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Author Topic:   Guardian 17, E-TEC 90 Propeller
gchilcott posted 12-17-2014 10:58 AM ET (US)   Profile for gchilcott   Send Email to gchilcott  
I'm brand new to Whalers, and power boats for that matter. I recently bought and refurbished a 1986 Guardian 17 (Montauk hull shape). The configuration is console and leaning post about 2-feet forward of typical Montauk position, and a rack for six scuba tanks just forward of the transom (six tanks are about 200-lbs). I think the dive configuration was original from Boston Whaler. The engine is an E-TEC 90. The loaded weight will vary quite a bit depending upon divers and gear, but I'd like to optimize the boat for a load toward the high end of capacity. Windage is probably about the same as a typical Montauk.

Since my setup is a little different than a Montauk, I could use help with an educated guess on which propeller to start with. I'm thinking of a Stiletto 13.25 x 15, but wonder if the extra weight will make the 13.25 x 13 a better choice. Input from the group would be welcome.

The boat will rarely get used in glass-smooth water--mostly in ocean conditions around Monterey, California. Eventually having two propellers for different conditions and loads would be okay.

Thanks in advance, Gavin

jimh posted 12-17-2014 01:51 PM ET (US)     Profile for jimh  Send Email to jimh     
What is the gear ratio on your E-TEC 90?

If the gear ratio is 2:1, and you hit optimum RPM of 5200, and the propeller SLIP is 10 (percent), then boat speed as a function of pitch will be

MPH = 28.9

PITCH = 15
MPH = 33.2

I don't have a guess which propeller or speed is more likely to be obtained. Do you have any trial run data to share?


gchilcott posted 12-17-2014 02:15 PM ET (US)     Profile for gchilcott  Send Email to gchilcott     
The only days that I've had the boat out have been too rough and windy to obtain representative speed/RPM data. Also, my current aluminum prop is not in great condition, so I assume there are differences there.

I will confirm the gear ratio. I didn't realize the E-TEC 90 was supplied with different ratios.

I had assumed (perhaps mistakenly) that it would be reasonable to start with the best guess for my boat based on others' experience with fully-loaded Montauks equipped with the same engine.

I'll get more information and report back.

Thanks, Gavin

jimh posted 12-17-2014 05:03 PM ET (US)     Profile for jimh  Send Email to jimh     
There are many prior reports of performance of a Boston Whaler MONTAUK with an E-TEC 90-HP engine contained in the archives. I don't have encyclopedic knowledge of all those reports, but, if you search for them and read them, I suspect you could get quite a bit of information on propeller selections and resulting performance. Be aware that performance is influenced by many factors, not just propeller pitch. Total boat weight is certainly a major influence, but other environmental factors affect performance and are often overlooked. The temperature of the air and water: colder is better. The salinity of the water: saltier is better. The air pressure and humidity: high pressure and low humidity are better. The aggregate of environmental influences can produce quite a divergence in performance. Don't compare performance reported on a hot, humid low-pressure day on very warm freshwater with performance reported from a very cold, dry, high-pressure day in Arctic saltwater.

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