Choosing correct prop and jack plate height

[patrickj]

Ok guys i just purchased a 2000 progator 186fs with a 150 horse 2 stroke mercury, it has a 22 pitch stainless prop. Its turning it at 52-5400 rpm, 52 mph on smooth water, test with dash guage, the gps on my hds, and an iphone gps app all are within 1 mph of each other. I feel it should be going faster and im sure it needs a different prop, It has a jack plate and its set at the lowest point so i know its never been setup correctly. The question is whats my optimal prop size for top speed with decent holeshot. also my hub is about 5.5 inches below my pad, what kind of distance from my hub to my pad should i shoot for.

 

[steelespike]

Re: Choosing correct prop and jack plate height

Actually slightly ripply water would be a little bit faster.
There is probably a measurable starting point but basically keep raising the motor to a point just before venting becomes a pain.
Not sure about your gear ratio but using 1.87 at 5200 rpm 52 mph you have about 10% slip.
an acceptable number. 5400 indicates about 13% a bit high.
If you don't have any venting now you may be able to raise the motor quite a bit.
Play with the jack plate see what you can get.Be sure the throttle opens all the way.
Bottom is clean and smooth.
I assume you have a Fish and Ski ,probably not as fast as those dedicated to speed
it does seem that a 22" prop might turn more rpm.
I wouldn't be getting a prop until you are sure the setup is right on.
Motor in excellent tune,prop in excellent condition.
There are others that can be more specific about props and what they think of your setup.

 

[jestor68]

Re: Choosing correct prop and jack plate height

Ok guys i just purchased a 2000 progator 186fs with a 150 horse 2 stroke mercury. It has a jack plate and its set at the lowest point so i know its never been setup correctly. The question is whats my optimal prop size for top speed with decent holeshot. also my hub is about 5.5 inches below my pad, what kind of distance from my hub to my pad should i shoot for.

A 21 or 22 pitch would be usual for that boat/motor combination.

What are the compression numbers on the motor? It's 12 years old.

The best motor height is dependent upon what you plan on doing today; trearing around or pulling a skier. At 5.5 inches below the pad, the prop is completely submerged; not good for speed. Adjust the height in 1/2" increments until you find the best height for best speed.

You'll likely end up with two settings; one for top speed and the other(lower) setting for water sports. Some will say the norm is 3.5 inches below the pad, but that varies from one boat to another.

Here is an example of a inset pad bottom. The measurement is taken from the inset bottom, not the back.

 

[dan02gt]

Re: Choosing correct prop and jack plate height

What size is the jack plate and what SS prop is on it? The winning combo for that size 150 powered f&s is a 6" jack plate with a 21P Tempest Plus prop, running between 4.25" and 3.5" below the pad.

Start with the plate at 4.25" and raise it 1/4" at the time till your RPMs go up but your speed doesn't (indicating slip) the water pressure starts dropping, or steering gets stiff.

Don't expect much more than 55 out of that setup.

 

[jestor68]

Re: Choosing correct prop and jack plate height

Deleted: What was I thinking?

 

[dan02gt]

Re: Choosing correct prop and jack plate height

Jestor, Sorry I didn't explain what I meant it's the distance the prop shaft center line is below the running pad. When measured like this:

Frequently asked questions and answers about Boat Propellers, Custom Props and Boat Propeller

There are a few really fast hulls (Allison, STV, Hydrostream, Stroker) that run the prop shaft center line above the pad, but most of them are capable of 85MPH+ and can surface the prop.

 

[steelespike]

Re: Choosing correct prop and jack plate height

Jestor, Sorry I didn't explain what I meant it's the distance the prop shaft center line is below the running pad. When measured like this:

Frequently asked questions and answers about Boat Propellers, Custom Props and Boat Propeller

There are a few really fast hulls (Allison, STV, Hydrostream, Stroker) that run the prop shaft center line above the pad, but most of them are capable of 85MPH+ and can surface the prop.

