Noob trying to understand relationship between motor trim and pulling to the side

[jim_s]

I've recently purchased an '01 Bayliner 160 w/ 90hp 2-stroke outboard - first boat, and my kids and I are absolutely loving the little thing. (wife is slightly less impressed, but understanding...

It came w/ a 3-blade prop (Michigan Wheel - something in the 12.75x21 range), which ran great, but w/ the 90hp engine, was lacking a bit in the ability to pull a slalom skier up. (a bit slow for the smaller guys, real slow for the medium-sized guys) I put a 4-blade Quicksilver Nemesis on it (12.8x19), which provides a very noticeable improvement in pulling the slalom skiers up, and makes pulling the tube easier, too - very happy with how its going overall.

The confusion is that w/ the 3-blade prop, the boat seemed to pretty much cruise hands-off - tracked straight, no real pulling in one direction or another. (The trim fin above the prop was dead-ahead straight.) With the 4-blade prop, it was pulling to the right really hard at WOT, and very noticeably at cruise speed. I adjusted the trim fin (tail end to the right) by a click, and that seemed to largely resolve the issue, I think.

I have subsequently put a set of SmartTabs SX on the boat (trying to improve hole shot further, and to get it planing at lower speeds for the sake of pulling the tube, and I'm a tinkerer...). Took it out for the first time w/ the SmartTabs on today, and the boat jumps on a plane almost immediately, and planes at ridiculously low speeds now. (the hole shot w/ a slalom skier seems improved, as well) Top end seems not to have been affected one way or the other. (It might be .5 - 1 mph slower, but not really noticeable.) However, the side-to-side pulling is going in both directions now, depending on whether I have the motor trimmed up or down more (this is all while on a plane). With the motor trimmed down more, it pulls to the right, hard. (its not safe to let go of the wheel when its pulling to the right...) As I trim it up farther, it reaches a pretty neutral feel (ie, side to side), but if I trim up farther, it starts pulling to the left (not as strongly as to the right, but a definite pull). I can literally steer the boat down the lake (on a plane) by trimming the motor up or down, depending on whether I need to turn left or right. (must be careful though, as the pull to the right is very strong, and the boat will whip into a nasty right-hand turn if I trim down very far from that neutral position).

Anyway, I'm not sure if I should play w/ the trim fin some more, or if finding that neutral spot means that I'm really at the ideal trim position, and I should just target that. (though the hard right pull at the lower trim concerns me a little, in terms of my kids driving it) I'd also like to understand the mechanics at work in the process, just for the sake of education.

I'm also not sure if the trim tabs are complicit in this behavior or not. I did not previously notice the left/right pull varying depending on trim, but I'd only run w/ the 4-blade prop once before adding the trim tabs, so I simply might have been too dense and excited about the 4-blade prop to notice at the time.

So, thoughts? ideas? explanations? suggestions? As mentioned in the title, I'm a noob, so I'm really hoping that somebody with some experience can tell me what's happening, as well as if there is anything that I can do to reduce the pulling tendency. (I love the 4-blade prop, so going back to the 3-blade isn't really something I want to do - I'll admit that up front... <

Thanks!

 

[jestor68]

Re: Noob trying to understand relationship between motor trim and pulling to the side

The only way to totally eliminate torque steer is with hydraulic(Sea Star) steering.

It's offered as an option by Bayliner(and others), and is pretty much standard equipment on high powered outboard boats these days.

There is no pulling and the steering wheel(and motor) stays where you set it.

Sea Star has a web site.

 

[jim_s]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Hah, that's awesome! Unfortunately, the cost of that system is worth a very considerable portion of my entire little boat!

 

[limitout]

Re: Noob trying to understand relationship between motor trim and pulling to the side

there is a trim tab on the motor and you can adjust that to counter acts the twist from the motors torque and take some of the twist out of the prop force so it doesn't pull on you.

 

[mike165]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Hah, that's awesome! Unfortunately, the cost of that system is worth a very considerable portion of my entire little boat!

Hydralic Steering is well worth the money,I have Ultraflex on my 215 Baliner

 

[dan02gt]

Re: Noob trying to understand relationship between motor trim and pulling to the side

The only way to totally eliminate torque steer is with hydraulic(Sea Star) steering.

It's offered as an option by Bayliner(and others), and is pretty much standard equipment on high powered outboard boats these days.

There is no pulling and the steering wheel(and motor) stays where you set it.

Sea Star has a web site.

