Mercruiser Alpha I (1) vs. the Bravo III (3) Choosing the Right Outdrive |

30 Апр 2014 | Author: | No comments yet »
Rinker 186 Captiva

Mercruiser Alpha I (1) vs. the Bravo III (3) Choosing the Right Outdrive

When considering Mercruiser powered boats, you often have a choice between the single prop Alpha I and twin prop Bravo III outdrives. The best choice depends on a combination of factors including engine horsepower, boat type, boating style, and personal preference. In this review, we cover the pros and cons of each sterndrive and the factors to consider based on our ownership of both models over the years.

The Similarities

Before getting into the differences, first we ll consider the similarities between the two drives:

Aluminum Construction

Through-prop Exhaust

Similar Transom Assembly, Trim System, Gimbal Ring, Steering System, and Trim Senders

Use of the Mercathode anti-corrosion system (standard on Bravo III, optional on Alpha I)

Single vs. Twin Prop The Alpha I uses a single aluminum or stainless steel propeller for propulsion. Advantages of a single propeller are:

Increased top speed vs a twin prop due to reduced drag

Lower replacement cost

Easy to swap propellers to favor acceleration (water sports) vs top speed (cruising) as needed

Less complex gearing in lower unit

The Bravo III use twin counter-rotating propellers made from stainless steel for motive force. Advantages of the twin-prop design include:

Better acceleration

Straighter tracking at all speeds due to torque cancellation

Better coupling of horsepower to water (especially over 260hp) for the same prop diameter

Outdrive vs. Engine Mounted Raw-Water Pump A major disadvantage of the Alpha I is its outdrive mounted raw-water pump. Servicing the pump requires removing the lower-unit of the outdrive. This is fairly easy to do on land, but impossible in the water. It also requires a full change of outdrive oil and is pretty messy. The Bravo III uses a pully driven pump mounted on the engine. Depending on your engine installation, servicing can still be a nightmare. but at least you don t have to deal with gear oil or handling an awkward lower unit.

Dog Clutch vs. Cone Clutch The Alpha I uses a dog clutch design for shifting. The dog clutch is known for its reliability, but not for its finesse. Alpha drives go in and out of gear with a pronounced clunk . Bravo drives use a cone clutch which offers smoother shifting that is perhaps a touch less distinctive to passengers. Either way, the difference is mostly aesthetic and not a big factor on performance.

Weight The Alpha is a lightweight compared to the Bravo III. A typical Alpha weighs around 75lbs where a Bravo III with props is close to 200.

Corrosion Twin stainless steel propellers on an aluminum outdrive create special challenges in corrosion protection. Bravo III s have a bad reputation for early demise due to corrosion. The net-lore somewhat overstates its frequency, but we recommend any Bravo III owner pay careful attention to their mercathode system and anodes. It is also true that most Alpha installations are on trailered boats whereas the Bravo III powers a large percentage of the non-trailerable express crusier fleet under 40 in length. All aluminum outdrives, be they Mercruiser, Volvo, or OMC are suboptimal for wet-slipped boats.

Choosing Between Outdrives

There are certain application areas where we feel the choice is clear for either the Alpha I or the Bravo III:

Single Engine under 22 and 230HP == Alpha I due to reduced weight. For this size/powered vessel, the weight penalty for the Bravo III will likely cancel any gain in low-end acceleration. Our 20 Chaparral cuddy with 205HP and the Alpha I could top out at close to 50MPH with a 3-blade prop and still plane out in under 5 seconds. If faster planing was needed for skiers, we could swap props in under 15 minutes with a single wrench.

Single Engine over 300HP == Bravo III due to power coupling. In the case of a performance boat, you might also be looking at the Bravo II for max speed, but for most users you ll enjoy better performance across the RPM range and much better handling with counter-rotation

Most Twin Engine Express Cruisers == Bravo III for better acceleration. This is less universal than the previous 2 rules, but generally speaking most express cruisers plane out a lot easier with the Bravo III. As the weight to horsepower ratio decreases, this becomes ever more important. Our Regal 2760 is an extreme case weighing in close to 10,000lbs loaded but powered by the basic 190HP Mercruiser 4.3L engine. Early versions of the boat shipped with Alpha drives and can have problems getting on plane, Bravo III versions have not had problems even though the Bravo III is not normally used with this little horsepower.

The In-betweens For those cases where either drive is suitable, we suggest you consider the likely boating style.

Performance boaters who do a lot of watersports are probably better off with an Alpha given the ease in switching props for high or low end performance. An inadvertent encounter with a tow-rope or the bottom will also be less painful to the wallet. Some discourage the use of stainless steel props on the Alpha, but the general consensus is that SS props are just fine (though be extra wary of corrosion if you wet-slip).

