2006 Sportfish 1850/150 Optimax - Prop Questions

[311Hemi]

Also, how full was your gas tank? If it was full that is 39 gallons of fuel, which is close to an extra 250 lbs.

[Big_10]

Originally Posted by 311Hemi

FYI, your rpms at wot trimmed out are not far off from where I am at, especially depending on how much weight and the distribution vs me.

Also, I have found my tach is off slightly by running a tiny tach on the outboard. I believe I am off by around 100 rpm.

Last, when your running reach up and move the wires around for the tach under the dash. Both of the sportfish I have owned have had a loose connection and I could get the rpms to move some depending on how I moved the wires. Alonist like there was a lose connection or small short somewhere.

I will be back up with the boat this weekend, so I will pay a little closer attn to my rom and trim level.

Were your issues with analog gauges or the smartcraft gauges? I am running the smartcraft and they were pretty much spot on compared to the computer and the dyno.

I am doing all testing with a full tank of gas (and I agree, that much fuel is heavy)

[Big_10]

Originally Posted by REW

I suggest that you try both a 17 pitch prop and if not running the correct engine rpm, also try a 15 pitch prop.

You need to reduce the prop pitch and or diameter until your motor is turning its suggested WOT rpm when running with a typical load.

Also, it is nice to carry a prop that is pitched 2 inches less, for the times that you might want to do some heavy pulling, like tubing or skiing, and or if you ever plan to run your engine at elevations.

Since you are having a difficult time turning the motor in one direction, you should make a point to check the setting of the trim tab on the cavitation plate. Basically, you want to set the trim tab so that with the engine trimmed to optimum, at an optimum cruise speed - say 36 mph or so, you want to have the trim tab set, so that if you take your hands off the steering wheel, the boat does not pull either right or left. Remember, at a faster or slower speed - or with a lower or higher trim setting, the motor side to side trim is going to change. So you need to set the trim tab for the speed and motor trim setting that you use more than any other.

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Since you are from Bismarck, you are not running at high altitude. It does sound like your motor's performance might be down a bit. It would not be a bad idea to have your motor checked for perfect operation and correct total power by a good mechanic.
Normally, I would think that this motor should spin a 19 pitch prop on your boat at about 5400 rpm or so.

See if you can Dyno the motor to measure the actual hp of the motor. You would like to see a minimum of 150 hp, but many of these motor put out considerably more than 150hp if they are in excellent shape.



The other thing that you can try, would be to lift the motor so that it is lifted to at least the 3rd hole up - such that the motor is sitting about 2 inches above the top of the transom, with the cavitation plate - if the motor is vertical and sitting on a trailer - have the cavitation plate about 1-2 inches higher than the bottom of the transom. If the motor is currently too low, (possible), lifting the motor might increase the engine rpm by 100-200 rpm if motor drag is currently slowing the boat.

Here is a shop in Mandan, across the river that has an outboard dyno tester, so that they can verify the hp output of your engine. It would be worth it to get the motor tested to verify its hp output. If you find that you are low on power, you can work that issue before trying a bunch of incorrect props for your rig.

https://www.facebook.com/boatworksnd

If you do get your motor dyno tested, would you be able to post the results?



Good luck

Dyno results came in today. There was another run to ~5800 rpm, but unfortunately, that data was not available. Data to 5400 rpm is below. All data has been corrected per DIN std.


Rpm Power (hp) 4500 95.28 4600 102.7 4700 107.6 4800 114.7 4900 123.5 5000 130.4 5100 141.3 5200 146.8 5300 155.8 5400 162.6
Thoughts? 163 hp@5400 rpm doesn't seem bad to me, but I have nothing to compare to beyond the 150hp sticker on the motor. The torque (hp) rise also seems pretty steep, but maybe this is a characteristic of the optimax's. If this data is accurate, I'm leaving a lot on the table operating at 4700 rpm. When doing the run, I know he spent a lot of time adding load at 4800 rpm, so I'm fairly confident in that number (as well as the 5400 rpm).

Rew - you recommended a 15P prop for heavy pulling etc. Unfortunately, most of the Mercury stainless props recommended for this motor (except the enertia and vengeance) aren't available below 17P. I'm thinking a four or five blade for pulling, so that rules out the last Vengeance and Enertia. Any recommendations on what to look at for a 15P 4 or 5 blade prop? should I look at Merc 115hp props? Or maybe a different brand?

Thanks in advance for any input you may have.

[REW]

Big,
For a spare prop for heavy loads, you don't have to run stainless if you don't wish to run a stainless prop.

As much as anything , you want to find how your rig is running when you run a given pitch prop.

Pick up a 15 pitch aluminum, in the largest diameter that you can fit under your cavitation plate and see how it goes for you. I also wouldn't worry initially about using anything more than a 3 blade prop for this test. If, later, you want to run a 4 or 5 blade prop - fine. But, just do your initial testing with a 3 blade large diameter aluminum prop in a 15, 17 and 19 pitch prop and see how they all compare for you and your rig and your driving habits.

You can theorize all day long, but put the prop on the motor and put the rig in the water and do a bunch of testing to really understand how everything is working for you as a system.

Pay attention to your tach, as well as your gps for speed runs.

Good luck

[311Hemi]

I am running the analog gauges at this point. I have a digital hooked up to one of the plug wires to verify rpms on the analog guage.

I still have not had a chance to get out and do any testing. Wind was out of the south all weekend and Mille lacs was rolling good on the north end.

I can't see you needing to drop to a 15. Maybe a 17 tempest would be worth a shot. Not sure why you would be 400-500 rpms lower than me with a 19 tempest unless you have that much more weight in your boat. Both our hulls are the same weight and I push 5200 rpm and 47 mph gps with the 19 tempest. I don't test with a full tank of gas though, and usually don't have anyone up front when testing.

One other thing I forgot to mention is I have a 8hp Merc 4 stoke kicker, so I have a little more weight in the rear.

[311Hemi]

Big_10, any update on anything here?

I was finally able to get out again this past weekend in smooth water and do some testing.

I could hit 47 mph consistently at 5210 RPM's based on my tiny tach (included a shot of the analog gauge as well showing just under 5200). This was with 1/2 of gas, one another adult and two 50 lb kids sitting in the rear.

BTW, my spray line is maybe 1-2' up from the bow.