One thing I think not mentioned but assumed is the ground needs to be level to get an accurate dimension.
Pavement is usually pitched or raised in the center to improve drainage and of course topography may not be level.We can't assume it is level and be sure of accurate measurement.

 

[patrickj]

Re: Choosing correct prop and jack plate height

Ok compression is 120 on all 6 except number 2 on the left its got 118, the prop that son it is a 22p power tech 3 blade, it has a 6 inch slide master manual jackplate with a 1 inch wedge it the top. RPMS are 5250 looks like at 52-53 MPH, hub is almost exactly 5.5 inches below the pad, and is at the lowest possible setting on the jack plate. The motor is 12 years old but has 58 hours on it and thats after i put nearly 9 hours on it this past weekend, recently had the carbs rebuilt and impeller and plugs changed after sitting in an insulated building for quite a few years just as a precaution, i know little about props but it seems like if i raised th emotor up to more like 3.5 inches below pad and bumped to a 23-24 pitch prop it would put my rpms at about the max reccomended and give me more top end. or am i confused

 

[steelespike]

Re: Choosing correct prop and jack plate height

I would raise it but wait for the results before selecting a prop.
Usually suggested to do one thing at a time and test.

 

[dan02gt]

Re: Choosing correct prop and jack plate height

Ok compression is 120 on all 6 except number 2 on the left its got 118, the prop that son it is a 22p power tech 3 blade, it has a 6 inch slide master manual jackplate with a 1 inch wedge it the top. RPMS are 5250 looks like at 52-53 MPH, hub is almost exactly 5.5 inches below the pad, and is at the lowest possible setting on the jack plate. The motor is 12 years old but has 58 hours on it and thats after i put nearly 9 hours on it this past weekend, recently had the carbs rebuilt and impeller and plugs changed after sitting in an insulated building for quite a few years just as a precaution, i know little about props but it seems like if i raised th emotor up to more like 3.5 inches below pad and bumped to a 23-24 pitch prop it would put my rpms at about the max reccomended and give me more top end. or am i confused

I doubt your going to gain any performance by doing that. More than likely the jack plate is all the way down because the power tech prop slips really bad when you try to raise it. What you're trying to do with the jack plate is tune the setup. That means you want the most amount of speed with the least amount of slip. I hope I explained that good.

Also, I doubt you'll be able to turn a 23-24 prop even by raising your motor. Unless your hull is under 1500lbs dry a 150 just doesn't have the power to turn a higher pitch prop on that hull.

The 21P Tempest is the prop you want. It is made for heavy boats like your fish and ski and can provide you with the bow lift you need to go faster and carry a load. It should also let that 150 (I'm assuming XR6) turn to it's max WOT RPMs giving you the best performance. I would also loose the wedge. It's giving you more negative trim (tuck with the motor all the way down) to help the boat get out of the hole, but by doing so it's taking away from your positive trim which is going to hurt top speed. Get it setup right and you shouldn't need it.

All that being said what kind of speed are you trying to get out of that setup?

 

[patrickj]

Re: Choosing correct prop and jack plate height

Well I test drove several other fish n skis before I purchased this one, this one weighs less than any of the ones I drove, I drove several 18'6" ers with 150's and they topped out anywhere between 58-65, yes it's an xr6. Maybe this will help... This thing Porpoises terribly, could the wedge cause that? On my trim gauge I'm half way between full down and middle guage before it porpoises so bad I have to trim down a little.

 

[dan02gt]

Re: Choosing correct prop and jack plate height

Well I test drove several other fish n skis before I purchased this one, this one weighs less than any of the ones I drove, I drove several 18'6" ers with 150's and they topped out anywhere between 58-65, yes it's an xr6. Maybe this will help... This thing Porpoises terribly, could the wedge cause that? On my trim gauge I'm half way between full down and middle guage before it porpoises so bad I have to trim down a little.

