Offset Drivelines in 1/8 Hydroplanes

[circus circus]

Just want to get some feedback on this subject. It is in my opinion that offsetting the driveline helps with offsetting engine torque and even heard it helps propwalk.

I have no experience with offsetting drivelines in 1/8 scales only on smaller 1/12 and 1/10 hydroplanes, does it make a difference? Im working on a RcBoatCompany hull SG-121H and would like to know if this is a good idea on a modern day hydro design. Please share your opinion.

Thanks guys

 

[Duck899]

I'll be interested in this too..... but my opinion is run the strut in the center of the hull.

 

[Samuel Hagan JR]

I'll be interested in this too..... but my opinion is run the strut in the center of the hull.

I'm also interested.

 

[Douglas P Shepherd]

move 3/8 to 5/8 to the left side of boat with strut 1.0 to 2.0 deg pushing to the inside of couse

 

[circus circus]

move 3/8 to 5/8 to the left side of boat with strut 1.0 to 2.0 deg pushing to the inside of couse

Due you mean move the driveline to the RIGHT since we are turning that direction to help with torque and turning?

 

[Douglas P Shepherd]

NO, You Move the strut to the left side of the hull(JUST LIKE YOU WERE SETTING IN THE HULL) To aid in the helping of torque problems. You want the left sponson to help turn the boat.

 

[Grimracer]

Im with Doug on this.

My Oberto and Super Sport 45 both have offset drive lines. Boats are ROCKETS in the corners!

My Oberto has the motor centered in the hull with the drive line offset 1.5deg. This moves the strut left about 1/2"

My SS45 has the motor offset right with 1.5 deg offset. This put the prop center of the hull.

The Oberto is a tick better in the corners!.. but not much!

Grim

 

[circus circus]

OK then Im confused, why would I move my engine and driveline to the left when Im turning right? This will put more weight on the outside sponson causing a less affective turn, I always thought putting weight closer to the right will aid in turning and help with counter balance engine torque?

You guys have seen the early 80s Miss Budweiser how they had not just the driveline but the entire cockpit and canopy area offset to the left to help aid in turning left.

 

[P THOMAS]

Always thought any strut angles were to help a boat run straight with more neutral rudder? The prop tends to pull transom . So setting the boat up with a left angled strut helps. Offsetting the motor helps with the balance of the hull. Some boats would like weight on the left to hold the sponson down others can use weight on the inside to help cornering.

When in doubt just Run it all down the center of the engine well. That is the way all my setups are done for my boats i sell, tweaking them is up to the builder, but you dont have to find a way to make my boats run well.

 

[lohring]

The thrust from a prop is a combination of the force along the propeller axis from the propeller blade action, a sideways force from the paddle wheel effect, and a lifting force from the blade entering the water as well as water flowing radially off the propeller. Turning this into a force that pushes the boat straight in all three dimensions is a balancing act. The paddlewheel effect can be offset either by angling the shaft counterclockwise or by offsetting the shaft to the right for counterclockwise propeller rotation. Both methods, or even a combination of the two, work.

Prop torque is another factor that needs to be offset. This can be done by weighting the boat on the left side for standard (counterclockwise) engine rotation. Engine offset can also be used. You could then end up with an engine offset to the left and a shaft offset to the right. I haven't seen that done, but I've run an offset shaft with a centrally mounted engine. I used weight to offset torque in both my electric 1/8 scale and my gas scale. The electric boat has all the battery weight on the left with a motor and shaft offset to the right.

Lohring Miller

 

[Samuel Hagan JR]

move 3/8 to 5/8 to the left side of boat with strut 1.0 to 2.0 deg pushing to the inside of couse

Strut pointed toward the left front sponson correct.

 

[John Finch]

I agree with Phil. Everything should be in the center of the boat. I also agree with Doug on letting the left sponson aid in turning. I have tried all the different tricks, but at this point I feel like sponson angles, turn fin design, and rudder location can accomplish all that is needed without disrupting the triangle shape of the three ride surfaces.

John

 

[anthony_marquart]

I'm about to start setting up a sport40 boat. So,.. if I understand all this correctly,.. a good recommendation would be to,

-center the engine in the hull

-use battery weight to keep the left sponson down, (lifted from torque)

-maybe add a shim to the strut to keep the boat from pulling into the course. This helps with SAW speed reducing rudder input to keep it straight.

