For many years I have been using a Mercury MIRAGEplus 17-pitch propeller as the primary propeller on my boat, a 1990 REVENGE 22 Walk-Through Whaler Drive with a 2010 Evinrude E-TEC 225-HP engine. The Mercury propeller is one of many Mercury propellers that use a field-replaceable hub kit to couple the propeller to the propeller shaft. This method allows for two advantages:
- for the boater, a propeller strike should tend to result only in damage to the Delrin plastic insert in the hub kit, which will yield under high stress, presumably before anything made of steel (such as the propeller, the propeller shaft, and all the gears in the engine's gear case) might yield. In addition, the boater can replace the damaged Delrin plastic insert in the field, perhaps allowing him to quickly resume operation of the boat; and
- for Mercury, the field replaceable hub kit permits their propellers to be adapted for use on other non-Mercury outboard engines, giving their propellers a wider market to be sold into.
Mercury branded their Delrin plastic hub kits as FLO-TORQ hub kits. In my case, I was able to buy a FLO-TORQ-II hub kit that would adapt the Mercury MIRAGEplus for use on the Evinrude 225-HP engine in about 2009. However, around that time Mercury introduced new models of FLO-TORQ hub kits that provided additional features. These newer hub kits, branded as FLO-TORQ III and IV, used a combination of Delrin plastic components connected by metal rods, and the rods were designed to deflect under torsion, producing a much quieter shifting from neutral to forward gear or neutral to reverse gear. They eliminated the CLUNK, which was a somewhat notorious feature of a Mercury outboard engine gear case shifting with a FLO-TORQ-II hub kit propeller with a heavy steel propeller.
More recently, even more advanced hub kits were introduced by Mercury under the FLO-TORQ SSR branding. The SSR acronym represents Soft Shift Rubber. In a news release, Mercury described them very positively:
The Flo-Torq SSR utilizes Mercury’s proven Soft-Shift Rubber technology in a quiet hub kit that provides an NVH upgrade for Flo-Torq II hub applications where the maximum reduction of noise, vibration, and harshness is desired. It also Replaces Flo-Torq III and IV to simplify Mercury’s hub kit offering while providing an increase in performance at a reduced cost without sacrificing durability.
I was curious to know if there was any way to use the FLO-TORQ-III or IV (or even newer model SSR) hub kits with my Evinrude engine, so I sought some expert advice.
KEN REEVES from PROPGODS
There are many posts and threads regarding propellers in which advice is offered by a participant in the thread to defer to Ken Reeves from PropGods. His reputation is excellent. Having never actually consulted with Ken myself, I decided to give him a call to ask about using these newer Mercury FLO-TORQ III and IV hub kits with my Evinrude engine.
Ken advised that he did not think the new FLO-TORQ hubs would work with Evinrude engines, but instead suggested I try the SOLAS hub kit, which is something of a hybrid between the old rubber pressed-in hub and the new Delrin plastic field-replaceable hubs. SOLAS calls these hubs their RBX models.
A SOLAS RBX hub has a rubber coupling that fits into the recess in the propeller and has a metal (aluminum or bronze) coupling to the engine propeller shaft molded into that rubber insert. In this way you get the softer rubber coupling and the ability to replace the coupling in the field--the best of both worlds. I chose the aluminum insert for this test. The bronze insert model is about $30 more, and finding one in stock was difficult. Bronze might be the choice for saltwater use, but the anodized aluminum should be good for freshwater.
Solas does not make any outboard engines, so their aim was to permit their RUBEX propellers to be used on many brands of outboard engines. Thus they make RBX hub kits for just about every outboard brand, model, and horsepower.
The inference I made from Ken's comment was that the dimensions of the recess in the RUBEX propeller into which the RBX field-replaceable insert is positioned must be the same as on the Mercury propellers for the FLO-TORQ plastic insert. So in this case, I could use a SOLAS RBX hub to mount a Mercury propeller designed for a FLO-TORQ hub onto my Evinrude engine by using the SOLAR RBX kit for an Evinrude. Ken gave me the model designator for this application: RBX-100.
