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Posts: 426
| I've got a 2016 Lund Rebel XS 1750 with a 2016 90 hp merc 4 stroke. Currently running a 13/17 Vengance prop. I currently run at 5800 rpm trimmed. The prop starts slipping at about 5700 rpm, I'm hoping a 4 blade will bite and handle better and let me fully trim out and handle better in mid range operation. Any thoughts? Thanks in advance. |
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Posts: 3480
Location: Elk River, Minnesota | Hiya!!
On your particular rig, a 4 blade is something in my humble opinion you should not need. The vengeance propeller is a decent all-around propeller, but does not have the trailing edge cupping needed to stay hooked up as much as say a tempest propeller.
I'm curious as to your top speed when you are trimmed out just before slipping, and am also interested in what bolt hole the motor is mounted in on the boat (i.e.. one bolt hole up, flat on the transom etc)
These are two variables to which can say a bunch about the set-up of the boat/motor/prop combination, and with that information, I can offer an opinion of what I think you might be able to do with the rig.
From the outset, I do feel you should not need a 4 blade on that boat as the lund boats ride high in the water and run fairly flat to the water as well (not a high-bow ride). After looking at the vengeance prop specs, I think what you have is basically a steel equivalent to a stock aluminum, which will give you just a touch extra performance things...a touch more handling (very little) and maybe a touch more speed. The prop is more or less going to be one that is essentially more durable that the equivalent aluminum propeller.
Due to the size of your motor, mercury has a very limited selection of propellers to go from. my suggestion is to look at some aftermarket props that have an aggressive prop design. One that comes to mind is a michigan Ballistic propeller. That is a very aggressive design, and it will have the lifting and handling capabilities I believe you are looking for. This is just a starting point for looking at props, though... something that has high rake and good trailing edge and tip cupping can and will do wonders for your rig.
Steve |
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Posts: 426
| Motor was factory mounted by Lund. Boat is in storage but I believe it is flush or one hole up (will check height Friday and post exact location). Top speed is between 39 and 41 mph with two people on a dead flat lake. I was considering the Ballistic prop in 13/17 pitch as well but was un sure of pitch due to the design of prop. Michigans' generic prop table recommended a 3 blade 13/21 Ballistic which I thought was too big. Mercury was recommending the 13/17 pitch in the 4 bladed , their Spit Fire series. I would prefer an after market prop over a Mercury one. Thank you for your response.
Edited by 7ovr50 12/28/2016 9:28 PM
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Posts: 1087
Location: Hayward, WI | You may also look at getting your prop worked over by a good prop shop. Tell them what you have going on and they may be able to tweek your current prop for what you are looking for. |
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Posts: 3480
Location: Elk River, Minnesota | With the prop that is on it, having it reworked will do very little as the blade geometry is not designed to be much more than a stock configuration. Cupping would help, but you would lose RPM, pushing you out of the pitch you could use. By the time you do all the tweaking on that prop to get something worthy to work with, you could purchase a different prop with the configuration you need, and already has the engineering in the prop to be efficient.
Your numbers are not too far off from max now and the speed you are getting is right in the ballpark, so I am thinking a 17 pitch would be about right. The ballistic might even give you a touch more top RPM, and...if the motor is mounted flush or one hole up, you can move that motor up another notch to gain another 100 RPM or so.
Now...if you are running 5700 with two people and gear, you are right where you need to be as if you run just by yourself you'd be hitting the 6000 mark which is the maximum for your motor.
If on the outside chance you find that the prop is turning too many rpms at top, then we can definitely move the motor up and go up in pitch. This would gain you top speed, but as with anything, there is always a trade off... here, it would be hole-shot, and the higher you move the motor, the less handling you have at trim. The nice thing about an aggressive prop design is it allows for higher motor heights without much sacrifice in handling...to a point. The boat rides higher and handles very well.
now...if you do a bit of exploring, powertech props have a huge selection of sizes and styles to consider. The blade geometry I would recommend would be something like an OMC raker...the only drawback to getting a raker prop is it will not have the right spline count to work. You will notice the blades are swept back a bit (called rake), and they are not huge round ears either... The design should have a decent amount of trailing edge cup (stern lift) and tip cupping (bow trim and handling). Most designs like this will have vent holes as well to help hole shot...
Lots of options and no doubt you can get into a prop that will do much more than your current set up now. If you do some calling around, you might be able to find a dealer that offers a demo prop program where you can try a variety of props in different designs, pitches and diameters. it is time consuming, but if you enjoy the process, testing, etc., it can be an enjoyable experience, and when you find the right prop for what you are looking for, the boat will just float along at cruising speed, will corner nicecly in a moderate turn, and will have the top speed you are looking for.
Steve
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Posts: 426
| ^^^^^^^THANKS^^^^^^^^ |
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Posts: 106
| What is the value in trimming all the way out ?
I don't think I have ever been in a boat that could be trimmed all the way out, and if I have it was only at near dead calm in a strait line at wide open.
