Effects of extended struts on Hydros .

[Steve White]

Steve,

Have you ever used a "cheater bar" on a wrench?

Same, same.

Essentially, the CG of the boat is really not a factor as far as prop walk is concerned. It only comes into play, at least laterally, in the turns. So extending the strut doesn't change the CG of the boat, relative to the string between the turn fin and the rudder. The CG DOES, however, come in to play, in regards to a tendency for the boat to blow off. In the relation of CG and the string between the turn fin and the prop, extending the strut does move the CG forward, which increases the props leverage against the attitude of the boat.

At the end of the day, extending the strut is a trade off of vertical leverage for lateral leverage. It's a trade off of a force that you can't easily counter without additional trade-offs, for one that you can.

Thanks. Brad.
Titan Racing Components
BlackJack Hydros
Model Machine and Precision LLC

I understand the leverage concept. So, the unload on the prop from moving it back is more than offset by the increase in leverage from the lengthening after-plane.

Over the years I've ran mono's & hydros. Huey 4 point, dragon fly 20, wing ding 60, several 40 & 60 crapshooters. Some of them ran nice and straight, probably would have ran fairly straight at full throttle without a rudder. Others, it took so much left rudder to track straight that it would swerve one way or the other depending upon power level and speed.

I've always ran the rudder on the RH side of prop, I think the next build it's going to be on the left for a starting point - that will probably be another trade-off between straight line tracking and turning. I'm going to find out.

Thanks for sharing your experience and expertise.

 

[dwilfong]

David,
Get rid of the recurve and you will see a whole new boat! You are correct about the efficiency of the prop without the rear “training wheels “ lol . When the c/g is correct you will need very little lift in the prop and launching is not a problem! I have been running true 3 point hydros for a very long time and in my opinion there is nothing faster in the corners period.....

I will go back to it again and give it an other try.
Yes a clean back end with no crutch is the direction to go for sure.
I have a few ideas to try when I build the next test tub.
Prop testing is the most important thing when try this.
1470 was the ticket on the last set up.
The wide rudder is the best thing I have found to keep the prop walk under control.
As long as the thickness in the back is the same a wider rudder will produce LESS drag from the reduced angle of attack it produces.
Learned that one from Andy.

 

[Steve White]

^^^ Yes, wide rudder blade is the ticket - found that out when taking the tapered rudder off a Crapshooter and replacing with Octura wedge rudder - orders of magnitude improvement. Eliminated prop walk and turned better as well.

 

[dwilfong]

^^^ Yes, wide rudder blade is the ticket - found that out when taking the tapered rudder off a Crapshooter and replacing with Octura wedge rudder - orders of magnitude improvement. Eliminated prop walk and turned better as well.

Steve Woods makes a 1.5" rudder that fits in the CMDI style bracket with water inlets on both sides of the blade.
B&B makes the rudder bracket.
You will need to make a custom strut bracket to do this.
You need to line up the trailing edge of the rudder with the leading edge of the prop.
This keeps every thing close to the transom.

 

[DON MAHER]

Ok let’s get down to the question of what controls propwalk. I am sure that most of you at one time have hit something in the water and kicked the rudder back. What happens ? The boat goes into a right turn! Why? Because the rudder is more or less the controlling factor for propwalk! Placement and size of the rudder,prop selection, after plane,and tail weight all have an impact on propwalk! So to control it you have to test,change,test change and test some more! Been there and done that !

 

[Steve White]

^^^ Add strut angle & depth, and some more testing!!!

 

[DON MAHER]

Steve , you are so very right, I forgot to add those two elements!

 

[Steve White]

^^^^ ..... and some more testing!

Discussing prop walk brings back some frustrating times at the pond. Probably the most struggle with it was the days with the early Crapshooters - between prop walk and just getting them to turn at all using the tapered rudders that came in the kits. I was out in California back then (mid 70's) and running OPS engines with exhaust throttles and pipes. I believe Ries and Worden were running carburetors and short straight pipes on their setups and it just didn't translate.

Took a year or so and many test sessions at the pond to finally get things sorted out.

 

[David Bryant]

I have long struts on all of my hydros and mono

beautiful boat!

 

[dr gary turner]

beautiful boat!

Thanks

 

[dr gary turner]

I understand the leverage concept. So, the unload on the prop from moving it back is more than offset by the increase in leverage from the lengthening after-plane.

Over the years I've ran mono's & hydros. Huey 4 point, dragon fly 20, wing ding 60, several 40 & 60 crapshooters. Some of them ran nice and straight, probably would have ran fairly straight at full throttle without a rudder. Others, it took so much left rudder to track straight that it would swerve one way or the other depending upon power level and speed.

I've always ran the rudder on the RH side of prop, I think the next build it's going to be on the left for a starting point - that will probably be another trade-off between straight line tracking and turning. I'm going to find out.

Thanks for sharing your experience and expertise.

Going to the left crests the wrong angle between the rudder and turn fin unless you run a VERYnarrow spread on the front sponsons/ turn fin

 

[dr gary turner]

Recurve and extended strut
Boat does NOT unhook

 

[dr gary turner]

Sorry video will not play

I can never get a video to play in IW

 

[Wasted wages]

Plays for me....
Red hydro...haulin' azz !!

Love how that engine sounds almost the same in the turns as well as in the straightaway... hardly sounds like it's loading !!

 

[Ray Sametz]

Played for me, just sideways. Hauling the mail!!!

 

[Steve White]

Going to the left crests the wrong angle between the rudder and turn fin unless you run a VERY narrow spread on the front sponsons / turn fin

Video played for me, no sound but picture was good.

I don't understand the concept of "crests the wrong angle between the rudder and turn fin".

Do you have anything to illustrate?

Thx

 

[dr gary turner]

I have been told, again not ORIGINAL WITH ME, that 17-20 degrees is ideal between the rudder and turn fin

 

[dr gary turner]

Plays for me....
Red hydro...haulin' azz !!

Love how that engine sounds almost the same in the turns as well as in the straightaway... hardly sounds like it's loading !!

You are right, We feel the key to a fast hydro is one that runs FREE BUT NOT LOOSE

 

[Wasted wages]

For the uninitiated and trying to keep up with the conversation....

What is crutch ?
and recurve....?

 

[dwilfong]

For the uninitiated and trying to keep up with the conversation....

What is crutch ?
and recurve....?

Crutch is just what I call any thing on the back of the boat used as a running surface to hold the *** end up.
Recurve is the part of the boat in the back that comes up as a angle to release air pressure from under the back of the boat.
It sucks the *** end down at speed.