Sold my 50, buying the Etec90

[Starscream]

Here is my experience with noise and smell so far:

According to the dealer, the motor is programmed to use an immense amount of extra oil for the first two hours, then a significant amount of extra oil for the next 23 hours, then go to a conservative "normal" oil burn. He warned me to expect some extra burnt oil smell for the first 25 hours.

I may have just passed the two hour mark, but what I experienced was not bad at all. The first engine start was accompanied by a puff of oil smoke, but only that start: every other one since then has been normal. I have noticed a bit of two-stroke smell when idling or with a following wind but it is actually much less than I expected, and in my subjective opinion it is no worse than I had with the Honda. Actually if I had to pass judgement I think the Etec in extra-oil mode smells less than the 4-stroke Honda.

With regards to noise: from previous posts I expected the Etec to be very quiet in comparison with the BF50...but it isn't. It's about the same at idle maybe just marginally quieter, and at full throttle it is quieter but only barely so. The real advantage seems to be when cruising at somewhat less than full throttle: I can go as fast as I did with the BF50 at much fewer revs: when I was running at 16mph with ballast full it was much easiER to have a conversation in the cockpit but by no means quiet. With the BF50 16MPH required a screaming 5500 RPM and empty ballast.

I have to say I am a bit disappointed with the top-end speed though. I love it with the ballast full: 21MPH is just fine like that, but I was really expecting 28 or 29 with empty ballast and I can just get 24 (mast up/2people/4800 rpm indicated/14x11x3 prop/bottom paint/medium load/GPS average in two directions). So far I have two votes for a 14x9 prop. I think this might be the way to go but am hoping someone will give a technical explanation as to why a 14x9 would be better than a 13x11. The reason I am thinking about the 13x11 is that the tip of the prop would be half an inch deeper in the water, and I noticed that the back of the X at speed creates a large depression in the water just behind the transom, and a lot more of the motor is dry than I expected. The depression was so deep that I was worried about cooling water intake.

[Tomfoolery]

I have to say I am a bit disappointed with the top-end speed though. I love it with the ballast full: 21MPH is just fine like that, but I was really expecting 28 or 29 with empty ballast and I can just get 24 (mast up/2people/4800 rpm indicated/14x11x3 prop/bottom paint/medium load/GPS average in two directions). So far I have two votes for a 14x9 prop. I think this might be the way to go but am hoping someone will give a technical explanation as to why a 14x9 would be better than a 13x11. The reason I am thinking about the 13x11 is that the tip of the prop would be half an inch deeper in the water, and I noticed that the back of the X at speed creates a large depression in the water just behind the transom, and a lot more of the motor is dry than I expected. The depression was so deep that I was worried about cooling water intake.

I retract my recommendation (for what it was worth anyway ) for the 9" pitch. The theoretical speed at zero slip and 5500 rpm engine speed with a 2.00:1 lower unit reduction ratio and a 9" pitch prop is only 23.4 mph. Zero slip is unattainable unless surfing down a giant wave, but the prop wouldn't be pushing at all in that case. Even 11" pitch has a theoretical zero-slip speed of only 28.6 mph. It's like sailing dead down wind - you can never go as fast as the wind as long as the wind is pushing the boat.

So it sounds like you've already crossed the line where pitch has to increase to get the speed and diameter has to be decreased to keep the engine within design speed. An 11" pitch and 25% slip gives about 21.5 mph. 20% slip is 22.9 mph. To get to 28 mph, assuming it's even possible with that engine, would require around 14" of pitch, with 25% slip. I believe slip will go up as pitch goes up, as a general rule, and diameter will have to go down to allow the engine to run at full speed. The danger there, of course, is too great of an angle of attack of the blades for the boat speed, resulting in very high slip and possibly blade stall and/or cavitation.

So I have no recommendation at this point, but wanted to give you a little logic behind prop sizing to think about. It also adds credence to the results of anyone with a much higher pitch prop than what you have now. Higher pitch for higher speed, but at the loss of diameter, which means less water being pushed against (in a manner of speaking) so greater slip. There will be a best balance between the two for a given hp, prop speed, and boat hull/speed, but I don't know where that is. That's where first-hand experience with the same model boat and engine really is valuable.

[mastreb]

The recommendation to go to 14x9 is the simplest calculation to get to the correct WOT RPMs, which is where you need to be for maximum performance.

What it doesn't do is define performance: Do you want speed, or do you want thrust? The difference is in the pushing power behind the speed, similar to torque in a car motor.

Reducing pitch increases RPM without increasing slip by reducing the power required to turn the shaft because the boat is not being moved as far per rotation, which naturally requires less energy. It creates more cavitation (and therefore drag)at the ends of the rudder blades however because a larger diameter means higher speed at the tip. Cavitation is drag and power loss that creates no forward motion, and you want to avoid it at all costs. 4-blade props cavitate before 3 blade props, and 3 blade props cavitate before 2-blade props.

Reducing diameter increases RPM by allowing more slip. The smaller the prop diameter, the more slip will be allowed.