My current boat, Skeeter 1825 MX with F150 Yamaha, I run mostly between 50 and 80% trim depending on conditions. |
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Posts: 426
| It's not about top end only. My mid range is more the issue. I want my boat to hold plane better at a lower rpm |
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Posts: 106
| 7ovr50 - 1/1/2017 9:24 AM
It's not about top end only. My mid range is more the issue. I want my boat to hold plane better at a lower rpm
A 4 blade prop will likely allow you to stay on plane at lower speeds. So will a hydrofoil, at much lower cost than a new SS prop. |
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Posts: 3480
Location: Elk River, Minnesota | Hiya,
To be honest, a hydrofoil only works if the lower unit is low enough in the water to where the foil is making contact with the water, and it is a bandaid for a set-up issue. Most boats that benefit from a hydrofoil are ones that are underpowered or those that have a prop that just does not have the capabilities to do what the owner wants but does not know other props exist out there to deal with the set-up issue.
If a boat is set up correctly for most efficient running, the anti-ventilation plate will actually be above the water line, thus rendering a hydrofoil useless. The right prop will be able to raise the entire boat out of the water more, thus giving a better ride, decent handling, and when propped correctly, the boat will just float along at cruise without it falling off plane.
Granted a 4 blade prop will help keep a boat up on plane at lower speed, they are really only needed on really bow-heavy boats or boats that have the motor raised up off the transom significantly. Most are used on heavy rigs or ones that people are pulling tubers and skiers with as well...
A classic example of needing a good 4 blade prop would be the older Ranger 690 series of boats that had the gas tank up in the bow. Ask Sled about his rig... He's running a mercury Rev4 on his rig which is a 4 blade version of the mercury tempest propeller. Its designed for lifting the bow, and maintaining handling. It's a great prop for that rig, but on a lighter aluminum boat, trimming would be very very sensitive.
I'd highly advise to NOT go with a hydrofoil... Unless the motor is way underpowered for the boat (the rig in question is not I believe), the foil will do nothing more than disguise the real issue... Get the issue at the source...
Steve |
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Posts: 106
| I'm not trying to be argumentative just posting my experiences.
My current boat is a Skeeter MX 1825 DC/WT with a Yamaha F-150 and 13-1/4 dia 19 pitch Reliance prop.
Top speed so far is 48.6 mph at 5940 rpm trimmed back about 80%. and good hole shot.
Due to good past experience I added a SE sport 400 hydrofoil. Top speed, rpm and trim stayed the same. But hole shot is a little faster with less bow rise and the minimum on plane speed dropped from about 22 to about 18.
My last boat, a Ranger 618 tiller with 90 4-stroke Suzuki. I had similar results. No change in top speed, 35 mph at 6000 rpm. But a noticeably quicker hole shot with less bow rise and a lower on plane speed.
Also several friends have had similar results. |
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Posts: 426
| I agree with VMS the prop is the issue. I've tried hydra foils before with little success. Maybe it was wrong for the set up I had but all the boats I've ever owned have been maxed out hp wise including this one. I've changed stock props on every one and got improved performance. My problem is the dealer I dealt with for years has retired. So my days of taking 3 or 4 props out to test are done. I have an idea of what I need based on experience. The reason I started this thread is because Lund only offers a 4 bladed Spit Fire prop for my boat this year. My 13/17 Vengence is not a factory option. I've got a lot of feed back from this post. My goal is to buy ONE PROP, hopefully the right prop. Thanks to all who have participated. I appreciate all the input.
Edited by 7ovr50 1/2/2017 4:58 AM
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Posts: 3480
Location: Elk River, Minnesota | ranger618 - 1/1/2017 7:07 PM
I'm not trying to be argumentative just posting my experiences.
My current boat is a Skeeter MX 1825 DC/WT with a Yamaha F-150 and 13-1/4 dia 19 pitch Reliance prop.
Top speed so far is 48.6 mph at 5940 rpm trimmed back about 80%. and good hole shot.
Due to good past experience I added a SE sport 400 hydrofoil. Top speed, rpm and trim stayed the same. But hole shot is a little faster with less bow rise and the minimum on plane speed dropped from about 22 to about 18.
My last boat, a Ranger 618 tiller with 90 4-stroke Suzuki. I had similar results. No change in top speed, 35 mph at 6000 rpm. But a noticeably quicker hole shot with less bow rise and a lower on plane speed.
Also several friends have had similar results.
What you mention here makes sense as my gut instinct would say the hydrofoil was not even in the water at top speed, and probably skimming the top at a minimum speed. With hole shot, the fin forces the bow down more to help pop the stern out of the water... trailing edge cup does the same thing without having to drill holes through the anti-ventilation plate reducing value.
Depending on what prop was on the boat, the same characteristics could be obtained with more efficiency and better handling to boot, by raising the motor off the transom more, having a prop that has better cup and rake, and most definitely one with vent holes. It is amazing the amount of engineering goes into these things.
This is definitely not meant to cut down others experience, as every boat is unique in and of itself, even if two boats are made from the same form (fiberglas).
Steve
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