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Posts: 422
| Hi,
I have a couple questions regarding the prop on my rig. First off, I am running a Crestliner 1850 fishhawk with a suzuki DF140 fourstroke. My prop is a suzuki 3X14X20 and does have some vent holes. Max RPM for this motor is 6200. Motor is mounted in the middle hole and the anti-cavitation plate (the fin just above the prop) appears to be just at or below the keel. The keel on crestliners run the entire length.
Today, out on the river with the wife and two young kids and full tank of fuel three batteries and TM, I got 39-40mph up river with about 5600 -5700 RPMs and then down river I got 44mph and 5700 - 5900RPMs but that was all the way trimmed throwing rooster. Just a note, the ol'miss was running a little high and swift today.
Just trying to tweak the set up to attain maximum performance for the motor. I would like to think I could get a few more mph's out of this, but I thought I would ask here for some opinions. I am thinking of taking the prop to a shop and having it changed to 19pitch to get the rpms up to the correct max. I can also have the motor raised two holes yet so I was considering that, but not sure how that would affect things. Would that in itself add rpms or does it do something entirely different? On top of that, crestliners like to run flat so would any of this add some bow lift?
A lot going on here, and the boat does run well overall now, just interested in getting it tweaked to run the best it can.
Thanks
Craig |
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Posts: 1096
Location: Hayward, WI | I would leave it mounted where it is. A good prop shop can rework your prop and it should help some. Mercury's Trophy prop works well on the Crestliners with Suzkis, has very good lift for the bow of the boat. |
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Posts: 422
| Thanks for the suggestion. |
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Posts: 3508
Location: Elk River, Minnesota | Hiya,
The first thing to consider is where are the RPM's when the boat is loaded with just you and your gear. If, when loaded this way you are under your max RPM, there is work that can be done, which may or may not mean getting the prop reworked.
In most circumstances, the standard motor mounting is one bolt up off the transom, which usually puts the anti-ventilation plate at or slightly above the lowest point on the transom. For most boat owners, this set-up allows for decent speed, and good handling and is best for aluminum props as they usually will not perform well at higher motor heights.
I am assuming here since you have vent holes in your prop, you are running steel...on that rig, I would say that is a good thing, and usually will allow you to play around with motor height to some extent, given the prop has a good trailing edge cup on the fins.
A couple of things come to mind...first and foremost, if you can do a quick test on how well the rig runs when lightly loaded in terms of speed, handling and hole shot, we can see what options might be available to get a more efficient rig.
In most cases, a good steel prop that has decent rake and cup will help the bow out tremendously, while lifting the entire rig out of the water. For bow lifting capabilities, a good amount of rake (the angle the blade meets the hub) will help lift the bow as will tip cupping on the blades. Trailing edge cup will help lift the stern, thus when combined will lift the whole boat more and maintain good handling capabilities. The nice thing here is the operator can usually raise the motor a bolt hole or two, or even 3 if possible to gain more speed and rpm without a major loss in handling. For every inch you go up in motor height, you will see about a 100 RPM increase.
When the combination is found (motor height, prop, optimum RPM etc) the motor will just seem to float along at cruising speeds and yet still have the "umph" for low end hole shot and optimum top speed.
No matter what, though, propping and finding a good set-up for your use is an exercise in being able to compromise.
If you can start with the basic numbers, then a plan of options can be considered.
Steve
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Posts: 422
| Thanks Steve, that has a lot of the info I was looking for. Yes, it obviously is a steel prop and I know it does have some cupping at the tips, I can feel that. Not sure how to check for trailing edge cupping and if it has a "good" rake. I can post a pic if you think that will help at all. Next, I will find time to get back to the river and go bare bones to see what numbers I get. I thought testing everything out with a "fishing" type load was what I should do, but I will try and get to the river at some point in the near future to test it out. I have two holes available to raise the motor if necessary. It may be a little bit before I can get to the river, we are going camping this weekend but I will get it done asap and let you know.
Craig |
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Posts: 422
| So I finally got out to the river today and was only able to get 5600 to 5700 rpms with no fishing gear, and it didn't matter if I was going up river or down, however I did gain a mile an hour or two heading down river. Any suggestions now?
Craig |
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Posts: 3508
Location: Elk River, Minnesota | Hiya,
With the numbers checked a second time, I would say you are over-pitched by about 2 inches....
If you can find a used prop that will fit, I would say find a Raker propeller in an 18 pitch. My guess is your hub is a little bit bigger than mine...if it was the same, I'd let you try mine...I have a 13-1/2 x 18 on my 90 and it does really well. I am thinking, though with your motor you would need the larger hub and a 14 x 18.
dropping in pitch by the 2 inches should give you about 400 or so RPM's, and then if you chose to raise the motor one hole, you would be right about there...
Steve |
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Posts: 422
| Thanks for the info Steve, I will see what I can find. Do the raker propellers come in 14 X 18, or do you know what brand does?
Craig |
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Posts: 3508
Location: Elk River, Minnesota | Hiya,
The raker propellers are 14-1/2" in diameter, so going from your 14 x 20 to the 14-1/2 x 18 will probably gain you about 200 to maybe 300 RPMs. If you raise the motor on the transom a hole or two, you'd be getting close...real close...
http://www.ebay.com/itm/JOHNSON-EVINRUDE-RAKER-14-5-X-18-STAINLESS-...
Steve |
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Posts: 422
| Thanks again for all your insight Steve.
Craig |
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Posts: 1096
Location: Hayward, WI | Don't think that Raker will fit, need to find 13.5x18 to fit a 4.25" gearcase, the 14.5x18 is for 4.75" gearcase. I would try a 19" Trophy. |
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