prop shrouds

[waterwar]

Remember Freedom of speech is only valid if you have something worth saying.

Loose talk is noose talk!
Brazil (the movie)
I don't think my active military friends would share your beliefs at all You might be suffering from brain freeze - try putting your head in an oven for an hour or two.
Do you want buy some real good hats for up there in the Great White North? I can practically let you have them for a song! You wouldn't have to worry about peskie ruskies* sniping at you if you wore these babies! Most of em appear to still have their Red star in place right above the front flap. Its nice 'cause you can pull that right down and not see no evil, hear no evil, as you do,or maybe not, do evil.A true hat for the morally challenged. Hell you'd be right at home dropping walruses, grizzly bears, penguins, baby seals with this outfit. Not you personally but I bet there's plenty of 'em that do
*I can't account for Sarah Palin she'll shoot anything that moves, like Sub Tom flying in his plane not so long ago....
http://www.youtube.com/watch?v=yn7UzxXv8p4


cheers
Stew

The Boat pictured below is USN ballistic missile one. I just shot this quick video capture pic, with my underwater spy cam deep off in the Marianas Trench, it was starting WWIII! Guess its 'On the Beach' for you Aussies good luck! You get maybe 3 months till fallout reaches You!(I forgot your handle...it went something like: 'drink till midnight piss till dawn' similar to my favorite haunt in my youth. Please spear some fish for me in the Great Barrier Reef...I'll never be able to fulfill my bucket list now damn.... !
everyone better duck and cover!http://www.youtube.com/watch?v=6X0FjlybCqs
* No offense to any of the Sovereign Nations mentioned is intended. We all live in one world.
The 'old balance of power' Mutual Assured Destruction that's real crazy thinking...not requesting information, like I have in my own special way! I have this thing about sharing knowledge and getting the word out: its really annoying to some... others like it, go figure..I guess it has to do with responsibility for one's own actions and the legacy we leave behind.... silly stuff: like that and all.

 

[waterwar]

.

Quote:
Originally Posted by erik818
Most of the outboards amongst my friends and relatives are small, typically around 10 hp. None of them have shrouds. If the outboard is more than a few years old the propeller is usually more or less dented. To my experience, all small boats and all small outboards eventually hit a rock (at low speed because you know you're in shallow water). It's more fair to compare the efficiency of a dented unshrouded prop with an undented shrouded prop.
Erik
Erik makes a point anyone care to address it?


'

 

[gonzo]

All this says nothing about the claims of the superior performance at high speed of shrouds. It is political double-talk and misdirection. Let's get back on track. Waterwar: it is much easier to respond if you put one post at a time. That is, if you want to discuss facts.

 

[waterwar]

I just heard from the dhs Gonzo,seems 'you' are to hop on 'next banana boat heading North' unquote. I couldn't quite figure out why... All they said was 'quarantine immediately, it's suspected to be a case of highly contagious <removed>

Back to the thread (now that greetings and small (tiny) talk is over)
Erik has a post below. I think that he has a very intelligent point that is both valid and concise with broad reaching conclusions that are extremely pertinent to this open forum.
Quote:
Originally Posted by erik818
Most of the outboards amongst my friends and relatives are small, typically around 10 hp. None of them have shrouds. If the outboard is more than a few years old the propeller is usually more or less dented. To my experience, all small boats and all small outboards eventually hit a rock (at low speed because you know you're in shallow water). It's more fair to compare the efficiency of a dented unshrouded prop with an undented shrouded prop.
Erik
*Jet Pump propulsion is an advanced technology. Its application to military applications is apparent, civilian applications are a spin-off
I certainly am not fond of complex devices for pushing my old 'crate' around. I have two outboards a 9… kicker and a 1957 OMC 40hp. its a 17 foot aluminum Orlando Clipper v - hull, its a work boat for me, I want a simple design that works without dogging performance at high speeds too! I Trailer my rig to lakes, swamps, rivers and prop shrouding would be desirable.

Does propeller design (single prop not, jet pump) influence the efficiency and performance of a shroud? Do screw - type propellers work better than blade type?
How about all the marine rescue units throughout the world what do they use? Wouldn't they seek the best propeller match and the best most efficient guard type device? Or is the fact: I slow at warning signs and do the same on land. So,I guess my inquiries are not relevant to race boat racing at all! Therefore, so 'nuts to me' ? Cute and childish? You decide! Take North America‘s moose. I have had the pleasure to fish in several pristine lakes in Quebec and Ontario, provinces of neighboring Canada. A Moose frozen in headlights was the biggest fear of each long road trip there in my youth. Next,that is, to losing fingers landing sharp - toothed ’muskies’. I similarly, really don't want to hit any 'submerged objects' in the water. But it happens... To every captain of their vessel be it so small to whatever you wish! The evidence of close encounters with propellers is overwhelmingly apparent to all. Florid'a shallow inland waters the grass beds are marked with so many prop trails that its viewable from my spy satellite!(ok, its just a balloon with a kodak tied on it).
Guess all those props are really messed up as far as performance and all chopping up little nasty coral noogies and such tidbits (crunchies)! How many 'captains' have touched (yeah- ground) sand with their propeller? Would a poll reveal the truth?
Erik makes a point anyone care to address it? I ask several inquiries: addressing those will ensure confidence in the astute reputation gained by this fine board.Its long standing reputation as a open forum has been so useful to all searching for answers on nautical issues. Respected expert opinion is just that.
*pictured last below;Propulsor MK 50 ducted propellor on a torpedo.
*I accepted some friend requests ...... you know how that goes... they posted!
"Life is like a field of newly fallen snow.
Where I choose to walk every step will show."
Denis Waitley

Regards to all
Stewart Loeblich
Red sky at morning, sailor take warning;: Red sky at night, sailor's delight

 

[anthony goodson]

nasir ,I would assume baeckmo removed his e-mail notification from this thread ,as I did ,so if he doesn't come back on this ,pm him for a definitive answer, I'm sure he won't mind.