A large diameter prop will push the boat around with more force, giving better hole-shots and better stopping power than a small diameter, large pitch prop. The small diameter large pitch prop has weaker performance at the low end, but allows a higher overall speed to be reached --if-- the boat is capable of getting fully on a plane and is light enough to stay there.

Props are analogous to gear ratios: do you want a low gear ratio that has plenty of low end thrust but is speed limited, or do you want a high gear ratio that can maximize speed but takes a long time to get there? Thing of it as having to pick a gear on a manual transmission car and stay in it throughout your driving session. With higher gears, you have to feather the clutch until you get to speed. That's the slip you experience with a smaller diameter prop.

For maximum thrust here's what you want:

1) the largest diameter that will never cavitate at WOT

Then

2) whatever pitch it takes to get that diameter of prop to WOT.

For maximum speed, what you want is:

1) The exact pitch required to get to the speed your boat and motor could possibly achieve (based on power to weight calculations)

Then

2) whatever diameter will get that pitch to WOT.

So it's pitch first for speed, diameter first for thrust. The problem comes in when you have a diameter so small that the prop will never be able to get to it's designed speed because of a lack if power. Just because you want 28mph does not mean that your motor has the HP to get your boat to that speed, and if it can't, a small diameter prop will slip terribly and be less efficient than the lower pitch prop, which will get your boat up to whatever speed it can efficiently.

The bottom line is that being wrong about pitch gives dramatically better real world performance than being wrong about diameter, because it remains efficient when it's underperforming.

The problem is complicated enough that real world experience guided by understanding the theory is the best way to go.

I'd buy both a 14x9 and a 10 3/8s x 14 and try them both. 14x9 will dramatically outperform the 10 3/8s in all aspects except top speed, and my bet is that you'll hate the faster prop when marina docking and you've got to really rev it to stop your boat. But a prop is only $100 or so, so try both and post your results.

[darrenj]

I think the only way to get the best prop for your boat is to experiment with your boat.
Getting the right prop seems to be more art than science.

Be careful when using prop slip calculators such as this one:
http://www.mercuryracing.com/propellers ... ulator.php

According to it my prop slip is minus 5 in wake board mode

Prop pitch = 13
Gear Ration = 2.59
Engine RPM = 6300 (as measured from ECM via interface cable to garmin)
GPS Speed = 31.4 miles per hour (on a lake with no current)
Calculated slip = -5

Here is the summary of my top speeds and rpm with my 26X and DF90A and 3 blade/ 14 inch / 13 pitch prop:
Wake board configuration(no ballast, no mast): 31.4 MPH at 6300 RPM
Loaded for bear, no ballast: 23 MPH at 5300 RPM
Loaded for bear, with ballast: 20 MPH at 5100 RPM

Please keep us posted if you do some experimenting as your findings could help many of us here.

[beene]

FWIW

I have the Merc 75 4s with a 1600cc block

I have ran a
14x11
14x13
13.75x15

Best results were the 13.75x15

Best hole shot was 14x11

Best tops speed and cruise is the 13.75x15

G

[Starscream]

Here is the summary of my top speeds and rpm with my 26X and DF90A and 3 blade/ 14 inch / 13 pitch prop:
Wake board configuration(no ballast, no mast): 31.4 MPH at 6300 RPM
Loaded for bear, no ballast: 23 MPH at 5300 RPM
Loaded for bear, with ballast: 20 MPH at 5100 RPM

Please keep us posted if you do some experimenting as your findings could help many of us here.

Well that makes me feel a bit better, thanks for the info. I was hoping for a bit better without ballast where I have only hit 24MPH with a medium load. I get 21mph loaded for bear with ballast at 4800 RPM, so there's no difference there.

I am headed out to the thousand islands region this afternoon, I have a Piranha 14x11x3 composite prop on...will post any difference I see compared to the same prop in aluminum.

If anyone is around Grenadier Island Center this weekend just come on by...should be on the beach.

[darrenj]

Beene, do you remember the RPMs with each of the props?

I am going to get a second prop as a spare and would like to try a different prop as an experiment to see if it is either faster or better fuel economy.

I am considering 14x11 or 13.5x15.

My guess is the 14x11 will allow me to get to 5850 rpm heavily loaded no ballast. Current 14x13 runs at 5450. I don't think I will gain any speed though. Also I think it will increase the RPM necessary to go 6 or 7 mph (normal cruising speed to maximize range) which will increase noise.

I have no idea what the 13.5x15 will do. I am leaning towards trying this anyway.

