Another prop question

[thelump]

So I have been trialling a couple of props (thanks murf). Boat is a Yalta555 and F115 Yamaha. I don't like the mid range speeds I get with the standard 17K Yamaha prop. In a bit of current I need to have the motor around 4600-4700rpm to get 40kph(21KN) this is using around 23LPH. I was hoping for better economy. So I tried a 13 1/2"x 16"pitch rubex prop and was similar figures to the 17K except some pretty decent vibration when idling in gear. So I then put on a 13 1/4 x 17"pitch New Saturn Solas prop. This was fantasic in the mid range with 3900RPM achieving 43km/h (23kn) and only using around 17lph. Unreal I thought until I tried WOT. Wringing its neck and trimmed way way out I could achieve 5500rpm. But this was with a light load and only half a tank of juice. Now I know I should be getting better RPM @WOT but my question is will this damage my engine? It seems to run smoothly and hole shot is pretty good. I want it to be OK but the reality is it probably isn't.

[Moonlighter]

Hi Jason

What is the max rev range Yamaha states for your engine?

You generally want to get into the upper half of the rev range with a normal load. So, if your rev range is 5500-6000, you would want to get around 5800 rpm. In such an example, getting only 5500 rpm lightly loaded would be undesirable. 5200rpm would be danger zone.

Have you checked engine height to make sure it is not buried too deep? That should be the first thing you do. Lifting engine 1 hole could get you a couple hundred more revs and top end speed, plus better economy across the rev range. Anti-ventplate should be just skimming the surface, not under water, at fast cruise speed (eg around 4800-5000rpm).

Here is what Ken from the Propgods says about this topic on the Verado website: these guys are the experts on this topic, and the comments apply to all motors, not just Verados:

6. Now look at your rpm...- it should be in the top half of the mfr's recommended top end rpm. For example, the Verado’s range is 5800-6400 rpm. Therefore I should be at least 6100, 6250 would be ideal. But don't get hung up here, anything over 5900 rpm is ok, you won't be hurting the motor. A few more hundred rpm may get you a bit more speed though. But less than 5800 is going to do long term damage to the motors. It will cause the motor to add gas to the oil, raising the oil level and diluting the protection the oil gives the motor. Eventually the crank will fail and it will not be warranty.

[Horse]

Take it for a run with a bit of ballast to see how it runs. If you supply the beers I'm sure Team Sumo can oblige.
I would have expected significantly better economy fron the F115. What did you get with the old 2ST

[cobiaman]

Take it for a run with a bit of ballast to see how it runs. If you supply the beers I'm sure Team Sumo can oblige.
I would have expected significantly better economy fron the F115. What did you get with the old 2ST

Sounds good, meet at jumpinpin?

[tenzing]

Gidday Lump
As the others have said it will do damage to not get in the top half of the rev range.
I have also done a prop test on the weekend. My new outboard has been buried as I was getting ventilation all the time. I was given a different version of the same prop ( 15 x 21 ) - both props brand new out of the box.
The second one was a different thing altogether, with better speed across the lower and mid range , but at 5500 I put it all down and hardly got a whimper from the motor. topped at 5850 ( about 300 - 350 below the old one)
So my answer is to lift it a hole or two ( off to the shop 6.30 tomorrow), but that the new prop is closer to the money.
It is quite a worthwhile exercise to use the prop slip calculator mentioned in the earlier link.
Actually this is easier if your speeds are in kph
http://continuouswave.com/cgi-bin/propcalc.pl
slip will decrease as you get towards WOT, mine ended up at about 4%.
If you use the calculator and put in a figure of 0% for slip, and use the max revs for your donk it will give you the theoretical top speed that size prop. Quite interesting that whatever you do you just wont get any more out of it than that, no matter what load, trim etc ( except for wind I suppose)
Good luck with yours, I am hoping mine will feel like a new boat by weeks end
Cheers
Brendan
PS, It is a bit of a worry that 2 props with the same nominal spec can be so different (new)

[Darren Mc]

Hi Jason,

The 17k prop that comes standard on the f115 is a pretty ordinary prop in my opinion.
I have a 585 baysport with the 2012 f115 and I took that 17k off cause I was getting heaps of prop slip.
I was happy with the top speed of 35 knots but that was all I was happy with cause the rest of the time it drove like crap really.
terrible out of the hole, would not stay on the plane below about 4500rpm and I felt like I was spinning the wheels every time I took off.

Enter my new Solas HR Titan SS 13 1/4 x 15p 4 blade.
Much better out of the hole with less throttle, will stay on the plane at 3900- 4000rpm and there's no where near as much prop slip.
I lost about 2 knots top speed(33Knots) but gained about 3 knots mid range cruise speed(25 knots) at about 2.1km's per ltr and approx. 21ltr's per hr. My wot is about 5800rpm now down from 6000rpm with the 17k.
I paid $311 delivered to my door from the states and it took about 3 weeks.

I have to say that my boat feels a lot better now and it was money well spent for sure.

[thelump]

Thanks for the detailed responses fellas. Much appreciated. Firstly I dont think the motor is too low as the 17K does what it is meant to I just don't think it is a good prop as DarrenMc has stated. Darren you have sparked my interest with that reply. Just a question. Is the speed you are getting taken off GPS or the Yammy gauges? Also at what RPM are you achieving 25 knots? With the fuel usage at 21lph I am guessing around the 45 - 4600rpm And the last one did you test up and down hill and was there much difference between the 2?

