---

I have a 1986 Outrage 18' with a 2006 Mercury 4 stroke 115 hp EFI engine. I recently damaged the prop and want to replace it. The boat came with a spare prop (new in the box) but the one on the boat is aluminum and size 14x13p while the new spare in the box is size 13.25x17p. My question is why would they be different and which size is correct?
Thanks for any help!

---

What size is the damaged prop?

17 pitch sounds more like it...

Sell the new 13 pitch if not needed.

---

Joe, the one that was on the boat and is now damaged is 14x13p the spare is 13.25x17p. You think I should just get the hub kit for the 13.25x17p and use that?

---

13 pitch sounds awful small for a 115 hp motor.

What were your WOT RPM's with the 13 pitch you had on there?

---

17" is way too much pitch. Whether you need a 13" or a 15" pitch prop (or something close to it) depends on whether your Mercury 115 four stroke has the 2.07:1 gear ratio or the 2.33:1 gear ratio. 1986 was around the time they changed it.

---

Joe, the RPM was around 6000 (I think) and cruised nicely when throddled back to 5000 RPM at on plain.

---

Tom, the engine is a 2006 Mercury EFI 4 stroke 115 hp, I have no idea what the gear ratio is or how that changes the prop I need. The one I have ready to install now is 13.25x17p. Is this the wrong prop to replace my 14x13p prop??? Should I just order the same one that was damaged?? This is very confusing and Mercury seems to rate a variety of different size props for this engine. I'm trying to push a 1986 Outrage 18' with a 2006 Mercury 115 hp 4 stroke. Thanks for any thoughts.

---

I went on QuickSilver Propeller web site and it seems that they are recommending 13" x19" for my boat. If I knew the specs for the 1986 Whaler Outrage 18 I might be able to get a better answer but I don't know the weight fully loaded and some other questions so I just got the reccomendation from the length of 18 feet at this site.

http://www.qsprops.com/prop-selector/...tor/#step5

NOW I have a totally new set of numbers to ponder!

---

Yes, as I already explained.



No, not necessarly. You should only replace it if you know it was the perfect propeller. There are lots of propellers out there and the frequency of boaters needing propeller advice and replacement propellers is an indication that many, many of them are not propped correctly.

---

The gear ratio of your motor is listed on the Specifications page of your Owner's Manual and sometimes Mercury outboards have the gear set identified on the gearcase itself with a decal.

At any rate, I am reasonably certain your 2006 motor uses the 2.07:1 gear ratio. Answer a few questions and we will see what propeller recommendations we can come up with. The Quicksilver prop calculator is obviously doing a lousy job of recommending a prop.

How fast does your boat go at WOT?

What is the engine speed at WOT?

Where on the transon is the motor mounted? What set of bolt holes is being used now?

Do you have any unusually heavy accessories onboard your boat?

Where and how do you use your boat? What is a typical load for you?

---

I just worked with my friend to prop his Outrage 18 1984 model with a 2006 115HP Mercury 4-stroke Saltwater edition motor.

This motor has a 2.07 gear ratio. The aluminum 13.25 x 17 Black Max prop performed well producing 40-41 mph average at WOT. That is what he is running now.

A 13.25 x 19 Stiletto stainless steel prop was too much for the engine and top speed was around 35-37 mph as we took too long to get on plane and performance was sluggish.

We have ordered and are awaiting delivery on a Stiletto 13.25 x 15 pitch stainless steel prop.

Before we settle on a prop we will probably also test a 13.25 x 17 Stiletto prop unless the 13.25 x 15 ends up getting the motor to 5750 - 6000 rpm at WOT.

(I do not want to confuse this post with his tachometer readings because his tach is not working correctly but, the tach works good enough to see how the change in pitch affected the RPMs. I hope to have the tach fixed before the next round of testing.)

---

If the 13-1/4" x 17" BlackMax is hitting 40-41 MPH at WOT the engine speed can only be about 5200-5600 RPM.

That is WAY too low for a motor with a recommended WOT range of 5800-6400 RPM.

---

Tom thanks for all your info I was hoping someone would just tell me what to buy. lol I don't know my boats top speed at WOT because I don't have a speedometer on the boat. I noticed that changing from Fish and SKi to Off Shore Fishing on the Quick Silver Prop calculator, gave me the 13.25x17p propeller that I have now. Otherwise it keeps recommending the Black Max aluminum 13x19p. The gear ratio is 2.07:1 the motor is mounted on in the middle of the transom with four bolts through the transom. The average load seems to be about 700 lbs. I plan to use it for fishing and pulling the kids on a tube. both in salt and fresh water. With the broken prop 14x13p I would run at 6000 RPM with the WOT but throttled back to run at 5000 RPM because I thought it was bad to "red line" the engine. This is my first boat so excuse my ignorance, I've already drove over a stone wall submerged in the middle of a lake!!