[beene]

My 75 has a low rpm spec as it is the same block for the 90 and 115

Much more torque at lower rpm

All I can recall of my rpm with those different props was, all were within spec, the higher the pitch, the lower the rpm, the more speed per rpm, the less fuel burn at speed, hole shot performance went down

Lower pitch, all reversed

With my 13.75x15 I get 3700rpm at 17kts nil ballast

G

[raycarlson]

dump the plastic Pirhana prop, their junk for testing. A lot of confusing info here for someone who isn't sure what their doing. Your first priority is to get your motor to attain max rpm at wot. i.e. spec is 5500-6500, when lite empty you want motor to rev to 6500rpm, when loaded heavy the same prop will give you the 5500rpm end of the spectrum. You really need to get to this rpm level FIRST before you start playing with other scenario's. And don't worry about cavitation, that has nothing to do with prop selection and just confuses the issue. Cavitation has to do with the elevation of your lower unit in relation to bottom of hull, if to shallow in tight turns your prop will start sucking air into your blades causing it to overrev in which case you would lower your motor one bolthole at a time until cavitation stops. However if your motor is adjusted to its lowest setting from the start that cane cut 2-4 mph off your top speed if it doesn't actually need to be that low.

[Starscream]

Well it's official: I don't understand propellers.

I changed my aluminum 14x11x3 prop for a composite 14x11x3 prop and the RPM went up by 200 RPM to 5,000 and top speed down by 3mph under all conditions. Say what? Well I had about 100 lbs more water on board than last time but other than that conditions were pretty similar. I don't get it, obviously.

The only advantage I can see of the composite prop is very slight weight and space savings, and possibly the ability to better survive a strike. Other than that the performance seems lousy. I'll disassemble it and keep it on board as a spare so it's not a total waste.

[SENCMac26x]

The composite is probbaly flexing and losing effeciency

[csm]

I hesitate to post as the info I offer with regards to weight is not 100% accurate , but here we go; I installed a 90 pontoon series with a13-3/4" x 13 three blade stainless prop and achieved appx 5300 rpm. First tried a 15 pitch but just barely reached 5000, so dealer recommended the 13 pitch. Just prior to installing the 90 I weighed the boat and trailer with a 70 installed. The scale read 4440# on the axles and 860# on the tounge. The problem is that I was in a hurry and didn't unhitch from the truck; I tried to "eyeball" when the trailer hitch was "unloaded" but based on the 860# tounge weight, I'm thinking I was probably lifting the truck a bit. Considering I added an axle, beefed up and galvanized the frame, and have two spares near the tounge, I'll guess the empty trailer is 200-250# heavier than the factory x trailer. Hopefully someone will chime in with the factory trailer weight, so an accurate estimate of the loaded boat weight can be determined. The total crew weight was about 450#. I'd also like to give a huge shoutout to Mike Galles of Galles marine in Wisconsin Rapids; not only did he beat all my local dealers by better than$1500, but the install was VERY nice and he spent half a day in 40 deg 30 mph driven rain working to get the boat properly propped. Oh, and I have bottom paint and

no wegdes.

[csm]

Forgot to mention, I now HAVE REVERSE. The difference between the 15 and 13 is unreal

[DaveB]

I wonder at pounding in a 2 ft. chop at 20mph or greater will do to the centerboard lift line and piviot bolt.
That centerboard lift line/ bolt would have to take a much more stress than cruising at hull speed.
I think Bill with the 140hp will chim on this.
Dave

Here is my experience with noise and smell so far:

According to the dealer, the motor is programmed to use an immense amount of extra oil for the first two hours, then a significant amount of extra oil for the next 23 hours, then go to a conservative "normal" oil burn. He warned me to expect some extra burnt oil smell for the first 25 hours.

I may have just passed the two hour mark, but what I experienced was not bad at all. The first engine start was accompanied by a puff of oil smoke, but only that start: every other one since then has been normal. I have noticed a bit of two-stroke smell when idling or with a following wind but it is actually much less than I expected, and in my subjective opinion it is no worse than I had with the Honda. Actually if I had to pass judgement I think the Etec in extra-oil mode smells less than the 4-stroke Honda.

With regards to noise: from previous posts I expected the Etec to be very quiet in comparison with the BF50...but it isn't. It's about the same at idle maybe just marginally quieter, and at full throttle it is quieter but only barely so. The real advantage seems to be when cruising at somewhat less than full throttle: I can go as fast as I did with the BF50 at much fewer revs: when I was running at 16mph with ballast full it was much easiER to have a conversation in the cockpit but by no means quiet. With the BF50 16MPH required a screaming 5500 RPM and empty ballast.

I have to say I am a bit disappointed with the top-end speed though. I love it with the ballast full: 21MPH is just fine like that, but I was really expecting 28 or 29 with empty ballast and I can just get 24 (mast up/2people/4800 rpm indicated/14x11x3 prop/bottom paint/medium load/GPS average in two directions). So far I have two votes for a 14x9 prop. I think this might be the way to go but am hoping someone will give a technical explanation as to why a 14x9 would be better than a 13x11. The reason I am thinking about the 13x11 is that the tip of the prop would be half an inch deeper in the water, and I noticed that the back of the X at speed creates a large depression in the water just behind the transom, and a lot more of the motor is dry than I expected. The depression was so deep that I was worried about cooling water intake.

[Dimitri-2000X-Tampa]

IIRC, the stock 26X trailer was around 700#. My aluminum double axle is much bigger and over 1100#.