 

[John Finch]

I'm about to start setting up a sport40 boat. So,.. if I understand all this correctly,.. a good recommendation would be to,

-center the engine in the hull

-use battery weight to keep the left sponson down, (lifted from torque)

-maybe add a shim to the strut to keep the boat from pulling into the course. This helps with SAW speed reducing rudder input to keep it straight.

Anthony,

Everyone has there opinion as you know. What works for one might not work for another. I would ask the manufacturer or someone who has your particular hull. Not just anyone, but someone who's boat works really well. Seeing is believing, not what someone says on line. I have seen boats that worked really well on line but sucked big time at the lake. It is all relative. With that said.......i would start out with it set up just like you said if you don't have other input. Then, if you have to hold a lot of left rudder to keep the boat straight I would start changing things ONE THING AT A TIME. Keep in mind.........the sponon that hits the water the hardest will make the boat veer in that direction. I am sure that is part of what Doug is doing with shifting the strut to the left of centerline. I would rather add a couple of ounces of lead on the left sponson if needed.

The rudder mounted on the right of centerline will help push down the left sponson. It will also make left hand corrections easier without blowing the boat off the water. If the rudder is kicked back even the slightest it will lift the transom and the prop will walk the boat to the center of the course. So the rudder as well as the strut depth plays a lot in controlling prop walk. Etc. Etc. As you already know. There are so so many variables and so many ways to counter issues that I think it best to start simple and take the issues one at a time. I like to add a bit of a wedge to the right sponson sometimes to counter torque. Maybe 1/2 degree more than the left sponson AOA. Of course unsharpened props and oversized props cause prop walk but we are talking hull set up right now. Too small a rudder will let the boat walk to the right because as you said.....the rudder is what keeps the boat from walking right. I have found that setting the rudder with the right side parallel to the center line of the hull with the left side of the wedge hitting the oncoming water to be the best rudder centering. I would set the rudder in that manner and then start adjusting other things ONE AT A TIME to pull the boat into harmony with the rudder. Make the boat go straight and not crab.

The hard thing about a scale boat, unlike the versitility of your rigger, is getting the weight enough forward so that the boat does not blow off the water yet have enough weight on the prop that it doesn't get high out of the water and walk the boat into the course. Don pinckert told me one time a long time ago, and it is so true............if the tail is higher than the nose the boat will not blow off the water. Do it by making the strut deeper rather than letting the prop ride high out of the water. Also keep in mind the higher the tail is off the water the less AOA on the front sponsons. I am rambling now.....got to get back to work.

 

[anthony_marquart]

excellent post,.. thank you for your input. A quick question,. specifically on a sport 21,.. why would I not want to use a lifting prop such as the 14 series? There are no rear sponsons to lift the hull from the water,.. does the wide hull do the lifting with air? Some set up a sport boat with the strut deeper, to get the hull to actually run level. Would it not be effective to set the hull up as designed to run, level, and use a lifting prop to keep the tail out of the water?

 

[RobertWurster]

Thats a good ? But i tried a lifting prop on my sp 20 a year a go and it wanted to spin out on me in the corners.Hope others with give there thoughts.

 

[anthony_marquart]

did you change the set up all when changing between the prop styles. An X series will have to be planted lower in the water to get the hull set to level,.. you would have to raise the strut to get the same run height and maybe a little negative angle, when going with a lifting prop.. Mike had the same experience when trying a lifting prop.. but I don't know if the setup was changed.

 

[Mike Luszcz]

John, Just to clarify, these last few guys (Anthony and Robert) are discussing my GP310 and the GP400 (The one you drove when I visited a few weeks ago). Just trying to give you an idea of the hull style/ setup in question! Mike

 

[Grimracer]

excellent post,.. thank you for your input. A quick question,. specifically on a sport 21,.. why would I not want to use a lifting prop such as the 14 series? There are no rear sponsons to lift the hull from the water,.. does the wide hull do the lifting with air? Some set up a sport boat with the strut deeper, to get the hull to actually run level. Would it not be effective to set the hull up as designed to run, level, and use a lifting prop to keep the tail out of the water?

I see no reasion why you would not.. try it and let us know how your testing goes!

Grim

 

[anthony_marquart]

I will test and report soon. I have a couple different blades on the way!!! It would be cool if they came on Sat... (hint hint Mark)

Mike,.. did you change the setup between props?