Re Listing Prop Question with more info.

[valencehsift]

I have a 1989 Quantum 18 foot with a 7.5 foot beam which is a fish and ski boat. It has a shallow hull. All I can find on the prop is 13.5 x 17 P68.5. Right now I am redlining it. So yes, it is over reving. I am willing to sacrafice some efficiency for speed but with in reason if I can do such a thing. I listed a couple pics to give and idea. They are from the listing I bought the boat from so it is not me running the motor without water. But I am sure that pic is what caused me to change the impeller.

 

[kenmyfam]

Re: Re Listing Prop Question with more info.

I have a 1989 Quantum 18 foot with a 7.5 foot beam which is a fish and ski boat. It has a shallow hull. All I can find on the prop is 13.5 x 17 P68.5. Right now I am redlining it. So yes, it is over reving. I am willing to sacrafice some efficiency for speed but with in reason if I can do such a thing. I listed a couple pics to give and idea. They are from the listing I bought the boat from so it is not me running the motor without water. But I am sure that pic is what caused me to change the impeller.



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Only takes a pinch of ignorance to run without muffs and can cause a barrowload of issues. Good job to change the impeller. Does it cool O.K. now ??
Glad to see that you can still redline it though. What is redlining it RPM wise and is this the max RPM for that motor ?? You can lose RPM by increasing pitch but you need to know if that is the correct thing to do at this point. Load in the boat will affect RPM as well so you should typically prop your outfit to suit your normal load.
There are many experts out here that will help you "fine tune" it.

 

[valencehsift]

Re: Re Listing Prop Question with more info.

Yes, it seems to cool just fine now, thx for asking. Well the redline goes from 5500 to 6000, I get about 5850 when by myself. I dont no where to find what is suppsed to be the max rpm in the manual. My normal load will be mostly be two big guys, maybe around 450lb. I know, time to go on a diet. LOL

 

[kenmyfam]

Re: Re Listing Prop Question with more info.

Yes, it seems to cool just fine now, thx for asking. Well the redline goes from 5500 to 6000, I get about 5850 when by myself. I dont no where to find what is suppsed to be the max rpm in the manual. My normal load will be mostly be two big guys, maybe around 450lb. I know, time to go on a diet. LOL

Remember to add any and all gear you will be taking with you.
My 140hp V4 Johnson has a max RPM range of between 5,000 and 6,000 according to the handbook.
With a 14" X 17" pitch it will run at a little over 6,000 RPM
With a 14" X 19" pitch it runs at about 5,400 to 5,600 RPM depending on load. I do not know what your max RPM should be but you may just be O.K.

 

[hitace]

Re: Re Listing Prop Question with more info.

omg dont tell me you have the motor running without any water running to it

 

[Esox]

Re: Re Listing Prop Question with more info.

omg dont tell me you have the motor running without any water running to it

Did you read his post?

I listed a couple pics to give and idea. They are from the listing I bought the boat from so it is not me running the motor without water. But I am sure that pic is what caused me to change the impeller.

 

[jimmbo]

Re: Re Listing Prop Question with more info.

Looking at the picture, the ear muff is there. Installed from the back the device is just waiting to drop down into the spinning prop. Hmm, maybe that's the hose passing behind the motor and looping around in front? Whether the water is on or not...?

 

[valencehsift]

Re: Re Listing Prop Question with more info.

Good observation on the muffs, whether or not the water is on is unknown, regardless, the motor runs strong and the impeller is perfect. Now going back to the original question? Any other advice? The prop I am using has one good size ding in it. Can I get better performance from changing it to a different size and pitch?

 

[Esox]

Re: Re Listing Prop Question with more info.

What is your current WOT RPM's and speed with a normal load? Where is the anti ventilation plate in relation to the bottom of the hull? You said it turns 5850 with just you in the boat - do you have a speed to go along with that. If you can provide more detailed information there are many people here that can help.

 

[valencehsift]

Re: Re Listing Prop Question with more info.

Please excuse my ignorance, this is my first boat, I have studied the manual and have learned a lot. But I really don't know what WOT is. I will be putting the boat in the water this afternoon. I will measure from the antiventilation plate to the bottom of the hull. Speed? My speedometer doesn't work, I will try to find one today. I am guessing 40mph. I will be more specific in my posting tonight. Thx everyone, you have been a great help.

 

[Esox]

Re: Re Listing Prop Question with more info.

WOT = Wide Open Throttle.

As for the spedometer. Do you know anyone that has a handheld GPS you could borrow? Better to get speed from GPS as boat spedometers are usually inaccurate.

 

[valencehsift]

Re: Re Listing Prop Question with more info.

Ok I have a full tank of gas, it was very chopy out and invested in a cheap hand help GPS. I reached 38 mph @ 5700rpm but with the 15 mph wind behind me, but when I checked the GPS in the Jeep on the highway the GPS was slow by about 5 mph steady. I definently want to be able to go faster and I think it should. What is the best prop for speed? It is a 150 force, 18 foot quantum boat with a 7.5 foot beam. Its a fishing boat more then skiing. I have a need for speed, what can I do other then changing the motor to a bigger one?

 

[kenmyfam]

Re: Re Listing Prop Question with more info.

Ok I have a full tank of gas, it was very chopy out and invested in a cheap hand help GPS. I reached 38 mph @ 5700rpm but with the 15 mph wind behind me, but when I checked the GPS in the Jeep on the highway the GPS was slow by about 5 mph steady. I definently want to be able to go faster and I think it should. What is the best prop for speed? It is a 150 force, 18 foot quantum boat with a 7.5 foot beam. Its a fishing boat more then skiing. I have a need for speed, what can I do other then changing the motor to a bigger one?

Motor may be sitting too low. Did you check cavitation plate relationship to the water ??? Was that your best case with the trim 'fine tuned" Sounds like you are about there with your speed and RPM's. If you have a "good sized ding" in your prop then you should get it repaired before making any further prop decisions. Even if you do end up changing prop's it will be a fine back up for you.
I have never come across a GPS that is 5mph slow !!!! but I have come across several vehicles that read 5mph fast !!!

 

[Tredeb]

Re: Re Listing Prop Question with more info.

I have never come across a GPS that is 5mph slow !!!! but I have come across several vehicles that read 5mph fast !!!

Agreed, most arguements over boats or ski-doos are settled by GPS or a radar gun

 

[Jdeagro]

Re: Re Listing Prop Question with more info.

Valenc---;

I am assuming the previous owner choose the prop for improved performance (hole shot).

If you want it all: Better hole shot (35% faster), faster acceleration (0 to 30 MPH -10% ), smoother ride, better handling, no porpoising, and BETTER FUEL ECONOMY (10 to 12% overall) do the following:

1) Make sure the motor is at the correct height
2) Increase the pitch on the prop (3 blade Only)
3) install Smart Tabs SX series ($119.95 on iboats) SX9510-60

You should pick up about 5 MPH at WOT. Sound like Bull? NO just fact.

Now you have the propulsion system efficient and the Hull efficient.

Don't choose a prop for a hole shot improvement. Dropping down in pitch is simply down shifting into second, and since you have no other gears your RPMs are higher than required at any speed.

The tabs will eliminate the Hole / hill so all of the thrust will be used to move forward not driving up hill.

 

[Silvertip]

Re: Re Listing Prop Question with more info.

WOT = Wide Open Throttle!