88/89 Oberto: Finished finally!

[Hydro Junkie]

Running my 2000 Elam this weekend, I used something like 12 to 14 ounces in a heat with an OS9B equipped 67 greenhead and that's running slightly rich using 50% Powermaster fuel

 

[Dasboatman]

Hey Mark,

I think that is "Bum Dope". I don't know of anyone that has less that 20 ounces of 50% in a Scale boat that launches early. I'm carrying 22 ounces in mine and I may have 2 oz. left at the end of a heat - and I am running VP racing's blend of what used to be Powermaster fuel. CHEERS !!! Bob

 

[Hydro Junkie]

I run a pair of 8 to 10 ounce tanks, no header tank, and the second was between 1/3 and 1/2 full when I brought it in after six laps and roughly a 90 second mill time. That being said, I also wasn't running flat out due to water and wind conditions.

 

[BobGutsell]

Hey guys ran the boat for the first time this morning. It's taken me forever to get around to running it. But anyway, it runs quite bow heavy and the prop doesn't seem to want to hook up. Tried, X452 and X455 3 bladers along with a X455 2 blader. The nose diving was definitely less with the 455 2 blader.

Strut was set at 43 mm, I reduced that to 39 mm, for no real improvement.

Any suggestions what to try next?

 

[Wayne Johnstone]

Are those props to small? I run an x457 on my scale (Bert twin wing)

 

[Hydro Junkie]

I was thinking the same thing. Very few scales successfully run with anything smaller than a 57mm prop. The props you listed are normally used on sport 40 hulls rather than scales

 

[FloridaScaleBoater]

Are those props to small? I run an x457 on my scale (Bert twin wing)

Wayne, an X457-X457/3 would be about the smallest I would run.

1: X457 or X457/3 if you need tail end lift

2: X460 or X460/3 same as above

3: X560 an X460 with 10% more pitch

4: ABC 62X80

5: Prather 255 (has more lift than a X460)

6: Prather 250 if the 255 is too much

 

[FloridaScaleBoater]

I was thinking the same thing. Very few scales successfully run with anything smaller than a 57mm prop. The props you listed are normally used on sport 40 hulls rather than scales

I'd like to see the sport-40 that would swing those props!!!

 

[Hydro Junkie]

Swing which props? The 57mm and larger or smaller than a 55?

How about this, from the PMB Model Boats webpage:

http://www.prestwich.ndirect.co.uk/propuse.htm

Check out the 7.5 and 11cc sections and see which props they recommend

 

[FloridaScaleBoater]

Swing which props? The 57mm and larger or smaller than a 55?

How about this, from the PMB Model Boats webpage:

http://www.prestwich.ndirect.co.uk/propuse.htm

Check out the 7.5 and 11cc sections and see which props they recommend

I'm talking about ANY of the mentioned props X452, 55 or 57 A sport-40 won't "race" with those props And the PMB link says nothing about sport-40's

What they recommend and what works in the real world are 2 different things

 

[BobGutsell]

Cheers guys, am also running a 1/4" flat bottomed extended strut. Is there any chance that the strut is obstructing the Prop?

Secondly, thanks for the prop suggestions. Are you guys de-tonguing your props or running them with tongues?

 

[FloridaScaleBoater]

Bob,

Your flat bottom strut could be the root of most of your problems.

This is what we have had success with http://www.rossisales.com/transomstrut.html this part# SPDS-010-250HR 1/4" Strut XTD assembly, HYDRO, Round bottom $29.95

How much negative to you have in the strut?

When you say the prop won't hook up,,, do you mean it is just cavitating and won't push the boat forward?

 

[wayne middlemiss]

I can't see how the strut would obstruct the prop but 3/8 " would change things.

Got to ask of the angle of attack on the sponsons also they strut , is it slightly tipped in negative to lift the rear or neutral.

Also I have see mention through your thread of running 4:1 fuel mix , honestly if your trying too your wasting your time bob scale boats need a lot of power to get them motivated for the first part to get up on plane.

Your kit was an ml boat works so it's been designed with lots of power in mind to use every bit of the engine can give so the boat won't get to blow off point whilst racing( theoretically ).

Put it on on setup board an revise your setup.

Cheers wayne

 

[BobGutsell]

Thanks Rick and Wayne, I actually run 5:1, but it may well be the time to bite the bullet and run some nitro.

Rick it cavitates and won't get onto the plane. I was running 2-3 degrees negative.

 

[scottmeyers]

Nitro is the key! I've long used a CMB on 50 - 60% nitro with two 8oz tanks and it works fine. Depending on the boat I'll run x455/3 or a 255. The bigger props suggested will only increase the lift on the transom and worsen the trouble. Stay small on the prop until you get it to pop and go! I would reduce your strut angle as well and go to a smaller diameter, round strut (I use the Gary Jensen strut, beautiful piece). Hang in there... You'll get it and you'll learn a lot through the process!

 

[scottmeyers]

Just noticed... The stuffing tube exits the hull at a remarkably steep angle well forward on the hull, but the motor doesn't appear to be angled that steeply. Can that angle be softened somewhat? The more you make that shaft twist around the more power you're taking away from the prop!

 

[FloridaScaleBoater]

Thanks Rick and Wayne, I actually run 5:1, but it may well be the time to bite the bullet and run some nitro.

Rick it cavitates and won't get onto the plane. I was running 2-3 degrees negative.

Bob,

My advice. I'd round/soften the outside edges of the strut some,, and yes reduce the strut angle some, Start off close to 0* and go from there.

The set screw in the drive dog, sand or file that off and blend to the drive dog. It acts as an egg beater creating air to the prop.

Where does the hull balance out at? Is it nose heavy?

 

[Dasboatman]

Hey Bob,

Can you place your hull on a flat surface such that the rear of the sponsons are on the table, and rsting on the bottom of the strut in the rear, with the turn turn fin hanging over the side of the table so we can see what kind of sponson angle you are working with.

Here's a pic of one on mine as I'd like to see yours.

Was the MLB kit from Newton frame plan 137 per chance??? CHEERS !!! Bob

 

[BobGutsell]

Hey Bob, yes it's the MLB newton 137, why do you ask? My AOA is reasonably close, maybe a little less than what you have. Rick the COG is about 2-3 inches behind the Sponson transom.

Scott, the engine angle is the same as the angle of the stuffing tube where it exits the hull.

 

[ron upton]

you guys amaze me with your great paint jobs....