The porpoising could be any number of things. Having the motor so low is probably not helping that, but I don't think it's the wedge. I would raise it 1" to 4.5" below the pad and see if that helps, but watch for slip. How's the cupping on that prop? Is it really worn? If so it may not be able to hold the bow up and that would cause it to porpoise.

As far as speeds I'm not sure where your getting those numbers. Are they GPS? Pilot tube boat speedos lie like politicians especially when you start getting over 50MPH. Mine is dead on at 50MPH and dang near 4MPH off at 55. 58-65MPH on the GPS are 18' 150 powered single console bass boat speeds not fish and ski. What models did you drive? The Statos 486SF, Skeeter SL190, Nitro Z7 Sport, Ranger Reta 186, Triton Escape 186, and the Procraft Como 180 are all 52-55MPH boats on the GPS in the real world. Do you know the weight of your boat?

For reference my Nitro 188 Sport fish and ski with a 150 Optimax 6" jack plate and 21P Tempest will run a honest 57.x on the GPS with 2 people, 30 gallons of fuel, and all the other normal crap you have on a boat. It took a little money and time to get it there. It would run 53 on the GPS when I first got it.

What I'm trying to say with all this is your boat is really not doing bad speed wise for what it is. I think you can improve it some and make it drive better but don't expect 60+MPH.

 

[patrickj]

Re: Choosing correct prop and jack plate height

I drove a sprint 186 a ranger r77 and a Cajun 180 all with 150's but in those I was going solely off the dash guage as they didn't have gps's... Now that I've purchased this one I'm using my gps speed. I'll play around with the setup I have and try a few other props I have lying around if need be. The prop isn't wore out... I believe it came on the boat and it just has no use, no dings or even scratches. If I could get 55-57 with out the porpoising problem I'd be happy im gonna make a few baseline runs this weekend, then lift the motor an inch and try again and see if anything changes. I feel like I can get more out of it simply because it won't trim up as far as I'm used to because of the porpoising.

 

[dan02gt]

Re: Choosing correct prop and jack plate height

I think 55-57 is very doable. I think you're going to have to change prop to do it, but it will not hurt to play around with the setup before you do that. I spent a few hours dialing mine in with the jack plate. Do you have a water pressure guage?

 

[patrickj]

Re: Choosing correct prop and jack plate height

Yes I have a water pressure guage, got everything I need to get it set up right just needed a little more knowledge of where to start... I appreciate all the information, I will update after I try a few things tomorrow

 

[patrickj]

Re: Choosing correct prop and jack plate height

ok so i took the boat out and did a few baseline runs, i came out with 5100 rpm, 52mph. So i raised the plate an inch up to 4.5 inches below pad and i got the exact same numbers,raised it another half inch to 4.0 and i couldnt trim all the way out without loosing water pressure, so i backed the plate down a little at a time until i found a good spot for my water pressure. Now i can trim it fully still holding 12 psi of water but i only get 5200 rpm and 52 mph. what do i need to do next? go down to a 21 pitch prop?

 

[dan02gt]

Re: Choosing correct prop and jack plate height

A 21 pitch would help get your RPMs up a some. I think the big key to getting you a little more speed is figuring out what it going on with your setup. At 4" below the pad you should have no water pressure issues unless your prop is unable to lift the bow enough. This causes the motor to lift out of the water a little instead of the bow.

Go with the 21P Tempest Plus. Trust me you will be happy with it. It's big ears, high rake, and cupping will lift your boat's bow really well and you should be able to pick up a few MPH with it.

 

[patrickj]

Re: Choosing correct prop and jack plate height

well, right now its set at 4 and 1/4" and if i raise it a quarter inch the top hole for the water pickup is out of the water and you can see the prop, as soon as i lower it the 1/4 inch the hole is submerged and everything is fine, and i think the bow is getting up fine, when im trimmed all the way up i leave a very small foot print in the water.