Df 225 prop and tach question

[TXstriper]

Regular Lurker but first time post. My 2015 DF 225 is suppose to red line at 6000 rpm. However, the "limit" red light comes on in tach around 5600-5700. Is this normal?
Also, does it hurt anything to run a 14.25 inch prop on this motor? It came from factory with 16 in prop.
Thanks in advance for any enlightenment.

[Harper]

When your limit light comes on, does the engine react with a reduced RPM, or does it just keep running as it should? I think the 14¼" prop is too small. I'd think the pitch would have to be really high. My DF150 runs with a 16" prop, too, with an 18.5 pitch. Where are you in TX?

[TXstriper]

I am located in Canton, TX. fish mainly Tawakoni and Fork. The motor appears to slightly reduce the rpms when the red "limit" light comes on. I am running this motor on a 22'3" center console, it's pretty heavy. I ran a 3 X 14.25 X 24P on it very briefly. Could only get 5300 rpm out of it. I was trying a 3 X 16 X 19P Solas Lexor Plus when I was hitting rev. limiter. I am wondering if the 14.25 X 24P might be pretty good if I am going to rev limit at 5600-5700. I had previously been trying to get to 5700-5900, thinking I would limit at 6000. When I bought motor it had a 3 X 14.625 X 25P prop. on it. It would produce 5100-5200 rpm. I am now thinking of taking the 3 X16 X19P and having it converted to 21P. Lot's less expensive than buying another prop.

[Moonlighter]

I suspect that your tacho is not telling the truth regarding the rpm readings it is showing.

I assume that this is a Suzuki analogue tach with the warning lights on the bottom section?

[Harper]

I am located in Canton, TX. fish mainly Tawakoni and Fork.

Those are a couple nice reservoirs. I live a bit west of Fredericksburg, fish solely in the Gulf, either out of Port Aransas or around Galveston. I think your idea of converting your pitch to 21 sounds about right for that boat. My DF150 is pushing a 20ft CC with w T-top. My prop is a 3x16x18½ and seems just perfect.

[TXstriper]

Moonlighter,
I am suspecting the same thing. Is this a common problem? Can the service techs recalibrate or something? It is really not so important that I want to throw a bunch of money at it, in the type of fishing I do.

Harper,
I too have a T-top. First boat I have had with one. How much drag do those things produce?

Thank you both for your time and responses!

[Harper]

Harper, I too have a T-top. First boat I have had with one. How much drag do those things produce?

I'm not sure. A fair amount, subjectively speaking. I think of the drag mostly when I'm getting 9-10 MPG towing it to and from the coast.

But I think the whole combo works well. With my boat, engine, prop setup, with a hydraulic jack plate, I consistently manage 4-4.3 MPG at my best economy cruise (around 4000 RPM, 26-27 MPH).

[Moonlighter]

I re-read your original post - about running the 14.5” dia prop. I tend to agree with Harper’s earlier reply that this is too small dia, and I speculate that the prop is losing grip at those higher rpms …. Which is causing the over rev light.

Also just make sure that there is nothing on the hull ahead of the prop that might be causing aeration - anything that is within 6” of the prop radius can cause disturbed water to hit the prop - things like water pickups, transducers and the like - you want then to be well clear of the prop.

I am curious though - on my DF115 when the engine over revs, it cuts back revs, and I have to drop it back into neutral for a few seconds before it will rev high again. This has happened a couple of times when I have been crossing bars and the prop has lost grip due to highly aerated water after a wave has broken.

Does that happen for yours too?

And I agree that tuning the 3 x 16 x 19 and tweaking it to 21 is a decent option, assuming that can be done.

Perhaps have a look at the Suzuki USA website for your engine hp and select the “boat tests”, they have tested a lot of different boats with each engine and you might find something similar to your boat/ engine, and get some idea from the test data about prop sizes. Bear in mind of course that their tests are done with lightly loaded boats and in the best possible conditions.

[TXstriper]

Moonlighter- I do not have to move throttle to neutral. Just back off throttle to turn off red "Limit" light and proceed. Also, it was actually the 3X16X19 that was hitting the rev limit. I have also tried 3X14.25X24 and 3X14.625X25 neither of which would do more than 5200 rpm.

[Moonlighter]

Did you look at the Suzuki USA website boat tests to find something similar to your boat?

They have a couple of 23’ centre consoles tested there and they all run 16” dia props. Blade area is important on these engines and a 14~” prop is not suitable.

Here is a link to a Proline Sport 23’ and they run a 3 x 16 x 20” prop and get 45mph at 6000rpm. Theres another test there of a SeaPro 239 deep V and they ran a 3 x 16 x 17 and got 42mph at 6000 rpm.

http://www.suzukimarine.com/Product%...012/DF225.aspx

Something doesnt sound right. The rev limiter doesnt activate at lower than 6000 (true) rpm. Most engines its either 6200 or 6400rpm. That tacho reading has to be suspect. If it is actually an over rev alarm then the tacho is reading wrong.

What speed are you seeing with that 3 x 16 x 19 Suzuki prop? That would be another indication of the tacho telling lies or the truth. If you are around that 40 ~ 45 mph then ……

It may be time to get it hooked up to SDS to confirm what those codes really are, it will have recorded every over rev event. And they can also check your tach vs what the ecu is saying. What the ecu says is the true rpm.

[TXstriper]

Thanks Moonlighter. Yes, I had looked at the boat test on the Suzuki website. As you noted, most are in the 45ish mph, which I am also. I am thinking a trip to the shop, especially with winter coming on, might be my best bet. The "Limit" light coming on at 5600-5700 rpm has me concerned. I, like you, are thinking somethings is not right with tach.

I also knew this motor was designed to run the 16" prop. I just didn't know if it hurt anything to run a smaller diameter prop on it or not. I am just trying to find the right combination to get everything working optimally. I am not that concerned with speed. Much more concerned with motor longevity.

Thanks very much for your input.

[Moonlighter]

Ok well with your boat speed being in the 45 area then I think there is a high chance the problem is the tacho telling lies.

Im no expert on props but I gather that smaller dia props are likely to lose grip due to insufficient blade area for the torque from the engine.