A Question of Lift.

[Formula Jr]

Oky. This discussion has always gone way over my head. What are you guys talking about when you say a prop will give or not give lift. Is it Rake, Diameter, Cup or a Pitch to a particular weight of boat and power? And why would lift, not aways be a good thing? What are the disadvantages of too much or too little lift?

[roadtrip se]

Okay Owen, I will give this one a shot from my experience with different hulls and propellor dynamics.
The Classic purists may disagree with me, but lift is more of a dynamic having to do with hull design. Propellor design merely compensates or augments a particular hull design when it comes to the concept of lift.
Case and point. Stepped hull boats, while creating less friction in the water and therefore more overall speed, tend to fly flat in the water and plow their noses into the water. A four blade prop tends to generate more "lift" bringing the whole stepped boat out of the water, making the nose ride higher, but also setting up the unsuspecting driver for a spin out if not careful in turns. As with three blade props, four blade props with diferent rake give different results. The Hydromotive four blade performs better with less dramatic step designs, because it has less rake and less lifting effect. The Bravo 1 four blade has more dramatic rake and is favored on the more radical step designs because it gives more lift. Ironically, the latest Hydromotive four blades have begun to mimic the Bravo 1 in order to compete as stepped hull design has become more radical.
On the Classic straight hull designs, lift is less important, as the bow runs high any way, hence three blade designs in all the various flavors run better for more most folks. Now the Blackhawk hull and lift dynamics are a whole other story. If I remember right, that Formula Jr ran real high out of the water exhibiting its own version of great lift.
Excuse me, if I somehow missed the point here, but this whole mess is what comes to mind when someone mentions "lift".
Rambling right along to bed, Todd

[MOP]

Hi have been thinking about the lift issue, I have attended proping classes years back and I have been toying with trying a stern lifting prop on my 16. Has anyone tried this path to lighten the back end of the 16. To get my top speed I tickle the tabs just a little, might get a little more by losing the drag the tabs creat. Any thought anyone?

Phil / Long Island

[mattyboy]

yeah JR,
this goes over my head too. Roadtrip has put it in english, less the engineer lingo. I could be wrong but from what I understand rake is the backside of the prop opposite side from the cup, rake is what gives you lift. my prop has alot of rake to it, it is a ski prop and at the top end the ass end is very light and gets airborne at about 50mph. but it puts the boat on plane extrememly quickly, but then again it lets the engine rev to high, 6g's no problem.
I think road trip is right you must find the right balance for the hull and the type of performance you want!
I am hoping to try some different props at the spring dust off. anyone who wants to try mine is more than welcome.

this stuff is facsinating, could talk and read about it all the time!

Matt

[PaulO]

Here is a great way to think of this (v hulls only):
The object is to get as little wetted surface as possible since water is denser than air this results in less drag-more speed (the only caveat is that you want enough boat in the water for proper handling. This depends on hull shape).

All boats tend to lift the bow more than the stern at speed due to the basic shape of the hull and weight palcement. Some more than others.

The weight of the engine/drive coupled with the forward thrust of the propeller acting on the transom by using the outdrive as a lever will tend to pivot the nose of the boat up and the stern of the boat down at a pivot point that is close but aft of the center of gravity. If you picture it pivitong where the transom meets the bottom of the boat, you will have the right idea.

Now, the further back the center of gravity is and the greater the thrust from the propeller acting on the lever (outdrive) the greater the lift of the forward hull and the greater the downforce on the stern. This is one reason why outboards beat I/Os with similar power.

The tendency for a v hull to "tilt" or pivot backward on its transom at speed will be affected by the amount of "hook" or "rocker" in the aft sections of the hull. The more "rocker" ( which is a convex shape in the hull) the easier a boat will pivot the bow up much like a rocking chair does.

As far as props are concerned, there are no bow lifting props per se. There are only props which create less stern lift. Remember a large factor is the force of the prop thrust on the lever (outdrive). A prop producing more forward thrust in relation to the amount of lifting force will tend to lift the bow more where a prop with lots of stern lift (usually cleaver style props) will expend some more energy lifting the stern up and resisting the pivoting effect which lifts the bow. Typically, but not always, v hulls without hook work better with non stern lifitng props (mirages, lasers, etc) and tunnel hulls that tend to carry most of the hull on compressed air, can somtimes benefit from more stern lift.
PaulO

[Blewbyu]

