set-up for a counter rotating surface drive on a twin

This is a tough one.

We are looking at a twin installation with our new drive.

Now for the combination of the blackhawk/inboard or outboard combo thread with a little twist.

What will be faster, better handling, ect...

1) front props spinning inboard, rear props outboard

2) front props spinning outboard, rear props spinning inboard.

3) different ratio front and rear with different pitch to match speed or same ratio/pitch

4) # of blades front/rear 3x3 4x4 5x5 6x6 7x7 3x4 3x5 6x3

5) diameter


pat W

Pat, That sure is a tough 1 MAN so many combo's to try and test. Looks like you have a life time project on your hands, but have to say it's way koooooool. Jay "Kaama Drives"

Pat-

I would say...
Front prop RH, aft prop LH, to counteract torque of engine. This appears to be done.

Incoming water to each propeller will be at different speeds. Aft propeller will see a faster flow as it has already been accelerated by the forward prop. Aft either needs more pitch on same ratio, or lower ratio and same pitch (more shaft speed).

Blade area for the entire unit is more or less doubled, so I could see a reduction in either number of blades or a diameter for both wheels.

In the 2nd pic, is it me or is that drive really low?

Have you run with a single prop for a baseline, either forward or aft?

Do you need that much rake if the drive is so long? Does the boat need the lift?

Black boat, external lift points, duck bill scuppers, what is this thing?

Is it possible to get some more information? I'd like to look at it more in depth...from an "engineering student" standpoint.

Brad.

Tango, Thanks for the compliment.

Brad,

Pic #2 dive is trimmed all the way in. trailer is downhill also.

ran single front on a test but it would not plane. It would cavitate when the boost would come in. We will try single rear soon.

We are running high rake, low, diameter, pitch,blade count, and cup on the rear vs the 4blade 19x41 lead prop. The boat runs flat no matter what. The cg is way too far forward because of cockpit placement.

The boat is a 23 ft carbon prepreg, nomex core, autoclave cured. 24 deg non step single 315 diesel. We are going to step the motor to a 600hp diesel and change overall ratio to match the twin install. 6 seat open deck. We are going to finish initial testing before stepping into the new hull.

pat W

Pat, sounds like you have a fun little project. Is this by chance something for the Navy, maybe CCD or PMS 325?

600 hpnshould make that boat fly, especially with enough prop in the water to make it hook up. Out of curiosity, what diesel with that power/weight are you running? Thing has to be light to be in 23' of boat. Torque numbers have to be huge. 41" is big, but I'm sure shaft speed is low enough to pull it. Efficiency should increase as a result.

Let us know how it goes.

Brad H.

Pat, why such a tall pitch in front ? does she actually launch of the rear wheel to get on plane ? also what are the relative prop. rpm's ? equal or diff.from front to rear as BradH has suggested ? also is the diesel being over-driven ?

Hey Pat, what ever happened with this project?

Any update Pat? Really interested in this.

Regrouping is the easiest answer. Nothing wrong with the drive just the people involved with us on the project.

Working on the twin because the single is gone.

Tango,

The removal of the rear prop and not getting on plane showed that it was lacking in bite. Full revs and no boost. There was thrust just not enough to get on plane.

We can run any ratio combination front to rear. The initial testing was equal to keep things somewhat simple. We will eventually try as many combinations as possible to get some questions answered.

We have been experimenting on the twin gas boat with the new props and that has been interesting. We also recieved the latest props from Throttle Up to try and see if we went too far. The last set we recieved from them was excellent. When we get to test the twin diesel we will run the same props on the rear.

pat W

Also the initial question was directed to thoughts on running a twin engine twin drive installation.

pat W

I have a prop question for you Pat. the props your using are they the same thread for both as a blackhawk? reason I'm asking is a couple of the 20 cigs with big power and we can only find 31's... do you have some of higher pitches?

Pat,

I saw Tom Abrams 20 Cig in NYC with a Blackhawk. They had a surface style prop on the leading prop and somewhat of a round-ear prop on the trailing prop. Not sure why, just thought I'd mention!

Pretty cool stuff you're doing!

Quote:

---

Originally Posted by Geronimo36

Pat,

I saw Tom Abrams 20 Cig in NYC with a Blackhawk. They had a surface style prop on the leading prop and somewhat of a round-ear prop on the trailing prop. Not sure why, just thought I'd mention!

Pretty cool stuff you're doing!

---

thats how they come, i have a set of 27's and 31's, but with the set up I might need a higher pitch.

