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Not Your Father’s Outdrives |
The Island Pilot 395 comes standard with a pair of 260 HP Volvo Penta Dual Prop Stern drives. What’s this mean to you, the owner?
Two motors rather than one - Many of the fast trawlers in this size and class are fitted with a single diesel. The IP395 has a pair of marine diesels adding up to 520 HP. By having a pair of motors, you have the redundancy and handling of a twin screw boat, at no additional expense. (Many make the argument that most diesels failures, about 90%, are due to fuel problems, causing both motors to fail. That may be true, but that leaves 10% of failures caused by something else than fuel. When one of these failures occurs, at least you’ll have one motor still running. Also, even with fuel caused stoppages, both motors do not tend to fail simultaneously. That extra time on one motor may mean the difference between saving your boat or not!)
12 cylinders (total) - The Volvo Penta D6 are pure bred Marine engines - not converted industrial or truck motors. As a result, they are meant for the environment and use they are put to in a fast trawler that is going to see a lot of cruising. They are smooth, quiet, don’t smell or smoke (the exhaust is through the drive unit under water).
4 props - Each motor as a pair of counter rotating propellers. These are an extremely efficient way to get power from the motor to the water. Likewise, the stern drives have less drag than typical inboard installations, leading to even more efficiency, both at slower displacement speeds and at planing speeds. More efficiency means less fuel used per hour.
Latest Stern Drive Technology - There is much negative feeling about outdrives, some warranted, some not. With this latest generation of Duo Prop Stern Drives, Volvo Penta has created a product that is meant to survive in the ocean environment. They use the latest in alloys to avoid corrosion while adding oversized zincs (check these monthly). These stern drives should be no more work to maintain than your standard shaft, propeller, rudder, bearings, stuffing boxes, tiller arms, etc. In fact, most times when you hit something with the drive, it will kick up, avoiding all damage - no bent shafts, no bent props... And with preventative maintenance they will last the life of the motor and are easy to repair or replace. |
How does a 20% increase in performance sound? |
There is a good reason why many professionals use Volvo Penta stern drives - a 20% increase in performance. This translates into getting to where you’re going at a cruising speed of 20% more than your buddy who has a similar-sized craft with the same horsepower or using 20% less fuel at the same speeds! In an era of increasing fuel prices, this is a real benefit. (NOTE: Volvo Penta’s new forward facing IPS drive boasts an identical 20% increase in efficiency - most of the features are similar between this new drive and their stern drive - any added efficiency comes from the “tractor” propellers pulling the boat in clean water. You can read more about both systems at www.volvopenta.com)
Were does this performance boost come from?
Counter-rotating dual propellers. The after propeller captures much of the lost energy spun off by a single prop and converts it to added thrust.
Less drag. The lower unit of a stern drive presents much less water resistance than does all the gear associated with a traditional power train, whether it’s a single or dual. There is no additional rudder, struts, keel(s), shafts to disturb the water flow; only a sleek lower unit sized just big enough to house the gears.
Props are always running parallel to the the direction of the boat. With adjustable trim on the stern drives, you can always get them at the right angle to the boats motion through the water. Traditional drives typically have their props angled down, not the most efficient angle. |
What about maintenance? |
There is no free lunch! Yes, you do need to maintain your stern drives. But you also need to maintain a traditional drive.
The stern drives for the D6 motors are brand new, developed to handle the high torque of these new motors. They are aluminum alloys that Volvo has developed to resist corrosion. Each one has 2 big “sacrificial” zincs (much the same as your typical underwater shaft would have). The owner should keep an eye on the condition of these zincs (the reason they’re called “sacrificial” is that they take the brunt of the corrosion and gradually disappear, sacrificing themselves to the better cause). When they need replacing, it is a simple matter of removing the old one and screwing on a new one. There are an additional 2 zincs attached to the transom between the drives. Cost to replace these zincs is minimal.
Once a year, when the boat is hauled, the gear oil should be replaced and the splines on the shaft re-greased. All the rubber parts can be inspected at this time - typically, they are replaced on a 2 or 3 year cycle. Total cost, including replacing all the rubber parts, is about $500 per drive.
A well maintained drive will last a decade or more!
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Aren’t Stern Drives more Vulnerable? |
Not really! Yes, they hang down below the bottom. But with a draft of 2’8”, they most likely don’t hang as low as a traditional drive. The lower the propeller (and rudder) the more susceptible to damage by grounding. And a fixed propeller can’t get out of the way. A stern drive, on the other hand, will kick up when it hits something, most often avoiding any damage at all. Not so with a traditional drive. The stern drive avoids or minimizes damage by:
Less draft - less chance of hitting something in the first place
Kicks up - at moderate cruising speeds, a stern drive will kick up with little or no damage to the unit or propellers
And when your drive is damaged, Volvo guarantees parts in 72 hours! This means that even if the drive needs replacement, you’ll be out of the water no more than a week. The labor to replace a drive is minimal. If you’d sustained similar damage to a traditional drive, you may find yourself out of the water a month or more and a yard bill to go with it!
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Read Volvo Penta’s Press Release on the D-Series Diesels.
To read more about the Volvos, check out Bits & Pieces...
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