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View Full Version : Why aren't the props on the front of the outdrive?



Havasu Hangin'
12-14-2004, 07:30 PM
http://www.highperformancecars.com/hhangin/volvo_penta_ips_side.jpg
http://www.highperformancecars.com/hhangin/volvo_penta_ips_cutaway.jpg
Where's RD?

RiverOtter
12-14-2004, 07:31 PM
Bet you'd need a helluva trim pump for that drive. :idea:

Dr. Eagle
12-14-2004, 07:35 PM
Where's RD?
I bet he's programming the CNC machine as we speak... :)

coolchange
12-14-2004, 08:09 PM
Looks like more of a "Down 'n outdrive"

al cole'holic
12-14-2004, 08:18 PM
Where's RD?
:D

BADBLOWN572
12-14-2004, 09:31 PM
I remember a debate about which is better a while back. If I recall engineers say that it is actually better if the prop is on the front of the drive versus on the back. Something to do with clean water which will reduce prop slipage and cavitation. I am not an engineer so what do I know. I do know that the prop is 99% of the time on the front of an airplane pulling the air so it would make sense.

RiverDave
12-14-2004, 09:34 PM
HH, don't be putting posts up that make sense.. LOL It doesn't become you.. :D
RD

ROZ
12-14-2004, 09:50 PM
:notam: :cool:

mbrown2
12-14-2004, 10:04 PM
For low torque situations maybe it works...or if you have something (the hull to break up the water in front of it maybe....but most high speed outboard applications in a true tunnel setup (ie: Skater 21 with single ob), cause a tremendous amount of pressure on the lower unit; enough to break them...
Can't imagine a high speed outdrive with props in front of the skeg to break up the water......
But I am no engineer :coffeycup

Ziggy
12-14-2004, 10:09 PM
While you're at it, you may as well put a housing around the prop and direct the flow via a nozzle---wouldn't that be ingenious :rolleyes: :notam: :D :D

RiverDave
12-14-2004, 11:29 PM
For low torque situations maybe it works...or if you have something (the hull to break up the water in front of it maybe....but most high speed outboard applications in a true tunnel setup (ie: Skater 21 with single ob), cause a tremendous amount of pressure on the lower unit; enough to break them...
Can't imagine a high speed outdrive with props in front of the skeg to break up the water......
But I am no engineer :coffeycup
That's also becuase the lower unit is being "pushed" through the water.. If it's being "pulled" through the water then where's the pressure? It's not on being put on the front of an aluminum casting anymore.. but rather on a "point" on the front of a cast stainless prop.. Que No?
I went around and around on this deal a couple years back.. Turns out some guys did make little outboards with props on the front for circle racing.. They dominated the field but were quickly outlawed becuase of the type of racing.. The racing commission felt that with the small boats, people were often getting wet, and the odds of a person getting a fatallity injury via a prop strike, from the prop on the front were far greater then if it were on the back.. The only negatives that I read about was some handling "quirks" if they weren't setup right.. Being that these were pretty low budget, I'm sure with any real engineering budget behind them that could've been dialed out pretty easily. There was also a guy making a conversion kit for lower units waaaayyy back when, and on his add it claimed higher mph, and better fuel economy.. Being that I don't know anybody that has one or has ever heard of anyone that has one I can't verify that.. But as they say the "in theory." ;)
RD

mbrown2
12-14-2004, 11:42 PM
That's also becuase the lower unit is being "pushed" through the water.. If it's being "pulled" through the water then where's the pressure? It's not on being put on the front of an aluminum casting anymore.. but rather on a "point" on the front of a cast stainless prop.. Que No?
RD
You might be right...just seemed like all that pressure would now be on the props, but the props are turning and churning unlike the fixed lower..
Turns out some guys did make little outboards with props on the front for circle racing.. They dominated the field but were quickly outlawed becuase of the type of racing.. The racing commission felt that with the small boats, people were often getting wet, and the odds of a person getting a fatallity injury via a prop strike, from the prop on the front were far greater then if it were on the back..
RD
Funny, they were probably outlawed because Merc did not like getting beat by them the same way the Wiseman's were outlawed...Merc has a lot of pull in racing...
BTW, I am no engineer, so I was just taking a stab... :D

rrrr
12-14-2004, 11:43 PM
http://www.highperformancecars.com/hhangin/volvo_penta_ips_side.jpg
http://www.highperformancecars.com/hhangin/volvo_penta_ips_cutaway.jpg
Where's RD?
Because it would require four six volt batteries; two each in parallel and then the pairs wired in series.
:hammerhea

ROZ
12-15-2004, 12:26 AM
Because it would require four six volt batteries; two each in parallel and then the pairs wired in series.
:hammerhea
no no, you got it all wrong.. You're thinking of the dual jet....
12v paralel for the frontprop :D
Sorry Wes, couldn't resist :D

RiverOtter
12-15-2004, 04:08 AM
What about random sticks and debris. Seems like the props would have no protection.