+1 to this. It you can get your hands on one of these it will make your boat steer like a car. If not look at a dual cable no feedback system.

Check eBay for something used.

I hear people complain of steering torque some with 4 blade vs 3 blades.

You could also pick up a 19P 3 blade since you have the Smart Tabs to help getting you on plain. The Solas props a cheap enough the be feasible.

Lastly consider lighting up your Smart Tabs. It's possible they are set to stiff and causing some bow steer.

 

[jim_s]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Hmm... Interesting point/thought on the tabs. Thinking back a little, while it was pulling to starboard, it was listing slightly to port, and from reading online, that seems to be a common thread with bow steering (which due to your suggestion, I now know what that is - I didn't know it even existed previously <

I'll try lightening the tabs up a notch on the next trip out and see if they're still effective and/or if the pull/list goes away at all.

I love the idea of the hydraulic steering, and it looks like my little boat would be able to use the Bay Star setup (less expensive than the Sea Star), but you guys will lead me down the path to divorce court (far more expensive than hydro steering if I drop much more money into the boat any time real soon.

I appreciate the suggestions - I'll report back after the next trip w/ the lightened tab settings.

I could certainly go to a 3-blade prop, but the 4-blade has made such a remarkable difference (granted, at the lower pitch, so perhaps the 3-bl lower pitch would be similar), I'm real reluctant to give up on it quite yet.

Thinking further back (to the one outing w/ the 4-bl prop, before the trim tabs), I don't recall the pull being nearly as bad on that outing (ie, w/ 4-bl prop, but w/o trim tabs), so I'm putting some serious hope on dan02gt's thought on the trim tabs.

Thanks Again - you guys are very helpful and generous with your advice!

 

[jim_s]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Huh, the cable-operated NFB 4.2 systems seem pretty reasonably priced (around the same price as a 4-bl prop). Putting that on my wish list for the Spring, I think!

In trying to determine the proper length to purchase - do you measure the distance the cables would need to run from the steering wheel position back to the center of the motor? (ie, the path of the existing steering cable? - wheel to hull, hull to transom, transom to motor)

These things truly are holes in the water into which one pours money, aren't they?

 

[dan02gt]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Yeah you could measure it like that or remove your old one right before you order the new one and measure it outside of the boat.

 

[jim_s]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Wow. So I backed off on the SmartTabs settings by a notch (now at the lowest setting for the 40# actuators), and the torque steer intensity was decreased for sure - still there, but decreased. I've still got a very noticeable list to the left at WOT (regardless of motor trim setting), but the real problem was that I hit a wake side-on (ie, it was coming at me from the left, another boat had passed on my left going the opposite direction, so I was sort of skirting along it diagonally), and I thought for a moment that the boat was going to roll completely over to the left - really had to fight the wheel and quickly get off the throttle. Scared the heck out of me, and I'd never want one of my kids to encounter that.

I'd called up Nautilus (the SmartTabs folks) to discuss the list and pull w/ them (before today's outing), and they recommended that I go back to the 3-bladed prop, saying that the tabs would provide all of the advantages that I'd been hoping to get out of the 4-bladed prop (good hole shot w/ slalom skier, low-speed planing for pulling wakeboards and tubes). I was a little skeptical (but am willing to give it a try, as I trust their assessment of the situation far beyond my own, just didn't have time to swap props before today's outing), but after the side-on wake incident, I'm definitely going to give the 3-blade a try w/ the tabs on the next trip out. The ultimate question, I guess, will be whether the 4-blade or the tabs give me the better overall result - it seems that the two together are not a good combination. (Now, the other possibility is that the tabs just aren't working well on my boat, that it doesn't need attitude adjustment from the tabs, and its running too bow-down w/ the tabs - I'll have to carefully experiment w/ the side-on bow crossing w/ the 3-blade prop and the tabs on the next outing...)

Anyway, just an update, and see if anyone has additional input/commentary on things - this has been a very educational discussion for me!

 

[limitout]

Re: Noob trying to understand relationship between motor trim and pulling to the side

yep, someone above mention that the bow might be digging a little causing it to want to pull to one side or the other and that sounds like what might be going on for you.

 

[Rick Stephens]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Fascinating thread. Just wondering if possible small difference in tab mounting location, left from right, could account for variances in pull at different power settings? Worth the time to remeasure? Be really easy to be off a little.

Thanks for the discussion. Lots to think about.

Rick

 

[jim_s]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Valid question, Rick!