Jr-Take it from me,you don't need any more lift!!That FJr of yours FLIES!
Rake is generally the accepted method for BOW lift.Rake is literally that,the angle of the blades from the shaft.The further the blade tips from the transom,the more rake,which of course increases the "screwing"capability (more thrust)-which creates bow lift.Stern lift is mentioned in above post."Cup" is also used for increased thrust to a much lesser degree,but more commonly to prevent cavitation or blowout.CDMA-get your two bits in here would ya? :rolleyes:

[Blewbyu]

Re:Lift.......
Deep V boats high speed running angle/ lift characteristics are largely the result of intelligent design and placement of the "lifting strakes".Saw a 'one off'deep vee pre production 18 footer test mule WITHOUT strakes launch nearby years ago.Sure was embarassing to watch when they hit the throttle-the thing flopped around like a spawning salmon.Wouldn't even plane.
Foumula Jr's must be a bit different than Donzi strakes-Owens FJr rides much drier than my X-18 at the same speeds.As a matter of fact-I don't recall ever seeeing his hull IN the water except at idle. :eek: :eek:

[Formula Jr]

There is one thing I remember from the Donzi-Sidewinder Wars of the early seventies, was that a Sidewinder could always beat a Donzi unless there was a chop. In flat water or long rollers, Donzis never had a chance as the Sidewinder would have its butt sucked into the water making continuious power. I remember being in one at speed and the weird thing was that it never jumped, even on the backside of a roller, it just stayed glued down. A very wild ride, since you had to really hold on thru the negative Gs. It gave the boats a reputation as being dangerious. The Donzis would be flying around losing their prop to water connections. I have often wondered if my boat rides too far out of the water as I sometimes can't keep it connected at speed.

The Brother had a totally different way of driving. He would set the tabs much deeper and then trim up the drive alot further than I do. This takes 5 MPH off the flat water top speed, but keeps the boat much better connected to the water in the rough stuff. But that zone is so fine I always endup ventilating the prop and losing grip so I just like running dry and don't mind the walking wallow when I'm off the strakes.
I have noticed that the really fast boats, don't get alot of lift. They stay planted down, making a good connection all the time with the water. Like Jeff's boat - unless he goes looking for a crusier's wake. :D

[BigGrizzly]

Actually RT2 the Bravo prop was after the Hydro prop. The real fact is the merc prop guys want to beat the Hydro. On our Donzis the Bravo is the low end speed of all we tested on them. The Rev 4 beat it on 3 different 22 huls and a 22ZX. When I built my big motor, I borrowed 2 bravo props(one was lab finished). Of all I tested they were the slowest and the worst handling at WOT. The marage plus was a little better. The Turbos that tried werw significantly better. To clear the air I used three typs of Turbos: the Regular Turbo, the Turbo Lightning, and the Turbo Vector. The props used were pitched correctly for the boats. All are three blade. The lightning picks the whole boat out of the water. I tried a Hydromotive and that boy is rock solid everywhere and also faster on my boat then the bravos. The Bravo is a good prop. My real suggestion is try the other brands they may work differently on each boat. what works great on a Cigarette, may not work on a Donzi.

Randy

[Forrest]

Randy, who is the distributor of Turbo props and where can a person get a deal on one?

[Sam]

Forrest, there are many dealers that I have checked into but the best price I got was from a dealer here in Mich. Try Dan's Discount Propellers, @ 1-800-573-5533/ www.dansdiscountprops.com (http://www.dansdiscountprops.com)

Sam

[CDMA]

If I had to write anything on this topic I would write word for word what Paul O wrote. Really right on.

One thing regarding classics I have been noticing is that in most cases, not all, the Mirage/mirage plus props seem to be the way to go. I have heard people having luck with the Turbos and the Vengance but to me it seems the best prop on the classics is the Mirage. My boat runs best with a 21.

Chris

[Formula Jr]

So I guess everyone is in agreement that Rake is the principle aspect of Lift?


You guys just go right into the "where can I buy what stuff, stuff."

[CDMA]

Yes, but blade design also contributes.

Chris

Next time I go to paint my own boat remind me how much sanding is involved.

