150 yammie 4 stroke. more speed?

sullmate

Petty Officer 3rd Class
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Dec 23, 2008
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I have a 2017 Hurricane 188ss deck boat with 2017 Yamaha 150 hp engine. current prop is a s. Steel 14.5 X 17 in. prop. RPM's are 5400 at 45 MPH on speedometer. Thinking of getting a 14.5 X15 S.Steel prop to gain 250-300 RPM and maybe more speed? Any ideas or suggestions? Thanks
 

Sea Rider

Supreme Mariner
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Sep 20, 2008
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How loaded do you usually go boating ? If that's a heavy boat 2 les in pitch shoud theoretically increase + 400-600 wot rpm, will surely know with a new wot test as loaded.. That size Yams usually revs max 6000 rpm and some even 6300.

Happy Boating
 

ahicks

Captain
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Sep 16, 2013
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All else being equal, going from 17" of pitch to 15" of pitch is likely going to gain way more than 250-300 rpm as already mentioned. My bet is you'll be well over 6K with the 15". I wouldn't want to bet on any increased speed (should be close to the same by my way of thinking), but I would bet you WILL notice the boat getting up on top much quicker = more fun for water sports.
 

jimmbo

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I doubt you will see an increase in MPH, Depending on what rpm the engine makes its Peak HP, propping on either side of that peak will result in lower top speed, even if the rpm attained is within the Recommended RPM range. Want more speed, make sure the engine height is correct for the speed range it can run and for the type of prop you are running or will run. The hull needs to be straight, no Hooks or Rockers. Also the hull bottom needs to be clean, no plant or animal life clinging to it. Proper weight distribution is needed. Speaking of weight, get rid of unnecessary weight/ballast. That means; No wife or Kids aboard, No Mother-in-Law, especially her. Mistresses and Girlfriends are still allowable weight in a boat. If all this is done, then the only way to get more speed is to replace the 150 with a 175 or 200.
 

QBhoy

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Mar 10, 2016
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You’ll likely gain 300-400 RPMs going from a 17-15. Should see you still within range if it’s 6000rpm max. The important thing is being in the range.
As Jimmbo has said, perhaps unlikely you will gain speed, but if you are out of the Rev range just now, you just might, especially with a performance orientated prop. It will be marginal at best though.
 

porscheguy

Chief Petty Officer
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Jan 17, 2013
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441
How is your motor height?

If you look at performance data from other boats close in size to yours, you’ll see that a 20’ seafox CC is 1’-2’ longer and is hitting 45mph@ 6000rpm with a 17P prop, and a yamaha 150.

A 19’ Scout CC is maybe 1’ longer. With a yamaha 150, and 18P prop, it’s doing 49mph @ 6000 RPM.

O/Bs have several advantages over I/Os. chief among those advantages are half the weight, and the ability to change the motor height (which I/O people call the “x dimension).

But there’s something else going on because I just entered your info in the slip calculator and it says -3.5% slip. You can’t have negative slip. What makes this odd is that you’re showing negative slip and you’re not turning max rpm. Confirm your data if you can.
 

sullmate

Petty Officer 3rd Class
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Dec 23, 2008
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93
Thanks for the advise. My 188 hurricane deck boat is turning 5400 r p m. I usually run lightly loaded. I currently run a yamaha s. steel prop 14.5 X17. Max r p m is 6000.
 

Sea Rider

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Dial a less pitch prop for OB to run towards max wot rpm range while lightly loaded, will have oustanding hole shot. Once adding more load or passengers wot rpm will drop accordingly. Ideal would be to add more load or passengers till wot rpm drops to middle wot range, don't add more load, rpm will drop too much to the lugging zone.

Running middle wot rpm wiill dial losing best hole shot with slight speed increase, which is preferred, best hole shot or slight more top en speed ? It's entirely up to each boater, for me best hole shot while lightly loaded or counting with a fixed load.