I hear ya. I've seen a few different variations on the props.

The prop we have is different. I will check around. I know Nigel hook used to race one and they used to weld different configurations for his boat.

The ear on the prop changes the lift and they were using existing props / B1's

Andreas (platinum) just brought his 20 cig back from europe so I will quiz him on his set-ups. He has a 588 cid in his.

pat W

Pat - It seems to me that if the loading and torque is balanced between the front and rear props (net zero torque), there's no need to reverse the rotation(s) between the port and starboard drives. (The Swedes don't bother....) :

Quote:

---

Originally Posted by C_Spray

Pat - It seems to me that if the loading and torque is balanced between the front and rear props (net zero torque), there's no need to reverse the rotation(s) between the port and starboard drives. (The Swedes don't bother....) :

---

I would say correct.

I think there is a lot the current manufactures miss when it comes to performance vs cost. The tooling for the lead prop........ eeehhh, we will make them all Lh to counter the engine torque.

The rear prop on a dual is 30% less effective than the front.

Something tells me there will be a marked improvement in performance with the props running opposite.

I cannot wait to get some of this off my mind.:banghead:

pat W :reddevil:

You are outside my realm here, but. Some of the single engine races run left hand on all their setups to counter the engine torque at all times. If that is true, wouldn't the front prop always be the lefty and the rear same as engine rotation? The 30% seems to be the compromise for the tooling cost that would make sense due to torque.

What i never understood is why a LH against the tourque in a LH (standard)motor ???
Does not make any sense to me.
If u look from the back of the boat all the standard engines turn left,,so why would u want a LH drive on there ????
If that would be the case ,all the single engine boats build would have a LH drive on it ?! NO ????
My single 32 with 800HP and a SSM has a RH drive ,the boat is very light and it does not lean to either side at all.

Quote:

---

Originally Posted by shifter

This is a tough one.

We are looking at a twin installation with our new drive.

Now for the combination of the blackhawk/inboard or outboard combo thread with a little twist.

What will be faster, better handling, ect...

1) front props spinning inboard, rear props outboard

2) front props spinning outboard, rear props spinning inboard.

3) different ratio front and rear with different pitch to match speed or same ratio/pitch

4) # of blades front/rear 3x3 4x4 5x5 6x6 7x7 3x4 3x5 6x3

5) diameter


pat W

---

Nice Project Pat,

How much power can the drives handle ?

Thanks
Jon

Quote:

---

Originally Posted by DAREDEVIL

What i never understood is why a LH against the tourque in a LH (standard)motor ???
Does not make any sense to me.
If u look from the back of the boat all the standard engines turn left,,so why would u want a LH drive on there ????
If that would be the case ,all the single engine boats build would have a LH drive on it ?! NO ????
My single 32 with 800HP and a SSM has a RH drive ,the boat is very light and it does not lean to either side at all.

---

You're right, I guess. I was thinking reversed.

Now I gotta think. Hurts......:ack2:

Does engine torque go opposite of rotation under acceleration?

Quote:

---

Originally Posted by Ratickle

Now I gotta think. Hurts......:ack2:

Does engine torque go opposite of rotation under acceleration?

---

I would say NO,,,since the only thing rotating in 1 direction is the crank ,,the pistons are on either side ,,same ,,so no weight ?!

mmmhhhhhh,,:confused:

Quote:

---

Originally Posted by DAREDEVIL

What i never understood is why a LH against the tourque in a LH (standard)motor ???
Does not make any sense to me.
If u look from the back of the boat all the standard engines turn left,,so why would u want a LH drive on there ????
If that would be the case ,all the single engine boats build would have a LH drive on it ?! NO ????
My single 32 with 800HP and a SSM has a RH drive ,the boat is very light and it does not lean to either side at all.

---

Sorry my bad I meant RH... I always get that backwards because I am Left Handed.:willy_nilly:

The torque leans the boat to the right under accelleration so the impact of the blade to the water counters the action making it somewhat balanced.



We designed the drives to take big power as well as being very efficient. It will run very well with light power. The lead shaft is 110mm in diameter. the rear shaft is the same as a #6....see photo.
kind of gives you an idea we are not playing around.

pat W

Quote:

---

Originally Posted by shifter

Sorry my bad I meant RH... I always get that backwards because I am Left Handed.:willy_nilly:

The torque leans the boat to the right under accelleration so the impact of the blade to the water counters the action making it somewhat balanced.