I measured and marked like a man possessed when I was installing the SmartTabs, but just went out and double-checked, and I'm within 1/16" from the center of the transom on both tabs (measuring from a mark at the bottom/center of the V on the transom, to the inner-most edge of the tab. The left-side tab is the smallest bit higher than the right-side, but by less than 1/16", so I can't imagine that's contributing any non-trivial effect. I had to mount the tabs somewhat more toward the center of the hull than ideal, due to the position of my swim ladder (as it is, I had to make little blocks for the ladder mount, to hold it out about 2" further than normal when its down, so that the ladder doesn't hit the tab when the ladder is down). I talked w/ John at Nauticus about the position before mounting them, however, and he said they would be fine there. (Its still outside of the minimum required distance, which IIRC was around 10 or 10.5 inches - I'm at 12.5") Anyway, with them a bit more inboard than ideal, its possible that the hull could be planing up to a small surface on the rear of the hull, then tipping off to the left due to torque, but from what folks have suggested, and what I'm experiencing, it really does sound more like the description of bow steer. (I guess the too-little-surface-and-falling-off-to-the-left would be chine walking? except that it never oscillates from side to side - it just stays nailed over to the left)

The other thing that I didn't mention in the prior message was that Nauticus said that the 4-blade prop could be providing significant stern lift on its own, which coupled w/ the tabs, might very well be causing too much of a bow-down attitude.

Bottom line, I need to get back out on the water and experiment a bit further w/ the prop and the tabs, and see what the best overall solution is. Nauticus, of course, says that the tabs are the right answer. I'm still a bit enamored w/ my 4-blade prop, but will happily go with whatever works best, despite any emotional bias I might have.

The other thing that might be interesting to try, would be to step down to the next-smaller SmartTabs actuator weight - I think they make a 30# actuator - and see if that works better w/ the 4-blade prop, but I need to first see if going back to the 3-blade prop w/ the tabs (currently using 40# actuators) resolves the list and bow-steer-like behavior, *and* still lets me pull my heavier friends up on the 65" slalom ski (*and* lets me plane at the 12-14mph that I'm currently able to plane at w/ the tabs and the 4-blade prop!)

I wish it was a bit earlier in the season to do this experimentation - its getting harder to find volunteers to try to pull out of the water, now that the temps are dropping!

 

[Rick Stephens]

Re: Noob trying to understand relationship between motor trim and pulling to the side

I can't wait to hear back on this stuff. And it sounds like the mounting isn't going to be any issue. I could see how easy it would be to be a little sloppy on the layout - you should see how low I accidentally got my sonar transducer - and I do this kind of stuff for a living! Taking that out of the equation is optimum. Great to hear.

I been building on a new to me 1990 boat - having the same problem - now that I am winterizing and fixing everything in sight and making changes, I wanna put it in the water and test it all out. Getting cold though and even my kid, a fishing addict if there ever was one, begs off.

Post back. Looking forward to what you find.

Rick

 

[Silly Seville]

Re: Noob trying to understand relationship between motor trim and pulling to the side

This truly is a very interesting and thought provoking thread...thanks for posting it!
Please keep us updated as this will be invaluable information for others to learn from.

 

[jim_s]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Gonna get out to the lake for a bit this afternoon to try a few things out. Looking for suggestions on meaningful tests, to try to ferret out the issues and hopefully converge on the best overall solution. Sadly, I won't likely have anyone to pull up on a ski, or if so, not for long enough to run each of these tests while pulling someone.

My primary priorities are:
1. Safety/handling - the bow-steering thing at WOT is not workable given that I'll primarily be out w/ my kids on this boat, and they love to drive the boat
2. hole shot for pulling (mostly small'ish - assume 180 lbs or less - generally a good bit less) slalom skiers out of the water
3. ability to plane at low speeds (w/ 4-blade prop and tabs, I'm planing at 12-14 mph, which is perfect for the kids who like to go slow on the tube)

Things I'm planning to try:

On each iteration, I'll be checking:

- time to plane
- time to 32mph (ave slalom skiing speed)
- lowest sustainable planing speed (tubing speed for younger kids)
- pull/behavior at cruising speed
- pull/behavior at WOT (especially listing tendency, and keeping an eye out for bow-steering symptoms, such as sudden pulls to the side when encountering wakes side-on, etc)

Configurations of the boat I plan to try include:

1. 4-blade prop w/ tabs
2. 4-blade prop w/ no tabs (tabs fully retracted via a rope)
3. 3-blade prop w/ tabs
4. 3-blade prop w/ no tabs (tabs fully retracted via a rope)

Additional thoughts/suggestions on things to try? Any suggestions on things I can to do try to mimic/compensate for not having someone to pull up? It'll just be me (all 130 lbs of me...) and a full tank of gas for most of it. I'll likely have a buddy to pull up (approx 140 lbs, on a small-ish 65" slalom ski) for a short bit at the end.

