why do props hop

[Gary]

What is the reason a prop will hop on a Hydro boat. I know your changing the prop depth to bring this on but whats going on to make it happen? A deeper priop goes faster but brings this problem on.

[sjslhill]

The prop may have too much lift for that hull....some lift more than others. Also the angle may cause too much lift as well. my 2 cents on the subject

[detox]

What prop are you using?

[Gary]

I run a M645 modded and i find that its sometimes tough to get it on plane when it starts hoping. Some runs are perfect..others i have to abort early or it will crash. I might try some upward angle of the strut to help combat this now that i have heavier batteries in it now.

[NorthernBoater]

The prop may be cavitating.

[Doug Smock]

CG plays a role also.

What is your setup?

[kevinlew211]

CG plays a role also.

What is your setup?

im 2nd one on this, most of my boat hoping problem has been fix by move cg forward , i hope Fluid will jump in this topic.

[Fluid]

IME there is no single answer. The simplest is that the prop is providing more lift that the weight on the prop, so reducing the lift or adding weight to the transom can help. But sometimes it is a dynamic issue and moving weight forward may even help. Some hulls will never stop hopping at the end of a straight due to the hull design/power combination.

I suspect that the mods to your prop might have increased its lifting characteristics, particularly if you removed much metal from the leading edges of the prop or increased the trailing edge cup. The first thing I'd do is place the hydro on a flat table and adjust the strut to lay flat on the surface. This will reduce lifting from the thrust angle. If it still hops then I'd move the CG back and see what happens.

That hydro is this? What voltage/motor?



.

[Gary]

Its a 30" Dominator hull with a 1521 1.5 and a m645 prop , 7.5 lbs. It just seems that it will always go faster with a deeper prop but with more hop on the start of the run. I can eliminate this by running more shallow but than i loose speed.

[mickvk]

Its a 30" Dominator hull with a 1521 1.5 and a m645 prop , 7.5 lbs. It just seems that it will always go faster with a deeper prop but with more hop on the start of the run. I can eliminate this by running more shallow but than i loose speed.

Regarding the bad initial "hop"... I recently solved that problem a different way. Do you find that you can't ease in to the throttle? I think that some generic ESCs have very limited throttle resolution and basically go like three speeds. I upgraded to a Castle Hydra and I can lay on the power very smoothly now. No hop upon launch.

[Flying Scotsman]

Regarding the bad initial "hop"... I recently solved that problem a different way. Do you find that you can't ease in to the throttle? I think that some generic ESCs have very limited throttle resolution and basically go like three speeds. I upgraded to a Castle Hydra and I can lay on the power very smoothly now. No hop upon launch.

Rubbish... sorry .. the esc should have no bearing on initial throttle response unless it is a piece of crap or I am wrong..three speeds?

Douggie

[mickvk]

Rubbish... sorry .. the esc should have no bearing on initial throttle response unless it is a piece of crap or I am wrong..three speeds?

Douggie

Rubbish? Jeez that sure sounds abrasive. Yes, cheap-o ESCs in my experience exhibit that behavior. I have a black jack 26 with a stock cheap ESC on 4S that has the itchiest trigger finger I've ever driven. I fixed it with an ESC. Exact same thing with the generic cheap-o that came from Head of The River RC, Jhocheung's shop. I put a Hydra 120 in it and now I can get it on plane nice and easy before laying into the throttle. I was saying "like three speeds" to illustrate a point.

Have a good one. -Mick

[ozzie-crawl]

some of the cheapies dont have soft start up, and instead of a smooth soft start seem to just dump about 20-30% of throttle straight up. but i have the feeling if he is running a nue 1521 i doubt he is running a real cheap esc

[bab]

Propeller 101

Pitch
Pitch is the theoretical forward travel of any given propeller. This forward travel is measured in inches. The pitch stamped on the propeller tells you how far forward the propeller would move in inches if it was turned or screwed into a solid media such as cork or the ground.
Pitch can be "True" or "Progressive". True pitch describes a propeller that measures the same pitch from the leading or beginning edge to the trailing or following edge. Progressive pitch describes a propeller that starts low in pitch at the leading edge and increases its pitch as the water travels towards the trailing edge. Both styles of pitch offer benefits depending on the type of boat and engine package or set up a person uses.
Pitch is the final "gear ratio" adjustment on any given boat. Pitch controls the engine revolutions per minute or "RPM". Adjusting pitch for any given situation can change a boats performance anywhere in the rpm range and give the boater the desired performance they need while keeping the propulsion system working as the manufacturer engineered.

