3.5 Tunnel SAW record

[Russell Bear]

A downhill lake!

LMAO I was thinking about that earlier, any waterfalls nearby?

 

[Slideblues]

Ha,Ha, Yeah that might help Tim

This formula will get ya close, But I'm not kidding, at round 62 you hit a wall either with HP, drag, or aerodynamics.

Less than 4 lbs RTR, 3.2 HP @ 32,500, H-4 cupped bout 3.2, perfect water, = 60 + MPH

 

[Slideblues]

And ya gotta be ready to not get back as much as ya started with too

 

[Grimracer]

Gener

Who in the heck buit that POS h34r: ..... it broke in two like a twig...LOL... We can do better...

we can rebuild Him

we have the technoligy...

GO Wicked WANDA..

GRIMSPONSONBUIDER h34r:

 

[shoboat]

Gene,

As you may know, I am driven by SPEED. I did some calculations: your motor

was pulling 24,459 RPM @ 3.2" of cup @ 63 MPH. Now if you want to go 65+MPH

you will have to do either 25,235 RPM or 3.3" of cup on that H-4 PROPELLER.

These are very accurate calculations. We got plenty of H-4's,but will that motor

pull them at 3.3"? That is the 65+ MPH QUESTION Gene! I updated the numbers

I had a little error,sorry. These numbers are correct,it was a little late for me

last night. I think the best way is to try 3.3" of cup on a new boat and setup.

By the way,what was the NITRO CONTENT GENE? :unsure:

Thanks,

Mark Sholund

Props-4-U

 

[Chris Wittrig]

Mark:

What percent of prop efficiency/prop slip are you factoring into those calculations?

 

[shoboat]

Chris,

I factor aprox. 15% slip. Propeller efficiency is a whole different ballgame

Chris. If you would like to do some figuring try my web site under Prop Charts.

http://www.props4u.com/

Thanks,

Mark Sholund

 

[GTR]

Hi Guy's

Wouldn't reducing the diameter just a touch, adding a tweak more pitch allow both higher revs & higher speeds. NR motors will definately pull the RPM if you let them. Really dumb question - what altitude above sea level did you run your speed at Gene. Being at sea level is definately worth a few MpH.

Re the tunnel design wouldn't you want to narrow the ride surface some and maybe take a few degrees of angle out (12-14deg). You guy's know way more about this than I do but these were a few thoughts I had. Almost forgot everybody is trying for low profile frontal but narrow is actually more important and it helps to streamline the OB and helps stability in a straight run. Food for thought.

GT

 

[TimD]

Gene,

Would it run with the pipe shorter and the same prop? Figure on 3/4" - 1" shorter to get the rpms. More pitch might be the preferred option if the motor is in it's peak band at the original length...

Tim.

 

[izitbrokeyet?]

I have another trick for you......given the exact same setup I go about 2 mph faster in Salt water than I've gone in fresh water........both at sea level.

Go figure

I always thought salt water was a little harder than fresh so I couldn’t figure out why...........................If you have the answers; I'd sure like to hear em

 

[casey]

saltwater is more buoyant the fresh water.

i use to race offshore boats, before i started racing drag boats and we were always 4-5 mph faster in salt water.

 

[Slideblues]

Mornin Guy's

Kev the same reason I float in seawater, and my butt sinks at the lake, Bouyancy :lol:

Fer the rest o this stuff I gotta get some coffee,

Back in a few,

Ahh dats much better

OK here we go:

JD, I agree prob bout 30" sound reasonable on length

Mikie, more like who was drivin that dang thing

Mark, I like dem numbers Buddy!!!!

Gary, Elevation was 981 feet, and yes the lower style was over a year ago, Deadrise was way lower than stock, Agree that "Thin is In"

Tim, Runnin shorter, She was screamin at the top end of the run, maybe dont know,

The header I used was cut SHORT, Just long enough to barely slide the coupler on.

Dat the best I can do on one cup :lol:

Gene

 

[izitbrokeyet?]

Ok…….here’s my dilemma with the salt water thing/ speed

The specific gravity of Salt Water is 1.021 which without too much arithmetic gymnastics means your boat is 2.1% more buoyant in salt water than it is in fresh water.

2.1% of 5 lbs running weight is only 1.68 oz in weight.

My dilemma is that I am unable to reconcile 1.68 oz of weight equaling 2mph or more.

I was thinking that because of the density increase in the water: it was something more to do with the slip factor reducing, or prop efficiency increasing that accounts for the speed increase.

Maybe the answer is all the above?

now I'm glad to have that out

 

[Propjockey]

You're right on target, Kev. The density of saltwater gives more bouyancy, but causes more drag. Dense water DOES allow more prop 'bite' (less slip)...to a point.

 

[Russell Bear]

Dense water DOES allow more prop 'bite' (less slip)...to a point.

Maybe I'm thinking too much into it, but wouldn't denser water need more horsepower at the prop to reach the same speed?

 

[Propjockey]

Yes...BUT if the prop is more efficient, less RPM is needed.

Propjockey Racing.....more posts than Nitrocrazed Racing!

 

[Russell Bear]

That makes since. Thanks....

 

[Bob Kensill]

Just for everyone's information,most of the fastest boat speeds in IMPBA have been at the Huntsville pond. The water there is "brackish" meaning that there are alot of suspended particles in it.The prop will get more bite,but it will take more horsepower to go fast. It also seems to affect cooling too. BTW I am shooting for 70mph with my SAW 20 tunnel.

Bob

 

[Slideblues]

70!!!! WOW!!!!! Care to release any juicy tidbits of info there Bob ?

 

[zuber]

The lakes must be frozen in alot of places