2006 Sportfish 1850/150 Optimax - Prop Questions

[Big_10]

I apologize in advance for the lengthy post, but I wanted to provide all of the relevant information up front, vs. making you ask the questions.

I recently purchased my first boat and am trying to prop the boat correctly. I am aware that this requires trying several different things (prop types, pitches, motor height, etc.), but given that I don’t have unlimited resources (time or money) I’d appreciate advice on what to try next.

My boat is a 2006 Crestliner Sportfish 1850 with 2006 Mercury 150 Optimax. The boat was purchased used in good overall condition with ~200 hrs on the motor. It came with a black max 14.25”x21 prop

This will be a family boat and therefore used for everything from watersports (tubing, skiing, etc.), to cruising, to fishing. It will not be used for tournament fishing and I have no need to go much more than 45 mph. In most instances, I’ll be more than happy with 40 mph.

The boat is loaded as follows for testing. This is the typical weight in the boat, but it can have +/- 400lbs of people/gear. I have found that this only makes a difference of +/- 150-200 rpm. All testing was done with no current and calm or very light chop conditions. All speeds are GPS.
Trolling motor and 2 batteries, ~30 lbs beverages, and ~40 lbs of people in front
~350 lbs of people and 100 lbs of gear in the driver/passenger seats and underconsole storage
~120 lbs of people on the rear bench

The first time I took the boat out it was loaded 400 lbs heavier than noted above and was running 40 mph @4800 rpm, far under the recommended 5500-5750 rpm. Based on internet research and Crestliner’s MY2016 recommendations, I purchased a 19P Tempest Plus. I also borrowed a 19P Vensura. Test results and observations are below:

Tempest Plus 19P - PVS plugged

Motor trimmed for max speed
44 mph @ 5000 rpm
~1/3 of boat in water (splash at ~rear seat posts)
Rear of anti-ventilation plate at ~ surface of water, but front much lower
Prop sounded like it was ventilating slightly, but did not lose speed at this point
Nearly impossible to turn boat to the right, would turn left with nearly no effort

Motor trimmed for decent handling
40.5 mph @ 4700 rpm
~1/2 of boat in water (splash at ~windshield)
Anti-ventilation plate parallel with bottom of boat and parallel but 1.5” below surface of water
Prop sounded like it was fully “hooking up”
Boat handled well on plane and turned easily in both directions

Other Notes:
Ventilated fairly easily during tight, mid speed turns, even when fully trimmed down
Time to plane was acceptable at 4-5 seconds for full plane
Engine did not sound “happy” (lugging) most of the time including at cruise
When fully trimmed down, boat was very difficult to turn left, but would turn right with nearly no effort

Vensura 19P - PVS plugged

Motor trimmed for max speed
40 mph @ 4700 rpm
~1/2 of boat in water (splash at ~windshield)
Rear of anti-ventilation plate at or slightly below surface of water, but front much lower
Prop sounded like it was ventilating slightly, but did not lose speed at this point
Nearly impossible to turn boat to the right, would turn left with nearly no effort

Motor trimmed for decent handling
38 mph @ 4600 rpm
Anti-ventilation plate parallel with bottom of boat and parallel but ~1.5” below surface of water
Prop sounded like it was fully “hooking up”
Boat handled well on plane and turned easily in both directions

Other Notes:
Ventilated only on really tight turns (fully trimmed down), much better than Tempest
Time to plane was good at 3-4 seconds for full plane
Engine did not sound “happy” (lugging) most of the time including at cruise. Seemed worse than tempest.
Reverse was not great as expected
When fully trimmed down, boat was very difficult to turn left, but would turn right with nearly no effort



I was kind of surprised that I did not gain rpm with the Vensura (I’ve heard that the tempest is “hard to spin” compared to other props of the same pitch). I was also surprised how much trim affected handling (steering force) on plane. Otherwise the results were as expected based on my first experience with this boat. I’m thinking I need to raise the motor a hole or 2 (+200 rpm/hole?) and go to a 17P prop (+400 rpm?), but I’m a novice in this area. Below are some questions I have:

