Boat is drifting back and forth why????

[THEMACDADT]

hello all, i have a 175 with the 3.0lx power steering on a gen.2 when im ideling or going slow the boat steers left to right or vice versa without the steering wheel being moved. can anyone tell me why, and how to fix?

thanks in advanced!!!

 

[fwebster]

That is just bow steer.....the bow leads one way and you correct it only to have the bow head off in the opposite direction. Its normal for an outdrive, but you might want to check to be sure the drive doesn't have abnormal play in it either in the steering linkage or in the outdrive pivot points. To avoid it, keeping your eye on a distant object instead of the bow of the boat tend to reduce over steering.

 

[sbw1]

Torque steer associated with a single rotating prop is the primary cause. Counter rotating twin outdrive props are more stable.

 

[shogun95]

When going slow and seeing the issue, make sure you are fully trimmed down. That should help but will not cure it.

 

[390x]

You could have a worn swivel shaft/gimble ring. This would also allow a lot of steering without steering.

 

[Phlorida]

SmartTabs help a lot with bow steer on a boat of that size. They help with a number of other things too - a great investment.

 

[jmlloyd526]

Leave it alone and you will end up where you want to go. It will move left and right subtly on its own but trying to correct it will make you crazy.

 

[Go Aweigh2452]

As has been stated, if you have trim tabs that can be raised or lowered, lower them all the way down will minimize the wander. Its the hull and lack of a deep Vee hull that makes you wander. Another alternative is to install a Wander Fin to the outdrive planes. Google for a look at what it looks like but it does improve the boat going straight. Also, just don't try to over correct, it will wander back with out your help...

 

[Red Horse]

You have a V hulled boat. At slow speeds they will wander back and forth with out input from the wheel. There is not much you can do about it. I would check your outdrive for excessive side to side play and correct if needed be. You can go a little faster to compensate or give minor inputs to the wheel. You can also just let it go provided you have the room. If you feel it go to one side, give it a bit and it will come back to the other side. You will get where you are going in a zig zag pattern. There are several things at work to make a boat turn. When moving, the hull parts the water deeply and quickly. This speeds the water moving away from the hull. As the parting process gets completed, the water slows and creates drag on the middle portion of the hull. This is kind of hard to describe with out visual aids... Picture a stick on the centerline of your boat all the way thru the hull. This is the pivot at which your boat turns. This stick moves foward and back considerably and slightly side to side based on speed, trim, and other factors. At slow speeds the pivot is far aft. When going faster the pivot is farther forward. Next time you are on plane, look over your left shoulder and safely turn to the left. You will see that the aft end of the boat moves to the right in with respect to your direction of travel. Your pivot is far forward. DOes this make sense? Hopefully.

 

[Gunn]

Same boat here and same effect. Like others said, trim down at idle speeds to minimize the effect. Leaving it alone didn't work for me, my boat would wander more one direction than the other. I got pretty good at anticipating the wander and correcting before it started, always steering back and forth.

Tom

 

[Lord Farringdon]

Here's an article that talks about this phenomnem which is sometimes referred to as deep vee wander. The article suggests the problem is less noticeable in duo prop configurations but the admiral would disagree with that statement since she is well aware of the wandering tendancy of our boat in slow speed conditions. Perhaps a single prop has a tendancy to wander a particular way while a duo prop wanders either way.

http://www.boatingmag.com/skills/seamanship/controlling-low-speed-wander

In any case, there is nothing wrong with the OP's boat and the principle can be easlily demonstrated by trying to push (with one finger) a kids small toy boat slowly by the stern while trying to keep it straight. It's almost impossible! Try pushing a leaf; same problem. Interestingly, a piece of wood plank that roughly approximates a scale length to beam ratio of most of our boats will exhibit the same behaviour but a long narrow stick can be pushed in a straight line generally without a problem. This problem is about longitudinal stability and in most of our boats it would be reasonable to suggest that they are not designed with slow speed longitudinal stability in mind. Instead, they exhibit divergent stability where side to side oscillations get worse, not better. As an earlier posted pointed out, this is related to the pivot point of the boat which is generally where the most resistance to the water is. This centre of resistance is about the middle of the boat where the hull sides are deeper in the water, and the wetted surface is greatest. As the sternleg or outboard pushes the boat, any minor directional inbalance causes the bow to swing. Water resistance on the now slightly offset bow assists the swinging which occurs about the pivot point. The stern offers little resistance to the swinging since the hull sides (especially in a vee bottom) are often only kissing the water and the outboard or sternleg offer little lateral resistance. Although not related to slow speeds, aircraft are beset by this problem as well with many larger swept wing aircraft having yaw dampers which are sensors sending signals to a processor which in turn signals rudder actuators to counteract divergent longitudinal stabilty.