Havasu Hangin'
12-15-2004, 04:46 AM
HH, don't be putting posts up that make sense.. LOL It doesn't become you.. :D
RD
Sorry...I'll try to do better.
The big question...was RD actually ahead of his time, or were Volvo engineers reading his posts? :notam:

RiverOtter
12-15-2004, 05:49 AM
Is that thing for real? :idea:

Havasu Hangin'
12-15-2004, 06:15 AM
Is that thing for real? :idea:
Yep. Hey...I'm not that creative...
:D

Jbb
12-15-2004, 06:43 AM
Yep. Hey...I'm not that creative...
:D
Noted.... :sleeping:

FastTimmy
12-15-2004, 08:05 AM
That's also becuase the lower unit is being "pushed" through the water.. If it's being "pulled" through the water then where's the pressure? It's not on being put on the front of an aluminum casting anymore.. but rather on a "point" on the front of a cast stainless prop.. Que No?
I went around and around on this deal a couple years back.. Turns out some guys did make little outboards with props on the front for circle racing.. They dominated the field but were quickly outlawed becuase of the type of racing.. The racing commission felt that with the small boats, people were often getting wet, and the odds of a person getting a fatallity injury via a prop strike, from the prop on the front were far greater then if it were on the back.. The only negatives that I read about was some handling "quirks" if they weren't setup right.. Being that these were pretty low budget, I'm sure with any real engineering budget behind them that could've been dialed out pretty easily. There was also a guy making a conversion kit for lower units waaaayyy back when, and on his add it claimed higher mph, and better fuel economy.. Being that I don't know anybody that has one or has ever heard of anyone that has one I can't verify that.. But as they say the "in theory." ;)
RD
WOW Dave! I thought you where just a beer drinker :D

1stepcloser
12-15-2004, 08:18 AM
Why aren't the props on the front of the outdrive?
Umm, cause that would be wrong. They're on the back. Imagine the setback required for a small tunnel..... :D

Magic34
12-15-2004, 08:21 AM
A lot of the new cruise ships have forward facing props.

dirty old man
12-15-2004, 08:32 AM
Way, way back in my time, people were experimenting with this. there are a lot of reasons why it will work/not work. remember, airplanes have been successful both ways. I saw a #3 SSM with a single cleaver on the front

phebus
12-15-2004, 08:43 AM
Props on back, tits on front. Two basic facts of life!! :D

spectras only
12-15-2004, 11:47 AM
[QUOTE=Havasu Hangin']
The big question...was RD actually ahead of his time, or were Volvo engineers reading his posts? HH , don't give volvo engineers too much credit. Check this link , you'll see not only a duoprop, but mounting on the front to boot :p :D http://www.hansonclan.co.uk/Royal%20Navy/tor_his.htm#The%20Lay

mirvin
12-15-2004, 12:39 PM
Dude, Volvo's kick assssss!!! Howcome they don't have a race team??
mirvin :D

sigepmock
12-15-2004, 01:50 PM
The owner of my company just installed two of those on his 40' day cruiser. He is really impressed so far with the performance and efficiency. He says he is saving a lot of fuel on his Catalina a back trips and actually seeing higher speeds at cruise rpm. Who knows :confused:

OGShocker
12-15-2004, 01:54 PM
Props on back, tits on front. Two basic facts of life!! :D
LMAO!

bigkatboat
12-19-2004, 10:30 AM
I helped a guy in Granada Hills Calif., back in the early 70's. I think his name was Carl Krumm, he was working on a drive he called the "KLEBBER DRIVE". It had one front facing 3 blade prop on it. I worked on the hull shape, and prop height. (X) With the prop in front you can use a much smaller diameter prop and often more pitch. It shows how much the "leg" gets in the way of water flow when the prop follows the leg thru the water. With the prop in front, 'blowout' is almost eliminated, even with high X mounting. Smaller prop needs less power, and I think it (being in front) is faster, with equal power. He ran out of money, and I was too busy racing and earning a living to follow up on it. I think the 'dual prop' thing is nice for heavy boats, but I want as few blades as I can get away with, in the water. Never want too much bite, always 'just enough', to keep it flyin'.