prop size on Lowe Stinger HP18 w/115 optimax pro xs

Shane14

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Mar 6, 2012
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I just bought a new Lowe Singer HP 18 w/ 115 optimax pro xs, went to pick it up today and the prop they had on there was a 22p and the boat was very hard to steer at 3000rpm. max rpm was about 5600 at 56 mph on the dash (not gps). I noticed at top speed and on plane the boat was easy to steer, but at lower speeds the boat was difficult to steer and felt very grippy or catchy. I left the boat there so they could order a new prop. ANY SUGGESTIONS??? Or better yet does anyone own one of these boats or know of anyone who does? THANKS
 

steelespike

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Apr 26, 2002
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Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

Assuming a 2 stroke with 2.07 gear ratio the numbers don't quite add up.
slip says less than 1%, very unlikely.The numbers don't seem unreasonable just not quite right.
Likely an error, wrong speed, wrong gear ratio, actually a 4 stroke?.Prop doesn't seem at fault Is the prop aluminum or stainless?
Probably can't get accurate numbers until broken in.
Hard to steer meaning stiff? Are you trimmed in(down) at reduced throttle?
Is it hard to steer in both directions?
Adjusting the trim tab under the anti vent plate may help.
Dealer should know how.
 

Philster

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Sep 15, 2009
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Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

Optimax = 2-stroker

Steering issues = need to see where the antiventilation (AV) plate runs/sits in relation to the water when running on plane. In lieu of that, a pic from the side with the engine sitting vertically that shows where the AV plate or prop sit in relation (height-wise) to the bottom of the boat.

2.07:1 gear ratio

5000-5750 Full Throttle RPM range

Probably came dressed with a Trophy SS 4-blade prop (?) <--- this prop would be a slam dunk on a boat like that, especially if engine height is done right. What prop is on her now and what pitch/size??

Also, have you ever driven a boat with this sort of power-to-weight ratio?
 

steelespike

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Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

He mentioned a 22" but no other info at this point.
 

Silvertip

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Sep 22, 2003
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Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

"Catchy" steering may be due to the "No Feedback" (NFB) steering system if the boat has it. At slow speeds you tend the NFB clutch may be making you think there is a problem.
 

Shane14

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Mar 6, 2012
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Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

The prop used was a stiletto 22p X 14 3/4. stainless steel. We were at 3000rpm and trimed up a little. We did go thru a few props and the lower pitch we got the better the steering was. The last prop we used was a 17p not sure on the dia. and was too small, the mechanic is going to order a laserII 20p X 14 1/2. And the steering was hard in both directions.
 

Philster

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Sep 15, 2009
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3,342
Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

That seems too small, unless it was a 4-blader. A 4- blader of that size would be a good choice.

You are knocking off pitch and diamter but you were already kissing the high-end of the WOT rpm range. Would only make sense if you were going to a 4-blader.
 

bass guy mn

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May 31, 2012
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Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

I also just purchased a lowe stinger 18 hp on Saturday I picked it up. The dealer put a Laser 11, 20 pitch on it and the rpm is redlining and there is still some trim up to play with. The motor is in the 3rd hole. It goes to about 6000 rpm when the alarm goes off. The rpm's would go up a little more if I would allow it to. My speed on gps is just under 51 mph. I am too looking for some help here with prop selection. About 10 gallons of fuel and fully loaded with gear and wife and 2 kids.
 

CrappieJoe

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Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

Shane,

If you go to the Mercury Marine website under Engines > Browse Models > Optimax > Optimax Pro XS 115 > Engine tests
they will show you to use a 13.5 x 22 3 blade prop for best preformance.

I just bought a new Lowe Singer HP 18 w/ 115 optimax pro xs, went to pick it up today and the prop they had on there was a 22p and the boat was very hard to steer at 3000rpm. max rpm was about 5600 at 56 mph on the dash (not gps). I noticed at top speed and on plane the boat was easy to steer, but at lower speeds the boat was difficult to steer and felt very grippy or catchy. I left the boat there so they could order a new prop. ANY SUGGESTIONS??? Or better yet does anyone own one of these boats or know of anyone who does? THANKS
 

dan02gt

Chief Petty Officer
Joined
Aug 30, 2012
Messages
463
Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

Hard steering is generally a sign your motor is too high. I would have them lower the motor down one hole and see if it improves. As far as props the small gear case hurts your selection some but I would recommend a Trophy Plus or Laser II for that boat and the 22P would be about right.
 

dan02gt

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Joined
Aug 30, 2012
Messages
463
Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

I also just purchased a lowe stinger 18 hp on Saturday I picked it up. The dealer put a Laser 11, 20 pitch on it and the rpm is redlining and there is still some trim up to play with. The motor is in the 3rd hole. It goes to about 6000 rpm when the alarm goes off. The rpm's would go up a little more if I would allow it to. My speed on gps is just under 51 mph. I am too looking for some help here with prop selection. About 10 gallons of fuel and fully loaded with gear and wife and 2 kids.

Have them replace the 20P with a 22P and see where that gets you. The Laser II is a good prop for that boat so stay with it.
 

jestor68

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Jun 12, 2012
Messages
2,308
Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

If you put your numbers through the Mercury prop selector, you will see recommended a Laser II at 13.25 X 21" pitch, or 13.5 X 22 pitch. Either of these would be the correct pitch and brand/model prop for your motor.

Optional on that boat is tilt steering w/ HYDRAULIC steering. Have that fitted and you'll never feel an steering torque again at any speed/trim setting.

You can adjust that "trim tab" all day, but you will never get rid of steering torque at ALL speeds/trim angles.
 

jestor68

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Jun 12, 2012
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2,308
Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

The prop used was a stiletto 22p X 14 3/4. stainless steel. We were at 3000rpm and trimed up a little. We did go thru a few props and the lower pitch we got the better the steering was. The last prop we used was a 17p not sure on the dia. and was too small, the mechanic is going to order a laserII 20p X 14 1/2. And the steering was hard in both directions.

The largest diameter prop that will fit on the intermediate gear case is 14".

The Laser II, etc props for that motor in the 21/22 pitch sizes are 13-1/4, 13-1/2 diameter.
 

jestor68

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Jun 12, 2012
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2,308
Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

Bass Guy:

A 20" motor on a 20" transom mounted in the third hole? How high is the AV plate above the keel? Three plus inches?

The second hole would be the preferred mounting method on an aluminum boat.
 

bass guy mn

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May 31, 2012
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Re: prop size on Lowe Stinger HP18 w/115 optimax pro xs

Shane14,

Bass guy here, I ended up with laser 11
23 pitch. Works good, fully loaded with all gear & 1 passenger it runs at the lowered end of the rpm range but go lighter load & rpm is at the upper rpm range. I to have harder steering in the 3000 rpm range turning both directions. The lake has 20 inches of I've but when it melts I will I will play with the steering issue some more. I tested at least 5 different props and the 4 blade was better with steering but on rough water the boat would launch completely out of the water and when you hit the water it would through you vigorously in any direction and one time was almost tossed right out.
 
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