Volvo vs. MaxProp

I’ve waited over a year before posting this blog.  I wanted to be certain of my conclusions and test, verify and test again.  Which props are the best -- the 3-blade Volvo or the 4-blade MaxProps??

Before I provide the answer, here is some background on the testing I’ve performed.

I have both props aboard Field Trip.  I used the Volvo props for about a year, the MaxProps for about a year and I had one MaxProp and one Volvo on each shaft for six months.  I know this is overkill, but I wanted to make sure I had a very good feel for the best answer to this question – and using them in different situations has given me a definitive answer for our sailing needs.

MaxProp

Volvo with MaxProp in background

Our answer - we elected to stay with the Volvo props.  Below are several charts outlining the data we’ve gathered.  I’ve provided an explanation of each chart with more information behind the data.

The speed tests are not subjective.  We had a Volvo prop on the starboard shaft and a MaxProp on the port shaft.  The conditions were nearly identical - same boat, same wind, same current, same everything.  I measured the RPMs of each shaft independently of the analog gauges to assure they were turning the same RPMs.  The measurements were taken within five minutes of each other, and we used the ‘Average SOG’ function of the Furuno instruments for 3, 3-minute averages on each prop.  We had some current, mostly flat water with 5-8kts of wind forward of the beam.  The most important data point is the % difference of speed.  Actual SOG (speed over ground) is a function of current, wind direction and speed, sea state, clean bottom, clean props and boat weight (full fuel and water vs. empty), etc. 

Speed Comparison in Knots

Finally, I created this comparison chart to help make our decision.   Here’s the bottom line.  If you plan on staying in a general location such as the Caribbean, Mediterranean, Bahamas, or similar, I would have the MaxProps on my boat.  The driving factor is the MaxProps are significantly better in reverse, an important factor to consider when maneuvering around tight marinas, fuel docks, etc.  In addition we found that we did not motor a lot in the Caribbean or Bahamas.  We picked our weather window and could sail the majority of the time.

For long distances, crossing oceans, and circumnavigating I would (and did) opt for Volvo.  The driving factors are the efficiency of the engines, lower consumption of fuel per nautical mile and ease of maintenance (no zincs), no grease.  When making long passages, we have found periods where we needed to motor 24-48 hours, and the Volvo props make this a no brainer.

For coastal navigation, it is better to have the strong reverse and maneuverability of the MaxProps.  The difference between the two props is significant.  In over 10kts I would be very cautious about maneuvering Field Trip in a tight Marina with the Volvo props.   It is easy with the MaxProps.  I was pinned along a dock with the Volvo props and wouldn’t have been with MaxProps.  I never regretted the MaxProps as we toured the east coast of the US.  We were in and out of tight spaces all the time, and having the precision of boat movement with strong reverse was excellent.

An average of 18% more distance per liter/gallon burned is important.  We had our fuel capacity (tanks) switched at the factory so we carry more fuel than water.  A decision we’ve never regretted, especially as we go farther and farther away from easy access to diesel.  You can always make water, but you can’t make fuel.

The last question to answer is – “Can’t you adjust the MaxProps to increase the pitch, and therefore the efficiency?”  Yes, you can.  

I tested this scenario for three months.  I over-propped by one setting the MaxProp, while I had the Volvo on the starboard side.  I was able to close the performance gap to 5% (still in favor of Volvo).  The issue is over-propping your engine.  For the Volvo engines, I was only able to achieve 2,800 RPMs when over-propped vs. the standard 3,200 RPMs.  While it may not seem like a lot, this can be hard on the engine and is not advisable. 

Are my MaxProps for sale?  No.  I plan on keeping them when we eventually go from passage making to coastal sailing sometime in the future.  So for now we will enjoy the ability to easily (1 hour, in the water) switch between the two as our sailing needs require.