Hydro-Physics?

[mercguy]

How is lift measured? lift is typically measured from the zero line. If for instance someone talks aboout 2" of lift at the front or bow of a hydro they are referring to a curve that would end 2" above the zero line or planing surface. To measure an existing boat it may be misleading to assume that the zero line begins at the aft end of the boat. The zero line may be established in further forward in the case of a rocker bottom. Some of this is confusing because boat racers do not always talk in nautical terms. So as you move from east coast to west coast the same term could mean two very different things.

And what is its effect on performance? The overall lift is not as critcial as where it begins and how dramatic the change is. On a hydro plane lift is just a point in space at the bow until the air is trapped and compressed then you are getting into the critical area of the lift dimension.

Too much? determined by a number of factors, speed of class, weight of driver, skill of driver. Lift may need to be more conservative for a new driver than for a more experienced driver. And bottom lift is not mutually exclusive of the shape of the deck.

Not enough? Jacoby or Sid

What are the effects on performance of afterplane length? The afterplane only establishes the pivot point for the fin location and the lift dimension from the bottom that you place your outside sponson. As speed increases the afterplane has been traditionally lengthened an the lift is stretched out (less dramatic)

Bottom width characteristics? The boat (hydro) does not know how wide it is in a straight away. More narrow will displace a little less air going forward in space but the width will help the boat stay flatter or more stable in the turn. Not rolling over on the outside chine as much. 20SSH was brutally unsafe before someone put it on a CSH, the first 20SSH boats were 30" and narrower. 36" bottoms made the class driveable, along with other evolutions.
But as the boat tends to stay less roll over the fin will stay engaged better and your attach angle as you exit the turn will be better.

Is there something I could read to get some propeller intelligence? Read all you want, most people will agree it is a dark science no one can explain at least not me.

These are all opinions developed through the consumtion of a great number of Labatts Blue bieres. If you disagree with the information above, start drinking beer then come back to this post after every third beer. By the time you get to 24 you will believe me to be a brilliant boat aficionado on hydro racer. If you cannot make it to 24 you need to practice.

24 beers?? ****, uze East Coasters drink alot!!!!!!!! LOL!!

well said though Scott and if there was a "magical" set of dimensions that were perfect, then all boat builders would be using them. So, apparently there is not. I believe these measurments can be specific to each individual driver and their driving techniques/skills.

[johnsonm50]

[

These are all opinions developed through the consumtion of a great number of Labatts Blue bieres. If you disagree with the information above, start drinking beer then come back to this post after every third beer. By the time you get to 24 you will believe me to be a brilliant boat aficionado on hydro racer. If you cannot make it to 24 you need to practice.

Yes...Great, that helps me a lot, thanks, I appreciate it very much.
Not only informative, but witty and humorus as well. I obviously have been drinking the wrong beer.[/QUOTE]

Ditto x 2, advise/beer. I heard of a hydro being raced currently that has a rocker, was told its good for turning on throttle.

[Al Peffley]

Aerodynamics 101?

Thanks Scott, for sharing some good thoughts on hydro design references for the non-designers. When I asked a similar set of questions earlier this year on HydroRacer I got a lot of comments I perceived to be just political rehtoric(sp?) about boat builders secrets, mostly with no substance (the tunnel boat design book is an excellent reference source, and I am now on their email list for their TBN newsletters.) I did not find this to be the case talking about hull design features with Jon Steen, Marc Johnson, or Anders Dickfors.

I always felt that even though many of us don't build our own hulls, every racer shoud know something about what he or she is ordering or buying so that one does not modify features out of a hull that the designer built in to help it achieve its "intended" (see producibilty variance comment below) performance and safety features. Jetty starts (LeMans style racing) require unique changes to the tunnel width, weight distribution, and bottom planing surface features (addition of a flow diversion wedge, rear pads, etc.).

I am still learning that many boat builders can have some interesting design features that are hard to repeat from hull to hull -- just like the significant performance output variances between two props of the same basic design from the same manufacturer can operate 3-5 mph differently on the same hull with the same motor setup.