1) Should I really base my prop selection off rpm at “max speed” when the boat is not controllable at this trim and I therefore won’t be operating in this condition? Or should I go off of the rpm when the boat handles well, which is where I would run it.
2) Is it normal for a prop to start to ventilate near max speed?
3) Is there anything that can be learned from how this boat handles on plane (difficult to turn unless the anti-ventilation plate is parallel with the bottom of the boat)
4) Thoughts on if my rpm estimates above are accurate?
a. Will I gain more than 200 rpm/pitch since I am running such low rpm and the engine torque curve is therefore likely much steeper than if I was in the recommended operating range.
b. Any experience with how the rpm may change switching from a tempest to a different 3 or 4 blade or the high five?
5) Will different pitches of props require different motor heights, or is a given type of prop happy with a given motor height regardless of pitch?
a. Basically, I’m wondering if I should dial the prop in a little closer before raising the engine, or if I should find the right engine height for my existing prop first.
6) I expect that raising the motor will not help blow-out during turns.
a. Will going to a smaller diameter prop help with this (the top of the blade is lower in the water than a larger diameter prop)?
b. Would you expect I could run a high 5 prop at the higher engine height and still see an improvement in blow-out during tight turns
7) Any thoughts on how hard it will be on the engine running it “as-is” for a couple more days until I can find the right prop?

I’d appreciate any feedback this group would be willing to offer. I am most familiar with Mercury props, but am willing to try other brands. I also understand that I want a lot from this boat, so I am willing to eventually have 2-3 props such that I can install whichever one best meets my needs on a given outing. As I stated above, I’m aware this is a process and I’m willing to try a few different props at a couple pitches and engine heights. However, I’m hoping that I can find something that works “OK” without having to go to that extreme and investing a week in the process.

[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.

----------------
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

[staylor]

I ran your numbers for the 19 Tempest to check and see if perhaps your tach was set incorrectly- but the numbers made good sense- around 15% slip-and the next thing to look at is the engine height and engine condition- so I'm seconding REWs post.

Sometime around 2006 there was a bad run of Opti coils- and motors running these coils have a habit of having cylinders drop out at higher speeds. A Merc dealer with a certified Merc Tech mechanic should be able to run a scope on the motor and check it out. Just mention the lack of top end and tell him you were wondering if your motor has the bad "Chinese" coils and he'll know what you are talking about. You can also ask them to put in a new set of spark plugs at this time, along with a new fuel filter. When they scope the engine they will check for proper fuel pressure- and an Opti has two fuel pumps and fuel rails with several rubber diaphragms that can leak air as they age that will cause a loss in power.

Check the position of the motor's cavitation plate relative to the bottom of the boat at the keel line with the motor trimmed so that the cav plate is parallel to the bottom. Ideally it should be at least even with the bottom of the boat at the keel line or anywhere from 1-2 inches above the keel line. If not, then the motor needs to be raised up using the series of mounting holes on the motor.

If the motor checks out OK, and your engine height is in the ballpark, then you can look into a lower pitch prop. I would skip the SS props for a trial and start with a 17 pitch Black Max aluminum- which a Merc dealer should lend you for a test for free as it is a very common size.

I ran a 2002 Opti for many years on a SF176 Starcraft- and when trimmed for top end it did have a lot of steering torque. The Opti 150 normally came from the factory without a trim tab under the cav plate- just a flat plate. If you have the flat plate then you can bolt on either a standard plate with an adjustable trim tab, or the so called high performance plate, which has an offset tab to clear the blades of the Tempest props. The plate runs around $25 bucks at a dealer- and he may refer to the plate with the offset tab as being for Mercruiser outdrives- but they are interchangeable. If this doesn't cure the steering torque then you can add a skeg mounted tab- for around $20. and some epoxy, and this will fix the steering torque. On my 150 Opti I ran the flat plate since the motor was raised very high and the tab was out of the water at high speed- this should not be an issue with your rig.
Doug

[Big_10]

Thanks for the recommendations.

The motor is currently installed in the second from top hole (second lowest setting) with the anti-ventilation plate ~.5” above the bottom of the boat when it is parallel to the bottom. I’ll likely move it to the middle hole once I get the rest of these things figured out.

Staylor – I ran the calcs on the tempest as well and got ~8.5% slip using 5000 rpm, 44 mph, 19P prop and 1.87 gearbox ratio (based on the merc prop selector). The slip seemed a bit low to me and your calculations seem more reasonable. Maybe I did something wrong with the calcs. What did you use for a gearbox ratio? I’m wondering if maybe the motor doesn’t have the ratio I think it does. Also, does a bad coil have any other indications beyond low rpm? The boat has decent hole shot and doesn’t sound “off” at high speeds, but I’m not sure if you can pick up 1 cylinder not firing by ear. When the bad coils “drop”, is it possible for them to fire when you are coming on plane, and then drop when you get to higher boat speeds?

