115hp Etec Prop Question

[jeffb5.8]

Prop: Viper 13 7/8 x 19"

2/2016 115HP Etec

Stacer 539 Alloy Easyrider (Bowrider) (Boat & Motor weight 790kg)

Normal Load 2 Adults (200kg) 3 kids under (150Kg), full tank 90ltrs fuel, so food and drinks and light fishing gear.

My max RPM is 6,150rpm on smooth water with a light wind 

Motor trimmed out to 38 on the trim gauge, Seems to like mid to high 30's, once it gets to about 45 on the gauge I get some Porpoise(ing)

Top Speed is 36knots (67km or 42Mph)

Now I have had 70hrs trouble free motoring and actually love the boat again, I would like to pick up some top end speed. 

Which prop would you go to bring the revs down a little but also pick up to Top speed. Perfect top revs is about 5800rpm

Do I need a 4 blade or just a different pitch 3 blade.

The boat is used like most bowriders, towing a Donut / knee board, fishing and sightseeing

[GoingFishing]

I actually think the stats you have noted above are incredible. That is some really good performance considering total combined weight. I dont do much towing but would have thought that 67km/hr is sufficient for towing.

Not sure how much speed your going to get by changing the prop, but i imagine it wont be significant.

[Plethora]

I have the same 2016 115 Etec motor on a 2016 Stacer 509 Searunner and I have put a SE Sport 300 hydrofoil and now it jumps out of the water and top speed of mine is 38knots and has no Porpoise(ing), quite fast and very smooth ride on flat surface. (I trim around 48 on the gauge)

only 77Ltrs of fuel on mine and hull slightly lighter

[jeffb5.8]

9 minutes ago, Plethora said:

I have the same 2016 115 Etec motor on a 2016 Stacer 509 Searunner and I have put a SE Sport 300 hydrofoil and now it jumps out of the water and top speed of mine is 38knots and has no Porpoise(ing), quite fast and very smooth ride on flat surface. (I trim around 48 on the gauge)

only 77Ltrs of fuel on mine and hull slightly lighter

Hey Plethora

What RPM does your top out at?

What Prop spec does your have?

Yesterday on Syd Harbour it was smooth water and little wind, I had 3 adults, two kids and flat out trimmed to 45 (6,150rpm) and I didn't lose any speed by pulling the throttle back to drop the rpm to 5,850.

My mate next to me in a F/Glass 18ft bowrider with a Yamaha 115 saltwater series, similar loads (3 adults and 1 kid) doesn't take off as fast (Not much slower) but leaves me for dead on the run down the river to Rydalmere., So I would love to get a few extra knots as it doesn't need to hit 6,150rpm.

[jeffb5.8]

22 minutes ago, GoingFishing said:

I dont do much towing but would have thought that 67km/hr is sufficient for towing.

Yeah I don't tow at top speed as its way to fast, and this boat has tonnes of spare hole shot to get skier's up, its more the race to the ramp, especially on New Years Eve or busy days, getting over taken by 3 or 4 boats with smaller motors in not fun.

Plus I would like full throttle to not be over 6,000 rpm, but needs to be over 5,650 rpm for the exhaust valve functioning on the Etec.

[Plethora]

sorry could not tell you the RPM as I do not remember - as I normally don't run flat out as its too fast - with just my self and a mate and on half a tank on a glass flat surface (Port Hacking) my best speed is 42knots (too fast for me)

[Plethora]

sorry do not know what prop - I will have too take a look (what ever it came with from the factory I guess)

[Welster]

28 minutes ago, jeffb5.8 said:

Yeah I don't tow at top speed as its way to fast, and this boat has tonnes of spare hole shot to get skier's up, its more the race to the ramp, especially on New Years Eve or busy days, getting over taken by 3 or 4 boats with smaller motors in not fun.

Plus I would like full throttle to not be over 6,000 rpm, but needs to be over 5,650 rpm for the exhaust valve functioning on the Etec.

Hi Jeff what do you mean by exhaust valve functioning? 
 

[Plethora]

it is a Stainless steel - Viper 

[Plethora]

An exhaust valve is a valve that releases burned gases from a cylinder. The exhaust valve closes during the initial part of the induction stroke. The inlet valve usually opens a little before top dead center and the exhaust valve remains open a little after top dead center.

[jeffb5.8]

11 minutes ago, Welster said:

Hi Jeff what do you mean by exhaust valve functioning? 

The Etec has a power valve, which is why they need to be propped and driven above 5,500 Rpm on each use, if you don't open the valve regularly they can seize up and that affects the engine. Very expensive to fix although there is work arounds, if they seize the motor usually wont rev when required.

It doesn't mean you have to run all the time at 5,500rpm or above but they do say to give it a blast each run.

It feels similar to the old 2 stroke motocross bikes when they hit powerband.