If the "as-drawn" lift (and hull twist) design dimension callouts are achievable to measure lift and surface contours correctly and accurately after the hull is built, CAD systems have helped to define and clearly picture the intended lift dimensions on most new hydro hulls. Before CAD technology, one would need to know how to "loft draw" (a formal drafting skill) the hull's aerodynamic "flying" and planing surfaces and added control surfaces to understand lift and turning surface (sponson) features.

I worked in electrical engineering and therefore never learned any pertinent mechanical/aero loft drawing skills. A good lofter can see three-dimensional features from a fairly simple two-dimensional drawing by remembering real hull features they learned to build hydros from a master boat builder like Ed Karelsen, Jones, and others who have built many different classes fo hydroplanes from outboards to unlimiteds. A good thread!

Al

[ZUL8TR]

Hydro Dimensions

Here is a post that I provided to Al that has some physics basics. Other related posts are in this thread.

http://www.hydroracer.net/forums/showthread.php?t=8853

[ZUL8TR]

Thoughts on lift

[QUOTE=reed28n;121941]How is lift measured? lift is typically measured from the zero line. If for instance someone talks aboout 2" of lift at the front or bow of a hydro they are referring to a curve that would end 2" above the zero line or planing surface. To measure an existing boat it may be misleading to assume that the zero line begins at the aft end of the boat. The zero line may be established in further forward in the case of a rocker bottom. Some of this is confusing because boat racers do not always talk in nautical terms. So as you move from east coast to west coast the same term could mean two very different things.

And what is its effect on performance? The overall lift is not as critcial as where it begins and how dramatic the change is. On a hydro plane lift is just a point in space at the bow until the air is trapped and compressed then you are getting into the critical area of the lift dimension.

--------------------------

Something else to complicate the issue:

In addition to the lift you described above there is also a total minimum lift (TML) dimension that can easily be measured and is a measure of the minimum angle of attack that the hull can have. This has a direct effect on angle of attack of the hull with respect to the water surface and the resulting aero and hydrodynamic lift (and drag) of the hull that includes the compressed air under the hull that contributes to the total hull lift.

The TML can be visualized with the rear of the hull touching a flat surface and the rear of the sponsons on the flat surface. The TML is the vertical distance from the flat surface to front of the hydro leading edge (not to the tips of the pickels). This distance includes the effect of the sponson depth and is the minimum distance that the hull can have in racing attitude since the sponsons trailing edge will be on the water at the TML. This TML will set the minimum angle of attack of the hull and minimumx air split point at the front that will go under and over the hull. Properly set up stock Hydros ride with the sponsons off the water so the angle of attack is greater than the TML.

The TML is effected by the afterplane length, sponson depth and the planing surface lift you note in your response above. As an example if the afterpalne length is increased and all else remains the same the the TML is reduced thus lower angle of attack.

[mdaspit]

3/4 Rule

How will design change for CSH with the 3/4 depth rule of 2007?[/QUOTE]


What is the 3/4 depth rule of 2007?

[sam]

The TML is effected by the afterplane length, sponson depth and the planing surface lift you note in your response above. As an example if the afterpalne length is increased and all else remains the same the the TML is reduced thus lower angle of attack.

Very good post. Don't forget that the bottom of the boat does not 100% represent the aerodynamic angle of attack unless the bottom and deck are exactly parallel (they usually aren't these days). The aerodynamic angle of attack will be closer to the average between the deck and bottom lines.

The old Swifts and Sidcrafts did have nearly parallel bottoms and decks. The old Swifts and Sids were something like 8 or 10 inches high at the back from the deck to bottom. Modern designs use an airfoil shaped deck that tapers down in the back to nearly nothing in relation. This changes the relationship of the the aerodynamic angle of attack (as the boat meets the air) and hydrodynamic angle of attack (as the boat meets the water).