Happy Boating
 

porscheguy

Chief Petty Officer
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Jan 17, 2013
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441
Thanks for the advise. My 188 hurricane deck boat is turning 5400 r p m. I usually run lightly loaded. I currently run a yamaha s. steel prop 14.5 X17. Max r p m is 6000.
As I said, the data you have provided yields a -3.5% prop slip. You can’t have negative prop slip. Let me reiterate, it is impossible to have negative prop slip.

Yamaha has a performance bulletin on the 188SS w/115 yamaha w/17P aluminum prop. The 115 uses a 2.15 gear ratio.

Under a light load, That boat topped out at 37.7mph at 6000rpm. They used a 17 pitch aluminum prop. They had 16% prop slip.

You could have something slowing you down, or you could be receiving inaccurate information from your guages. If your boat, with a smaller, less powerful engine can turn a 17P prop all the way to 6K rpm, then I assure you, the problem is not your prop.

I would verify your speed with GPS. The test boat had the motor mounted in the #2 position and the anti ventilation plate was 1/4” above the boat bottom. I would look at yours and see where it is. It doesn’t cost anything to look at the back of your boat. It shouldn’t cost much to get an accurate speed.

If you’re actually doing 45mph, then your tach is inaccurate. If your GPS speed is 38-40, then your tach is accurate. Then it brings us to motor mounting height.

Verify speed with gps.
Check motor mounting height.
Check the height of the anti vent plate in relation to the bottom of the hull.

do these things before spending money on a prop.
 

sullmate

Petty Officer 3rd Class
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Dec 23, 2008
Messages
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Engine is in the second mounting hole from the top .Boat and motor are 1 year old. No hooks on hull, used in fresh water only. Max r p m for this engine is 6 K. 25 inch shaft. Boat is lightly loaded. Can't believe porsche guy says the boat will go only 38-40. Gear ratio is 2.0 to 1. This model hurricane has no windshield Anticavitation plate. is about 1 inch above the hull bottom. 115 vs. 150 hp should = more speed. Have to wait till spring, snowing like crazy now. Regards to all.
 

QBhoy

Fleet Admiral
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Mar 10, 2016
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8,286
Engine is in the second mounting hole from the top .Boat and motor are 1 year old. No hooks on hull, used in fresh water only. Max r p m for this engine is 6 K. 25 inch shaft. Boat is lightly loaded. Can't believe porsche guy says the boat will go only 38-40. Gear ratio is 2.0 to 1. This model hurricane has no windshield Anticavitation plate. is about 1 inch above the hull bottom. 115 vs. 150 hp should = more speed. Have to wait till spring, snowing like crazy now. Regards to all.

Hi there.
Porsche guy didn’t actually say it will only do 38-40. I would imagine he was getting that from the calculators and revs provided.....I assume, at least ?
 

porscheguy

Chief Petty Officer
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Jan 17, 2013
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441
What I said was the test boat ran at 38mph @6000rpm, with a 17P prop that had 16% slip. And it used a 115 motor.

People are telling you to drop in pitch, and I’m telling you that boats of a comparable size with the same engine and prop are running 45-50 at 6000rpm. If They can do it with this setup, you can do it. Hull efficiency on recreational boats from one brand to the next is largely a matter of splitting hairs.

i employed the prop slip calculator to see if your data looked normal. Your data was not normal. A negative slip means that your prop is operating beyond its theoretical ability. This is not possible. 45mph @5400rpm= -3.5% slip. Again, this is impossible.

Now lets assume your indicated speed of 45mph is the actual speed you’re traveling. But let’s also assume that your engine is turning 6000rpm. Now we enter this data into the calculator. We get 6.81% slip. This is quite a reasonable number.

You have since provided updated info. It appears your motor is properly mounted. So you can scratch that off the list.

Right now, your best course of action is to get a confirmed top speed via gps. If it says you’re doing 43-47mph, then tell the dealer you want your tach fixed.
 
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