TV-18 handling

[J B]

Hi everyone, I recently joined this great forum and have some questions for you TV-18 owners.



I recently traded up to a '03 TV-18 115hp, from a '92 TX-17 60hp. The new TV-18 is powered by a 115 Mercury and 22" LaserII prop, motor bolted in the second hole from the top. Max top end with one person and gear, is about 5200rpm and 52mph (speedo). I am very pleased with the boat, especially for stability, storage, and roominess. It fishes really well. I am specifically looking for some feedback on a couple of handling issues...



1) This boat seems to take very little trim-out before it starts porpoising. Too little trim and the bow digs in. In choppy water (not rough) it seems to porpoise quite a bit. My old TX-17 seemed to ride up over the chop with little porpoise. What do you think about about adding a hydrofoil or transom trim tabs?



2) At WOT and motor trimmed-out, the hull lifts nicely. However, as the bow rises, it starts a slight heading to the left, causing me to correct with a right steering input. Since I have the no-feedback steering, I am not talking about steering wheel torque...just the

direction of the boat moving left. Possibly I have over trimmed the engine, but my RPM's are in check, and speed is rising. The outboard torque tab is factory set to one notch left of center. Wind does not seem to be a factor because it happens both directions.



Do these issues sound normal for the TV-18? Maybe I'm too used to the TX-17 handling since I owned it for 11 years.



Thanks for any input you all might have. This is a great forum and I look forward to the feedback.

 

[Bruce Yeaton]

Congrats on the new boat.



Your porposing issue may have something to do with the motor height. I'm no expert but my 90 is set to the very top hole (lowest hieght) and no porposing for me no matter how hard I trim out.



Again, just some advice here, your center torque tab may need to come back to center. Also, I seem to get harder steering when I over trim mine, what does your guage read when trimmed up? Mine reads a hair over the quarter mark.



Hope some of this helps. Some others should jump in and help soon. Have you called your dealer to see if they can help?



Enjoy the new boat!

 

[Andrew Zuber]

I've seen the exact same results as Bruce...I also have the 90hp motor...Mine is also set as low as it goes...this may be your issue with the porposing...



az

 

[Mark Hofman]

Jethro:



I've got a 150, and it also takes very little trim to get it zero'ed in. Generally I get the needle up a shade above zero between zero and 1/4 on the gauge. Any higher and it does start to bounce. In rough water, I'll bump the trim back down by just tapping the switch a time or two.



Motor height may have something to do with it, but I'm too chicken to go messing with it. Tapping the trim switch up or down gets me what I need to run properly.



I don't have a trim tab on my outboard, so I don't know how to correct the pull to the left in your situation. I don't get that kind of a pull unless I'm out of trim.

 

[J B]

Thank you all for the info. Maybe I am trimming too much. The boat seems fine with the trim just over the zero mark as you described. When I trim higher, at the 1/4 mark, the left pull starts and the boat really seems to be "flying", but RPM's are good (5100). Is this what you describe as "out of trim"?



My dealer also suggested moving the trim tab, so I'll try that next trip out. Also, my cavitation plate is even with the keel when trimmed down. Seems like the motor would be too low if I drop down to the top hole.

 

[Mark Hofman]

Jethro:



(I've posted this elsewhere, so please forgive me if you've already read it. This is for the benefit of anyone who is lurking...)



Finding the "sweet spot" for trim is a skill. Too many people simply rely on the trim gauge and end up hunting and pecking trying to find the ideal trim spot.



To find your sweet spot, IGNORE the dial!



Tuck the motor DOWN as far as it will go. On the gauge, you'll actually see negative trim of about 3 degrees. The prop shaft is pointed aft and down. This helps get the stern of the boat up out of the water and the boat up on plane.



As you hit the throttle, the speed will increase and your stern will come up. How quickly this happens is referred to as the "hole shot".



Once the boat is up on plane, the prop cannot be left in this "negative trim" position because it also forces the bow down into the water, and the driver will feel the steering wheel pull to one side (torque steer). The prop shaft is not parallel with the surface of the water, and the result is poor steering performance, a loss of speed and controlability.



So, once the boat is up on plane, come back on the throttle a bit to keep control of the boat. Begin tapping the trip switch UP. As the prop shaft comes up more toward parallel, the bow will rise and you'll see a bit of an increase in speed.



Keep bumping the trim UP a tap at a time until the bow begins to bounce up and down. That motion is called "porpoising" and is the result of the prop begin pointed AFT and UP. The motor is trying to push the stern down and the bow up, but the hull won't let the bow stay up. Your boat is out of trim. So...bump the trim switch DOWN until the boat stops porpoising.



At this point, you shouldn't be running at Wide Open Throttle (WOT), so apply some power. The boat will accelerate. As you accelerate, bump the trim switch UP until you experience the porpoising again. Bump it back down until it stops.



When you're running the boat wide-open, and you aren't porpoising or plowing water (torque steer), look at your tachometer and make a mental note of the RPMs. You can "fiddle" with the trim to try and coax a few more revs out of the engine. When the RPMs are maxed out without the bow bouncing, you've found the sweet spot.



The sweet spot is when the prop shaft is parallel with the surface of the water, regardless of the power settings. The only time a boat should be out of trim is during the hole shot, when the outboard should be tucked in as tight to the transom as it can be.



NOW you can look at the trim gauge to see what your WOT trim setting should be. As power is decreased, when you enter into a tight turn, or when you're dealing with less than ideal water conditions, you'll need to trim the bow down a bit. It's very similar to an airplane. As power settings are adjusted, the vehicle needs to be re-trimmed for ideal performance at that power setting.



On my boat and motor, with the current prop, the most I can coax out of the engine is 5200 rpms. If I want to try to raise that closer to the theoretical redline of 5400 to 5600, I either need to change the motor height or use a different pitched prop (go down from a 23 to a 21).

 

[J B]

Thanks MOFish, I'll need some more seat time to get it adjusted. As I said, this rig handles different than my old TX-17. That boat did not have anti-feedback steering so I could "feel" what was happening with the trim adjustment. This boat has the anti-feedback steering, so I don't get the same feel. I was concerned about the boat turning left as I trim-out, but maybe this is just the torque going the other way as I overtrim and the motor is no longer parallel with the water.



Is your motor also mounted in the second position from top, or do you have a jackplate? The other guys mentioned their motor was all the way down, so maybe I also need to look at that.



Thanks again for the response.

 

[Mark Hofman]

I've got five mounting holes on the motor for each bolt. The motor is currently set up mounted in the middle hole. I can go up two holes or down two holes, but I'm fairly content to leave it where it is.



A manual jackplate might be a good way to go, but I'd experiment with the trim settings first, then fiddle with the trim tab a little bit at a time. To me, a lower motor height will make the boat more sensitive to trim. If you raise the motor, you're going to need progressively more trim to raise the bow or to get out of the hole. But that's just speculation on my part.