on the image at left to open up our annotated Bravo III photo to follow along. The Bravo III outdrive has 5 major subcomponents - the lower unit, upper unit, bell housing, gimbal ring, and transom assembly.

Lower Unit - The lower unit attaches to the upper unit at the cativation plate (which improves water flow over the propelers). It houses the drive shafts, gear oil drain, water intake pipe, and through-prop and secondary exhaust which operates at high pressure.

Upper Unit - The upper unit houses the main gearbox with shifting mechanism, u-joint, and drive coupler which connects to the engine. The lift rams for the drive trip also attach to the upper unit.

Bell Housing - The bell housing serves as an interface between the engine and outdrive for the drive coupler (protected in a bellows), shift cable, raw water hose, and gear lube tube. Depending on the installation, the bell housing may also have an exhaust bellows.

Gimbal Ring - The gimbal rings is the primary load-bearing attach point for the outdrive. It attaches to the outdrive upper unit at two horizontal pivot points to allow for drive trim. The trim limit switch which sets the maximum travel for normal and trailer trim is attached to the port (left) pivot while the trim position sender which provides information to the outdrive trim gauge at the helm is mounted on the starboard (right) pivot pictured below. The gimbal ring attaches to the transom assembly via lower and upper swivel pins. The upper swivel pin is gripped via a u-bolt which is torqued via two nuts on the face of the gimbal ring. Improper tightening of these nuts is one cause of loose steering (although overtightening can lead to a more severe drive failure).

Transom Assembly - The gimbal ring attaches to the transom assembly at the lower and upper swivel pins. The upper swivel pin is captured at its top by the steering arm inside the transom. This interface commonly corrodes over time and creates loose steering. Unfortunately, the repair is difficult and expensive with most shops suggesting that the engine be removed to perform the fix. The u-joint bellows, lower shift cable, gear lube tube, raw water hose, and trim sender wires all connect to the assembly or pass through it into the engine room.

Mercathode, Anodes, and Bonding Wires - While not structural components, the Bravo III’s anti-corrosion elements must be kept in top shape to avoid expensive corrosion damage. Mercathode is an active protection system which uses a small amount of battery power to help reduce current flow between dissimilar metals and the water. It is normally connected directly to the batteries and will drain them over a few days without recharging.

Aluminum anodes are required in salt water environments (magnesium in fresh) and are located at two places on the cativation plate, on each lift ram, and on the prop nut. Bonding wires connect each outdrive component in turn to a common ground on the engine. A break in one of these wires drastically reduces the total corrosion protection of the system. Click on the image below to see our gallery of anode locations and a picture of the Mercathode electrode.

Our Review

After two years boating with a 20′ Chaparral in front of the Merc Alpha I, we upgraded to a Regal 2760 powered by twin 4.3L Mercruiser engines and Bravo III drives. We were fortunate to find a 2001 model that had been dry stored since new and had never been bottom painted. Its outdrives were in excellent shape - expect for the upper swivel pin corrosion problem on the port engine.

The 2760 is a 28′ class express cruiser and weighs in at around 8500lbs dry. To maximize cabin room, it was designed to use the V6 4.3L engine and is about the largest you dare go with V6 power in a planing hull. Early versions powered with Alpha I outdrives are notorious for having problems getting on plane. With the Bravo III, our boat planes out in approximately 10 seconds without tabs with 1/3 fuel, full water, 2 adults, 3 children, and supplies for 2 nights on the water. We have had 8 adults aboard and were still able to plane (although full use of tabs and some weight distribution was required). Top speed is 43mph at 4500rpm and our optimum cruise is in the 3400 - 3600 RPM range which yields 29 - 32mph per the GPS depending on water and wind conditions.

Once we had the upper swivel pin and steering arm replaced, idle tracking was much improved. The boat tracks very straight at all speeds and is surprisingly nimble in turns for its size (as long as power is added to counteract the additional drag). Shifting and overall running are much smoother than with our old Alpha. Anecdotal evidence from the prior owner of our boat was that our Regal with the Bravo III was ~5mph faster than a same year volvo duo-prop powered 2760 in his marina at cruise. Given that we have not seen much change in cruise speeds for different loading in our boat (including a full fuel trip to the Oriskany sinking), this big a difference would have to be engine / prop / bottom condition related.

The Bottom Line

While the Bravo III has its problems, this is not unique to this design or to Mercruiser. The boating environment is tough on just about any mechanical device. With proper care and upkeep, the Bravo III should provide years of good service and reliability. We do allow that if you’re looking at long term in-water storage, the Bravo III is a poor choice (as are inboard/outboards in general). Please add your experiences good and bad by commenting on this article.

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This entry was posted on Saturday, September 9th, 2006 at 9:41 pm and is filed under Boat Photos and Video, Boating Product Reviews, How-To & Troubleshooting, Bravo III, Mercruiser. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.