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| i'm over-propped on my new rig...only getting 3000 rpms when starting out, which makes for a hard time getting out of the hole. also limited to 5100 rpms and 38mph top-end with the motor trimmed all the way up before it starts sucking air.
motor is a 90hp Optimax; came with a 13 3/4 x 21p Trophy Plus 4-blade prop.
the Merc prop selector tool suggests the following props:
for overall performance, mid-range, and handling:
- Trophy Plus 13 3/4 x 21p (current prop)
for acceleration:
- Trophy Plus 13 3/4 x 19p
- Vengeance 13 x 18p
for top speed:
- Trophy plus 13 3/4 x 19p
- Laser II 13 1/4 x 19p
i'd like to stay with a 4-blade for the lift getting on plane; does anyone have any suggestions for what i should try next?
or...could it be a motor height issue? mounted too low? it's in the 4th deepest hole, so it could be raised as much as 3 holes higher.
Edited by lambeau 5/21/2010 2:53 PM
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Posts: 440
| Cheapest will be raise that sucker 2 holes and see what happens. I bet that will take care of the issue. Maybe go to a Tempest Plus. Sometimes a 3 blade gets out of the hole just as good. | |
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Posts: 433
Location: Cedarburg, Wisconsin | I'd definitely get the motor heigth right first, or as right as possible with that prop. Then when you change props you'll see some predictable difference. If you are dragging the anticavitation plate, you're just wasting hp and the speed will remain pretty constant even with the rpms going up and down. Judging from what I saw on my rig when I tried a Trophy Plus, it definitely gets a better bite than my three blade prop and needs more venting on the holeshot (Take out some PVS plugs). I'd keep raising the height until your water pressure drops too far or until you start to blow out when the boat breaks onto plane.
When changing props the diameter can have a pretty big effect even if the pitch stays the same if your present prop has double digit slip or practically none at all. I went from a 23" Solas to a 23" Tempest Plus and it was 100 less rpms and 4 mph faster results, just from running with less slip do to the increased diameter and maybe blade geometry.
I'd think a 17 pitch Trophy would be in the ballpark when the motor is raised. It gives you some nice lift and you don't have that nasty motor torque driving the left side of the boat down at low trim levels you get with the Tempest.
Edited by Almost-B-Good 5/24/2010 2:43 PM
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Posts: 3480
Location: Elk River, Minnesota | Hi Mike,
Not sure what happened to my other post, but given your information, I have no doubt that it is a combination of over-pitched and too low on the transom. Not sure if the tiller model is the same design in the rear as the console model, but if it is, you can raise the motor all the way to the top and be just fine without any huge loss in water pressure. From what I recall seeing on TJ's boat last August at Vermillion it had a setback built in to the hull which allows for higher motor height.
But...seeing as though you are at 5100 rpms with a max of 5750 on that motor, it will be more than just lifting the motor. Going all the way up will gain you roughly 300 rpms, but a change to a 19 pitch 4-blade will get you close I believe. The 2" less in pitch will be right around 400 or so more RPM's, which will also help your holeshot tremendously. When you consider what you found in the prop selector, notice that the selector shows the 13-3/4 x 19 for two things: Acceleration and top speed....
I would get a handful of 4 bladed props and head to the lake for some testing....I'd start with the 19 pitch Trophy plus if you are looking for a 4 blade...but...if you decide to try a 3 blade a Tempest in a 21 pitch should be close as well. I have heard many good things about the tempest prop...grabs well and good top end. For your rig, that might be a good trade-off and still give you good stern lift as well.
Steve | |
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Posts: 32886
Location: Rhinelander, Wisconsin | This is a 90 HP, and takes a 17 to 19 pitch in a Trophy to make her run well. The transom is 25", and the motor height already in the clean water 1 hole up by design. Two holes up and you won't use all the trim any more from my experience. All the way up and the boat won't run at all. Two holes is probably too much considering the additional weight of the Pro Kicker. A 21 Tempest.. IMHO the 90 won't turn it. The two I have tested ran 17 pitch Trophy props, and probably could have turned a 19. | |
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Posts: 3480
Location: Elk River, Minnesota | So Steve, when they set these rigs up do they put a 20" shaft motor on them? From the pictures it looks like there is a designed set-back in the hull, which would allow for a higher motor height, but if they put a 20" leg motor on there, moving the motor up would be detrimental and would make sense not working..
Mike...is your motor a 20" shaft?
If the motor cannot move up without undo ventilation, then I would agree with Steve on this, and I am thinking with the numbers you have, a 19 would still work. There is a point of diminishing returns that will be met and if the 21 pitch is over that, a 19 could very well be turned in the correct range. My yamaha 90 cannot turn a 19 without losing close to 600 rpms, but put a 17 on it, and it is good to go...
Steve | |
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Posts: 720
| Hi Mike,
Steve is right that prop is way over pitch. Another thing I would suggest and this is especially with wanting four blades is playing with a prop with a smaller dia. I would look into a 13 1/4" or even a 13" prop. I personally would try out the Vengeance in a 19 if the make it or the Laser II. Because it seems to me by the way you describe the boat's performance that its having trouble with the prop's weight.
