1/6th scale prop cavitation

[MattBaker]

We are having a problem with our ml boatworks kits one is a 95 smoking joes the other is a 94 bud. The boats will not plane out. What strut depths and angles are you guys running. I put a ABC 3018 on the smoking joes to try and at least load the prop but that didn't help at all. If it would be easier to call me my # is 806-382-2861.

Thanks

Matt Baker

 

[Blackout]

I have absolutely no experience with these boats, but was wondering if CG could be an issue? What is the CG at? Measured relative to the sponson backs. Kinda curious....

 

[MattBaker]

The CG is 4" behind the sponson trips.

 

[wayne middlemiss]

Pics of setup may help may help for answers, also how much aoa on the sponson running surfaces have you got??

 

[Glenn 787]

That's a big prop! What motor are you running?

I'm sure one of the WA guys could help with the cg.

 

[Don Ferrette]

The CG is 4" behind the sponson trips.

For starters the CG needs to be 1.5 tp 2" behind sponson transom. I would also start with a more conservative prop, try something like a 6717/3 to get dialed in on.

 

[Mike McKnight]

Start with a stock 6717/3 385LL or 390LL and work your way up.

 

[MattBaker]

I meant to say the cg is 4" behind sponson transoms I put scales on sponson transoms and strut today and got 8 lbs 11 oz on left sponos on 8 lbs 12 oz turn fin side and 4 lbs 8 oz on strut I raised the strut to .75 deep and put 2716 20 degree 2 blade and it still won't plane out water is coming over the center section behind the front canards

 

[MattBaker]

We finally got both of them on plane. First problem was the struts were not deep enough and props were to big. To get them on plane the smokin' Joes strut ended up about 1.437 deep and flat with a H660 prop I least I think that was the prop Buckshot Shackelford started going through his nitro props until we found on that worked. Second problem we have is the RCMK Gizmo modified K30 do not have enough power to carry these beasts for more than a few laps if any water got in the back of the boat it would come off of plane immediately. Third problem is pipe length we tried shortening to get any kind of RPM but would not have enough torque to plane out if I lengthened the pipe it would have too much torque and bury the nose so I ended up with a pipe length of 13" from the front of the exhaust flange to where the cones meet on the pipe. If anyone has any other suggestions please let me know.

Matt Baker

 

[jwo]

Like Don and Mike said. Start conservative with prop size. Strut depth is determined on sponson depth. put a straight edge on the bottom starting at the transom, at the back of the sponson mark a line and then measure from the ride pad to the line. this is the depth for the strut. .5* angle should get you close. 13" pipe length sounds about right. Depends on prop and weight of the hull, Carb settings, Fuel type and so on. Remember what works on 1 hull usually doesn't work on another but will get you close.

 

[MattBaker]

finally got the Smokin Joe's running yesterday we had to add depth to sponsons and increase angle of attack. With a 2716 2 blade it ran awesome this is a ml boatworks kit pre extreme kit I don't know if he correct this on the extreme kit or not but finally its running.

Matt BAker

 

[MattBaker]

Here's a pic

 

[jeffaustin]

What engine did you end up with?

 

[MattBaker]

We ended up with RCMK K30R it has plenty of power to push these big boats it just wont spool up any RPM. We will probably start playing with different engines soon.

Matt Baker

 

[harvknox]

Matt, I'm running a T-6 hull with a Gizmo modded RCMK K-30RZ and a Voodo 1667 with unknown pitch. Without any nose weight the CG was about 2-3 inches behind the sponson rear. The engine had enough torque to carry the left sponson in the air on the straights. I've since added weight to the front of the left sponson to bring the CG about 1/2 -3/4 inches behind the sponson rear. This both helped the boat attitude and speed though making the boat heavier. The strut is level with the bottom of the tub and approximately in line with the bottom of the shoes. My boat has the same situation as yours in that if much water enters the boat, it goes to the rear and hurts the boat's ability to plane. I have drains in the transom and the rear of the shoes, like the real Bud, and like the real Bud they are closed when running the boat. I thought about about leaving the plugs out when running, but I'm afraid if the engine died and the boat was not retrieved immediately, the stern would completely fill with water and the Evansville retrieve boat guys would go on strike. Some of this stuff may apply to your boat.

Harvey

 

[MattBaker]

the props we have ended up running are 2 blade 2716 15 deg and a 2716 20 deg for some reason it does not like the smaller tboat three blade props I think we have maxed out the performance on the K30 it runs good just no RPM this winter we'll probably start playing with different engines.