We designed the drives to take big power as well as being very efficient. It will run very well with light power. The lead shaft is 110mm in diameter. the rear shaft is the same as a #6....see photo.
kind of gives you an idea we are not playing around.

pat W

---

Wonder how my Aero-Tek would run with this ??!! mhhhhh.
Also handling around the dock,,,,,whats the turning point from lock to lock on it in inches ???

We could make a nice WEISSMAN raceboat,,,u know ?! LOL
Back of my boat ,,,see pic.

Quote:

---

Originally Posted by shifter

The lead shaft is 110mm in diameter. the rear shaft is the same as a #6....see photo.
kind of gives you an idea we are not playing around.

pat W

---

thats the same as a blackhawk, we use a 6 lock nut on them. is throttle up making props for them? I have a brand new set of 27's for a blackhawk, never been on a boat.

Blackhawk ?????????? mmmmmmhhhh

I like you aerotek the way it is. Why do you have the water pick up on the right side? How is your slip #? Find one of my dry-sump #4 drives in the UAE. We did 10 of them. Contact victory team.

I was thinking of a 46 ft full canopy single drive center rudder raceboat.:26: something that can run some real mph.

The steering is 40 deg total 20 left 20 rt. Docking is always better with a DP drive.

Throttle Up is making all my props from now on. I have had great results with them so far.

I did not look at the blackhawk props when I started this design. I wanted to be able to use the bravo type props with the internals knocked ut and splined so people like Throttle Up could use the tooling for the castings they already have thus cutting cost. That is why we went with the 26 spline on the rear for the hp version. We can also run the bravo type 19 spline for the economic version of the drive.

The way I looked at it is:
single prop bravo smallblock baseline package
then dual prop up to 1000hp with bravo type thickness props
single high performance
dual prop high performance. with HP thickness props
stern drive
fixed trimmable no skeg with a center rudder.

Lots of combinations:reddevil:

pat W

Quote:

---

Originally Posted by shifter

I like you aerotek the way it is. Why do you have the water pick up on the right side? How is your slip #? Find one of my dry-sump #4 drives in the UAE. We did 10 of them. Contact victory team.

I was thinking of a 46 ft full canopy single drive center rudder raceboat.:26: something that can run some real mph.

The steering is 40 deg total 20 left 20 rt. Docking is always better with a DP drive.

Throttle Up is making all my props from now on. I have had great results with them so far.

I did not look at the blackhawk props when I started this design. I wanted to be able to use the bravo type props with the internals knocked ut and splined so people like Throttle Up could use the tooling for the castings they already have thus cutting cost. That is why we went with the 26 spline on the rear for the hp version. We can also run the bravo type 19 spline for the economic version of the drive.

The way I looked at it is:
single prop bravo smallblock baseline package
then dual prop up to 1000hp with bravo type thickness props
single high performance
dual prop high performance. with HP thickness props
stern drive
fixed trimmable no skeg with a center rudder.

Lots of combinations:reddevil:

pat W

---

Sounds cool.
Pat, my slip # is around 20% and i tried to contact team victory but got nothing,,,the drysump would be cool.:sifone:

Ps.: the pickup was there when i got the boat,,waterpress is fine ~ 18 psi @ WOT.

The water pick up is making a mess out of the water going to the prop. I would get it over to the center so it will get the bullet.. It is worth a try.

I will see if they have any more #4's.

pat W

Quote:

---

Originally Posted by shifter

The water pick up is making a mess out of the water going to the prop. I would get it over to the center so it will get the bullet.. It is worth a try.

I will see if they have any more #4's.

pat W

---

U think the PU matters that much ??? mmmmhhhh.

next time i have the engine out i try it,,because i need to move the drainplug and stuff.
Thanks.

Make the pickup horseshoe shaped so it clears the drain plugs. Water does not like 90 deg changes in direction. The pick up you are running causes lift and lots of drag and aeration to the water that gets in.

pat W

Quote:

---

Originally Posted by shifter

Make the pickup horseshoe shaped so it clears the drain plugs. Water does not like 90 deg changes in direction. The pick up you are running causes lift and lots of drag and aeration to the water that gets in.

pat W

---

What do u mean by horseshoe shaped ??? Picture please.

Horseshoe come out parallel with the bottom and loop back in clearing the drain plugs.



Here is a quick sketch.



---------
i
i
i
i
---------

pat W

Quote:

---

Originally Posted by shifter

Horseshoe come out parallel with the bottom and loop back in clearing the drain plugs.



Here is a quick sketch.



---------
i
i
i
i
---------

pat W

---

LOL,,,but ok i get it.