Appreciate any input!

 

[jim_s]

Re: Noob trying to understand relationship between motor trim and pulling to the side

So, spent some time on the water this afternoon. Bottom line, the 4-blade prop beats the pants off of the 3-blade prop for skiing, and the SmartTabs make a very noticeable difference in pulling up a slalom skier. (As well as providing significantly-lower planing speeds - 14mph w/ the tabs in action, 18 mph w/ them pulled up out of the water stream via a short length of cord on each, hooked onto the transom eyes).

I was using a buddy as my test dummy. He's a strong slalom skier, and starts w/ his rear foot out of the ski. The 4-blade prop and the tabs had him out of the water in about 3 seconds (this w/ a piddly little 90hp engine). He was laughing, as he noted that he found himself up and skiing outside of the wake before he was able to get his rear foot into the ski. (now, he was still only doing upper-teens/lower-20's at that point, but he was up.)

The sketchy handling at WOT turns out to be weight-distribution-related, but definitely associated w/ the tabs. When I was running by myself (130 lbs of me on the right side of the boat, along w/ 3/4 tank of gas on the left side), the boat ran level at all speeds w/ and w/o the tabs engaged. WOT had no tendency to dive to the left (or right) when encountering a wake side-on, etc. It took me 6 seconds to go 0-30mph both w/ and w/o the tabs engaged by myself. My top-end was about 1mph higher w/o the tabs engaged (43mph w/, 44 mph w/o). (this was all w/ the 4-blade prop).

When my friend arrived, he got in the boat (LHS passenger seat), we left the dock area, and as we subsequently got to WOT, the boat was listing noticeably to the left (w/ the tabs engaged). Disengaged the tabs, back to WOT, no list. Reengaged the tabs, went back to WOT (w/ the list again) and then I had him move to the center of the boat - the list went away entirely. The tabs clearly are causing the boat (recall, this is a little 16' boat, with the Bayliner 'bow forward' design, so its rather wide - 7'2" up front), to be very sensitive to side-to-side weight distribution. FWIW, 0-30mph took 8 secs w/ the two of us and w/ the tabs engaged, and took 7 secs w/o tabs engaged. Conversely, it took about 2 seconds longer to pull him up on the slalom ski w/o the tabs engaged, vs w/ the tabs engaged - so in a drag race (which, of course, I compete heavily in my little 90hp Bayliner... ;-), the tabs cost you, but in a real-world situation, they kick butt.

3-blade prop exhibited very similar behavior at WOT w/ the tabs engaged, though not quite as marked in terms of the listing - definitely still there though. (didn't do all the same tests w/ the 3-blade, due to time constraints, but wanted to check out the WOT behavior w/ the tabs).

I'm completely sold on the 4-blade prop and the tabs - the combination is a serious winner in terms of making the most of my little boat for skiing and tubing. (other claimed benefits of the SmartTabs, including overall smoother ride, reduced porpoising and *zero* bow-rise on the hole shot - its truly weird, but truly amazing - were in evidence, as well, though my top-end speed did not increase as some have apparently found it to)

I'm of a mind to contact Nautilus and see if I can get hold of a pair of their 30# actuators to try out, to see if they still provide the hole-shot and low-speed planing benefits, but perhaps reduce the weight-distribution-sensitivity issues a bit (still sounds like bow steer, though w/ my limited boating background, that's simply a term that I'm latching onto, as bow steer symptoms described by others seem to relate closely to what I'm experiencing). I need to do some more rigorous testing w/ the 3-blade prop, in all truth, but the season is drawing to a close (it was 65 degrees today, and its forecast to be in the 40's the remainder of the week, so this week is pretty-well shot - I may get another chance this coming weekend though).

Anyway, that's the latest update in the saga. This is *seriously* fun stuff - I should have gotten a boat a long time ago! (nothing has gone wrong yet, so its all sunshine, flowers and butterflies still

 

[Rick Stephens]

Re: Noob trying to understand relationship between motor trim and pulling to the side

All that said, makes me wonder if there might be a pressure difference between left and right actuators? Would account for the variables you note.


