Can I diminish prop walk more?

[Chenige]

First, I ran one of the Electrifieds this weekend with a Tacon 3650 with 2950 kv on a 5000 mAh 3s. X432 prop.

It ran almost too fast and with hardly any temp increase on the battery and ESC and just some on the motor even though it was often just plowing thru the water as I tuned it in.

My issue is prop walk. The boat under power had huge turning to the right.

The first run had the stinger centerline about 1/4" to the right and about 2 degree bending to the left . I had to keep the rudder to full left turn to get it to go straight under power. And when I let up it spun out due to the rudder angle.

I tried a 2nd run with the stinger angled some more but it still was not acceptable.

My last try is shown below. With the rudder trimmed as shown the boat would go straight w/o turning the rudder. Is this normal? What else can I do? I can see the back of the boat being pushed sideways as it takes off.

Do I need to add some kind of skeg? Move the rudder to centerline? Deeper rudder?

[driftah]

i have never sen a brass tube used for a stinger...or a stuffing tube bent like that before,just saying you may want to mount a small strut or stinger and straighten that brass tube out then look into other problems.the boat being pushed isnt a good thing you may be wasting forward thrust there bud and some powerful boats do have torque roll due to massive power being dropped instantly with a decent prop size but doesnt look like you have a crazy setup to cause that.plus that stuffing tube should be at the vertex of the transom imo.

[JackBlack26]

If I'm not mistaking, the new Pro Boat Impulse 26 uses a brass piece as a strut. Weird But it works, obviously.

[driftah]

ya it works but what about a bushing and or adjustability up and down?

[egneg]

I would change or cup the prop to narrow the thrust cone.

[jstolz]

I run my Electrified on 2S with a 27t brushed motor. I have to angle my strut, but not as drastic as your's is. It appears from the pictures of your boat that the rudder depth needs to be increased to help reduce prop walk. What prop are you running? A smaller prop will also help to reduce prop walk. Running 2s would also help to reduce prop walk.

[martin]

A stuffing tube like that is pretty common practice on Mono 1 & mono 2 Naviga race boats here in Europe all be it a much larger stiffer tube. Their put in at a given angle that works so no need for adjustments. Martin.

[Chenige]

x432

How deep below the keel should the rudder go? Does it matter that it is not centered?

[Chenige]

Rudder is about 1.25" below keel. How far should it go?

And should I center it?

I do use a brass tube for a water pickup in front of the starboard mounted rudder.

[dana]

i dont understand why the stinger is angled to the left here… what am i missing? what kinda boat is this? i would start by moving the rudder closer to the center of the boat….

[Chenige]

20" homemade wood. Used to be quite popular ~15 years ago or so.

Issue is that prop walk causes the back of the boat to go to the left which causes the boat to turn right. You angle the stinger to counteract prop walk. This boat really goes to the right probably due to a much more powerful motor setup than what they used 15 years ago.

[7500RPM]

Rudder is about 1.25" below keel. How far should it go?

And should I center it?

I do use a brass tube for a water pickup in front of the starboard mounted rudder.


I ran my boats with home made brass tubing struts with Octura teflon bearings for years, worked great! but you need to change the water pick up to one mounted flush with the bottom, the issue is the tube sticking below the transom like yours, it will cause the hull to do strange things! Also you will need to rebalance the hull from the old days as you are running Lipo's, the motor in the stock position will make the hull run wet, and push on the nose

[Chenige]

The water pickup upper surface is about 1/8" below the bottom of the boat. I will raise it up 1/8". Is this what you meant?
59419


With the battery straddled just behind the motor as shown below the balance point is 5.5" from the transom, about 28%. This really ran well.

I think I am going to put in a different mount and put the battery on the left side of the boat to counteract the torque and allow repositioning the battery for balance adjustment. However this will probably not help much with the prop walk?
59420

[siberianhusky]

Is the prop sharp enough to cut your finger easily? Dull props can cause severe prop walk.

[Boaterguy]

trim tabs may help a little, but not much
It ma yjust be that the hull is not built for power since it is 15 years old

[Chenige]

Is the prop sharp enough to cut your finger easily? Dull props can cause severe prop walk.

Very sharp

[Chenige]

OK, I think I have figured out what is wrong. Been having moment diagrams going thru my mind (for Engineers).
59451
My rudder is forward of the prop shaft centerline. The lateral prop force is rotating around the rudder and causing the boat to go right. Imagine if the rudder was held in place. The prop walk force would cause the boat to go in a clockwise direction (turns to right).

Now imagine the rudder is behind the prop. The prop walk force would cause the boat to go in a counter clockwise direction (turns to left).
59449
Does this make sense?

[MarkF]

First off your suppose to bend your strut to the left to keep it from pulling the boat to the right. Second you use trim tabs if you want to get rid of the prop walk or and put extra weight on the left side of the boat and this will help as well.

Mark

[Chenige]

First off your suppose to bend your strut to the left to keep it from pulling the boat to the right.


Photo just above is bottom view. Strut is bent to left.

[siberianhusky]

I think I'd try moving the rudder back about another inch, get it a little deeper into undisturbed water and mount a turn fin on the back starboard corner @ 90 degrees to the bottom of the boat.
Trim tabs won't do anything for propwalk, I always try to get my boats set up without them, they are a last resort handling cure for me.
That has a pretty shallow vee, I know next to nothing about them but you could look at Crackerbox and Jersey Skiff threads, If I remember right the plans I looked at for a Crackerbox had a skeg mounted on the centerline somewhere near the CG, I think this is the give the shallow hull a forward pivot point like a rigger or hydro. I've never seen one in person so thats pure speculation there. It looked like an upside down shark fin hangin' off the bottom!
I don't think the hull as set up has enough bite to keep it from sliding sideways across the water once it starts skipping and planing. The prop is able to overcome the only lateral resistance the rudder is able to provide, and being behind the rudder it has a bit more of a mechanical advantage.

[Chenige]

Thanks for all the input. Here is what I am planning on doing.

buy 75 mm rudder with water pickup
....install slightly closer to prop laterally
....install at least as far back as the prop
....install as deep as I can

Revise stinger back to where I started with 1/4" offset starboard of keel and just a degree or so of angle.

Make up new motor mount.
....lower motor slightly (1/8" or so)
....leaves room on port side for battery to be on bottom of boat.

Siberian, boat already has turn fins on both sides perpendicular to bottom of boat.

[MarkF]

My comments were made because you sad you bent the stringer to the right. The rudder needs to be at least 1" below the prop. Moving it around will only change how it turns and have nothing to do with prop walk. Adding trim tabs and moving weight to the left side of the boat will have everything to do with fixing prop walk however.

Mark

[siberianhusky]

lol couldn't see then in the straight on shots I looked at.

[Chenige]

My comments were made because you sad you bent the stringer to the right.

Mark
fixed