Overcorrecting for the problem only aggravates the situation. As with aircraft it has to be damped and that can only be done by pre-empting the swing which generally means steering non-intuitively in the opposite direction by trying to stop it reaching the heading you actually want it to reach. Once mastered, you can helm the vessel in a straight line but your passengers might notice alot of steering action going on by the skipper in order to maintain that pre-emptive situation. Any distraction or loss of concentration and she wanders again.

This whole problem goes away as soon as the bow lifts on power application and the centre of resistance forces head aft.

Terry

 

[melida]

Terry summed it up pretty well.
Even I have duoprops but single engine have the bow steer at idle or hull speed.
Trimming the drive fully down or deploying the trim tabs fully may not help 100%.
To correct this situation I'm engaging the autopilot and it does the job.
Just did it yesterday while leaving my berth where we are berthed stern to and bow ties comes from under water and tied to bow cleats.
While the wind is pushing from the sides boat wanders to the bow ties of other boats and have the possibilty to wrap them to my props.
Adding an autopilot would be a high cost item for 2 foot it is but it will save and profit it’s initial cost if you plan to keep your boat at least 4-5 years.

 

[Lord Farringdon]

Hi Sayat,

Yes, the article had a few suggestions in it that I didn't think would work, especially the trim tab suggestion. Tabs are for pitching forces not lateral forces. A rudder is used for that! Anyway, intersting to hear your autopilot automatically damps outs these oscillations at slow speeds. I don't think I'll be buying an autopilot anytime soon. Great if the boat had come with one but I would rather a radar before an autopilot. Does your auto pilot work on heading only or is it linked to throttle position for speed control as well? What is the minimum speed your autopilot can be engaged ie can you engage the autopilot in the marina while moving at no wake speed?

Terry

 

[sdarc]

In my experience with a single prop sterndrive dropping the tabs did minimize the wandering somewhat. With the twin props I have now the wander is less but still there.

 

[ChuckW]

In my experience with a single prop sterndrive dropping the tabs did minimize the wandering somewhat. With the twin props I have now the wander is less but still there.

Same here.

Chuck

 

[Lord Farringdon]

In my experience with a single prop sterndrive dropping the tabs did minimize the wandering somewhat. With the twin props I have now the wander is less but still there.

Same here.Chuck

A quote from the article :"Roy Ellis, senior project manager of product development for Monterey Boats, said it’s the result of water rushing aft along the sides of the boat and then collapsing into the hole behind it.This creates swirling vortices of water that exert suction on each side of the transom, pulling the boat back to the right and then left, Ellis said."

In the quote above it is suggested swirling vortices at the transom create the uneven force that sets the hull turning one direction or the other. Vortices are well known drag culprits. in aviation wing tip vortices are a major contributor to aircraft drag. This type of drag is created through high pressure (relative) under the wings attempting to equalise with low pressure (lift) ontop of the wings at the wintip. When atomospheric conditions are right, it manifests itself at lower speeds during approach as swirling white vortices at the wing tips. With the advent of composite materials, aircraft manufacturers have attempted to overcome this type drag by incorporating 'winglets' and even retrofitted them on older designs such as the B767. For the airlines (and boat owners), reduction in vortice drag equals a reduction in fuel costs.

So vortices are certainly a major drag on the hull and when you think about it this can be shown in a small dinghy. Try rowing fast in a small dinghy (no outboard to affect lateral forces) and then stop rowing abruptly. Most dinghies will immediately turn one way or the other quite sharply; a clear indication that transom vortices and their drag are at work.

