High Thrust props on non high thrust kickers......

[ReelSlim]

Again Dave would have to chime in about his mechanics comments. I wouldn't be concerned with the motor at all......just the lower end. Or is it really just that simple and the HighThrust kickers will be a thing of the past? Probably not? I tend to lean to the the "right tool for the job" moto..... However sometimes we need to make one thing do two jobs which is always worth a try.....IMO That is also why I always say that everyone needs 3 boats! lol It's just true.....except for the costs....time maintaining them and of course the whole wife thing? lol

 

[triplenickel]

I think this is being way over thought!

 

[trendsetter]

Again Dave would have to chime in about his mechanics comments. I wouldn't be concerned with the motor at all......just the lower end. Or is it really just that simple and the HighThrust kickers will be a thing of the past? Probably not? I tend to lean to the the "right tool for the job" moto..... However sometimes we need to make one thing do two jobs which is always worth a try.....IMO That is also why I always say that everyone needs 3 boats! lol It's just true.....except for the costs....time maintaining them and of course the whole wife thing? lol

There will still be high-thrust models because they have some features that standard motors do not. They are usually built a little differently, for example with 2 single throat carbs instead or one dual throat carb etc. They also have a lower gear ratio in the leg which allows them to produce far more thrust than the standard motors.

Putting a high-thrust prop on your standard kicker will give it more thrust but still not the caliber of the high-thrust motors.

I wish I had three boats!

 

[AquaDisiacIII]

There will still be high-thrust models because they have some features that standard motors do not. They are usually built a little differently, for example with 2 single throat carbs instead or one dual throat carb etc. They also have a lower gear ratio in the leg which allows them to produce far more thrust than the standard motors.

Putting a high-thrust prop on your standard kicker will give it more thrust but still not the caliber of the high-thrust motors.

I wish I had three boats!

High thrust motors don't change carb set ups. A regular 9.9 and a high thrust 9.9 only have one carb. Pretty sure it's strictly gear ratio and prop size

 

[jeffywestcoast]

I was told by the Merc dealer that they are the same except for the lower unit in the highthrust,my new Merc 9.9 has 2.08:1 gear ratio, the bigfoot and pro kicker models have a 2.42:1 ratio. just like in vehicles where torque n speed are inversely proportional.. kinda the same thing. because the bigger four blade prop provides more thrust it probably doesn't have to rev much higher to produce the same speed as the regular 9.9 (trolling speed).

 

[Dave S]

I'm surprised that the mechanic would say that, it's pure speculation on his part. It's far more likely that the new prop WILL allow the motor to reach it's recommended max RPM range. A 2.5" reduction in pitch will have a far greater effect than the increase in diameter.


If you really want to know then the test is simple.

1. Look up the recommended maximum RPM for your motor.
2. Hook up a tach to the kicker.
3. On the water, put the kicker in FWD and observe the RPMs at Full Throttle.

If the motor reaches it's maximum recommended RPM range then the prop is not negatively affecting the powerhead. If it does not reach the maximum recommended RPM range than yes it is putting additional strain on the engine which could lead to premature wear.

I'd wager your new 5" pitch prop will allow the engine to run at a higher RPM than the original 7.5" prop. The only way to know for sure is to test yourself.

Testing the max rpm's this motor hits with this prop on doesn't seem that simple. I don't have a spare tach, or have the knowledge to wire up my tach for my main into this motor. My instincts and ears tell me it doesn't hit as high of a rpm when compared to the original prop.

What I think you are not factoring into this pitch and diameter comparison is the surface area of the high thrust prop is much bigger than the original prop. Basically, the new prop grips the water much better and that is what gives it all the low end push, but lacks the ability to rev up to it's max recommended rpm.

Not my photo but great comparison

Also, here's a good write up on the high thrust props from Yamaha.
http://www.saltbossmarine.com/YamahaF8DualThrust.html

Still think it's a great way to give a regular motor more low end push for trolling. Obviously, each situation is different, and I can't promise the same results in all applications.

 

[trendsetter]

High thrust motors don't change carb set ups. A regular 9.9 and a high thrust 9.9 only have one carb. Pretty sure it's strictly gear ratio and prop size

That's what I thought too but last summer I was tasked with rebuilding/replacing a carb on a buddy's 03 T9.9. I found that the high-thrust models, for the most part used different carbs than the regular F9.9 models.

 

[trendsetter]

Testing the max rpm's this motor hits with this prop on doesn't seem that simple. I don't have a spare tach, or have the knowledge to wire up my tach for my main into this motor. My instincts and ears tell me it doesn't hit as high of a rpm when compared to the original prop.

What I think you are not factoring into this pitch and diameter comparison is the surface area of the high thrust prop is much bigger than the original prop. Basically, the new prop grips the water much better and that is what gives it all the low end push, but lacks the ability to rev up to it's max recommended rpm.

...
Still think it's a great way to give a regular motor more low end push for trolling. Obviously, each situation is different, and I can't promise the same results in all applications.

You can use a tiny tach (http://tinytach.com/) or even a multi-meter that has the ability to measure RPM.

 

[SpringVelocity]

I was told by the Merc dealer that they are the same except for the lower unit in the highthrust,my new Merc 9.9 has 2.08:1 gear ratio, the bigfoot and pro kicker models have a 2.42:1 ratio. just like in vehicles where torque n speed are inversely proportional.. kinda the same thing. because the bigger four blade prop provides more thrust it probably doesn't have to rev much higher to produce the same speed as the regular 9.9 (trolling speed).

There identical except different gear ratios to push bigger boat, and different props.

