222 won't track straight at low rpms

[Springman26]

Not sure why I haven't asked before but my 222 with an f250 will not track straight from 0-1500 rpms. The skeg and prop are both fine. Whenever I'm at those speeds I have to turn slightly right and left to try to keep straight. Any thoughts on why this is?

 

[seasick]

That's a normal characteristic for your configuration. If this boat is new to you, you may be over compensating at lower speeds but regardless it is going to wander a bit.

 

[mboyatt]

I agree with seasick. My Grady is a couple feet shorter than yours, but will do the same thing at lower speed. I try not to over steer. Takes some getting used to, for sure. I wouldn't stress about it.

 

[altouchet]

I find my 208 does less wandering if you find the perfect trim angle on the motor at that speed. Try experimenting with the trim.

 

[Salinity Now]

Very typical for deeper V boats to wander at low speeds. 25" or especially worse are 30" shaft motors, all that prop torque will cause the boat to walk to one side. Dual engine boats typically can cancel each other out.

 

[Doc Stressor]

While prop walk and wandering is a characteristic of many deep V hulls, it is a particular issue with the SV2 hull. Since the running strakes don't extend past the middle of the hull and the variable deadrise design is rounded at the transom, there is little to keep the stern from being moved off center by prop torque.

You can minimize the effect by trimming your engine as far up as possible. And I mean way up. Just before the prop starts to ventilate.

In any case, you'll get used to the wander and learn to make small adjustments that will keep you pretty straight. Picking up the rpm a bit will also help.

 

[Grady_Crazy]

I have learned how to deal with it. When the boat heads starboard turn a little to port, and when she just starts to turn to port, turn a little to starboard. Just small movements of the wheel is all it takes it takes. At first I would make big turns of the wheel and zig zagged all over the canal. You will get the hang of it.

 

[Springman26]

Ok thanks guys. I always thought if I trimmed the engine way up I would have even less control. I will have to try that. I have had the boat a long time and can deal with it but I always meant to ask why and kept forgetting to post here.

 

[lgusto]

If you have trim tabs run with them fully down, i.e. push the bow down. That puts more of the longitudinal components of the hull in the water and makes many boats track more reliably at slow speeds.

 

[onoahimahi]

You can minimize the effect by trimming your engine as far up as possible. And I mean way up. Just before the prop starts to ventilate.

Doesn't trimming way up maximize the prop walk (I think because the bottom of the prop will be biting more water then the top and therefore increase the sideways force pushing the stern to starboard (and boat to port)?

Does maximizing prop walk equate to improved stability when trying to go hold a straight line? :hmm

 

[Doc Stressor]

Bernoulli's principle is the major cause of prop walk. The water displaced by the hull near the surface is moving faster than the water further below the hull. Thus, a right hand propeller grabs "more water" at the top of rotation and propels it downward and to the port side. The result is the stern is pushed toward the starboard side and the bow moves to port. With a deep V hull running off plane, the bow will keep veering to port and this motion needs to be corrected constantly.

Running the engine trimmed vertical maximizes the difference in water velocity between the top and bottom of propeller diameter. Trimming the motor up minimizes the difference in water velocity between the top and bottom of the prop rotation and reduced prop walk.

That's more physics than you probably wanted to hear. But I got the tip to run the engine trimmed up directly from Grady White customer support.

Just try it yourself and you see the difference. Backing the boat will also be easier.

Also try putting the tabs down. You will notice that will just increase bow steer and veering.

I was used to an older pre-SV2 Seafarer which steered very straight at low speed. When I first got my current 226, the low speed handling characteristics and the list to port when running on plane drove me crazy. So I spent a fair amount of time trying to figure out both the physics of these running characteristics and trying different solutions.

 

[jaydub]

If you have trim tabs run with them fully down, i.e. push the bow down. That puts more of the longitudinal components of the hull in the water and makes many boats track more reliably at slow speeds.

Larry is right. I have a 222 and spend a lot of time in canals at slow speed or idle speed. I trim the motor down fully and run the trim tabs down fully (100%). That pushes the bow down and makes a huge difference in the ability to keep a straight track. Before I started doing that I was constantly having to correct to keep a straight track. Just don't forget to bring the tabs back up when you move out of the slow speed zone.

 

[Graybeard]

I'll tell ya what.....my Freedom 225 tracs way better at no wake speeds or in 6mph speed zones than my old Parker 21 deep vee. It's also less sensitive to people moving around while underway.

 

[onoahimahi]

Bernoulli's principle is the major cause of prop walk. The water displaced by the hull near the surface is moving faster than the water further below the hull. Thus, a right hand propeller grabs "more water" at the top of rotation and propels it downward and to the port side.

It's hard to wrap my head around this before finishing my coffee, and I'm not an expert at anything, but I think this might be backwards. Bernoulli's principle states that an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. Thus the propeller should be more effective at the bottom to the rotation (due to higher pressure/potential energy) propelling the water to the port side (rather then "grabbing" it at the top and throwing it all the way around to port.)

I am usually only concerned with this at very slow speeds when docking and I don't think Bernoulli's principle applies here. I think about it in terms of how much water the different parts of the prop have to push against. For example, in the limit, if I raise the engine until the top part of the prop is out of the water, only the bottom will be biting and clearly pushing the stern like a paddle wheel. I'm suggesting anyone do this - but it may be helpful to think about it in this way. I.e, when the boat is trim is up high, there should be more prop walk which can be helpful at times when maneuvering at the dock, especially with twins.

This paper explains describes the effect only in terms of shaft angle - I'm not sure I can wrap my head around this either this but it is consistent with the suggestions to raise the trim to minimize walk when underway. This was recommended above by multiple posters. It is not consistent with my slow-speed paddle-wheel argument at the dock.

http://www.cruisingschool.co.uk/icc/prop%20walk.pdf

Like I said, I am not an expert and would be happy to be corrected on any of this.

Cheers,
-Scott

 

[Graybeard]

Outstanding gentlemen. I studied fluid dynamics in college, but that was more years ago than I want to think about. I'm just very happy with how my 22 tracks

 

[Doc Stressor]

I should have been more specific and said that Bernoulli's Principle is the major cause of propeller walk in outboard boats where the propeller is aft of the hull and oriented in a more or less vertical position. There are other factors that contribute to prop walk in large ships and these have been well studied.

Bernoulli's Principle applies to outboards since water directly behind the hull is moving at different speeds in the vertical plane as the result of displacement by the hull. As the speed of a fixed volume of water increase, the pressure decreases. So the upper part of an outboard propeller is moving in an area of lower pressure relative to the lower part of the propeller. As you trim the engine up, the angle decreases this differential.

All hulls are different. It's best to take the empirical approach and see what works with your own hull and weight distribution.

 

[Doc Stressor]

Well, just for a hoot I tried running slow today with the tabs all the way down and the engine trimmed low. With a full tank of fuel and just myself on board the boat did RUN STRAIGHT! When I tried that earlier with 4 people and a bunch of gear on board the veering increased.

So live and learn. But I'll be damned if I can explain the physics of why the tabs all the way down works. :hmm

 

[SmokyMtnGrady]

Bob's principle - adjust the trim up or down on the motor and trim tabs so the boat rides the way you want, then sit back listen to some tunes and enjoy a beverage of your choice as long as it is legal and nobody else gets hurt.

Doc, thanks for the physics lesson. I vaguely recall this stuff from my college days. You are not a bad physiscist for a biologist (lol)....

I find trimming the motor up, not all the way up, seems to keep my 22 footer tracking well in those no speed zones. I have never messed with the tabs. Maybe I will erxperiment next time.