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Propeller Retention

When a new Piranha goes on a drive, not just the Propeller gets changes. Due to design differences, the hardware needed to attach the propeller to the drivesaft must be different. Except for the thrustwasher/ line cutter, all of the old propeller parts are replaced when a Piranha is used. This goes for 3-blade as well as 4-blade propellers. This is why Piranha supplies a 5/8″ Nylock nut and flatwasher with each Volvo replacement propeller hub it sells.

Volvo Propeller by Piranha . This propeller fits a little differently than the Volvo original. Because of this we supply a few extra components such as a propeller nut and flatwasher.

OEM Hardware used to retain the prop. The propellers use a streamlined and threaded tailcone plus a long allen bolt (on some models) to secure the propeller to the driveshaft. This system does not work on a Piranha prop, so Piranha supplies new hardware to use with its propellers.

Hardware used to retain a Piranha Prop. The Piranha parts are non thru hub exhaust design, but require some different hardware (provided by Piranha) in order to attach the propeller to the propellershaft.


…or is it Right-Hand?

Is the propeller Left-Hand rotation?

Rotation

Boat propellers travel one of 2 directions in normal forward use: clockwise (right-hand rotation) or counter-clockwise (left hand rotation). Most single installation outboards and sterndrives use right-hand rotation propellers. Only on twin applications does one commonly encounter left hand rotation propellers since the boat will be rigged so the two drives spin in opposite directions. If there is a single drive, you can bet it is probably right-hand rotation – unless the drive is a Volvo.

Left-hand, single drive Volvos are common. The boats were set up that way from the factory. Why? We don’t know the official explanation. There is nothing inherently bad about the choice as long as the boat as a whole was designed with this consideration in mind. On the practical side, this will definitely affect the availability of the propellers you have to choose from. In the Piranha line there are only 2 sizes available in left-hand rotation.

This doesn’t mean you have to use a left-hand rotation propeller though. Volvo drives can easily be changed to “standard” rotation. A simple 5-minute change in the gearcase changes the direction of rotation of the drive, no special parts required.

The downside to making this change is that the boat may or may not handle correctly after doing this. The weight distribution of the boat is usually designed with the propeller rotation in mind. If the propeller is right rotation, the driver probably sits on the starboard side, and on the port side if the propeller is left rotation. This is the most common, but not only method of dealing with the weight distribution. The result is that if the boat is correctly set up for a left rotation propeller and you switch it to right-rotation, you may suddenly find the boat pulls to the port side. Many factors are at play, so depending on the boat, you may notice nothing, but this is what to watch out for.

propeller Hub Length

It is not immediately evident when you look at a Volvo drive, but there are 2 different propeller shaft lengths in common use and this affects which propellers will fit. Volvo refers to these as “long hub” and “short hub” propellers. Even if you are replacing the propeller with an OEM Volvo prop, you must know which you require or the propeller you order may not fit.

3-Blade Piranha propellers will work on either shaft length. 4-Blade Piranha propellers will only fit drives having the 5-3/8″ length propellershaft.

Long-shaft = 4-11/16″

Short-shaft = 5-3/8″


To work correctly with a 4- blade Piranha prop, you must have a drive that can be trimmed up.

If the drive can’t be trimmed up, low rpm and speed will result from having a drive that is always positioned in the fully-down position.

Trim / Tilt and the effects on propeller Choice

4-Blade propellers are great for holeshot, mid-range response and super handling. Piranha 4-blade propellers have a high-rake design though that requires adjustable trim to to achieve optimum performance. In short, if you can\’t trim the drive up once the boat is on plane, the WOT rpm will be too low.

Volvo has produced various drives that did feature hydraulic trim systems. But not a lot. 290 drives were power trim as were a large percentage of 280 drives. 200 drives never had power trim, 250 drives didn\’t either. Some 1970s 270 models did, but they are uncommon. So, before trying a 4-blade propeller on a Volvo, make sure it is equipped with a power trim system. Otherwise, performance may be dismal.

Tilt position on an unpowered unit can be manually changed. This can improve the problem with the low WOT rpm. What this remedy giveth, it taketh away from holeshot performance. Usually this compromise is worse than the performance that could be had by running a Piranha 3-blade propeller instead.

Propeller sizing

Until 1994 Volvo single propeller sterndrives have evolved little since the 1960\’s. This is most evident in their propeller designs. If you\’ve never seen a straight pitch prop, an aluminum Volvo unit is as closed to that as you are likely to see. No progressive pitch here, just big blade areas and minimal cupping.

This is significantly different from the blade styles that Piranha manufactures. Due to the differences, some corrections in your selection process may be necessary. Using a blade style that has a significantly lower area will result in higher operating rpm. We typically recommend using the next higher available pitch size to correct for this. This usually keeps the rpm under control.

As the vessel itself becomes larger there comes a point where there is insufficient blade area available for the propeller to produce satifactory performance due to excessive cavitation. If the vessel is currently using a 16″ diameter prop, it is best to continue using the standard Volvo propeller instead of using a Piranha. For most applications that are currently using a 14″ or 15″ diameter prop, a Piranha will suit your needs well.

Standard Volvo propeller Geometry:

Distinguishing features of aluminum Volvo propellers are the rather LARGE blades areas / diameters and the non thru hub exhaust design. These propellers commonly have little or no cupping to the blades either.

Example OEM Sizes that are not a good match for Piranha:

  • 16 X 15 (L & R)
  • 16 X 17 (L & R)
  • 16 X 19 (L & R)
  • 16 X 21 (L & R)
  • 16 X 23 (L & R)

The Piranha blade geometry is based on more contemporary designs used on thru hub exhaust sterndrive and outboard motors. Blades feature greater degrees of cupping and progressive pitch design, but less total blade area. Keep these factors in mind when choosing your size.

Piranha Geometry: Sizes offered by Piranha feature smaller blade areas than the OEM Volvo units. Left-hand rotation are available, but options are limited as well. These sizes do work well, but you have to know how to pick them.

  • 15 X 13 RIGHT HAND; 1513A
  • 15 X 15 RIGHT HAND; 1515A
  • 15 X 17 (L & R); 1517A, 1517A-LH
  • 15 X 19 (L & R); 1519A, 1519A-LH