RT 188 Prop to Pad

[missinfish]

I have a ‘16 RT 188 Pro XS 4 stroke with the standard gear case and the fixed 4” setback. When the boat was new I played with props , had. 19 pitch X7, and currently a Laser 2 20p. Planning on making the switch back to an X7 but I think my prop is too deep. I don’t trust the stock tachometer but it struggles to push past 5500 rpm and on my graph it’s a struggle to break 43-44 mph. It didn’t matter for years because I was fishing such small water. Relocated and fishing bigger lakes now and it’s annoying. I can trim til the rpm’s start to come up, speed doesn’t increase and the prop will blow out. Hole shot isn’t terrible, overall just feels like it’s way slower than it should be. I recall being close to 47-8 mph with the X7 the short time I had it.

Does anyone have a fixed setback with these props and been able to hit upper 40’s, I’m in the second hole on the motor from the top. Considering trying the 3rd. I took a prop to pad measurement, leveled the hull, and the anti cavitation plate. Measured from the flat of the hull( right next to the center strake) and the center of the prop shaft, the difference is 8”. And high seems very deep, compared to old posts I’ve seen with boats running these props.

I know this is an old topic and I searched a bunch, didn’t find it exactly what I was looking for. I’ve never moved the motor so it’s in the factory spot.

[GeauxTide]

Running an X7 at HOLE #3. I get 5600 in the winter and 5400 in the summer. You're not going to get 47-48 with a 19" prop on that hull. I got 46 in a lighter Lowe 18hp with a 6" JP and the X7.

[missinfish]

Do you have the setback plate also? Thanks for the feedback.

[Bill Reynolds]

I am following.
I have the same boat with the 4 inch set back plate and until recently I had a 115 ProXS 2 stroke. I repowered to the same engine you have. I started with a LaserII 20 pitch prop that I removed from the 2 stroke and ran into problems right away.
I sent the LaserII off to have it re-pitched to 19 inch and bought a 19 inch 3 blade aluminum to run as a backup. The Laser has been returned but I have not had time to install it.
I plan to re-start the project late next week and hope to find guidance in this post. I will report specifics as I go.

[GeauxTide]

Do you have the setback plate also? Thanks for the feedback.

No plate or setback.

[Bill Reynolds]

missinfish, I got your PM but replying here cause it’s easier.

1) Both My motor and set back plate are mounted in the first hole from the top. My Optimax was mounted in the second hole so my dealer mounted my 4 stroke there initially but it was too high and got squirrely at about 1/4 trim. I found a Mercury Service bulletin showing that the distance from mounting hole to prop centerline on the 4 stroke is 3/4 inch shorter than the Optimax. The dealer dropped it one hole and it settled down. The proper metric is prop to pad and I don’t know what that is. I will measure it when I install the LaserII and start with a clean sheet.

2) I don’t have speed/RPM on the Laser but I am only able to pull 5400 RPM and 43.5 MPH with the 19 inch 3 blade aluminum. I will start testing the Laser at the same PTP so to get a comparison and then start changing the height.

3) I should mention that since the Laser was on the boat, I changed to Lithium TM batteries and took about 100 lbs out of the bilge.

When I re-start the prop evaluation, I will be careful to record each step. This is tournament week though so it will be late next week.

[bassfisher444]

Get rid of the Laser 2, they never worked that well for my on my Tracker aluminum even after sending them in and having them cupped. An out of the box Powertec PTR3 performed better than a cupped and worked laser 2. If it was me I would get a Powertec PTR3 or NRS3 in 19" pitch, should get you in the high 40s at least.

[missinfish]

Get rid of the Laser 2, they never worked that well for my on my Tracker aluminum even after sending them in and having them cupped. An out of the box Powertec PTR3 performed better than a cupped and worked laser 2. If it was me I would get a Powertec PTR3 or NRS3 in 19" pitch, should get you in the high 40s at least.

Im not seeing a Powertech prop listed to gust the standard size Mercury gear case, I don’t have a CT lower. I’m more inclined to try a 4 blade then another 3, I actually have a Solex 4 blade 19p that never made its way into the boat but I should at least try it I guess. Want to get a baseline now that I have the vessel view for rpm and go from there. It will be interesting to see what Bill does as well.

FYI Bill in the second hole I don’t trim much past 1/4 because the boat never got any faster, and will blow out if you keep trimming. Sounds like exactly what you saw. But it’s pretty solid at the 1/4 trim, just slow and the rpm’s don’t seem high enough. Thanks for the feedback

[bassfisher444]

Im not seeing a Powertech prop listed to gust the standard size Mercury gear case, I don’t have a CT lower. I’m more inclined to try a 4 blade then another 3, I actually have a Solex 4 blade 19p that never made its way into the boat but I should at least try it I guess. Want to get a baseline now that I have the vessel view for rpm and go from there. It will be interesting to see what Bill does as well.

FYI Bill in the second hole I don’t trim much past 1/4 because the boat never got any faster, and will blow out if you keep trimming. Sounds like exactly what you saw. But it’s pretty solid at the 1/4 trim, just slow and the rpm’s don’t seem high enough. Thanks for the feedback

Right here
https://www.getaprop.com/powertech-n...140-hp-mercury

https://www.nettleprops.com/store/p/...r-Mercury.aspx

[tcesni]

You should be able to get a minimum of 46 mph in cool weather. I get 43 mph in my 2014 RT188 with a 90 hp Optimax and 46-47 mph with my 2018 RT188 and a 115 Pro XS 4-stroke CT. Neither boat has a set back plate and both have the tabs. Good luck getting it worked out.