Jackplate and propeller combination

[dwonders]

Ive asked the question before and got mixed reviews about adding a jack plate to my 2005 SX180 Skeeter with a Yamaha 115. After speaking with one of the local marine shops, they said I would benefit from adding one so I added a TH Marine 5" offset Pro High Jacker HP. They brought the motor 3" above where it was located originally. My current WOT RPMs are right at 5400 with a 21 pitch 3 blade stainless steel propeller and 49.3 GPS MPH reading versus the original 47 GPS MPH reading at 5000 RPMs. Ive read on this forum that the optimal RPM range is 5800 even though the Yamaha specifications for the motor are 4500-5500. Would I benefit from going to a different pitched prop? I know decreasing the pitch will add RPMs and increasing will reduce RPMs so I want to make sure I am operating within the peek performance range of the motor. Any suggestions on this would be greatly appreciated.
Last but not least along the same lines, while having the jack plate installed, larger jets were added to the carburetors which to my understanding were to basically bring the motor up into the 130 range. Did this have any impact or was I just taken to the cleaners on this one? Thanks and appreciate anyone's feedback..........especially on the later of the two.

 

[hwsiii]

Re: Jackplate and propeller combination

D, I will just tell you I hope your arburetor had a problem before they hanged the jets, beause in my opinion you ertainly didnt get lose to a 13% HP inrease hanging the jets out. You gained 2.3 MPH hanging to a jakplate and raising the motor. And don't hange anything else, it is fine the way it is.


H

 

[dwonders]

Re: Jackplate and propeller combination

should I have the original jets reinstalled

 

[hwsiii]

Re: Jackplate and propeller combination

I an't say beause I don't know what they hanged from or to, sorry.


H

 

[4JawChuck]

Re: Jackplate and propeller combination

should I have the original jets reinstalled

Do some research first and find out if indeed the only difference between the motors is jetting, on my 2003 75 HP Merc the only difference between the 75 and 90 is timing and carbs. I swapped the carbs out and adjusted the timing and it sure runs better...especially on the top end. I bought the factory manual and compared part numbers for the parts and got the carbs from a local used boat/outboard dealer.

Better know what your talking about before blaming the repair facility for ripping you off.

 

[kick bass]

Re: Jackplate and propeller combination

It sounds like you have hit a good combination.
Jack plates move the engine back, away from the boat turbulance.(Over simplified)
Your boat will handle the jack plate, this is good. The prop you are running sounds like it is good.
If you are trying to hit the 50 number, wait till fall, and you will do it.
In GA right now it is pretty hot. When the weather cools down your boat should pick up a few R's and you will be impressed!
As far as running the engine above what the factory specifies, don't.
You have found that it costs money for speed.
A lot of people want to get the most bang for their buck, only to realize the small pops are expensive. You have picked roughly 3 MPH and this is good.
I have two boats, a bass boat and a hot rod boat. The bass boat is set up just like I like it. The hot rod boat, poor thing, I am always trying something on it. Speed is a funny thing. Most of the things recommended here will not cut down on the realiability of your engine. Nor will they make your boat unsafe. I run a 6" jack plate on my bass boat. I want it to run as fast as it can. BUT, I don't want to go so far as to make it not realiable.
So, Stick with what you have, run it in the fall when the temp is 60 degrees, and the humidity is about 60% or less, and you will be impressed.

 

[dwonders]

Re: Jackplate and propeller combination

Do some research first and find out if indeed the only difference between the motors is jetting, on my 2003 75 HP Merc the only difference between the 75 and 90 is timing and carbs. I swapped the carbs out and adjusted the timing and it sure runs better...especially on the top end. I bought the factory manual and compared part numbers for the parts and got the carbs from a local used boat/outboard dealer.

Better know what your talking about before blaming the repair facility for ripping you off.

The dealer was the one who recommended adding the jets to the carb not me. I honestly dont think it made a difference myself. And I trust that when a dealership tells me something about the performance of my motor, its because THEY are the professionals not me.
Its not about blame, its about getting the best performance out of my boat and motor combo.

 

[kick bass]

Re: Jackplate and propeller combination

It sounds like you have a good combination.
Whether or not the jets helped I can't say.
It sounds like they have done this combination on other boats and it
worked. Kind of like a kit. I would have to see the numbers before the jets and after the jets. It would have to be on the same day, same conditions, then I might could tell you. Try your boat different days, different conditions, see how it does. But, it still sounds like a good combination, I would enjoy it.