From Yamaha Site for this year's models:
9.9High Thrust:

Engine Type
2-cylinder Four Stroke
Displacement
212cc (12.9ci)
Bore & Stroke
56 mm x 43 mm / (2.48x2.29in)
RPM Range
5000 - 6000
Compression Ratio
9.46:1
Induction System
SOHC
Alternator Output
12v / 6 Amps
Fuel Delivery
Carburetor (1)
Starting
Manual and/or electric
Ignition
CDI Micro-Computer
Lubrication
Wet sump
Degree of Trim/Tilt
4 positions/70° or power trim / tilt
Exhaust
Through Prop / Water Cooled / Labyrinth
Cooling
Water/Thermostatic Control
Gear Shift
Tiller Mount F/N/R
Gear Ratio
13/38 (2.92)


Regular 9.9

Engine Type
2-cylinder
Displacement
212cc (12.9ci)
Bore & Stroke
56mm x43 mm (2.2 x 1.69 in)
RPM Range
5000-6000
Compression Ratio
9.46:1
Induction System
SOHC
Alternator Output
12v / 6 Amps
Fuel Delivery
Carburetor (1)
Starting
Manual or electric
Ignition
CDI Micro-Computer
Lubrication
Wet sump
Degree of Trim/Tilt
4 positions/70°
Exhaust
Through Prop / Water Cooled Lab
Cooling
Water/Thermostatic Control
Gear Shift
Tiller Mount F/N/R
Gear Ratio
13/27 (2.08)

 

[trendsetter]

There identical except different gear ratios to push bigger boat, and different props.

From Yamaha Site for this year's models:
9.9High Thrust:

Engine Type
2-cylinder Four Stroke
Displacement
212cc (12.9ci)
Bore & Stroke
56 mm x 43 mm / (2.48x2.29in)
RPM Range
5000 - 6000
Compression Ratio
9.46:1
Induction System
SOHC
Alternator Output
12v / 6 Amps
Fuel Delivery
Carburetor (1)
Starting
Manual and/or electric
Ignition
CDI Micro-Computer
Lubrication
Wet sump
Degree of Trim/Tilt
4 positions/70° or power trim / tilt
Exhaust
Through Prop / Water Cooled / Labyrinth
Cooling
Water/Thermostatic Control
Gear Shift
Tiller Mount F/N/R
Gear Ratio
13/38 (2.92)


Regular 9.9

Engine Type
2-cylinder
Displacement
212cc (12.9ci)
Bore & Stroke
56mm x43 mm (2.2 x 1.69 in)
RPM Range
5000-6000
Compression Ratio
9.46:1
Induction System
SOHC
Alternator Output
12v / 6 Amps
Fuel Delivery
Carburetor (1)
Starting
Manual or electric
Ignition
CDI Micro-Computer
Lubrication
Wet sump
Degree of Trim/Tilt
4 positions/70°
Exhaust
Through Prop / Water Cooled Lab
Cooling
Water/Thermostatic Control
Gear Shift
Tiller Mount F/N/R
Gear Ratio
13/27 (2.08)

Interesting that the high thrust models use different part numbers for the carbs but on breakdown appear identical to the regular models. Oh except for the price; high thrust carbs cost more! lol. Nicely done Yamaha.

High Thrust Carb $340.94: http://www.boats.net/parts/detail/yamaha/Y-6G8-14301-22-00.html

Regular Carb $331.13: http://www.boats.net/parts/detail/yamaha/Y-6G9-14301-22-00.html

 

[Flipper]

I have the 16 Arima Sea Explorer with a 6HP Yamaha Kicker. Yamaha sells 2 or 3 different props for that engine which includes a Dual Thrust Prop. The hub is designed to redirect exhaust flow away from the blades, so Dual Thrust models cut through "clean water" for higher efficiency and better acceleration. However, I found that the prop did little for my boat as far as speed. I was trying to cut down on my RPM's and instead they were increased to get the same speed...Looking for a 8hp.

 

[Dave S]

I have the 16 Arima Sea Explorer with a 6HP Yamaha Kicker. Yamaha sells 2 or 3 different props for that engine which includes a Dual Thrust Prop. The hub is designed to redirect exhaust flow away from the blades, so Dual Thrust models cut through "clean water" for higher efficiency and better acceleration. However, I found that the prop did little for my boat as far as speed. I was trying to cut down on my RPM's and instead they were increased to get the same speed...Looking for a 8hp.

What kind of speed are you trying to hit? I found with my set up on the 8hp, the high thrust wouldnt get the same top speed as the original prop, but the low end push was way better with the new prop.

 

[trophywife]

I have the 16 Arima Sea Explorer with a 6HP Yamaha Kicker. Yamaha sells 2 or 3 different props for that engine which includes a Dual Thrust Prop. The hub is designed to redirect exhaust flow away from the blades, so Dual Thrust models cut through "clean water" for higher efficiency and better acceleration. However, I found that the prop did little for my boat as far as speed. I was trying to cut down on my RPM's and instead they were increased to get the same speed...Looking for a 8hp.

i had a sixhp with an 8hp high thrust prop. modded the linkage a lil more, got all i could out of the six.. definately not more speed, but a whack more thrust or push which was what i needed for trolling in current and wind. the 6hp yami is the same as the 8. save yer money, mod the 6.

 

[Fishalot]

Dave has provided me with the part number and I am getting one next week. As Dave mentioned its 9" x 5 pitch. By comparison the T8 high thrust prop is 11.75"x 5.75 pitch stock. Quite different, I don't think there will be any undue strain on motor with this change. Looking forward to the change as I have the same boat as Dave.

 

[LowTide]

In your Yamaha Comparison, the bore and stroke are quite different. Also they don't state whether the carbs are the same part or not, just that there is one on both units. This makes sense for engines that serve different uses.