Fitting low water pick up to outboard engine

[ima75man]

if 100 hundred people witness a car wreck, you would have 100 hundred different answer to what happen. lots of people draw outside of the lines, don't mean they wrong, do whatever that works for you.

[Bill Van Steenwyk]

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

Jeff:

Did NOT say it was ALWAYS correct about 2 blades, but the main reason outboard powered hydroplanes went to multi-bladed props in the late 60's was for controllability reasons, not speed. You could run less lower unit in the water and still maintain control and speed better in rough water or a turn than with a two blade prop.
Look at Drag boat propellers, that only run in a straight line.


Phillnjack:

Think you are missing the point. Go back and read the FIRST paragraph of my post again. Why do you think that tunnel boats experimented with "water brakes" at one time, consisting of rods that came down into the water from above the planing surface of the boat. The reason is DRAG, in that case to slow the boat quickly before entry to the turn.

Most everybody on this forum likes and enjoys a lively discussion, but I can certainly understand why someone might take offense at being called "thick minded" when they are trying to answer your questions to the best of their ability.
After all, they took the trouble to try to help YOU, with a question YOU asked, in a very civil manner.

My answers to your question are based on 40 years of racing experience, as well as others who have tried to help you. If you do not want to avail yourself of that experience, then don't ask for help. We may be right, we may be wrong, but insulting our answers to your questions does nothing for our willingness to try to further answer them.

[Krazy Karl]

Since I started boat racing I have always pondered the dynamics of the propeller. I can understand the 3 to 6 idea and the loss on the 6 to 9 quadrant, but I never looked at it as drag. I see where that could be a very definite factor and it makes sense as the in coming blade is pushing harder. I always looked at it that the blade going into water is pushing against the whole body of water below the blade thus generating the majority of the force. As the blade goes from 6 to 9, it is trying to and does throw the water above it into the air where there is a lot less resistance, hence the rooster tail and less force generated. This is only my theory and I am not trying to argue with anyone, just throwing out my ideas and add to the discussion. I wish I knew more about propellers but most of what I have read applies more to completely submerged props.
kk

[phillnjack]

Now youve raced boats for 40 years and have the fastest boats that always win every race entered due to
you building ,designing and making the props yourself.
well i dint know that you were such a world authority on the props.
If i had known you were a grand master of science and physics with far too many degree's and doctorates on
the subject of hydrodynamics to mention, then ofcourse i would have to bow to your superior knowledge on the subject.

I thought you were just a boat driver who raced boats for fun.
drag factor on water is and can be a very misleading thing ,many new boats have come along over many
years and are said to be so efficient etc.
We see computer aided technology and the best brains in the world, yet many people still revert back to
older simpler and it would seem better ideas to win races.
prop development has come along way, but also a lot of the latest designs have actualy come from hit and
miss idea's as well.

Now when it comes down to talking about mercury or any maker spending millions etc to get the perfect prop,
then why is it that independant people such as the owner of this site can often make a better prop or am i wrong again?

and if i ask a question and get a silly answer im just supposed to live with it yeah ?




phill

[byrdsperformance@tds.net]

It explain's quite a bit of info

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.

[Danny Pigott]

Funny I see Bill Van's name in the APBA Record book but not yours Phil.

[88workcar]

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

I do agree with this Phil, But thoery does not always work and some things need no explanation, and regaurdless of theory and understanding sometimes experiance prevails. I will stay out from now on, good luck, keep us posted with progress.

[Glenno]

Hi phill,

I have been pondering on the good questions you have raised about surface props etc.

I will try to explain what I have found with surface piercing props through the years I have raced, I have been told I explain thing like crap by my apprentices over the years so bear with me.

1) You need to think of the water not at rest but at speed, yes its the same water but it responds differently at speed.
example: If you fall off a water ski at 25 mph you sink below the surface very fast, even the initial hit leaves a big hole in the water but if you fall off a water ski at 70mph the water is like concrete and you barley scratch the surface till you slow down.

2) Its very true what you are saying about props blades being fully submerged get better thrust (I can't aggree more) but also at speed- having that much gearcase and prop blades in the water is not eficient for creating better speed because of the drag factor. At a decent speed if you are getting enough thrust with only 2/3 or 1/2 the prop blades in the water why would you bury the motor deeper creating more drag, losing rpm and making the motors job harder, then you would have to lower the pitch of the prop blades as there would be more drag (more potential thrust yes very true but you only need so much for a light race boat) you would end up back with the standard factory set up as that is best for thust and every day boating. I have found with a surface piercing prop set up corectly you can run around 40 to 50% bigger pitch and sometimes smaller diamiter works better (on a light boat set up well) than a the factory props that come on the outboard while hitting better rpm than the factory props. I have also found once you get the surface props up to speed they grip very well and on one of my boats I am only getting 2.1% slippage.

3) A snow mobile can drive on water at speed, so can a motor bike car- look on you tube, good examples of water at speed!

I hope this helps,
Glenno

[Fast Fred]

30 feet of depth = one atmosphere of presure, 60 feet deep = two atmospheres, and so on. this is 3rd grade stuff 45 years ago. every bodys a tuff guy sittin at some key board hidin at there desk usein a fake name. i am Fast Fred, hear and ware i'm standin.

[Tim Kurcz]

How about water pickup at the bottom of the skeg? This allows positioning of the gearcase bullet at/above the water, eliminating drag almost entirely without risking loss of cooling water. From that position, all prop theories can be safely tested.

Tim