By the way that is a very nice engine. I hope you enjoy the new rig. | |
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Posts: 32886
Location: Rhinelander, Wisconsin | VMS,
It's an XL shaft, 25". transom height is close to 26". Cavitation plate to running bottom is probably 3.5". I've run one of these setups with several props and several attempted engine heights. Second hole is about right from what I've seen. | |
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Posts: 3480
Location: Elk River, Minnesota | That makes sense, then...3.5 inches to the running bottom is about all you can get...
Steve | |
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Posts: 247
Location: Uxbridge Ontario | Diggen up an old thread here as I have a few questions as well.
I feel I am having issues with my boat plowing and not getting the nose out of the water. My RPMs seem inconsistent as the type of weather I am in changes how the boat operates. What is the best way to get the nose out of the water?
Engine is a 75hp Optimax on a Lund 1750 Outfitter ss running the stock 13x19 Black max Al prop. Engine position is in the middle on the transom. Now, I am looking to get a stainless prop regardless and keep my current as a spare and shallow rocky water prop, but am a little confused about the best option to go with. My RPMs with (what Ill call) good water conditions is 5500prm at 41mph and my RPM in bad water is around 5100rpm at about 36mph (GPS speeds). I am currently able to run what I think is a lot of trim, but on the bad water days, am constantly blowing out the prop as the boat just doesn't seem to feel right.
There are a few guys selling used SS props near me that I would much rather benefit from than going brand new (especially to try out). Just not sure which one "should be better".
13-1/4 x 20p Turbo ($250)
13 x 17p Apollo ($150)
13 x 19p Laser II ($300)
What makes more difference for lifting nose? moving engine position or prop... or a combo of both?
Have gone through quite a few Topics, but still done have a firm grasp of Advantages and disadvantages of SS over Aluminum and what the different materials and their characteristics do for me.
Edited by HomeTime 8/11/2010 9:11 AM
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Posts: 3480
Location: Elk River, Minnesota | Hiya,
I assume the hot sticky weather was the issue with the motor in your other thread?
The best way to get the nose out of the water is to get a prop that has more tip cupping, which when placed at the tip will give the motor more ability to raise the bow out of the water. In a nutshell, I would bet your motor has more in it with a good prop change. The black max prop is pretty much a standard aluminum prop which gives good overall performance and handling characteristics at lower engine heights. As soon as you raise the motor off the transom a hole or two, the prop has very little capability to stay hooked up in moderate turns and at higher trim heights.
So...here is what I would suggest... Get to a stainless of some sort, or at a minimum, get a Solas aluminum in a 13-1/4 x 17 (or something to that affect). Out of the three that you mention, I would say you will have a hard time turning any one of those with your motor. Usually when one changes over to steel from aluminum, it is recommended to go about 2 inches in pitch lower than the current aluminum. The reason for this is due to the extra flex that a stock aluminum prop will have. In effect, your black max prop is probably acting more like a 16 pitch than a 17 pitch while under load. Steel will not flex anywhere near as much as a standard cast aluminum, thus a lower pitch is needed in most cases.
In the solas aluminum, what you get there is less flex due to a process called squeeze casting, which instead of the aluminum being poured into a cast, it is put in under pressure, which allows for the prop to be shaved thinner, yet keep flex down. So...it is a good prop when steel is not giving you much, but the aluminum is not good enough. I carry a solas as my spare from a michigan ballistic prop, and both are about the same in peformance and handling.
The ballistic prop when switched in place of a stock aluminum, I have not seen any sort of fall-off in RPM's, but that also was offset by raising my motor up to as high as it can go, and then some with a 4" manual setback plate. If I switched without raising the motor, I saw roughly a 300 rpm decrease over my stock aluminum.
If you can find one, I would suggest finding a ballistic in a 17 pitch, or something like a 15 pitch michigan rapture (no longer in production). I would feel a 17 pitch rapture would be a bit too much for your motor due to how thick it is. The ballistic is a thin bladed, highly cupped prop that does not drop off as much. If you happen to go this route, I would highly suggest moving the motor up to it's highest position on the transom.
Lots of variables here, but going steel will give you more lift, and the right prop will allow you to be at the motor's highest mounting position and still give good handling and top end performance.
Steve | |
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| What I might suggest as a potential option for you is to talk with your dealer and see if they will allow you to try a couple different props to find which one suits you best.
My boat came with a 21 pitch prop stock, I was reaching about 6000 RPM, which is about right for my 150 Suzuki. Well, I had and issue and my prop got dinged up so I ended up getting a loaner prop until my other one came in. Problem is the loaner was a 23 pitch.
I was curious how the 23 would work to begin with and welcomed the chance to try it and not have to buy it. After using the 23 for several weeks it was obvious that this was not meeting my performance needs. I hit 5500 rpm, but the holeshot was not very good.
See if they will let you water test a couple different ones to find the right combo for your boat. My guess is that you will settle around a 19 or so for best overall performance. | |
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Posts: 247
Location: Uxbridge Ontario | Steve,
what about that 13 x 17p Michigan Wheel Apollo prop i listed at the top? You know anything about it?
There is a guy local to me selling a brand new never used and for a great price, and as you mentioned I should try a 17 pitch, but I cant find much info though.
The prop that came on my boat is a 13x19 Black max... same as the 90 and 115 optis. | |
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Prop Question