So how do trim tabs help to stop these oscillations? As evidenced by the comments above by sdarc and ChuckW they seem to help but do not overcome the problem entirely. I stated before that they are effective in pitching moments but have no effect on lateral sideways forces. However, the angle of attachment of trim tabs in a deep vee suggests there are components of both so their in lies part of the answer. The other reason extending the tabs may be of some help is that coupled with the transom vortices drag, they create more resisitance at the rear of the boat. More real world examples here. Sailing vessels in heavy following seas will often extend rope or even chain out the rear of vessel in order to keep the bow straight and resist broaching. In this case and the case of trim tabs being extended, the centre of resistance is being moved aft which gives more longitudinal stability.

I personally have not noticed trim tabs having any affect whatsover on the wandering problem however this may be due to size of the tabs on my vessel (Melida has often commented that increasing tab size has numerous benefits) coupled with very slow 'no wake' speeds that, in my case, would reduce their effect.

Sorry for continuing to contribute to this thread (that probably should have died by now) but I find the subject interesting and just couldn't help myself :grin: . Anyway, it's more boat related than talking about Wayne! :lol:

Terry

 

[melida]

Hi Sayat,

Yes, the article had a few suggestions in it that I didn't think would work, especially the trim tab suggestion. Tabs are for pitching forces not lateral forces. A rudder is used for that! Anyway, intersting to hear your autopilot automatically damps outs these oscillations at slow speeds. I don't think I'll be buying an autopilot anytime soon. Great if the boat had come with one but I would rather a radar before an autopilot. Does your auto pilot work on heading only or is it linked to throttle position for speed control as well? What is the minimum speed your autopilot can be engaged ie can you engage the autopilot in the marina while moving at no wake speed?

Terry

Hi Terry,

My boat didn't came with an autopilot installed but had gps and radar.

I needed the autopilot firstly for long cruises but it helped me to correcting listing when I'm solo cruising.

It's raymarine as same as the gps and radar and they hooked to each other, tough they work independently. The networking helps to track a waypoint or a route I've created on chartplotter and could follow the remaining distance and time to the target wp or route. But ih has it's own heading sensor called fluxgate compass which from gets the heading parameters. It's indifferent from throtle and I wish there would be an alarm gotten from radar while an object approaches
faster on the mfd and engine cuts the throtle before collision.

There is no minimum speed for engaging the autopilot however a car's cruise control needs to run at least 30km/h. My idle speed is 3,5 knots and autopilot keeps the course straight as same as at 18,5knots on plane or higher.

Some times I think that autopilot is a better investment than the bow thruster which I need for it on summer since our docks are cement and don't want to damage my blue hull.

Radar and AP is almost same price here don't now how much there but strictly recommended if you cruise long distances can amortise its cost.

 

[melida]

I personally have not noticed trim tabs having any affect whatsover on the wandering problem however this may be due to size of the tabs on my vessel (Melida has often commented that increasing tab size has numerous benefits) coupled with very slow 'no wake' speeds that, in my case, would reduce their effect.

Terry

It will be hijacking this thread if I start to comment on my extended trim tabs.:grin:

But Just can say that, always thought that what I'm gonna do if they fail or broke when I'm too away from home port.:smt089

 

[hholleb]

Hi everyone,
I have to admit I was ready to give back the 2010 185 Sport I just purchased due to this annoying zig zag affect. We traded in our 2004 Regal 1800 and didn't have this issue at all. The Volvo Penta IO must not have the same issue as the Mercruiser IO motor! Or the hull on the Regal must be a little less v shaped. At wake speed it is very tiring and I hope I can get somewhat use to this issue!

 

[320Bob]

I'll offer my 2 cents on this topic since I now have a single stern drive boat with dual props that has no appreciable stern wander. However, when I was demoing boats a Crownline 255 with a Bravo III drive had horrible stern wander while a Cobalt 242 and a 2007 Chaparral 256 SSX, both with Bravo IIIs did not. The only major difference among the three was the Cobalt and Chaparral had the equivalent of stern pods to help getting on plane while the Crownline did not. I cannot say for sure but I have a feeling that the stern pods dampen the stern wander more compared to boats without them. My old 1999 Mariah Z280 had a more traditional hull design with a single Bravo III drive and it had a lot of stern wander at slow speeds.