Unless I have some epiphany, I plan to have the motor dyno’d next week and will post the results. This will answer a lot of my questions (engine performance issues, tach issue, wrong gearbox, etc.) for a reasonable cost. Plus, dyno traces are just awesome to have
I’ll also look into the trim tab.

[311Hemi]

I have a 2007 Crestliner 1800 Mirage with a 150hp Opti, pretty much the same boat you are running. I installed the front seating options and the rear bench from a Sportfish (found these on a Sportfish that was being parted out), so the interior is the exact same as a sportfish now.

My motor is mounted in the same hole as yours, 2nd from the top. I am curious through, are you sure your anti-vent plate is .5 above the bottom of the boat? I am pretty sure mine is at least 1" below the bottom on mine. Maybe the transoms are different, but I didn't think so.

I am currently running a Tempest 19 and I run about 47 mph at around 5200 RPMs when trimmed out for speed, which I calculate about a 6% slip (you should have a 1.87 gear box). This is with two batteries mounted in the bow and the trolling motor, and starting battery at the stern, and two adults (450 lbs) and two kids (100 lbs) (nobody in the bow). When I am running this about 1/4 of the boat is in the water if I remember correctly.

BTW, my vents have the largest hole plugs in. I get good holeshot, but I do get some searching of RPMs at certain cruising speeds where it starts to ventilate from the open holes in the pvs (I plan to install some smaller holed plugs). I have the same steering effects that you have. At WOT, it is very difficult to turn right. My Opti did not come with a trim tab, so I am thinking I need to buy one to help with the high speed turning. No issue getting adults out of the water when skiing with this setup.

I did try a 19p Ballistic SS prop, and got slightly higher RPMs but otherwise the performance was somewhat similar. Maybe not quite as much bow lift.

My plan is to lift the engine 1-2 holes, but that might not happen until next spring. If you do this please post your results. I would think this is where you would want to start before buying a bunch of other props.

[311Hemi]

Originally Posted by staylor

I ran your numbers for the 19 Tempest to check and see if perhaps your tach was set incorrectly- but the numbers made good sense- around 15% slip-and the next thing to look at is the engine height and engine condition- so I'm seconding REWs post.
Doug

Are you sure on this slip? I plug my numbers or big_10s in a calculator and your number is higher than what the calculators show.

[staylor]

Originally Posted by 311Hemi

Are you sure on this slip? I plug my numbers or big_10s in a calculator and your number is higher than what the calculators show.

The stock Tempest Plus is fairly heavily cupped, so you have to add around 1 inch to the 19 inch base pitch to compensate. I used 1.86 for the gearing, 5000 rpm, and 44 mph which yields 14% slip.

As for the coils, they can either break down at top end, or sometimes cause the motor to stutter on a hole shot. The coils in question have several different failure modes due to some lousy quality control- or lack of same. The problem is that if the motor has always done this since you bought the rig you may not notice the difference. I recall an old 175 V-6 Evinrude I traded in and told the dealer one cylinder was almost dead from a weak coil or bad powerpack, and was dropping above 4000 rpm. The dealer forgot this and eventually sold the motor to a fellow who said it was one of the nicest running engines he ever had....an Evinrude V-5? Seriously, the Opti- and most V-6 2 strokes are very smooth running, even when something is acting up a bit. Hence it's a good idea to have your motor checked out with a scope. The dealer can also run your serial number and give you a history of any repair that has been done at the dealer level.

One other "wild card" you should check is the throttle shutter to make sure the motor is actually going to full throttle. With motor not running, put it in forward gear and open throttle all the way. The throttle shutter at the top of the intake horn on the front of the engine should be open until it almost touches the stop- about .03 play to the stop is normal.
Doug

[Big_10]

Thanks again for all of the information.

I'll be picking up a trim tab this week and the boat is scheduled to be dyno'd/scoped next week. Hopefully I can raise the motor in the next couple of weeks. I'll post results as I get them.

I also checked the throttle shutter and the gap was .040" to .045". Not sure if this is far enough off to cause any problems...

[staylor]

Originally Posted by Big_10

Thanks again for all of the information.

I'll be picking up a trim tab this week and the boat is scheduled to be dyno'd/scoped next week. Hopefully I can raise the motor in the next couple of weeks. I'll post results as I get them.

I also checked the throttle shutter and the gap was .040" to .045". Not sure if this is far enough off to cause any problems...

Your throttle shutter is OK at .04-.045, so this can be eliminated as a possible cause of the low rpm....at least it's an easy thing to check....
Doug

[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.