[thelump]

Take it for a run with a bit of ballast to see how it runs. If you supply the beers I'm sure Team Sumo can oblige.
I would have expected significantly better economy fron the F115. What did you get with the old 2ST

Never really did any tests with the 2 stroke as I figured it was just a gas guzzling motor. That is why I got the 4 stroke. I am not unhappy with the economy I get I just think I can get better with a better prop.

[tenzing]

Thanks for the detailed responses fellas. Much appreciated. Firstly I dont think the motor is too low as the 17K does what it is meant to I just don't think it is a good prop as DarrenMc has stated. Darren you have sparked my interest with that reply. Just a question. Is the speed you are getting taken off GPS or the Yammy gauges? Also at what RPM are you achieving 25 knots? With the fuel usage at 21lph I am guessing around the 45 - 4600rpm And the last one did you test up and down hill and was there much difference between the 2?
Yeah Jason, In regard to the motor height, I was only meaning that I think that now that I have found a better prop ( if not best?) , now I can look at positioning MY motor at the right height with respect to cav plate position etc.
You sound as if your height is right so maybe a little overpropped ( re decreased WOT)
Cheers
Brendan

[Gon Fishun]

Hey TL
What is the actual size of the 17K prop? EG 13 1/4.diam x 17pitch ? The reason I ask is I am assuming ( never assume), the 17 is the pitch. If the prop Daren put on is the same diameter but lower pitch, 17 down to 15 his rpm should increase not decrease. :-?
I have mucked about with the prop my Haines and was interested how you go, so I have been looking about on the net and there is a lot of info regarding the Yammy 115. And a lot of dribble.
Cheers.

[thelump]

Yeah all good Brendan. Just frustrating. Glad you got yours sorted mate.

[thelump]

Hey TL
What is the actual size of the 17K prop? EG 13 1/4.diam x 17pitch ? The reason I ask is I am assuming ( never assume), the 17 is the pitch. If the prop Daren put on is the same diameter but lower pitch, 17 down to 15 his rpm should increase not decrease. :-?
I have mucked about with the prop my Haines and was interested how you go, so I have been looking about on the net and there is a lot of info regarding the Yammy 115. And a lot of dribble.
Cheers.
The 17k is 13" dia x 17" pitch 3 blade. Darren put a 4 blade on his. I have tried a 17" pitch 4 blade as well but could only get 5200rpm out of it. Thats why the 15" pitch 4 blade is spinning about 5800 on his boat.

[honda900]

According to this Yamaha site, the rev range for that engine is 5000-6000, which means your right in the middle with that test prop..

http://www.yamahaoutboards.com/outboards/Inline-4/specifications

Regards
HOnda.

[Gon Fishun]

FWIW. Copied this from the net. A bit more info.
I am not an outboard mech, and would never profess to be one. ( ignorance is bliss).


Firstly - you can't over rev any new Yamaha 4 stroke engine as they all have automatic rev limiters on them. For a 115 the limiter cuts in at 6150 rpm. The motor does not cut out it just sounds like the engine is surging. It is VERY important that you let this engine rev. With just one person it the boat and a light load of fuel it should rev to 6000rpm. If you prop it for a lower level the boat will be slow out of the hole (take-off) and will not reach maximum top end speed. It will also cause the engine to do a strange thing call "add-oil". What happens is that if you have the engine wide open and the engine cannot reach its maximum designed revs , gas will be blown past the rings and will dilute the engine oil with gasoline. Check you oil level and see if you have too much oil - if so change it and put on the prop that will reach 6000 rpm (for you Princecraft try a 13 1/4 X 17 in as a starting point. DO NOT WORRY about over reving your engine - it is made exactly for this rpm range, only old 2 strokes rev 5200-5500. I have owned a F100 (pretty much the same engine) and it has about 30,000 miles on it. It's proped for 6000 rpm (I nornally cruise at 4200rpm which is a sweet spot on this engine) and it starts, runs and performs EXACTLY the same as it did the day I brought it home in 2001.

If you can only get the engine to rev at 4500-5000, you are only letting the engine deliver about 80hp!! This engine has got to rev to get the full potential out of it and it if you lug it at wide open throttle you will damage the engine by either washing down the cylinders with excessive fuel being blown by the rings or in extreme cases by detonation (this will destroy the engine - better known as pinging)

[Dicktracey]

Lump It will come down to budget at the end of the day mate.
I just spent $300 regrinding a DF200 prop, it ran fantastic under no load but when loaded up will Full eskies and and couple of mates it took an extra 1000rpm to achieve same planing speed due to to slip.
If you can imagine a raised area on the leading edge dropping away leaving a low pressure point which caused cavitation "showed up in prop scan", I also had 1/2" of pitch removed to move cruising speed to the rev range I wanted.

[Darren Mc]

Hey Jason
Speed taken from gps and your right, 25 knots at about 4500rpm from memory. Nah I didn't do the up hill down hill test.
Once I felt the way it changed the feel of the boat I was happy and kind of lost interest in mucking around testing to much more than the basic's. Just wanted to go fishing.
Yeah when going to a four blade you need to drop 2 pitch to maintain your current rpm or close to it.
My original prop was a 13 x 17p 3 blade.

This is the chart that I used to make my choice in prop.
http://www.solas.com/newweb/propeller/products/brandSearch.asp
Don't worry about the left and right rotation thing just look at the numbers.