It also sounds like you should be more confortable in the drivers seat, because that fat wallet you had, is way thinner and easier to sit on.
Bad Joke, please don't get upset.
Thanks

 

[4JawChuck]

Re: Jackplate and propeller combination

The dealer was the one who recommended adding the jets to the carb not me. I honestly dont think it made a difference myself. And I trust that when a dealership tells me something about the performance of my motor, its because THEY are the professionals not me.
Its not about blame, its about getting the best performance out of my boat and motor combo.

The only way to know if the jets made a difference is to swap back to the original and test, you changed too many parts at the same time to know what did what. Most engine model differences require hard parts changing. Jetting affects mixture and swapping jets would mean the factory setup was lean to begin with...not very likely.

Get a factory manual and check out the part numbers between the models yourself and do the testing. I was lucky enough to have a guy here who let me search through his spare carb parts bin and found all three carbs for my motor by part # to make the 90HP swap, I did the timing/syncronizing on the muffs in my driveway...I am very happy with the increase in performance...it was worth taking the time to do properly.

BTW I picked up 3 mph from a 6" jackplate and another 3 mph from the carb change on a 75/90 HP Merc on a late 80's 16.5' Tuffy Walleye/Musky boat. For reference my speeds are almost identical to yours although my sponsoned hull is sensitive to added weight...4 passengers and extra trolling battery +gear drops my WOT speed 7 mph. I run a 22" Laser II with all PVS holes plugged and hit about 6000 @ 48.6 mph rpm trimmed out with a single person and single battery.

What kind of prop are you using?

 

[dwonders]

Re: Jackplate and propeller combination

It sounds like you have a good combination.
Whether or not the jets helped I can't say.
It sounds like they have done this combination on other boats and it
worked. Kind of like a kit. I would have to see the numbers before the jets and after the jets. It would have to be on the same day, same conditions, then I might could tell you. Try your boat different days, different conditions, see how it does. But, it still sounds like a good combination, I would enjoy it.

It also sounds like you should be more confortable in the drivers seat, because that fat wallet you had, is way thinner and easier to sit on.
Bad Joke, please don't get upset.
Thanks

No harm..........wallet has been flat for some time now before I did the adds....

 

[dwonders]

Re: Jackplate and propeller combination

The only way to know if the jets made a difference is to swap back to the original and test, you changed too many parts at the same time to know what did what. Most engine model differences require hard parts changing. Jetting affects mixture and swapping jets would mean the factory setup was lean to begin with...not very likely.

Get a factory manual and check out the part numbers between the models yourself and do the testing. I was lucky enough to have a guy here who let me search through his spare carb parts bin and found all three carbs for my motor by part # to make the 90HP swap, I did the timing/syncronizing on the muffs in my driveway...I am very happy with the increase in performance...it was worth taking the time to do properly.

BTW I picked up 3 mph from a 6" jackplate and another 3 mph from the carb change on a 75/90 HP Merc on a late 80's 16.5' Tuffy Walleye/Musky boat. For reference my speeds are almost identical to yours although my sponsoned hull is sensitive to added weight...4 passengers and extra trolling battery +gear drops my WOT speed 7 mph. I run a 22" Laser II with all PVS holes plugged and hit about 6000 @ 48.6 mph rpm trimmed out with a single person and single battery.

What kind of prop are you using?

Not sure who the mfg is on the propeller because I dont see a stamp on it. Only markings is 13 1/2 x 21-K. Ive searched every and anywhere on it to see if I could find something but didnt have any luck.

 

[4JawChuck]

Re: Jackplate and propeller combination

I have had a few props on this boat (8 to be exact) and the 21 Laser II was a great holeshot prop but it was turning too much over the rpm range so I went and got 2 identical/different 22 Laser II's.

One of the Lasers is the older model and has built in vent slots and the other has the PVS holes, believe it or not there is 200 rpm up top between the two of them with the PVS model being the lower rpm prop of the two, I have blocked off the PVS holes on that prop.

Same speed though...so much for PVS holes not doing anything at WOT at top speed. The 22 pitch puts me right at 5450 rpm@44mph fully loaded which is perfect.

I have tried every height in the search for more speed and once your slip goes above 10-12% the speed drops off. I have tried High Fives, all kinds of four blade props but the best luck I have had is with the Laser II's, nice they are so readily available is such a wide range of pitches.

I had the best luck with setting the motor height so that the "stern wave bubble" (Is that a word?) is hitting the antivent plate about 3/4 forward of the prop when the boat is fully loaded, this give a little insurance once its just you out for rip on the water. Its a fine line as 1/4" higher on the jackplate is all it takes to ruin the speed and slip starts going up.

