UCD Boat Dyno project; Any help is appreciated!

[bean]

Hi, my name is Ben Cunningham. I'm a senior mechanical engineering student at the University of Colorado at Denver. I am on a small senior design team that is working to develop a dyno that would work on a small boat in a lake. The platform we're working on is based on an outboard motor, using strain-gauges and accelerometers.

I was hoping to get some insight into how boats are tested for racing, and what telemetry is useful in boat performance. We're not necessarily trying to invent something new, but just trying to see if we can come up with something that would be useful on a complete boat system.

We're constantly realizing more and more variables, and things we can't control in the lake scenario, but we're working to develop ways of predicting them in order to include them in the data. One of the concepts I'd like some clarity on is "prop-slip" exactly what parameters are used to determine this efficiency.

If you'd be available and interested in helping us with this project, please let me know, and I'd love to have a discussion with you regarding our ideas, and what we're still not thinking of.

Thank you for your time,
Ben

[mark da shark]

Dyno project

Ben your best resourse that most of us out west are familar with is a guy by the name of Bob Wartinger. He holds many of the records in Outboard racing is associated with some of the top engineering people in the country.A very interesting person to talk with. Sorry but no phone numbers can be given out without his concent. thanx. Mark.

[bean]

contact

Does he subscribe to these forums often? Is there a screen name or email that I could contact him with through this system?

Thanks

[tomatoface]

Bob wartinger@boeing.com

[roperz111]

Dyno question

I'm curious about something, and would like to ask this if you can tell me. What type or brand or model water brake are you using? Or whatever it is you're using to measure the torque of the output shaft?

Thanks!

Chris Johnson
111-Z

[bean]

???

That email address didn't work. I wonder if it's old or maybe their system blocked me out.

[bean]

no water brake

We're not using a water brake to get the torque. We're actually planning on using strain gauges to measure the forces acting on the boat, due to the motor, apllied to the transom. It was a concept that I came up with while speaking to Dave Kahlow from Mercury Racing. Once we can come up with the theoretical speed of the prop, we'll use our actual speed and the forces due to the motor and drag to come up with our telemetry. We can then go back and make adjustments to the trim and jack-height, and even different props to make comparisons. Does this make sense?

[nbranews]

Dyno testing

We use a dyno sold by Land and Sea. It is a cerified dyno accuarte within 1/100th HP. It's kind of costy but it has proven to work well. It can be adopted to opperate on the water and gives you horse power and torque curves.

[roperz111]

HP calculations

Ben,

The classic formula for determining horsepower (as I'm sure you know this already) is: HP = (rpm x torque)/5252.

What formula do you use for your determinations finding HP using the method you outlined above?

Thanks!

Chris Johnson
111-Z

[bean]

HP calculations

Yeah, that's rotational HP. Power can also be described by Force*velocity, taking the rotational torque out of the equation. So, by knowing the prop's pitch, you can convert the rotational speed to a linear, and should be able to come up with a comparison of actual linear power to theoretical HP giving a similar calculation to prop-slip. The big step is to measure the force applied to the boat with as small of an error as possible.

[alky6]

That seems like a really great idea! Very applicable to boat racing as it would be non-intrusive way to immediately tell how the engine/boat setup is performing. To get back to one of your original questions regarding telemetry. We looked into using full telemetry put out by Pi. Too expensive for our use at this time. However, we are now using instrumentation by Digatron that includes 2 hours of data recording with RPM, exhaust gas temp, lap counter, etc. Nice little unit that is easy to use. If you wish to discuss this further let me know. I would love to discuss as my senior project at Cal Poly was a sound proof dyno room to run our outboards in.

-Paul Fuchslin
paul@gyttja.com

[Bob Wartinger]

Outboard Dyno

Hi Ben,

Recieved your message a rounabout way through the efforts of a couple of poeple....Thanks Guys!

Ben, let's talk...I may have some resources that can help. Best contact is my cell phone at 206-409-8978, my e-mail is bobwartinger@comcast.net. The Boeing one that is listed in thread is inactive and I know a lot is not getting through(poeple still have it in their address list)...this e-mail works a lot better.