[jeffb5.8]

44 minutes ago, Plethora said:

sorry do not know what prop - I will have too take a look (what ever it came with from the factory I guess)

No Problems be interested to know but no rush.

My 2016 115hp is fitted with a 19" and yet my mate has a 2015 130hp and his is fitted with a 17", I would have thought it would have been the other way round but hey it works for his boat, which incidentally is the Stacer 540 the 1yr older version of my boat .

 

Edited July 8, 2020 by jeffb5.8

[noelm]

It's not quite as simple as it sounds, you put a bigger prop on, you drop RPM, so, top speed remains the same, but, getting on the plane and towing suffers, the prop you have seems pretty well right unless you have some friends with the same prop fitting you can borrow to test.

[zmk1962]

Hi Jeff, the rule of thumb I noticed was that each movement in pitch (up or down) will affect your theoretical speed about 6% at a given RPM range.

Its the propeller RPM that will determine your speed (assuming your motor has sufficient torque to spin the selected prop at low and max rpm,)... so when you mention engine 6150RPM... you need to take into consideration the RPM reduction in the lower leg gearing ... usually somewhere between 1:1.75 --- 1:2.08... then you will have the prop RPM.

Here are two sites you can model the effect of spinning different pitch propellers.

Simple MAX theoretical speed calculator (enter prop rpm and pitch)... You can use this to work out what the max speed is, and then what you are observing and hence your propeller slip factor....if its more than 15% you need to tweak your prop set up.

http://www.rcpro.org/rccalc/PitchSpeed.aspx

This is a more complex calculator where you have all the relevant variables -  it will calculate the answer for whichever variable you leave blank. 

http://www.csgnetwork.com/marinepropcalc.html

I used both of these sites extensively when I was modelling my repower.

Regarding your mates boat - are the propeller diameters the same? Are the boay weights and weight distribution the same. There are many many variables. When I spoke to sites that had repowered boats like mine and prop pitch selection, they gave me an example of two identical boats (in that case Carribean ReefRunners) where one was successful with a 16p and the other 17p. The only difference was how the owners had set up the boats.

Hope this helps.

Cheers Zoran

[jeffb5.8]

1 hour ago, zmk1962 said:

Hi Jeff, the rule of thumb I noticed was that each movement in pitch (up or down) will affect your theoretical speed about 6% at a given RPM range.

 

2 hours ago, noelm said:

It's not quite as simple as it sounds, you put a bigger prop on, you drop RPM, so, top speed remains the same, but, getting on the plane and towing suffers, the prop you have seems pretty well right unless you have some friends with the same prop fitting you can borrow to test.

Thanks Noel and Zoran

I thought about a different Prop as 6,150 is right on the over Rev limit of my engine which is 6,200, this thing has very great hole shot and on the plane very quickly.

I did post this on Etec owner forum and one reply said go to a Viper 21" with the same pitch, will play with the calculators

P.s Right now I just don't go WOT to much to keep in away from Redline.

[zmk1962]

In some ways it’s not about how often you get to WOT.  The main thing is your motor needs to be able to get to WOT With the fitted prop otherwise you are over propped (too much pitch) and putting undesired burden on your motor in lower RPM. 

if you hit WOT very easily then chances are you are under propped - and you may benefit from a higher pitch if you are chasing economy and speed - but you may lose some hole shot.  
cheers Z

Edited July 8, 2020 by zmk1962

[noelm]

You might be able to get your current prop cupped, it might take a bit of RPM off, props are very complicated to get right.

[PaddyT]

Had a thought bubble in the back of my head that said (and i think it came from an ancient conversation that i had with an ETEC owner)that ETECS should be fully spun out at about 5500 - found this link https://www.rubexprops.com/boat-propellers/rpm-range/?make=Evinrude which confirms my thought bubble-so im guessing you are underpropped, BUT on the side-36 knots in that sized aluminium boat is plenty fast enough- you may well end up compromising your ability to "hold"" on the plane in normal sea conditions-both uphill and downhill- i would rather loose top end than have my hull become over sensitive to throttle when im out at sea.

[wrxhoon1]

JeffB, 

Your motor may have a 2-1  or even 2.25 -1 gearbox, your mates 130 may have 1.85- 1 box , if you have a 2.25 and his is a 1.85 at the same RPM his prop is spinning faster than yours.

Your prop spins 2666 rpm at 6000 flywheel rpm (2.25-1 box) and 3000 (2-1 box).

His prop spins 3243 rpm at 6000 fly rpm.

Convert that to take in to account the different pitch props .

2666 prop speed (6000 rpm) 19" prop theoretical speed is: 77 kmh  

3000 prop speed  ( 6000 rpm) 19" prop theoretical speed is: 86 kmh.

Your mates 130 with 1.85 box spins the prop 3243 rpm at 6000.