 

[Boat Design Net Moderator]

I'm sorry Anthony - I just split Nasir's post from this thread to its own - < http://www.boatdesign.net/forums/bo...turbine-diffuser-augmented-turbine-37118.html > as I think it deserves its own new thread.

 

[anthony goodson]

Yes ,thankyou ,that was why I suggested a pm rather than letting him become embroiled in the confusion here.

 

[BertKu]

unquote. I couldn't quite figure out why...

Waterwar, nor me, why some people like to destroy a topic of interest. I have read right through your interesting information. As a result I am going to try the shroud out on my project. I may even make two twin bladed propellor in tandum with a shroud. Nothing lost if it does not work. My speed will only be 3 to 4 knots maximum.

Jeremy, your info on the sensors building into the motors were spot on. I could not get the Honeywell types, thus I used a different make of sensor, same result. Thanks you both.

Bert

 

[chartman]

Propeller Guard Test Protocol draft for comment

ABYC (American Boat and Yacht Council) and CED Investigative Technologies were contracted by the U.S. Coast Guard to produce a test protocol for propeller guards. The draft of that test protocol was recently released and is available for public comment until April 11, 2012.

We posted the draft, a recent presentation on the Propeller Guard Test Protocol project at the Miami Boat Show during the USCG Accident Mitigation Workshop, and instruction on how to submit your comments at:

http://www.propellersafety.com/4574/test-propeller-guards/propeller-guard-test-protocol-rough-draft/

chartman / gary polson
Propeller Guard Information Center

 

[Submarine Tom]

From the above doc:

"We asked everyone to pass along the material to other interested parties in an effort to ensure the widest possible peer review, and encourage the maximum number of constructive comments. So there is no objection to your posting the attached material on your site.Thank you for your interest and we look forward to receiving your constructive comments."

April 11th 2012 is the cut off day for comments.

-Tom

 

[chartman]

Prop Guard Test Protocol Tank Test w/ No Hull

I would be especially interested in any comments you might have about the decision to test the various types of guards for protection levels provided from the front, side, or behind at various speeds, directions, and horizontal center lines (distance to the side from center of the prop hub) as the outboard circled in the State University of New York (SUNY) CRESE tank at Buffalo without the presence of a boat hull. The drive is just suspended over a circular tank (like a circular running track) and motors around tied to a large rotating arm while it rides a small platform on some rails on top of the tank and its leg is suspended into the water.

We have a brief video of similar tests ran long ago.
http://www.propellersafety.com/wordpress/wp-content/uploads/SUNY-propeller-test.mov

They suspended gel samples as seen in the image below
http://www.propellersafety.com/wordpress/wp-content/uploads/CED-prop-guard-testing.jpg

We contend the absence of a boat hull (they tested at SUNY without a hull) moving forward, stationary, or in reverse results in significantly different streamlines and local pressures near the propeller guard than if a hull were present, making the results (whether the suspended gel samples were sucked in or struck or not) not transferable to the same situation if a boat hull were present.

We posted a piece titled, "The Emperor Has No Boat", on our site to point that out, but just like in the Emperor's case, nobody seemed to notice.

To us it seems a lot like the situation discussed in several papers on propeller - hull interaction.

Do you guys have any thoughts about the validity of testing the sucking in or striking of suspended gel samples without a hull to similar tests with a hull?

gary polson
Propeller Guard Information Center

 

[Luc Vernet]

Hi all,
Although this thread, in last posts, has deviated from the original subject of speed gained by the presence of a nozzle (pump jet, etc...), a question to which a rather clear general answer has been given (= no gain!), and if you people do not mind getting somewhat closer back to the original subject, I did not see two things considered in these posts. I am no expert at all in this and asking the more knowledgeable people here about it:

One concerns only torpedoes, and is the fact that the diameter of the propeller is, AFAIK, limited in most cases by the diameter of the tube. The power (I suppose very high) required for the very high speed these monsters achieve nowadays would probably like to make use of a larger propeller (although tip velocity is limited...), which is not possible for the reason here-above. Would not that be, then, one more reason why torpedoes have props in nozzles?

Another one, and which is very much related to the here-above consideration, is that modern commercial airplanes engines, which are improperly still called "jet" engines, are actually propeller engines, the propeller being called the "fan". These fans are basically multiple blade propellers in a duct, actuated by a turbine. We know that the usual comparison between airborne or "waterborne" propellers is valid up to a certain speed, as air can be considered incompressible a low speeds, but that in this case (very high speeds), the comparison between air and water does not stand up very well.
However, I understand that airplanes with conventional propellers would not be able to reach the speed those airplanes do, with their multiple blade fan in a duct/ nozzle (chose what you like). So, would this be, in some circumstances, be applicable to propellers in water (surface or submersible crafts), and would a certain type of ducted props make possible to reach speeds that more conventional one could not reach???