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Replacement Prop Suggestions?
ToddSky	#21  Posted on 08/25/11 - 6:26 PM
Member Personal Page Posts: 36 Comments: 2 Joined: 05/05/11	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. 1986 Outrage 18'
Fishmore	#22  Posted on 08/25/11 - 11:05 PM
Member Personal Page Posts: 270 Comments: 0 Joined: 11/20/07	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.
Tom W Clark	#23  Posted on 08/26/11 - 7:06 AM
Member Personal Page Posts: 4280 Comments: 7 Joined: 09/30/05	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.
Fishmore	#24  Posted on 08/26/11 - 7:58 AM
Member Personal Page Posts: 270 Comments: 0 Joined: 11/20/07	Thanks Tom.
ToddSky	#25  Posted on 08/26/11 - 4:46 PM
Member Personal Page Posts: 36 Comments: 2 Joined: 05/05/11	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! 1986 Outrage 18'
Tom W Clark	#26  Posted on 08/26/11 - 5:16 PM
Member Personal Page Posts: 4280 Comments: 7 Joined: 09/30/05	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?
ToddSky	#27  Posted on 08/26/11 - 6:12 PM
Member Personal Page Posts: 36 Comments: 2 Joined: 05/05/11	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?? Edited by ToddSky on 08/26/11 - 6:17 PM 1986 Outrage 18'
Tom W Clark	#28  Posted on 08/26/11 - 9:57 PM
Member Personal Page Posts: 4280 Comments: 7 Joined: 09/30/05	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.
ToddSky	#29  Posted on 08/27/11 - 1:58 PM
Member Personal Page Posts: 36 Comments: 2 Joined: 05/05/11	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! 1986 Outrage 18'
Fishmore	#30  Posted on 09/04/11 - 6:50 PM
Member Personal Page Posts: 270 Comments: 0 Joined: 11/20/07	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.