3243 prop speed  (6000 rpm) 17" prop theoretical speed  is: 84 kmh.

His theoretical speed is higher than yours if you have 2.25-1 box and yours higher by 2 kmh if you have a 2-1 box.

All well and good but theoretical speed doesn't always transmit to real speed.  A lot of other factors come in to it.

The boat itself, the position of the engine ( how high or low in the water it is fitted) anything hanging of the transom that is in the water when on the plane ( transducer, water pick up, etc..)  prop efficiency, a prop that suits my boat may/not suit yours and so on, trim of the engine, even how you load the boat. Don't go by trim numbers on the gauge , that doesn't  mean much. My boats transom maybe XY degrees from vertical and yours could be XYZ. 

In any case if your top speed is only 67 kmh and it is accurate speed your slip loss is about 14% far too great .

You say "some Porpoising" that can be an indication of the engine mounted too low especially if the steering feels heavier on one side . You should be able to find a trim position where the steering feels very neutral. Does the prop cavitate when you turn hard at or close to full speed?

If you spin at 6150 with your normal load  that is too high. If your prop in in good nick, no dints bends or any other marks, even small can effect it, you need to go up in pitch and or try a different prop, as a rough guide every 1" pitch you go up you will drop 200 RPM. If what you say is correct on RPM and speed a 21" pitch will drop your RPM to 5750-5800.

A 4 blade prop will give you better hole shot but lower top end everything else being equal.

Edited July 8, 2020 by wrxhoon1

[jeffb5.8]

On 7/8/2020 at 4:47 PM, wrxhoon1 said:

You say "some Porpoising" that can be an indication of the engine mounted too low especially if the steering feels heavier on one side . You should be able to find a trim position where the steering feels very neutral. Does the prop cavitate when you turn hard at or close to full speed?

Hi WRX

i feel my motor is to low but posted a photo And video on ETec forum and got heaps of different views, Most saying it’s find, I say to low as the amount of water running over the cav plate is a lot.

if I have the motor trimmed in the 30s. On the gauge, When planning I do get that sweet spot where the steering is light and direct.

It will have cavitation if it’s trimmed up in the high 30s and you do a sharp turn like whipping the tube.

Edited:

Checking my model Number I have 

E115DSL     390 lbs / 177 kgs20" / 508 mm

Model Gear Ratio2.00:1

Will  check what my mate has just out of interest and will pay more attention to his engine height and Revs

Edited July 10, 2020 by jeffb5.8

[noelm]

Best way to get motor height right is trial and error.

[wrxhoon1]

1 hour ago, noelm said:

Best way to get motor height right is trial and error.

Totally agree Noelm.

[wrxhoon1]

2 hours ago, jeffb5.8 said:

Hi WRX

i feel my motor is to low but posted a photo And video on ETec forum and got heaps of different views, Most saying it’s find, I say to low as the amount of water running over the cav plate is a lot.

if I have the motor trimmed in the 30s. On the gauge, When planning I do get that sweet spot where the steering is light and direct.

It will have cavitation if it’s trimmed up in the high 30s and you do a sharp turn like whipping the tube.

Why not lift it one hole and see how you go.

[GoingFishing]

On 7/8/2020 at 11:41 AM, jeffb5.8 said:

The Etec has a power valve, which is why they need to be propped and driven above 5,500 Rpm on each use, if you don't open the valve regularly they can seize up and that affects the engine. Very expensive to fix although there is work arounds, if they seize the motor usually wont rev when required.

It doesn't mean you have to run all the time at 5,500rpm or above but they do say to give it a blast each run.

It feels similar to the old 2 stroke motocross bikes when they hit powerband.

Im surprised this valve only opens up at such a high rpm.

Where did you read this? Can you paste any info plz

[jeffb5.8]

The valve opens on my motor about 4,300 Rpm, depending on the load on the motor.

But the selling dealer, the servicing dealer and the Etec Owners Forum all said to take the motor higher in the rev range to get the valve to fully open at least once each trip.

It doesn't mean you have to redline it each time all day, just give it a squirt up to the higher revs and get the valve moving, early models 2008 ect had a issue with the valve seizing, then they added a grease nipple and started tell everyone to make sure you open the valve regularly.

It easy to do especially in the waterways I use and who doesn't run top speed for a few minutes on most trips. 

You can really feel the valve when it open as its like a decent boost to the engine and it changes the engine sound, plus its a 2 stroke and they love to Rev.

 

Here is one I found 

https://www.etecownersgroup.com/post/exhaust-valve-question-9863355?highlight=exhaust+valve&pid=1305744352

Here is one where Huett Marine reply to the Exhaust question

https://www.etecownersgroup.com/post/exhaust-valve-question-9771312?highlight=exhaust+valve&pid=1304573504

Edited July 10, 2020 by jeffb5.8