---

Thanks for the information that 13.25x17p Black Max is what I have now to use. I have not tried it ,the Quick Silver web site keeps pushing the Black Max aluminum 3 blade 13x19p for my boat by weight and by length.

---

Tom, my understanding is that the service manual calls for WOT at 5000 - 6000 RPM at WOT. I double checked a few other sources to confirm. One source said max prop HP/RPM was 115.3/5500. So 5600 should be a good rpm for this engine according to that information. When my friend gets back from vacation I will check his service manual again to be sure.

Toddsky, try the 17 pitch prop and let us know what RPM you get at WOT. If you have a portable GPS (Garmin Nuvi or the like) it will display your speed over ground if you take it on the boat with you. When installing the new prop don't forget to grease the prop shaft with a waterproof marine grease and tighten the prop nut to around 55-60 foot lbs of torque.

---

If the Mercury 115 is a L4NA (and in 2006 I believe it was), then the recommended WOT range is 5800-6400 RPM and only getting to 5600 RPM at WOT is most certainly bad.

---

Todd, it might be wise to check the motor to see if it is a L4NA or not. My friends motor is not an L4NA and it was manufactured in the same year as yours but, you never know as stranger things have been true.

If your motor is an L4NA it might explain the 13 pitch prop you had on it before as that motor had a higher RPM at suggested WOT then it's predecessor of the same HP.

Tom, I thought the L4NA was manufactured in 2007? I believe it supported the Smartcraft gauges where as it's predecessor did not. I also believe that the cowling on the L4NA was rounded where as the older model was more rectangular.

---

Ok gentlemen here is the data I found the engine (I don't have the owner's manual) so here goes...Mercury 115hp manufactured in Jun2006 1732cc, Idle speed in gear 700, Max RPM 6400, weight 410 lbs, 115XL4S, Model #115F23HD.
I don't see anything that says L4NA. My cowling is rounded at the top.
As for the sea test on my 13.25x17p prop it will have to wait we have a hurricane coming and work is getting in the way too. But I will let you know the speed at WOT and RPM because I do have a GPS. Thanks Again!!

---

Todd - Looks like Tom was right and you have the higher RPM motor. As Tom suggested don't bother with the 17 pitch prop it will not work well.

Armed with that information I would sell the 13.25x17 prop. Or you can see if you can trade it for a 14x13 Black Max like the one you damaged. If you can not get a trade then see if you can borrow a Black Max 14x13 pitch prop. Then run some WOT tests and post the RPM/MPH results for suggestions on a better prop.

---

With a L4NA Mercury 115 on an Outrage 18 with the 2.07:1 gear ratio, you are going to need a 15" pitch prop, so, no, the 14" x 13" is definitely not a good choice for a replacement propeller.

I also cannot recommend the aluminum BlackMax propellers. If you want a Mercury brand prop, use the 13-1/4" x 15" Vengeance stainless steel propeller.

---

Thanks for the advice. I will try the 13.25x17 prop, just because it's on the boat now and let you know how it performed. In the meantime I will order the 13.25x15" Vengeance stainless steel.

I love this webpage there are so many smart boaters on it! Thanks again.

---

Tom,

I value your opinion and I am not doubting your suggestion as my gut told me Todd should look at a 15 pitch prop or possibly a 13 pitch Stiletto prop.

However, before suggesting either of those options I looked further back in this post where Joe had asked Todd:
"13 pitch sounds awful small for a 115 hp motor.
What were your WOT RPM's with the 13 pitch you had on there?"
and Todds response was:
"Joe, the RPM was around 6000 (I think) and cruised nicely when throddled back to 5000 RPM at on plain."

Given that Todd was saying his boat attained only 6000 RPM with a 13 pitch prop I thought he should go back to what he knows get some better readings and then ask for help again. My thinking was even if the 13 was not the "best" prop it is inexpensive and would be a better spare then the 17 pitch prop he had.

I would like to know why or what caused you to suggest going up in pitch? Wouldn't going up in pitch reduce his RPM's or is there something about the Vengeance that makes you believe the RPM's will not be lower? Actually I had assumed you might recommend the 13 pitch Stiletto prop so you really surprised me.

---

I do recommend the 13-1/4" x 15" Stiletto Advantage 4.25. The 13-1/4" x 15" Vengeance was merely the recommendation for a Mercury propeller. The Stiletto will equal or exceed the performance of the Vengeance and cost less too, but it might yield a little less RPM than the Vengeance.

A 13-1/4" x 13" Advantage will allow the motor to exceed 6700 RPM at 40 MPH even with zero (calculated) slip so I do not think it would be a good fit.

The reason why I think a 15"-ish pitch is right for this boat is that it should be good for 40 MPH as you yourself have demonstrated. At 40 MPH with a 2.07:1 gear ratio a 15" pitch prop will be needed to reach 6300 RPM with 7 percent (calculated) slip or 6000 RPM with 3 percent slip.

