AeroMarine Research Site...

[Kris Flynn]

Hey All,

just wanted to makesure everyone knew about the aeromarineresearch.com website and about the products/information you can get from there...anyways back to my point, Jim Russel, who is the main guy behind it all, has just joined this site because i mentioned it to him and he said he would check it out...

now it is my understanding that alot/most of the concepts on a real F1 tunnel apply to RC Tunnels, so he should be able to help us out with any of the technical stuff

so anyone got any questions for Jimboat?

Kris

 

[Jimboat]

Thanks, Kris. Any site that loves tunnel boats has to be good! I'll help however I can! Love to talk tunnels!

/Jimboat

http://www.aeromarineresearch.com

 

[GTR]

Hi Jimboat,

Great to have you here we need as much technical knowledge as we can acquire. We have some legends on the board that have years of designing models behind them inlcuding Jerry Dunlap (JD living legend) and MikeZ - Grimracer designer of the villian. I guess here is our chance to look at the dynamics of models v fullscale. I think our power to weight is somewhat better than full size and speeds are proportionately higher. These factors may be leading to some of the handling issues for models.....just maybe some of the experience with models travelling faster may have some helpful flow back to full size.

Glad your here....welcome aboard

GT ;D

 

[Jeff Torgalski]

Kris, way to go getting some real knowledgeable people to study with.

Jimboat, I have a question,

Kris asked about steps in Tunnel Hull sponsons. What are thier purpose?

So what changes to our models of today do you think would make the most performance improvements?

try saying that 10 times really fast

 

[Propjockey]

Yeah Kris, thanks! 'Bout time we got some intelligent, boat savvy people on this forum! ;D ;D ;D ;D ;D ;D ;D ;D

I'm just messin' with ya, Jeff I know what you meant. ;D

And welcome aboard Jimboat! Glad to have you. (we like pics--purty ones with lots of colors ;D hint, hint)

 

[TomMoorehouse]

hey it is nice to have a full size tunnel hull designer on here.

i got a question... i hear that the modern tunnels use 4-5 blade props.... what does this do for you?

 

[Jimboat]

Propeller Design

Thanks for the nice welcome words!

Prior to development of the surface-peircing propellers, most racing and sports boat propellers were 3 bladed. With the significant increase in pressure on the props blades caused by running at the surface, 4, 5 and 6 blade propeller technology took off. With the improvement of propellers, it has been found that with an increase in the number of blades the pressure is substantially reduced. On a three bladed prop, each blade carries 33% of the load, whereas on a 5 bladed prop each blade only carries 20% of the load, a very substantial reduction. So the reduced load on each blade, allows the propeller designer to make the blades lighter and thinner, which is more efficient, while still being strong enough to carry the required load. Multiple blade props were developed for boaters looking for maximum low end and mid-range without sacrificing top end.

It's all a pretty neat topic....propeller design

/Jimboat

 

[TimD]

Welcome aboard Jimboat!

The multiple blade prop question Tom raised is very interesting.

Just out of curiousity, what sort of prop RPM's with these 5 &6 blade surface piercing props are we talking here? My understanding was that the more blades on the prop, the less efficient the prop would be. Maybe this is false - I don't know.

Tim.

 

[hg-md]

No Tim you are correct.

 

[Propjockey]

??? Don't nuclear subs use 6 bladed props?

 

[Jimboat]

6 blade props...

Good question...actually the question about nuclear subs is particularly interesting, 'cause in my previous job, I worked for a (the) company that designs powerplants for nuclear stations and submarines....

I find that the "rule of thumb" that more blades = less efficient just doesn't work all the time. In fact, most rules of thumb don't work very well for propeller design or selection, since the application can be influenced by so many factors.

In general, the addition of blades increases the surface area of the propeller, which allows it to generate more lift and more thrust per revolution. It will also have, on the other hand, more 'surface drag' due to the increased area. So there's a tradeoff. But the lower load distribution on each blade (compared, for example to a 4-blade prop) means that the blades can be thinner, which makes for less 'induced drag'...another benefit.

So, whether all the tradeoffs are a net benefit to the hull setup or not, depends on the specific application. Generally, however, if the hull setup can benefit from either more thrust or more (aft) lift, then the switch from 4-blade to 6-blade prop can be helpful.

 

[TimD]

Good question...actually the question about nuclear subs is particularly interesting, 'cause in my previous job, I worked for a (the) company that designs powerplants for nuclear stations and submarines....

I still work for the corporation that invented the silent sub prop technology and also builds powerstations...... wonder if were talking the same company? I work on office equipment tho.....

The loading on each blade I think may not be such an issue with our little boats as the amount of hp is considerably less and our props are made from a substance that would be considered strong enough (berylium copper or stainless) for the size and power output.

Jim, I am curious to know what your thoughts are on r/c outrigger hydro sponson designs. Do you think there are any potential gains to be made in this area that the r/c guys have not picked up on?

Tim.

 

[JAMES D IRWIN]

HEY JIMBOAT ,, RIGHT ON WITH THE ARTICAL ABOUT THE PROPS , I USE A THREE BLADE TO HELP HOLD THE NOSE DOWN IN THE WINDY CONDITIONS WE HAVE . EXTRA LIFT IS ONE KEY FACTOR FOR ME JD IRWIN