Look forward to talking to you soon.

Bob

[Blackhawkguy]

Hi, my name is Ben Cunningham. I'm a senior mechanical engineering student at the University of Colorado at Denver. I am on a small senior design team that is working to develop a dyno that would work on a small boat in a lake. The platform we're working on is based on an outboard motor, using strain-gauges and accelerometers.

I was hoping to get some insight into how boats are tested for racing, and what telemetry is useful in boat performance. We're not necessarily trying to invent something new, but just trying to see if we can come up with something that would be useful on a complete boat system.

We're constantly realizing more and more variables, and things we can't control in the lake scenario, but we're working to develop ways of predicting them in order to include them in the data. One of the concepts I'd like some clarity on is "prop-slip" exactly what parameters are used to determine this efficiency.

If you'd be available and interested in helping us with this project, please let me know, and I'd love to have a discussion with you regarding our ideas, and what we're still not thinking of.

Thank you for your time,
Ben

Prop slip is a mathematical way to determin if your propeller is doing what it is supposed to do. Think of a propeller as a screw, the pitch is how far it is supposed to move per turn. If you where to screw it into wood, it would move excactlity the amount it was supposed to, then if you screwed it into foam it may not move the same didstance per turn as it did in wood, but it is the same pitch. So now that you are confused look at it this way. You have a prop that is say 20 pitch, it is supposed to move 20" per revolution, you need to know what gear ratio your lower unit is so you can figure out the mathematical distance it is supposed to move . By taking the known, engine rpm,pitch of prop, gear ratio, you will be able to tell how fast your prop should go at what rpm your motor is turning, this would be zero slip. What you get in reality is less than what it is supposed to go, there is a formula, do not have it on the top of my head, that will tell you how much slip you have, racing slip is considered around 10% or less, pleasure boats are considered good 10%to 15%. What is effecting your slip ratio is air bubbles, prop to small for hull, prop to close to bottom of boat, you get the idea. If you are using the same set up, prop, everything for your test then it does not matter how much slip you have. I can see how you would want to know though if there was something from one test to the next that was off. A dinged or damaged propeller can cause a change in slip ratio. Ron Hill had a book you could buy at one time that had all kinds of slip ratios figured for different gear ratios, all you had to do was look up the ratio, prop pitch and rpm and it was all ready figured out for you. Good luck, and if you have not already figured it out, I am a prop guy

[RogerH]

Like your Strain Guage concept

Hay Ben,
I'm a retired electrical development engineer and I really like your approach using the strain gauge as the "water break" for your real life "dyno". You are obviously getting wiser about the large number of factors that are in play with an outboard driven hull. Once you narrow down and learn how to cope with the most important ones (prop slip, drag, gearing, drive angle, etc...), you will have a very unique tool to set up a boat for competition. Currently this can only be done by the seat of the pants method. The horsepower of the motor is obviously important, but utilizing that power most efficently will win races.
I hope you will continue to refine and create a usable system. Please be sure to keep the forum informed as you proceed. There is a welth of amazing talent lurking about the forum, and you've just begun to find a few.
Roger Hinsdale
hinsdale@bellsouth.net - if I can help in any way.

[hydroplay]

So how are you going to accurately determine the exact prop pitch? While this may seem fairly elementary, just take the manufacturer's word that a 19 inch pitch prop is really 19 inches, it would seem that this isn't necessarily accurate enough for your needs. Many people have gauges that can measure pitch at numerous places on a blade, how do you integrate those individual numbers to find one simple pitch to identify that blade? Are you then going to assume that all blades are identical? A true-pitch prop would simplify things here but most all racing props have progressive pitch and some cup at the trailing edge to confuse a simple one number pitch description.

Most small outboard racers don't know much about pitch and none are worried about efficiency. Put it on a boat and let's see how fast it goes, how good it accelerates and how good it handles the boat and maybe even what kind of lap times you can get. Now a map of pitch numbers on that prop may give some insight as to how another prop may work or maybe where you want something different. Propellers at the racing level are a black art. Trying to quantify all that for one of your baseline measurements will be an issue.