I tried an Inline Merc small ear chopper for an afternoon but all it did was vent and take forever to get up to speed, they don't work well on heavy boats like ours...surfacing props are very weight/wetted surface sensitive. The boat has to be light and out of the water on a pad to work a chopper or cleaver properly.

My water pressure is still pegging the meter at WOT over 30psi so I have good water flow to the motor, I recommend you plumb in a pressure gauge to monitor the pressure...if you drop below 12-15 psi your in for a big bill. I just have a cheapo vacuum/pressure gauge used for automobiles in the dash, cost me 12 bucks.

You don't mention if the speed you are getting is loaded or empty, if it's loaded I would say your right on the money with the pitch...if not a 20" might be a better all around pitch for pulling skiers and kids around etc. You won't lose much speed, I will probably have my second non PVS Laser 22" repitched to 21" just for tubing and skiing, it makes a huge difference out of the hole...and for the fun factor!

Have fun!

 

[dwonders]

Re: Jackplate and propeller combination

I have had a few props on this boat (8 to be exact) and the 21 Laser II was a great holeshot prop but it was turning too much over the rpm range so I went and got 2 identical/different 22 Laser II's.

One of the Lasers is the older model and has built in vent slots and the other has the PVS holes, believe it or not there is 200 rpm up top between the two of them with the PVS model being the lower rpm prop of the two, I have blocked off the PVS holes on that prop.

Same speed though...so much for PVS holes not doing anything at WOT at top speed. The 22 pitch puts me right at 5450 rpm@44mph fully loaded which is perfect.

I have tried every height in the search for more speed and once your slip goes above 10-12% the speed drops off. I have tried High Fives, all kinds of four blade props but the best luck I have had is with the Laser II's, nice they are so readily available is such a wide range of pitches.

I had the best luck with setting the motor height so that the "stern wave bubble" (Is that a word?) is hitting the antivent plate about 3/4 forward of the prop when the boat is fully loaded, this give a little insurance once its just you out for rip on the water. Its a fine line as 1/4" higher on the jackplate is all it takes to ruin the speed and slip starts going up.

I tried an Inline Merc small ear chopper for an afternoon but all it did was vent and take forever to get up to speed, they don't work well on heavy boats like ours...surfacing props are very weight/wetted surface sensitive. The boat has to be light and out of the water on a pad to work a chopper or cleaver properly.

My water pressure is still pegging the meter at WOT over 30psi so I have good water flow to the motor, I recommend you plumb in a pressure gauge to monitor the pressure...if you drop below 12-15 psi your in for a big bill. I just have a cheapo vacuum/pressure gauge used for automobiles in the dash, cost me 12 bucks.

You don't mention if the speed you are getting is loaded or empty, if it's loaded I would say your right on the money with the pitch...if not a 20" might be a better all around pitch for pulling skiers and kids around etc. You won't lose much speed, I will probably have my second non PVS Laser 22" repitched to 21" just for tubing and skiing, it makes a huge difference out of the hole...and for the fun factor!

Have fun!

We are still tinkering with things and one of those is going to a 4 blade 20. I use the boat strictly for fishing and the boat when I ran my speed was loaded with my typical gear (rods, tackle and vests) I usually keep the tackle to a minimum anyways. Once you get used to what the fish bite on here, there is no sense in carrying stuff I wont used.
The boat is going back in to have a water pressure gauge added.
Going to try the 4 blade to see how it performs and if there is too much slip, I will go back to the 21.
All in all the package thus far has already increased the performance of the motor so now it just a matter of fine tuning to the best possible. I guess it helps knowing the owner of the shop too.

 

[hwsiii]

Re: Jackplate and propeller combination

D, if it was me I would ask them where the extra air that is needed for an inrease in HP is oming from sine the arburetors weren't hanged and the venturi are the same. I used to build engines, but it has been a long time and the way they design engines now a days I don't believe hanging to larger jets without being able to get more air to mix with the fuel does anything or they might have alled it a 130 HP. This is just my opinion, but I doubt I ever would do business with them again unless, I went to another Yamaha shop and they told me that itwould give me those extra HP, beause I don't believe they will say that at all. If that is not true then what if your eally have an expenisive problem in the future.
If you notie huk had to hange the whole arburetors out.

H

 

[dwonders]

Re: Jackplate and propeller combination

made the decision tonight to have the originals back in and let well enough alone. Its a 115 not a 225!. She gets me from A to B and gets me on the water so for that I am thankful enough...........Thanks for your help AND advice.

 

[hwsiii]

Re: Jackplate and propeller combination

You are very welome D.


H