Underpowered prop selection

[1Cj]

Guys,

I need some help in my next prop selection, I live on a HP restricted lake and I have a 175 tracker with an 18hp, I have a CNC tilt and trim unit and a mechanical jack plate (might be removed soon) attempting to get the most out of this motor..... the setback is approx 13" with both the CNC 6" and jack plate 7". the Center line of the prop is 4-1/2" below the bottom of the V pad.

I filled in the info below, however if you have any suggestions I would LOVE to hear them,

I was looking at the options on the solas website put in the manufacturer and hp then let it tell me what was available but I know set up is HUGE

and I am just confused, 4 blade- 10" X 5 or 7 pitch...... 0r three blade........


Thank you in advance!

CJ


1. Year, make and model of boat 2014 TWX bass tracker
2. Length, width and base weight of boat, look for boat decal on back of boat 17-7 dry weight=993lbs
2a.What is the maximum recommended HP for your boat 75 hp max
3. Number of people and gallons of gas normally on boat 2 people and 10 gallons
4. What do you use the boat for Fishing
5. Is it a Deep Vee and if so how many degrees of deadrise 10 Degree's of deadrise
6. Year, make. manufacturer and model of motor 2001 tohatsu 18hp
7. HP and gear ratio of motor IMPORTANThttp://cgi.ebay.com/ebaymotors/Tacho...Q5fAccessories 18hp 1.85
RPM __3200 WOT____ Speed _____9 mph______ No. of people ______2______ Gal. Gas ____15____
14. Are you at sea level or a higher elevation, give us the elevation in feet 330 above
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM yes
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop its a 3 blade 9.25' X 9 pitch
17. Does the prop show any damage that you can see its perfect
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations- obviously it needs to get closer to 5800 RPM to achieve hp rating
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

 

[flyingscott]

Honestly you are wasting your time trying to optimize that set-up. Set back and jackplates wont help at all. I would find the cheapest 3 blade, I could find that would let the motor rev into it's RPM range and call it good. You are so underpowered that spending money on a good prop is a waste. Prop optimization is for boats that can actually plane with the motors on them.

 

[1Cj]

Thanks for your opinion Flying Scott, I was not asking the question thinking that I was going to get 25 mph out of it. I was simply asking if anyone had any actual suggestions on making the only option I have run as best as it could. I didn't think that spending a $100 on the right prop was too much.....simply didn't want to spend 500 with 4 props that didn't work on the shelf.

 

[1Cj]

Ok maybe I will simplify my question, only at 3400 rpm - at a 9.25 X 9 pitch my choices are,

A solas 9.25 X 7 pitch.....3 blade or
10 X 7 4 blade or
10 X 5 4 blade.

I understand this probably isnt worth your time thinking about but if you had to pick one prop....which one would it be? Thank you in advance, Cj

 

[flyingscott]

Save your money for good oil and a good fuel treatment for carbon prevention. The prop you have on it is as good as it will get for you.

 

[1Cj]

Thank you for absolutely nothing, You typed out a bunch of words and throughout all of them you couldnt have picked a prop selection, you sir are a deuchebag,

 

[Faztbullet]

1) Raise motor as high as possible without slippage or cooling interference.... 2) Check RPM at WOT... 3) Use the largest pitch to keep RPM in the upperside of the recommended operating range...This will give you the most speed from the set-up.

 

[flyingscott]

Thank you for absolutely nothing, You typed out a bunch of words and throughout all of them you couldnt have picked a prop selection, you sir are a deuchebag,

I gave you a quality piece of advice and you act like that. Go home and get some manners and some experience. Maybe when you come back you won't act like a spoiled child. But You are right I am sorry you can't read, as post #5 clearly states keep the prop you have. Lets do the math for the for the prop you actually need. You are at 3400 and you need to get to 5000 rpm. Now 1" of pitch is 200 rpm theoretically so you need to drop 8" of pitch from your current prop. Now go find a 9.25" x 1" of pitch good luck with your motor.

 

[WesNewell]

This one is your best bet to get rpm up into wot operating range. In your situation I think I'd get a smaller much lighter boat. Could probably double your speed with a light 16' aluminum bass boat at under 650# dry weight.
5113-100-05

 

[ahicks]

The set back and jack plate are doing nothing for you, just adding weight. If you want to optimize performance, get rid of those and anything else that can't be justified.

As far as 3 vs. 4 blade, the 4 blade would be about providing max thrust/bite on the water, at the expense of extra drag caused by the extra prop blade. At the speeds this motor/boat combo are going to see, I'm not sure you would notice the difference between them. Either will work fine.

Because I doubt this boat will ever plane out, having the engine red lined at wide open throttle is of questionable value. That's why several have suggested prop selection isn't all that critical here..... Something close will work just fine!

 

[1Cj]

Thank you, Faszbullet, WesNewell, Ahicks, And FlyingScott- As I stated unfortunately I have a specific situation that requires me to have a limited HP, this is not optional. Before actually posting here I had done several days of reading and have seen hundreds of posts that FlyingScott had commented on. Obviously he and all of you or most of you are much more qualified than I would ever be with the rigging of an outboard. (Hence my submission here) Many of you people have thousands of hours of trial and error. while I am still yet to crack 100. But as dumb as I am I did figure a few things out in my previous rigging projects.

First, is the correct elevation is big (hence jack plate) to be removed once the correct height is found, second be able to trim in out ( for me I put a CNC on it )and finally found the correct prop to get it into the higher RPM range and it was the difference of 8 mph. I realize most of you would laugh at this improvement as its a little more than headway speed however I was able to achieve 16 mph-.but the difference is a 50% increase in speed.

Where else are you going to be able to make a few minor modification that would have that much of a dramatic effect by any type of rigging change? To me this was a major success.

I am going to take all of your suggestions. Even yours Mr FlyingScott. I will try to mind my manners, My response was reactionary and I was rude and I apologize, I think it was you suggesting I was wasting my time and that a prop change that would have no positive effect on anything that put me off a bit.


Thank you for your time and help! It is greatly appreciated.

Cj

 

[Scott Danforth]

if you run a jack plate, you also have the associated set back. you cant pick a height with a jack plate and equate to a hard-mounted height with less set back. you have two jack plates for a total of 13"

you will loose speed if you remove the manual jack plate and move the motor forward and not lower it down because the setback is different

your best bet is simply use the boat as it sits. you can spend hours and dollars to not gain much because you are grossly under-powered due to the hp limits. you already spend $320 on a manual jack plate and maybe more on the CMC unit (you didnt state new or used). However its yours time and money

my recommendation, learn manners, if a Mod catches that, you can be banned. many have been banned for less

regarding your boat, either live with the 13" of set back or not, just realize that your height will be different without the jack plate, and if you ever go to a different motor, you will need a different height then as well.

pick a prop that gets your RPM up.

then live with it. your 6mph increase will most likely go away with the least amount of current or a head wind or a shift in where you put the beer cooler

 

[flyingscott]

I dont believe your #s add up at all. Put up a video of before and after speeds GPS.