Rick

 

[jim_s]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Hmm, another good question, Rick... I'll see if I can get a rough measurement tonight - some kind of jury rig w/ a bathroom scale and a few different lengths of wood or such (to ensure they're the same pressure at different compression distances, as they're allegedly non-linear compression across their range of movement)

If there were a pressure differential though, I'd expect the listing problem to:

A) still be present w/ me in the boat by myself (boat ran perfectly level w/ the tabs engaged, and just me on one side and the gas tank on the other. 18 gal tank was about 3/4 full, so at ~6lb/gal, that should be right around 80 lbs of gas, vs my 130lbs of weight (and the gas tank is a bit farther outboard than my seated driving position, which should further equalize the forces, I'd think)

B) still be present regardless of the passenger moving to the center of the boat (was listing left w/ the passenger on the left, and leveled out when the passenger moved to the middle. If I'd been thinking better, I'd have had him move completely over to my side, too, to see if I got right-list.)

Neither of these is the case though - boat runs evenly in both of those cases (w/ the tabs engaged).

Good thing to rule out though, and should be simple enough to get a seat-of-the-pants idea on, so I'll take some rough bathroom-scale sanity-check type of measurements tonight, and report back.

(Why didn't I have him sit on my side of the boat?? Egad. <

The Nauticus folks are at a trade show this week, so wasn't able to talk w/ them today. Coming up on my 30-day money-back period (I don't want my money back, just to try out a set of 30# actuators, if they think that'd be appropriate), so a bit anxious to get hold of them.

Thanks for the thoughts and ideas!

 

[jim_s]

Re: Noob trying to understand relationship between motor trim and pulling to the side

Ok, well, the measurements were somewhat rough - bathroom scale, with several lengths of wood, which allowed me to position the tabs at 4 different angles across the range of movement - but gives me some level of confidence in the comparative, if not absolute, pressures being exerted by the tabs. Bottom line, they track each other pretty much identically (within the accuracy of your run-of-the-mill bathroom scale...)

Interestingly, the pressure on them increases as they are compressed further and further. This makes perfect sense in terms of what you'd expect a spring to do (even a gas spring), but goes counter to what I thought was my understanding of the behavior of the actuators. I'd been under the impression (need to track down where I'd read the thing that led me to this belief) that the pressure somehow magically *decreased* as they were compressed further, so that they would be more easily kept out of the water flow once on plane. Perhaps it was a damping function or delay that changes as they are compressed further - I didn't try to measure any of that - I was simply measuring downward force. Additionally, my method is somewhat flawed, in that I was measuring only the downward force perpendicular to the ground. With the tabs further down, and thus with the force pressing down at an angle, I'd expect the vertical component of that force to be somewhat decreased, compared to the more-compressed position, where the tab is perpendicular to the ground, and all of the force is being directed straight down. Even with that in mind though, there was a pretty significant increase in pressure as the tabs were compressed - around 10 lbs difference, which on a 40# actuator (the most I saw was about 32 lbs, but I have the actuators set at the lightest pressure position), is pretty significant. (Figure a 45 degree angle should decrease the measured pure vertical force by 1/2, so 25 degree would be a little over 1/2 of that, and I measured about 22 lb at the low end, and around 32 lb at the high end, so perhaps that is actually the difference I'm measuring...) I suppose that to be a bit more rigorous (bearing in mind my measuring instrument and technique... , I should pull the actuators from the tabs and measure their force that way, but I'm not trying to reverse-engineer the tabs/actuators, just make sure they're working as they should be working, which it appears outwardly that they probably are. Certainly, they're acting the same, regardless of whether its right or wrong.

So, I still need to talk w/ the Nauticus guys. Reading the Chaparral forums (those guys love them some SmartTabs! , a lot of folks with much heavier boats than mine found themselves going an actuator size below the Nauticus-reccommended size (guys with 2200+ lb boats going w/ 60 lb actuators, where an 80 lb actuator was recommended - my little dinghy weighs about 1300 lbs, by comparison), so it doesn't seem out of the ordinary that I might be a little over-tabbed (I claim coinage on this term, if it hasn't already been coined ;-) Granted, those guys are running IO's, which are better balanced than my 3-banger hanging off the back, but still...

Thanks Again, Rick, for suggesting this avenue of exploration!