Ken further endorsed the combination by mentioning that he runs a MIRAGEplus propeller on his boat with a SOLAS RBX hub. That was a very strong endorsement for me, both for the propeller and for the RBX hub kit. I was planning to order a SOLAS RBX-100 hub kit from Ken, but he did not have any in stock.
AMAZON SELLER
To facilitate getting a SOLAS RBX 100 hub kit, I looked on Amazon.com, where I found one advertised at a reasonable price, about $41 with tax and shipping. I received an RBX-100 hub kit about six days later. I got around to installing it a few days after that.
The first thing I noticed was that the sender on the package was listed as a fellow with the last name of Escobar, with a company name of "Import Export International" and an address in Hollywood, Florida. When I picked this up at my PO Box at the little post office in the village, I got a laugh: I was thinking the postmaster was probably wondering what the heck I had ordered from a guy named Escobar in Florida.
When I saw the product advertised on Amazon, my impression was the seller was doing business as "SOLAS", but on further review, I discovered that the listing only contained the notice "Brand: SOLAS" and reviewing my order, I found the seller was doing business on Amazon as "LandMarine Toys." But I digress. Let me continue with the narrative.
INSTALLATION
The rubber coupling fit perfectly into the recess on the Mercury propeller, and the metal components mated perfectly with the propeller shaft on my Evinrude engine.
The RBX-100 hub kit was marked as SOLAS part number 170253100, and it included a new thrust washer, the rubber-and-aluminum insert, and an appropriately sized metal spacer to match the propeller shaft on the particular engine model for which the hub kit is intended, my Evinrude 15-spline 4.25-inch gear case. For the RBX-100 hub kit, the components are:
Thrust washer: #81013250
RBX hub: #81023250
Aft spacer: #81053250
The hub kit does not include the propeller nut, the propeller keeper washer, or a cotter pin. The Evinrude OEM components are used for those three elements of the propeller installation.
The included instruction literature was dated "FEB2012." The engines suitable for use with the RBX-100 are:
Evinrude or Johnson 90 to 140-HP large gear case, 1991 to present, 15 tooth spline
Evinrude or Johnson 150 to 300-HP, 1991 to present, 15-tooth spline
OMC or Cobra sterndrive Models 800/Cobra/Cobra King, 1991 to 1994, 15 tooth spline
INSTALLATION CONTINUED
Installation of the RBX-100 hub kit into the Mercury MIRAGEplus propeller was simple. The fit was perfect. I applied some water-alcohol mix to the rubber to help reduce friction on the initial insertion. A 2x4 wood block and a hammer were used to tamp down the RBX hub to be flush with the metal of the propeller.
The thrust washer was already in a small plastic sealed bag and had a coating of light grease. It fit the taper on the Evinrude propeller shaft very nicely.
The propeller with rubber hub in place was then fitted onto the propeller shaft.
The aft spacer is then added, and next the OEM propeller nut is threaded onto the propeller shaft. Initially the aft spacer appears to be too long, but once the propeller nut is tightened, the rubber insert will be pressed more deeply into the recess, and the fit then becomes correct.
The propeller nut was then tightened to 55-foot-pounds using a torque wrench. That figure is from Evinrude not SOLAS.
Finally the OEM keeper washer was positioned onto the nut and retained with a suitable cotter pin.
The fit between the propeller hub and the gear case on the outboard was excellent.
In some correspondence with SOLAS regarding the use of the RBX rubber insert hub kits with other brands of propellers, they noted that their intention in making the RBX hub kits was for use with RUBEX propellers (their brand), and thus when used with non-RUBEX propellers the hub kits will not be guaranteed or warranted.
Unfortunately, I cannot end the story with a report on how well the RBX worked to quiet the shift noise. While the propeller is on the engine, and all is ready for testing, the weather has gone foul. There are 20-MPH easterlies, waves building to two-feet or more, and rain forecast all day. Testing will have to wait for a dryer, calmer, and less windy day. And since I started writing this article, wave height as increased to three-footers with occasionally higher.
[Updated to mention the Mercury FLO-TORQ SSR products.]