I am trying to find something about the blade causing drag but not getting any info from anywhere else.
is there somewhere i can find proof of this to be true ?
phill
I am trying to find something about the blade causing drag but not getting any info from anywhere else.
is there somewhere i can find proof of this to be true ?
phill
Mr Phil, you keep asking questions. That means that you do not know every thing. So why do you argue with every answer that is given to you? There are many very experianced people here that are tring to help you. Try to listen, just a little.
Helping folks out around the globe.
No it's not true, thats why Mercury spent millions over the last 60 years on lower unit and propeller technology, not to mention all of the aftermarket support of nose cones and prop makers. All the pictures you see of Champ/F1 boats are merely photoshoped to make them look cool, the new video posted of the F60 is smoke and mirrors.
to test out the ideas said, usein a hull with the "sweet spot" in the center hole, ( sweet spot is the best all-around hole on the transom, not to high not to low)
( usein the center hole so to test one up and one hole down from center) stay with me, based on the prop drag idea, if we drop down,one hole,(deeper) the hull is slower, she may not make max rpm, lugin it. one up from center, she may be faster top end, but she blows out, over revs, lightin the limiter these would be the outcome of this test............
Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052
Lets pretend the prop has NO FUNCTION as far as propelling the boat thru the water, other than the fact it is there in it's normal location, on the prop shaft, and in the water. In this visualization, propulsion is being achieved in this example by ANY other means you might imagine EXCEPT the propeller. Could be water pump, sail, oars, or any other type power that will move the boat forward through the water EXCEPT that prop on the motor.
Now imagine it raised on the transom so only a part of one blade is in the water at any one time.
Now imagine it lowered on the transom so ALL of the blades on the prop are completely submerged in the water at one time.
Which location of the prop (depth in the water) do you think will give you the best speed, all other factors remaining the same.
Same thing applies when the prop is driven by an engine and that prop is the sole propulsion for the boat. The more blades in the water, the more DRAG. It also may be easier to imagine the prop as a complete disk. The bigger the disk the more drag. If the disk has holes or slots cut into it, drag will be reduced. That is also the reason a jet airplane is faster (among others) is an airplane with a propeller generates much more drag than one without. Add more propellers (think 4-6 engine bombers) and more drag. In addition, the tips of the propeller reach supersonic velocity while the vehicle itself is much below the speed of sound, also leading to propeller inefficiency. That and drag is why a prop jet is slower than a pure jet.
There is much more to it than just this, just as air is much different than water insofar as the way it acts when moving through it with a propeller or any other object,and that is where number of blades, pitch, diameter and other factors enter into the equation. BUT one of the large things to effect a prop (or any other object moving thru air or water) is DRAG. This is also the reason that some still run props with only two blades when racing, although not a lot anymore. If water conditions will permit, a two blade will probably be faster (taking into a lot of other factors) than a multi blade prop, especially when you are running a surfacing type prop, is there is LESS DRAG with 2 blades than 3 or more. This is not always true, depending on handling problems you might encounter in rough water, etc. You can raise a multi blade prop higher out of the water and have the boat have better handling capabilities because of that word again, DRAG. Eventually you get to a point where handling and prop efficiency become more important than drag reduction, especially if you can not control the boat anymore because of lack of directional control which the lower unit/prop combination in the water give you.
Unfortunately there is no magic formula which will allow you to calculate this point. The only formula is testing and good record keeping.
Hope this helps.
I have to agree with Jason/88workcar these people here know so freaking much it's not even funny, some more then others. Like fast fred said go experiment if you don't believe.
Hey, Bill: If your theory is correct, then why the advent of 3, 4 and 5 bladed race props when TWO (by your theory) would be far better?
Jeff
No i would not believe someone trying to tell me that the water within range of a raceboats prop is heavier at the bottom than top.
Anyone thinking this would be realy thick and shouldnt be allowed near machinery.
Now just because someone has something that works perfectly and does what they wanted it to do when they first invented it,dont mean they know how it works scientifically.
That we only have to look at the wright brothers to see what i mean about that.
Although they got mans first flight in a aeroplane to work,it wasnt the way they thought it was that actually got the plane off the ground.
Now then comes the nice long theory by Bill van steenwyk
he wrote
"Now imagine it lowered on the transom so ALL of the blades on the prop are completely submerged in the water at one time. Which location of the prop (depth in the water) do you think will give you the best speed, all other factors remaining the same. "
well to answer this one would look at a torpeedo or submarine.
The only place where the prop is not as efficient is where its attached to the torpeedo or submarine.
If this is just attached through the hub and no skeg or fin to disturb waterflow then the prop is efficient 360 degrees
of its travel..
I can understand that surface props are made a certain way to cut into the water at surface, and probably a lot more going on than just that at that moment.
But once the blade is submerged its trying to pull itself through the water.
It would be exactly the same if it was trying to pull through a solid medium.
With surface i can see the prop is basically doing nothing for 50% of the time if the bullet is level with the water.
And i can see there is going to be a touch of water slippage at the point of the skeg.
But for the prop not to be pulling at the 6 to 9 oclock does not seem right and no reasonable explanation for this.
the water is no different between 6 to 9 than 3 to 6 other than it will have a drop of air with it carried in with it by the blade out the water.now that blade to me is obviosly not working as hard as the one thats lost its air !!!!!!!!!!!!.
so therefore the blade from the 6 to 9 would infact be the one pulling harder if anything !!!
For those that dont like answers being questioned then i suggest you get a life and dont just be sheep.
Yes i am argumentative, and thats my perogative , as i want to find out the true answers to things not just accept anything told by someone else who dont realy know the answer.
without questing things we would never get any improvements in anything at all let alone props.
the Prop shop shop experts are allways comming up with new improved props to give better performance.
so they too must be questioning the effects of blades in the water and how they are realy working.
I thought the whole idea of a forum was to get answers and have debates to find out a lot more on the practical and the theory of the workings of boats engines and propellers.
if this is not the case then i shall just sit and read and wont bother asking anything.
phill
Phill I guess you have a point there.
Phill'
At one time quicksilver by mercury had a book. I think it was called ALL YOU NEED ABOUT A PROPPLER.
If you can find one of these it's a help.
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