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Location: Lake Saint Louis, MO | I'm puchasing a new rig which comes with a Merc 115 HP Four Stroke equipped with a 3 blade 13.00" X 19 Black Max prop. I'd like to purchase a Comp Prop as a back up, and my choices are 13.5" X 15, 12.8" X 17 or 12.7" X 19. All three alternatives are four blade props. Which one will give me the performance closest to the 13.00" X 19 Black Max? Thanks! |
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Posts: 410
Location: one foot over the line | Lots of missing info, kind of boat, typical load, types of numbers that you are running currently, blah, blah, blah. Could maybe check out the mercury web-site, i think they have a prop-selecter option that might help you out. |
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Posts: 3508
Location: Elk River, Minnesota | Hiya,
I'd say just get another aluminum in the same pitch and diameter. If you hit something hard and any sort of speed, you will have lower unit damage...a comp prop will not save you.
If you check ebay, you can pick up a good used prop or even a new one for under $100 and probably cheaper than the comp prop anyway...
Steve
Edited by VMS 5/1/2013 12:22 PM
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Location: Lake Saint Louis, MO | Steve,
Following up on my prop thread from last May... I'm hoping you can help me do better on propping my boat. The boat is a Lund 1875 Impact, with a Merc 115 four stroke. The factory mounted the motor on the middle hole, so the cavitation plate is about 1/2" above the bottom of the keel. The rig came from the factory with a 4 blade Merc aluminum prop, 13x17 pitch. This prop actually gives me the best performance of anything else I've tried so far, but the tach hits the rev limiter (6100 RPM) with some left in the throttle. Hole shot is good, cornering is good, and top speed is 38 (GPS).
I thought I could get better performance with a steel prop, so I've tried a Mercury Vengance 3 blade stainless steel in 13 1/8" x 16 pitch. The hole shot is fine, but I hit the rev limiter (6100 RPM) with a lot of throttle left. The top speed with two guys, 1/2 tank of fuel a regular load of muskie gear is only 34 (GPS) and the steel prop seems to lose grip if I trim it as high as the 4 blade aluminum. I thought this rig would break 40 MPH with the steel prop, but actually my top speed dropped 4 MPH.
I also tried the rig with a Mercury 13 1/4" X 17 pitch Black Diamond aluminum. Hole shot was fine, and top speed was about 36. Again, it felt like there was a lot of throttle left when I hit the limited 6100 PRM. That prop did not corner as well as the 4 blade aluminum.
I'm not necessarily trying to optimize top speed, but I would like to find a steel prop that give me the best all-around performance. I'm not a big fan of operating outboards at WOT all of the time and would like to maximize fuel economy when I'm on big water and making long runs, keeping the RPM in the 4000 to 5,000 range for cruising.
Recommendations? Thanks!
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Posts: 1096
Location: Hayward, WI | Rev limiter shouldn't kick in til closer to 6400. Your 13x17 4 blade sounds about right. |
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Posts: 3508
Location: Elk River, Minnesota | Hiya,
In doing a bit of research on the motor, and assuming it was new last year, I would be interested in checking with a dealer on the rev limiter. The max hp operating range puts it up to 6400 rpm, so if it is topping out at 6100, I believe there is a potential issue there.
Now...given the rev limiter is correct and is set for 6100, you could go up in pitch on all counts. If it is limiting out, it means you have room to play with a higher pitch.
The Vengeance 3 blade is a great prop...I think the issue you may have had there is that going down in number of blades, then dropping in pitch is why I feel it didn't perform as you may had hoped. If you can try out an 18 pitch you, you might find it to be a little more to your liking, and may give you more throttle usage before hitting the limiter. I would not be surprised if the 18 pitch 3 blade steel was close. If it still hits a rev limiter, add another inch in pitch and try again.
The 4 blade felt better for handling due to the extra blade, which is also why it stays hooked up a little better than a 3 blade as you have more contact with the water.
Another prop brand to try on that would be Michigan rapture or a ballistic.
If you can get a chance to get the rev limiter checked to confirm the 6100, go up in pitch. That boat should be a 40 - 42 mph boat. With the gear ratio you have, you should be able to reach that mph when you are lightly loaded and be right at the rev limiter.
I think there is room to play with higher pitch.
Your other option is to go to a larger diameter. This will increase the handling of the boat without being too sacrificial to hole shot. If you go that route, you will not have a speed demon, but it should handle well.
Steve |
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Location: Lake Saint Louis, MO | Thanks Steve! |
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Location: Lake Saint Louis, MO | Steve: I just wanted to follow up and let you know I followed your advice in a subsequent PM and purchased a Michigan Wheel Rapture in 19 pitch. My top speed rose to 41 MPH on the GPS. The trim is very responsive, allowing me to trim the motor higher without blowing out. And I can cruise nicely at 4300-4400 RM and get 30 MPH. Works perfect for me and the IPS hull on the Lund Impact. Thanks for your help! Randy |
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Posts: 3508
Location: Elk River, Minnesota | You are very welcome :-). I'm glad I was able to help out. |
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