Now if your data is bad, and an Outrage 18 cannot go 40 MPH with a 115, then all bets are off. This is why it is so critically important to collect accurate speed data when testing propellers. The tachometer must be reasonably accurate, the speed measured by a GPS and speed runs conducted in two different directions and the results averaged to cancel out the effects of wind and current.

---

Thanks Tom.

---

OK GUYS here is the results of my runs on the lake with the 3 bladed Black Max aluminum 13.25x17 prop. Now I am not sure about how accurate the tachometer is but...I achieved a speed of 31 MPH at WOT while reading 4900 RPM's.

Honestly the boat was faster with the 14x13p aluminum Black Max 3 bladed propeller and WOT registered 6000 RPM and what I would guess to be 35 MPH.

So where do I go from here? IF I am still going with the Vengeance 13.25x15 stainless steel is that 4 blades or three? And if there is a better prop I will get which ever one you guys recommend or can come to some agreement on. lol Thanks Again!

---

Again, I would not expect the 17" pitch BlackMax to be the right size for your boat. Let's review what we know:

31 MPH at 4900 RPM with the 13-1/4" x 17" aluminum three blade BlackMax propeller.

35 MPH at 6000 RPM with the 14" x 13" aluminum three blade BlackMax propeller.

This 2006 Mercury L4NA 115 HP EFI motor uses the 2.07:1 gear ratio and has a recommended WOT range of 5800 - 6400 RPM.

Furthermore, we have reliable data that suggests an Outrage 18 with 115 HP should be capable of 40 MPH or so.

There are three glaring irregularities here that I see.

- The propeller slip with the 17" pitch is 19 percent. That is way too much.

- The propeller slip with the 13" is only 2 percent. That is way too little.

- The best speed reported so far is only 35 MPH and the engine speed is well within the recommended WOT range. It should be closer to 40!

While different models of propellers will yield higher or lower calculated slip values, in this case the two pitches tested are the SAME MODEL of propeller.

I strongly suspect some bad data here and I do not think it is the tachometer.

How has speed been measured? Have test runs been run in two directions with the results averaged? Have the two props been tested in similar conditions and with similar loads? Has the motor bee trimmed out to its optimal speed?

---

I got the speed from a hand held Garmin GPS. It was the same in both directions on a small lake serveral times. and Yes I trimmed the motor and got the boat up on plane for some distance at a steady speed WOT while only getting 4900 RPM. You asked earlier about the position of the motor. It is bolted in the center of 5 holes on the mounting bracket at the transom. Also I am just guessing at the 35 MPH speed on the original 14x13p prop because I never took the hand held GPS on the boat to see how fast it went it was just an estimate off the 31 MPH reading today. the 14x13p was definitely faster and seemed like it had more thrust. But that prop is history now. SO are we back to the
13-1/4" x 15" Stiletto Advantage 4.25??

---

Using a GPS is good. The motor being two holes up is good too. I suspect the 13" pitch prop yielded a speed less than 35 but even at 35 MPH, I am baffled as to why this boat is not faster...a lot faster.

Is your lake at high altitude?

I still think the 13-1/4" x 15" Stiletto Advantage 4.25 is your best bet. You don't even need to buy a new hub kit for it. It can be had for as little as $220, delivered.

---

Tom,

The lake is in CT and not at a high altitude. There is a good chance this boat is waterlogged because I had to replace the drain tubes they were all rotten. I took it to the truck scales and the boat, 6 gallon external gas tank, two batteries, motor (460 lbs?), the anchor and the trailer weighed in at 3200 lbs on the scale. That seemed a little high to me but I can't think of anything else that could be wrong.
I will purchase the prop you suggested and post the results of the speed and RPMs.

Thanks again for your input!

---

Todd, we finally got to test my friends 18 Outrage with a 15 Pitch Stiletto prop today. Now his Outrage has a motor one model year behind yours, it is rated for 115 HP same as yours and it has the same gear ratio. However his motor's top RPM is 6000 and yours is 6400.

I still thought the test might provide more information. The tests were conducted with a full tank of fuel all the standard gear except fishing tackle and three men two of whom weigh around 200 lbs and a third weighing 300 lbs. We tested a 15 pitch stiletto prop on the boat and reached 5930 RPM @ 39.5 MPH against the tide and we reached 6030 RPM at 40.3 MPH going with the tide. Top RPM on this motor is supposed to be 6000 RPM. We had a 17 pitch Stiletto prop to try also but, my friend did not want to run it. He felt that the 15 pitch was perfect for his uses. The prop had good performance coming up and on to plane and it ran well. At about 4300 RPM we were comfortably cruising at 26 MPH.

Hope that helps.