[Composite Specialties]

Exactly

[QUOTE=ZUL8TR;121989]

How is lift measured? lift is typically measured from the zero line. If for instance someone talks aboout 2" of lift at the front or bow of a hydro they are referring to a curve that would end 2" above the zero line or planing surface. To measure an existing boat it may be misleading to assume that the zero line begins at the aft end of the boat. The zero line may be established in further forward in the case of a rocker bottom. Some of this is confusing because boat racers do not always talk in nautical terms. So as you move from east coast to west coast the same term could mean two very different things.

And what is its effect on performance? The overall lift is not as critcial as where it begins and how dramatic the change is. On a hydro plane lift is just a point in space at the bow until the air is trapped and compressed then you are getting into the critical area of the lift dimension.

--------------------------

Something else to complicate the issue:

In addition to the lift you described above there is also a total minimum lift (TML) dimension that can easily be measured and is a measure of the minimum angle of attack that the hull can have. This has a direct effect on angle of attack of the hull with respect to the water surface and the resulting aero and hydrodynamic lift (and drag) of the hull that includes the compressed air under the hull that contributes to the total hull lift.

The TML can be visualized with the rear of the hull touching a flat surface and the rear of the sponsons on the flat surface. The TML is the vertical distance from the flat surface to front of the hydro leading edge (not to the tips of the pickels). This distance includes the effect of the sponson depth and is the minimum distance that the hull can have in racing attitude since the sponsons trailing edge will be on the water at the TML. This TML will set the minimum angle of attack of the hull and minimumx air split point at the front that will go under and over the hull. Properly set up stock Hydros ride with the sponsons off the water so the angle of attack is greater than the TML.

The TML is effected by the afterplane length, sponson depth and the planing surface lift you note in your response above. As an example if the afterpalne length is increased and all else remains the same the the TML is reduced thus lower angle of attack.

Exactly! You are the only one that mentioned a huge part of lift, that is the sponson depth and compression.

[seanp3]

How will design change for CSH with the 3/4 depth rule of 2007?

What is the 3/4 depth rule of 2007?[/QUOTE]


For the CSH class the center of the prop shaft must be 3/4" below the bottom of the boat

[Kev43V]

[QUOTE=MJR;121998]

Exactly! You are the only one that mentioned a huge part of lift, that is the sponson depth and compression.

Now what about the air across the top of the boat?

[mdaspit]

[QUOTE=MJR;121998]

Exactly! You are the only one that mentioned a huge part of lift, that is the sponson depth and compression.

Is it too simple to think that the greater the sponson depth the more air can be compressed, therefore more lift created?

[sam]

Sponson depth and "compression" are actually "angle of attack"

As stated by ZUL8TR, sponson depth only sets the minimum angle of attack, not maximum

It is possible to have too much angle of attack. For aerodynamic angle of attack, excess means blow over. For hydrodynamic angle of attack excess means more water drag.

Since under idea conditions the sponsons only touch during turning, sponson depth is about the maximum amount of boat you put in the water when turning and quickly getting the boat back to flying mode from wet mode

Deck topsides are about the other side of a wing airfoil and clean, straight airflow.

The whole package deal of boat design is about balancing power against the 2 drag loads and the quick transition from full boat to semi airplane. Different props will work on one boat and not another depending on what angle the prop's rake adds to the mix ... also affected by the driver's weight & placement in the boat. A boat that works for one driver may not work for another driver with the same motor & prop.

[MN1]

[quote=Kev43V;122004]

Now what about the air across the top of the boat?

You mean like on this boat? I believe that it does provide lift. My design is the exact opposite of a Sprint Car Wing.

Here's some info on Wing End Plates http://www.mulsannescorner.com/wingendplates.html
Mark N

[sws115]

good read thanks guys

[Dave M]

Balance

One important item I think is often overlooked in designing a race boat is balance. You have to consider the weight and torque of the particular engine you intended for the hull. In addition, factor in the weight of the intended driver. You need to devleope a certain amount of weight at a specific point in the hull to achieve this balance. Lighter is not always better in some cases. If you have a 80 pound boat, with a 130 pound engine on the back, you are going to need a lot of help to keep it in control. You need balance.

I am far from an exceptional boat builder/designer, but I have built and designed enough that I found this in my experiences. The next generation of hulls is not to far out...... watch for it.