Is counter-rotating drive worth the dough

[Publicnuisance]

I will soon have the alpha drives gone through, seals, bellows and general inspection. Installing a counter-rotating drive on the port seems logical but is it worth the 2 to 3 grand extra? The most I can gather from my mechanic and local prop shop is that the handling in reverse will be better, any other pros to the swap? Quicker plane? Better fuel economy? ?????????

 

[Presentation]

From http://destinsharks.com/reviews/105

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)


The Differences

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.

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).



From http://destinsharks.com/reviews/105

 

[rabyers1]

Presentation - That certainly is a thorough description of a single prop outdrive vs a duoprop. However, I think the OP was inquiring as to opinions on the benefits of upgrading to a counter-rotating engine/drive replacement for his port-side powerplant on his dual engine vessal.

 

[Publicnuisance]

Presentation - That certainly is a thorough description of a single prop outdrive vs a duoprop. However, I think the OP was inquiring as to opinions on the benefits of upgrading to a counter-rotating engine/drive replacement for his port-side powerplant on his dual engine vessal.

You are correct sir on both of your observations. I am currious about any possible advantages of refitting the port engine with a counter-rotating lower unit.

 

[Uplate]

I was unaware you had a choice. The port side is CCW by design, at least on my boat. I had the port lower unit replaced and the repair was delayed as the mechanic forgot to order the counter rotating spec. this was from SEI and I think it was only a few hundred $$ differece for the CCW unit. Not thousands. Alpha 1's here.

 

[Presentation]

Port side only? WTF?

 

[rabyers1]

I guess WTF means "Welcome to The Forum"?

 

[Sundancer]

Here is a thread where Iprof did what you are suggesting. I think it was around $3,300 for the new drive and he likes the results. His drive was blown or damaged and he had to replace it. It was done on a late 80's 300 DA similar to our boats.

http://clubsearay.com/forum/showthread.php?t=31630&highlight=counter+rotating+alpha

 

[keokie]

Counter rotating the drives on most hulls does make an appreciable difference in performance. Not only do you eliminate steer torque, but you can increase efficiency. Depending on which side you put the counter drive on you either improve bow lift, or stern lift. Often on heavy cruisers, improving stern lift in is beneficial. Cost in an already open drive should be in the hundreds, not thousands.

FWIW using correct drive toe-in creates noticeable improvement as well, as compared to a boat that is not properly set up.

 

[Gunn]

Port side only? WTF?

I think he means a drive on the port side that rotates opposite the rotation of the starboard drive... So that together, they are counter-rotating and eliminate the issues described above.

I don't think he meant an Alpha I on the starboard and a Bravo III on the port side (which is what I think you're thinking)! :grin:

 

[Uplate]

I think he means a drive on the port side that rotates opposite the rotation of the starboard drive... So that together, they are counter-rotating and eliminate the issues described above.

I don't think he meant an Alpha I on the starboard and a Bravo III on the port side (which is what I think you're thinking)! :grin:

You are correct sir. The lower unit gearing determines the prop rotation direction of the outdrive. Engines both turn in the same direction. Not sure why (stern or bow lift as Keokie stated), but my port is CCW and starboard is CW. Both drives are Alpha 1.

 

[Publicnuisance]

Cost in an already open drive should be in the hundreds, not thousands.

The best price I have found on a new, not reman, merc lower ccr is 2000, let me know if there is a better deal out there.

 

[Presentation]

I think he means a drive on the port side that rotates opposite the rotation of the starboard drive... So that together, they are counter-rotating and eliminate the issues described above.

I don't think he meant an Alpha I on the starboard and a Bravo III on the port side (which is what I think you're thinking)! :grin:

In that case...


[youtube]http://www.youtube.com/watch?v=V3FnpaWQJO0[/youtube]

 

[SCORPIO]

Cost in an already open drive should be in the hundreds, not thousands.

The best price I have found on a new, not reman, merc lower ccr is 2000, let me know if there is a better deal out there.

Sterndrive Engineering, or SE106 is an aftermarket replacement outdrive for Merc. Alpha I gen I. They are approximately $1500 for a new counter-rotating outdirve, about $300 more than their standard rotation unit.

I've thought about doing this mod if I needed to replace an OD in the future.

I'm still a little uncelar on the procedure to switch the shift cable to work with the counter rotating unit.

 

[Publicnuisance]

I'm still a little uncelar on the procedure to switch the shift cable to work with the counter rotating unit.

My understanding is that the shift cable is relocated, reversed, on the helm controls.

 

[Nehalennia]

Sterndrive Engineering, or SE106 is an aftermarket replacement outdrive for Merc. Alpha I gen I. They are approximately $1500 for a new counter-rotating outdirve, about $300 more than their standard rotation unit.

I've thought about doing this mod if I needed to replace an OD in the future.

I'm still a little uncelar on the procedure to switch the shift cable to work with the counter rotating unit.

That's what I was going to suggest for this age of boat. It makes sense.

 

[JimFromMD]

My dad now has counter rotating drives on his 1987 270 Sundancer repowered with 4.3L crate merc engines and Alpha I drives. We hit a tree branch out in the Chesapeake Bay, and the prop spun the branch up and broke off a good chunk of the cavitation plate. While the drive case was apart for replacement, the mechanic offered up that there was a Chinease company that produced a counter rotating drive that could be done for about the same price as the standard OEM replacement. We took the opportunity to change it out. This mod required the shift cable to be adjusted as someone mentioned. Also since we needed a new prop for the counter rotating side, we went with a set of 4-blade CR props.

Counter rotating did make a significant difference, as did the 4 bladed props. They run so much smoother than the three bladed props, which were not bent or warped at all.

 

[jpn867]

I am a new owner of an 87 300 sundancer which i have not even viewed in person yet. I have been reading this forum for ideas and this was one of them. My question after looking at the SEI website is this. If i replace my port side outdrive with the counter-rotating do i need to replace the entire outdrive or will just changing the lower unit do the trick? I guess i am confused as to where the actual change in rotation takes place. I will be pulling the boat soon to replace the port side engine and I am thinking of doing this while it is out. Any suggestions would be appreciated.

 

[Vince_nj1]

I am a new owner of an 87 300 sundancer which i have not even viewed in person yet.

Are you sure that don't already have counter rotating props?My friend had 1988 300 Sundancer/ Merc 260's Alpha 1's and it had counter rotating props. I forget if his drivers were different or if one of his engines ran backwards. (Different crank)

 

[Publicnuisance]

To my knowledge SeaRay never use a counter rotating engine, I have only heard of that is some early Chris Craft models.

To change to a counter rotating drive you would change the lower unit only plus reverse the direction of your shift cable.

I decided against it based on the advice from SEI and my mechanic. The logic is that the CCR drive uses the reverse gear to propel the boat forward. The reverse gear bearing on an alpha 1 is a ball bearing rather than a cone roller bearing. Since the thrust created is more than the ball bearing is designed for merc put some thrust washer/bearings on that end of the drive. On a boat lighter than mine that may be fine but it made me nervous so I went with 2 new standard rotating drives from SEI. The guy from SEI did say that the drives would be warrantied for three years regardless of which one I bought. Not installed yet and not back on the water but the drives look good and solid.