CR. how close is too close ?

[drwayne]

40" DRAG HYDRO

shiztngiggles for oval format

building
2x5692 12S @35k rpm
counter rotating props nestled in center the transom.
adjustable strut separation allows props 55->70mm diam with 10mm blade gap
Noting that full size drag hydros have 4->5" between blades at 14k rpm, outward rotation.


Competent thoughts ( interspersed with prophesies of doom ) most welcome

re: What distance between blades ?

[keithbradley]

Got any pics of the hull Wayne? Sounds cool...

[drwayne]

Sorry Keith, only pics I have are of first out of mold.
Colleague will finish and send hull next week.
Summertime down under, good build time indoors with days 100'f+ for weeks on end .. !

Our Nationals are end of April..
depending on work and health this could be an entry.

[carlcisneros]

Rudder location?

right, left, center (hope not)?

[drwayne]

rudder centered in dead zone between/behind props ( hydro-dynamically, why not ? )

' just like full size '

[srislash]

interesting,very interesting.

[jamie]

[carlcisneros]

done that in the past on racing cats (mainly nitro power). the boats hunt in the straight lines and can tend to do
some odd things in the turns. like starting to turn, freezing along the way, then wham, finish the turn so fast it will make your head spin and you are pointed
back at the on-coming boats. We were racing just about nothing BUT aeromarine hulls.

if in fact you are setting the boat up for racing, then set the rudder over on the right side of the transom.

There is ONE way to get around mounting the rudder in the center of the hull and that is to mount the struts
ON THE TRANSOM of each sponson. That way there is absolutely no water dispersal/spray conflict affecting the
rudder.

here is a link to Rummy's twin aeromarine sprintcat with the struts mounted to the rear of each sponson.

http://www.youtube.com/watch?v=wW5O3sMSBkE

like the twin mono in my avatar, I started off with the rudder in the middle, then wound up mounting it to the right.

[drwayne]

done that in the past on racing cats (mainly nitro power). the boats hunt in the straight lines and can tend to do
some odd things in the turns. like starting to turn, freezing along the way, then wham, finish the turn so fast it will make your head spin and you are pointed
back at the on-coming boats. We were racing just about nothing BUT aeromarine hulls.

nitro, been there , 25yrs of that.
same rotation props will always induce torque roll/prop steer and logically right turns are hectic.
Here is a twin nitro hydro.. experienced none of those issues.
http://forums.offshoreelectrics.com/...hp?albumid=379

if in fact you are setting the boat up for racing, then set the rudder over on the right side of the transom.

There is ONE way to get around mounting the rudder in the center of the hull and that is to mount the struts
ON THE TRANSOM of each sponson. That way there is absolutely no water dispersal/spray conflict affecting the
rudder.

here is a link to Rummy's twin aeromarine sprintcat with the struts mounted to the rear of each sponson.

http://www.youtube.com/watch?v=wW5O3sMSBkE

like the twin mono in my avatar, I started off with the rudder in the middle, then wound up mounting it to the right.

This is a 3 point hydro ..not a cat .. sponson mount drives ??? .

Here's a link to one my own sprintcat 40 twins, stingers mounted to transom.
http://forums.offshoreelectrics.com/...win&highlight=

Previously read and noted your twin mono rhs rudder reduced corner roll .
Not a situation Ive experienced in hydros.

Here's one a colleague shared of a hydro cornering at speed
gp.jpg

Thx for your comments.

[carlcisneros]

Frack,,,,,,,,,

you are right of course. I got off topic as far as hull types are concerned.

I have only seen a couple twin drag hydros on TV run and one had one of the struts break lose. wasn't very pretty ,,,,,,,,,,,

[drwayne]

All good.
your words most practical a cat !
Ive an rc colleague down here who has some exposure with the fullsize hydros.. and shares the occasional pic of their setups.(thx, m8 ! )
Intrigued, I hatched a plan to run one, scaled down.
Leading rudder edge is prop radius behind trailing face of props on the 2 full size twin drag hydros Ive researched.
Im 'goggling' for clues on optimal(minimum) distance between blade tips in our scale.
cheers
W

[drwayne]

The best view so far.. !

http://www.diecast.org/diecast98/html/asp/list_reviews/xq/ASP/id.GMP1804802/qx/reviewpix.htm

[srislash]

The best view so far.. !

http://www.diecast.org/diecast98/htm.../reviewpix.htm

She' a beaut'. I have often thought of doing this.I also used to have a bud that ran a T/A drag hydro.I'm thinking the hardest part with FE will be the launch and still having top end.I wonder if a two speed in there would help/hinder.Ideally a variable pitch prop but that would be impossible.Am I already over thinking.