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Author Topic:   Propeller for High Engine Mount Height

jimh posted 05-05-2008 08:38 PM ET (US)
On my Boston Whaler REVENGE 22 with Whaler Drive and a single engine, the transom configuration results in a rather high mounting height even with the engine mounted as low as possible. This illustration shows the dimensions involved with the current engine, a 25-inch shaft length mounted in the lowest position:
http://continuouswave.com/whaler/reference/images/propellerTest/ whalerDriveDimensions600x450.png

Because of this relatively high mounting height, I need a propeller which has excellent holding (i.e., does not easily ventilate or loose grip). I also need a propeller in the pitch range of 15 to 17-inches. Also, the typical speed for the boat is in the 22 to 27-MPH range; we seldom go much faster.
This spring we got an early start to our boating by visiting the Gulf of Mexico, where I was again reminded that the current propeller, an older SST 17-inch pitch, has trouble staying hooked up unless the trim out is kept to a minimum.
Please give me a suggestion or recommendation for a suitable propeller.
Tom W Clark posted 05-05-2008 08:49 PM ET (US)
14-5/8" x 15" Mercury Revolution 4 (or perhaps a 17" pitch modified to about 16" pitch)
14-5/8" x 17" Mercury Enertia
The Enertia (in limited testing on my own boat) seems to grip very well and when it does ventilate, it does so very gradually and never to the point when you need to slow down again for it to regain grip. It does not just let loose but slowly gains RPM as more air is sucked into the blades. In fact you can control the maximum RPM of the motor by trimming the Enertia WAY out and then trim it in again and reduce RPM.
I was even able to use this phenomena to achieve the maximum recommended engine speed (5500 RPM on my Revenge 25 operating on only a SINGLE motor and the 19" pitch Enertia). This is something to think about for those who own twin outboards and want single engine plane-ability for their boats.
Peter posted 05-05-2008 09:17 PM ET (US)
Based on the results from the 11 prior tests, the 15 inch Revolution 4 would be the first propeller I would try for your setup.
L H G posted 05-06-2008 02:44 PM ET (US)
Jim: Knowing your gearcase doesn't handle the Rev-4 very well, and with no Flo-Torq IV hub for OMC, I still think the 17" Vensura/Offshore prop would work well on your rig.
Your RPM will be held down to maybe 5200-5400, but that is ideal for economical long range cruising according to Mercury, and still within your RPM range.
For acceleration with the larger pitch, I would install the large vent plugs.
The only other prop I could suggest, and this might be an even better solution if you want more RPM, is a 15" or 16" (my recommendation) pitch Enertia. They are large diameter and hold extremely well. You might pick up a little top end speed besides. I have noticed that BW is beginning to use the Enertias on new models now.
Both of these props are designed for heavy hulls with lower relative HP. I think the Enertia would be your best bet.
Go for it.

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Author	Topic: Propeller for High Engine Mount Height
jimh	posted 05-05-2008 08:38 PM ET (US) On my Boston Whaler REVENGE 22 with Whaler Drive and a single engine, the transom configuration results in a rather high mounting height even with the engine mounted as low as possible. This illustration shows the dimensions involved with the current engine, a 25-inch shaft length mounted in the lowest position: http://continuouswave.com/whaler/reference/images/propellerTest/ whalerDriveDimensions600x450.png Because of this relatively high mounting height, I need a propeller which has excellent holding (i.e., does not easily ventilate or loose grip). I also need a propeller in the pitch range of 15 to 17-inches. Also, the typical speed for the boat is in the 22 to 27-MPH range; we seldom go much faster. This spring we got an early start to our boating by visiting the Gulf of Mexico, where I was again reminded that the current propeller, an older SST 17-inch pitch, has trouble staying hooked up unless the trim out is kept to a minimum. Please give me a suggestion or recommendation for a suitable propeller.
Tom W Clark	posted 05-05-2008 08:49 PM ET (US) 14-5/8" x 15" Mercury Revolution 4 (or perhaps a 17" pitch modified to about 16" pitch) 14-5/8" x 17" Mercury Enertia The Enertia (in limited testing on my own boat) seems to grip very well and when it does ventilate, it does so very gradually and never to the point when you need to slow down again for it to regain grip. It does not just let loose but slowly gains RPM as more air is sucked into the blades. In fact you can control the maximum RPM of the motor by trimming the Enertia WAY out and then trim it in again and reduce RPM. I was even able to use this phenomena to achieve the maximum recommended engine speed (5500 RPM on my Revenge 25 operating on only a SINGLE motor and the 19" pitch Enertia). This is something to think about for those who own twin outboards and want single engine plane-ability for their boats.
Peter	posted 05-05-2008 09:17 PM ET (US) Based on the results from the 11 prior tests, the 15 inch Revolution 4 would be the first propeller I would try for your setup.
L H G	posted 05-06-2008 02:44 PM ET (US) Jim: Knowing your gearcase doesn't handle the Rev-4 very well, and with no Flo-Torq IV hub for OMC, I still think the 17" Vensura/Offshore prop would work well on your rig. Your RPM will be held down to maybe 5200-5400, but that is ideal for economical long range cruising according to Mercury, and still within your RPM range. For acceleration with the larger pitch, I would install the large vent plugs. The only other prop I could suggest, and this might be an even better solution if you want more RPM, is a 15" or 16" (my recommendation) pitch Enertia. They are large diameter and hold extremely well. You might pick up a little top end speed besides. I have noticed that BW is beginning to use the Enertias on new models now. Both of these props are designed for heavy hulls with lower relative HP. I think the Enertia would be your best bet. Go for it.