Diameter
Diameter is the total outer circumference of the propeller measured across the center of the prop. In other words it is the distance across the circle the blade tips make as you rotate the propeller.
Diameters are limitless. Most propellers have a diameter pre-determined by the manufacturer as correct for the pitch, horsepower and application it was designed for. Diameter changes can affect the "attitude" of the boat or the way the boat carries it self. Generally, the lower the pitch of a propeller, the larger the diameter will be. Propellers running at deeper depths can be smaller in diameter while performance applications that surface the propellers while running can use larger diameters. Trained custom propeller shops can adjust diameter to aid in the operation of your specific vessel and its set-up.

Rake
Rake angle is measured in degrees. Rake is the amount of degrees the propeller blades angle perpendicular to the propeller hub. Rake can be slightly negative (leaning towards the boat), or positive (leaning away from the boat). The range of degrees could vary from -5 to +30 degrees. An average rake angle for most outboard propellers is 15 degrees. Rake can be progressive meaning it increases as you move out from the propeller hub to the blade tips. Or rake can be flat maintaining its degree of angle continuously from propeller hub to blade tip. Higher rake angles help to improve some boats ability to operate in aerated water situations by causing the water to adhere to the blades better than a prop with lower rake angles. The centrifugal force the propeller creates, throws the water outward and the higher and/or progressively raked propellers can hold and control that water better, increasing the thrust rearward. Higher rake angles can also help to hold a boats bow higher in the air, reducing hull drag and increasing speeds. However, low rake propellers can be a better choice for light weight fast hulls that carry the bow on their own since they direct thrust with less drag and can increase efficiency.

Rotation
Just as the word suggests, rotation determines the direction a propeller revolves around the axis of the propeller shaft. Rotation is determined by looking at the propeller from the rear of the boat. A right hand propeller will turn clockwise therefore moving down to the right hand side. Contrary, a left hand propeller will rotate counterclockwise or down to the left while looking at the propeller from the rear of the vessel. Changing rotations on single, twin, or triple engine applications can affect the boats performance too.

Number of Blades
A propeller with one blade would be the fastest and most efficient propeller if it weren't for the fact that the vibration could not be contained. The reason for its great speed would be the lack of blade drag caused by metal in the water. As blades are added to propeller hubs, the drag is increased. However, the ability to grab more water and decrease the time frame between load and unload is shortened. This means the propeller will "feel" smoother as it grabs water or loads the blades. The number of blades does many other things to the performance and control of a vessel. Performance type hulls tend to show the greatest response from adding and subtracting blades. Propellers typically come with 2 to 6 blades.

Source : http://www.lake-link.com/boating/props101.cfm

[Fluid]

That is a great site for explaining prop nomenclature and function. It addresses two areas that are commonly seen in BS post on FE sites. First, prop thrust has a dual cause - low pressure on the front of the blade and high pressure on the back - that combination is what pushes the boat. It is not like a "screw" progressing into wood, although that analogy is commonly used. If that was true, progressive pitch props wouldn't work - but they do and very well.

Second, the prop's rake is determined by the casting of the prop, not by cutting on the blade. It drives me nuts seeing the uninformed - some of whom should know better - stating that cutting away part of the trailing edge of the prop somehow changes the blade's rake. Impossible of course, see diagram below.



A propeller or "prop" is the final piece of the engine and its drive train. It is the part of the boat that transfers the engine horsepower to the water. The transfer is termed as thrust. Thrust is created as the propeller pulls water into the front of it, (the boat side) and pushes it out on the back side. This momentum change is caused by a pull push affect of the blades and the pressure differential from low to high and is the basis for the creation of thrust.

.