I repowered my last year with an E-tek 60 :and has a 14 X 9 3 blade designed for a pontoon boat. It is only getting 4,800 rpms at 8,000'. I have been internet searching for a 14 X 7 but none available. The E-tek is supposed to be rated at 5,500/6/000. Jim's Prop Shop said there is a standard run-a-bout 14 X 9 with smaller blades which might get another 3-400 rpms. If this prop gets me 400 and IF he can re-pitch it to 7 it may get me there.
But before I do the prop dance, I thought someone on this 4M might have an answer.
I am also not sure the engine's cavitation plate is at the correct height (too low). The looks like it has a slight rocker and the mounting bracket is sitting on the transom.
1) Anyone have experience with the correct prop---the E-tek and Big Foots use the same prop?
2) Suggestions from E-tek users about cavitation plate height?
My 26X is a 2002, the engine is a 2003 Big Foot 50HP EFI 4-stroke. I have two props, one for high altitude and the other for sea level. I have sailed at three different elevations. When I am running at sea leave, I use a 13P and when I am running at home ≈ 5000 feet, I use a 10P. This change brings my R.P.M into spec and increases boat speed. At 8000 feet (Steamboat Lake) the 13P runs at 3500RPM/13 mph and the 10P is 4500RPM/19 mph. The 10 is still under spec and I could probably go with a 9, but I hardly run at 8000 feet. (See spec table at end of this post)
At sea level I am able to reach 18 to 20 mph. I did hit 22 mph with the mast down with just me aboard. At 5958’ and 8000’ with the High altitude prop I can still hit 18 mph, even at 8000’. That’s with two adults and gear for the weekend. I did a test at 8000’ with the sea level prop and could only get 13 mph. So even with a 50 and the big foot the wrong prop won’t cut it.
You want a prop that will allow the engine to run in the top part of its recommended full throttle range, W.O.T. Mercury specs for the 50 HP Bigfoot is 5500-6000 W.O.T. Each engine manufacture and engine will have a different spec. It would be wise to check your owners manual if you have one or contact a dealer and give them the serial number. They will be able to tell you for sure.
Perfect prop size is a bit allusive because it can change depending on conditions. Sea conditions, boat weight, engine condition and the condition of the prop will have an effect on performance. Weather also plays a role in Horsepower. The air density; air temp, barometric pressure and humidity can rob up to 14% of the HP. The hotter and more humid the less power you will have at the prop, hence changing props between Colorado, Washington or going to Florida. So a dry spring day will give more power over a hot humid August day. You also lose power as you go up in altitude. Simply put; EFI only adjust the fuel mix for a given amount of oxygen, you will still have reduced power. If I remember correctly, you lose about 5% of your HP per 1000’ elevation gain. So with an outboard prop you must change the pitch to compensate for the power loss from going up in elevation. The pitch is the distance in inches that a propeller would move in one revolution. A change in pitch will adjust the RPM between 150-350 RPM. In other words, to maintain higher speed with-in the designed RPM range you change the pitch to adjust for power loss due to elevation increase. If the RPM is to low you would change to a smaller pitch. Changing props will give a 150-350 RPM difference between pitches sizes. Perfect prop size is a bit allusive because it can change depending on conditions. Sea conditions, boat weight, engine condition and the condition of the prop will have an effect on performance. Weather also plays a role in Horsepower. The air density; air temp, barometric pressure and humidity can rob up to 14% of the HP. The hotter and more humid the less power you will have at the prop, hence changing props between Colorado, Washington or going to Florida. A dry spring day will give more power over a hot humid August day. Humidity as well as elevation reduces the density of the air. Plus the prop size is theoretical; a 13 will not travel 13” in distance, it’s close to 10”.
FYI: Outboard engine companies use the I.S.O. (International Standards Organizations) for engine testing to obtain HP. The test values are produced at sea level, 30% relative humidity, air temp of 77F and a barometric pressure of 29.1
I scanned this table from my service manual
SPECIFICATIONS
-
Mercury/Mariner 60 EFI (4-Stroke) 2.3:1 Bigfoot
Special soft rubber hub propellers designed to reduce clutch rattle
Wide Open Throttle RPM: 5500-6000
Recommended Transom Heights: 20", 25"
Right Hand Rotation Standard
Gear Reduction: 2.31:1
IMPORTANT: These specially designed rubber hub propellers are rated for 60 horsepower MAXIMUM.
13-3/4 D x 15 P, 2000-2500 boat wgt., 16-18 boat length, speed range 25-32
14 D x 13 P, 2300-3200 boat wgt., 17-20 boat length, speed range 23-27
14 D x 11 P, 3000-4300 boat wgt., pontoon, speed range 17-21
14 D x 10 P, 3500 + boat wgt., pontoon/work, speed range 14-19
14 D x 9 P, 5500+ boat wgt., House boat/work, speed range 1-16
bscott a prop repair shop can change the pitch of most props by two inches, Might be the route you can go.
also check with evinrude they might have a way to adjust the engine for hi alt. before you change props. In fact Im pretty sure they can.
Mike
Thanks Graham,
Lots of work went into your reply, much appreciated. The power loss is 3% per 1,000' so my 60hp loses 25% at 8,000' = 45hp.
Mike, I'll be getting a used standard blade 14 x 9, 3 blade from my local (and only) prop shop and have him change the pitch to 8 with a possible redo to 7 if necessary as there are no lower pitch props available for either the E-tek or BF. I also checked with the only authorized E-tek dealer in metro Denver and there is no high altitude adjustments.
The dealer may have installed the engine to the wrong plate, 2.5" below the boat bottom
I just wanted to tell you my experience - - -I don't know prop pitches from carnival pitches - - -but I bought an M with a 60 Etec and factory prop and got full RPM's at WOT at sea level (MDR). Then I took the boat up to Big Bear Lake for a day - - no prop changes - - - 7,400 feet - - - and got the same RPM's at WOT and same speed
last year with an E-tek 60 :and has a 14 X 9 3 blade designed for a pontoon boat. It is only getting 4,800 rpms at 8,000'. I have been internet searching for a 14 X 7 but none available. The E-tek is supposed to be rated at 5,500/6/000. Jim's Prop Shop said there is a standard run-a-bout 14 X 9 with smaller blades which might get another 3-400 rpms. If this prop gets me 400 and IF he can re-pitch it to 7 it may get me there.
A WONDER PROP FOR SURE 