[BigGrizzly]

Chris, have you actually tried a Turbo lightning, a Turbo Vector, aaaaaTurbo, aVengence, Hill prop, or a Revolution prop on YOUR boat. I have personally tried all these props except the Vengence. Your and PaulO theories are correct but again they are theories. Untill you have tried A Lightning on your boat don't discount it. that prop likes reised X dimentions. Marage Plus is good but on 4 different Donzis they were not the best or the fastest. I was in a unique position of being to try these props at no cost to me except time and boat fuel. I also have not found more then 3->5 GPS from one prop to another including lab finished props. Again the only true test is to try the prop on your particular boat. A case in point is Our 16 runs fastest with a Michican Wheel 14 3/8X22 with the Volvo outdrive, at 4900->5000 rpms, but then I havn't tried all the newer props on it

Randy

[smokediver]

hey big griz, i looked at the turbo prop website and they have the lightning listed as a prop for outboards do they make that prop in the 14 1/4 dia. as well?

[CDMA]

Grizz again this is just what I have heard. I never claimed to have tried all of these just observing what others have luck with. On my boat I have tried the following:

21 cleaver
23 cleaver
21 mirage
Bravo 4 blade ( don't know the pitch but it was irrelevant because I could not spin it)
21 ( I think) Hill

My boat has an approx. 2 inch raised x dimension. As I said not in ALL cases but it seems most people have the best luck with the Mirage's. Your boat is obviosly one of the cases where a mirage is not the best prop. Mabye it is a hull difference, or the different CG of the Criterion or the different lower unit on the TRS or maybe the Turbo's are just better props. I have no experience with them and I am sure if they work as well for you as you say they are a good deal. While what Paul and I said was just theory that was exactly what owen asked , the theory behind lift. For me for now I am happy. The Mirage works well, is free and it even is what Ted says is best for my boat and he sure knows what he is talking about.

Chris

Returning to knowning nothing :confused:

[BigGrizzly]

First the Turbo lightning fits the mercs Bravo, and Alphas as well as Honda outboards. the particular Litning I use is a 14 3/4 28 pitch( not listed on the web site yet).
Chris the boats the turboa worked better on were Tom's 22 classic, JoeP's 22 classic, my son's 22ZX, as well a friends 24 Python and a 18 Python Viper(18 classic knock off) and my own boat. The viper gut though the lazzer was the best untill he borrowed the vector for a weekend. I actually didn't beleive it at first but they work! I put the props on the leathe and found the props rival the famed lab finneshed one. The marage were over 1/2 inch out fron the smallest to the largest. When I ran a 27 marage plus then the 27 Turbo the boat was smoother, not that it vibrated with the Marage at all, and faster. the cruise was 2mph faster at 3300 rpms, which I found impressive.
the reason people have best luck with the marage plus is because they only compare it to other mercs. Most people try it and like it because they have no other choices. The Merc Revolution 4 also out proformed the marage on all the boats mentioned above except the two Pythons(never tried it on them. It out proformed on my boat with the stock engine. Also another up and comming prop is the solas they work well also and the make stainless props for the Volvos.

Randy

[Bryan Tuvell 33ZX]

OWEN, my two cents from a newbie, the prop guy I deal with who is guiding me through this proping adventure explained the Bravo I prop as follows, it, at planing time, ie out of the hole lifts the rear more than the MPlus, Merc Offshore props, so it is the butt, not the bow, that helps me plane quicker/easier with less engine, in the rough it grabs more, keeping me on plane, where as the MPlus kept knocking the 26 double step hull off plane at landings mid or lower speeds.
I mean, if I am not trimmed down all the way at a stop I could almost never plane my tank, so this is a bit opposite of what most have said, but I am sure it is hull related.
On plane at 60MPH, when I trim the drive all the way the butt does bury and it is almost like overdrive in the 26ZX, 60/61 MPH is where she grabs the second step, less wet surface allowing for the higher speeds for same power packages in convention deep V off shore rides. This past Saturday was 70.4 constant on GPS at 5100 RPM with some engine left. No humidity and cool out. But I DID break the barrier! Blue printed prop/K&N.

As far as the dreaded spin, that area is N/A for me in this boat, after spinning the 22 I was ALWAYS gun shy, I will tell you, I have put this boat through some serious 50/55 MPH manuevers and with proper trim I can not believe she would spin. Not to be cocky, but once you have spun, you have a seat of the pants feel for the slide that begins in turns as small as 45 degrees at WOT or close to, which you know is DANGER, the 26ZX has yet to give me any feeling near that. The 26ZX is a much safer boat to put your family in.
See ya in KY, will you automatically get the tow award again this year? I wonder what the prize will be? Good luck and be safe.
Bryan

PS, what was the PROLINE sign awarded for and was it replaced with a DONZI one? Yeah Mike M., some of us remember! :)