Single-engine cruising favors the Bravo III. You get the extra acceleration at a small cost in top end speed. Straight tracking, especially at idle and in reverse is a major plus. Corrision risk may be slightly higher, but not of particular concern for trailer and dry-storage boaters.

Rinker 186 Captiva

Performance will ultimately dictate requirements for the twin-engine cruisers. For the case of sufficient performance with an Alpha I drive and wet storage, it will cost less over time by nature of lower replacement cost alone. Otherwise, the Bravo III is probably the better choice (neglecting an option for Bravo II).

Our Experienced-based Review

We owned an Alpha drived Chaparral 1935SS cuddy powered by the 205hp 4.3LHX engine. Over two years of constant use, we had no major maintenance issues with the Alpha. Minor issues included trim position sender failure (common to all mercs), stuck prop (fixed with patience and a penetrating spray lube), and a broken skeg (previous owner, no easy fix so we left it alone). We overhauled the raw-water pump as a precautionary measure although it looked fine after 5 years of light use by the original owner and changed gear oil a few times.

With 205hp, torque wasn t really a problem. The boat did have a bit of stern walk in reserve. Most boats this size wander like drunken sailors at idle and the Chaparral was no exception. We alternated between a 3 blade and 4 blade Vortec propeller (both aluminum). The boat did best with the 3 blade with good acceleration and top end near 50 and cruise around 35 at 3400RPM. The 4 blade was disappointing. It provided slightly better acceleration, but but 5mph from mid-range cruise and 8mph from the top end. The 4 blade was only 13.75 in diameter vs 14.25 for the 3 blade and I suspect this was a contributing factor.

Since April 2006, we have owned a Regal 2760 with twin 190hp 4.3L engines and the Bravo III. We currently have a 24P prop set which gives a top end of 43mph and cruise about 31mph at 3500RPM. I suspect we are a bit overpropped as WOT comes at the low end (4400RPM) of the suggested range. Tracking is much improved over or Chaparral (although we must also credit length and twin engines). Shifting is quieter than the Alpha and we ve had no drive related problems. We did have the starboard impeller fail and thanks to the engine mounted pump, we did not have to trailer the boat out of its lift for servicing.

We re hoping to drive a 23 Sea Ray deck boat next month with Bravo III so we can add a single-engine perspective of handling differences with the Alpha. We have also posted a detailed overview of the Bravo III. Share your outdrive experiences by commenting on this article below!

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6 thoughts on “ Mercruiser Alpha I (1) vs. the Bravo III (3) Choosing the Right Outdrive ”

I own a 2006 200 Select Sea Ray with the 260hp Mercruiser 5.0L MPI Bravo III. My friend owns the exact same boat with a Alpha 1. Both have wakeboard towers and literally the only difference is he has the wakeboard graphics and I have the boot stripe. I ve driven both both extensively. What are my conclusions?

1) When wakeboarding at 20mph I am running 2475 RPM and he is running 2950. This is a large savings in fuel. Also his boat also takes considerably more time to plane where as mine doesn t really care if I have 2 people or 6 people. His boat is extremly sluggish with 6 people

2) Top Speed: My boat is faster no matter what the load is. I think the biggest reason is that the Bravo 3 allows me to get almost all of he hull out of the water whereas his boat plows even at maximun trim. 3) I have perfect pass and when I have 6 people in the boat at 3500 rmp my speed is about .2 mph different than having 2 people.

4) Would I pay the $1800 again? Most definitely. To me my 3551# Sea Ray is in a different performance league with the Bravo III from top speed, accelaration and ability to keep similiar speed at each RPM with a light or full load aboard. I personally wouldn t own another boat with a single IO unless it was a Bravo III going forward.

I wish I could have found something on the internet with this comparison when I purchase my boat. Lucky for me I wanted a Pewter color 200 Select and the only one I could find was in another state and my only choice was a Bravo III as I purchased it in late July 2006. Prior to my purchase I thought I was wasting money because my boat was only 20ft (but heavy) and was I wrong! Please feel free to email me post my email because few people have two identcal boat to compare the Alpha I to the Bravo III and I d be happy to answer anyone else s questions on whether they should buy it.

Many thanks on the Bravo III comments. I am considering a Sea Ray Sun Sport. This is a 29.5 ft boat with twin Merc s and it appears that the Bravo III is the right choice.

Want to convert my inboard( staight shaft) to ajack shaft with a Bravo III.

Rinker 186 Captiva
Rinker 186 Captiva
Rinker 186 Captiva

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