Hydro-Physics?

[mdaspit]

Would someone help me with answers to some basic questions please?

How is lift measured?
And what is its effect on performance?
Too much? Not enough?

What are the effects on performance of afterplane length?

Bottom width characteristics?

Is there something I could read to get some propeller intelligence?

Thanks

[B Walker]

not exactly sure

You looking for the Physics principles, or the math?

Hydroplane design has more in common with Airplanes than boats in a traditional sense and the terminology used comes from aviation.

[sam]

All the raw physics is in these books: http://www.aeromarineresearch.com/stbd2.html

[mdaspit]

Thanks

Thanks, Im just trying to understand what it's all about, as it relates to what to look for in boats. For example, when I read an ad for a boat and it says "this boat has 2 3/4'' lift," What should that mean to me? or I read a debate about what's better?, a 72" afterplane, or a 69" afterplane, How does that effect the boat's performance? or bottom width?... or what ever.
So, I'm not a mathmatician or an Einstein, just a guy try to get a clue.

[Team B&H]

You will find that single specific measurements or dimensions are not horribly significant by themselves. What is important is how every dimension functions with all the other ones. One boat with less bottom lift may have the driver and/or motor set further aft so it functions equally well as one with more lift but has the center of gravity farther forward. What is better? If there were certain dimensions that were absolutely critical and exact, you probably would see most boats with that dimensions since we've been playing with and hopefully, optimizing them for years. But that is not the case in practice. You will find most competitive boats have a range of the dimensions you mentioned but you will also find that some at the extreme of these dimensions will work as well or better that boats having only the mean dimensions. You are searching for a simple answer and it isn't that simple.

[bh/]

Dave Geer, NA, published a book called Propellor Handbook about ten years back to fill a va***n on prop knowledge. It addresses large boats, cruisers etc, but some of his fomulas do work well with our runabouts. Hydroplanes, being more airplane than boat, do not compute.

http://books.google.com/books?hl=en&...result#PPP1,M1

[OMCFAN33]

Estaic lift (hope I spell right)

[dcrummett]

MDASPIT,

Check with Butch Webb bkw@aol.com. He designed the first picklefork back int he 60's and can help you with most of your questions. He's also OBRA's president and still a practicing engineer.

Dan
O-49

[sam]

No, the first pickleforks were made in the 1950's

[johnsonm50]

Thanks, Im just trying to understand what it's all about, as it relates to what to look for in boats. For example, when I read an ad for a boat and it says "this boat has 2 3/4'' lift," What should that mean to me? or I read a debate about what's better?, a 72" afterplane, or a 69" afterplane, How does that effect the boat's performance? or bottom width?... or what ever.
So, I'm not a mathmatician or an Einstein, just a guy try to get a clue.

Im on the basic 411, clue search too, not an expert, want to know more. If you were getting a custom made boat by a top builder, your weight, the classes / motors you run etc. would be considered. If your lookin for a used boat knowing a little about what that builder would make for you would help choose a suitable ride.
Will a longer afterplane turn as well? Will a narrower boat go faster. Is more lift good for heavier drivers?, Bad news for lightweights?!.. You know, reasonable answers to dumm qwestions.

[mdaspit]

Still Searching

Im on the basic 411, clue search too, not an expert, want to know more. If you were getting a custom made boat by a top builder, your weight, the classes / motors you run etc. would be considered. If your lookin for a used boat knowing a little about what that builder would make for you would help choose a suitable ride.
Will a longer afterplane turn as well? Will a narrower boat go faster. Is more lift good for heavier drivers?, Bad news for lightweights?!.. You know, reasonable answers to dumm qwestions.

Yes, exactly my questions. That's what I need to know, the basic principals.
I realize it takes years for boat designers and builders to find their "Sweet Spot", and I understand that has a lot to do with what makes the difference between one brand of boat and another, but... aren't there some basic fundamentals that are fairly easy to explain?

[reed28n]

Dimensions

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.

[mdaspit]

Thanks...Really

[

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.[/QUOTE]

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.

[drbyrne55]

great replies

Also consider, airflow characteristics other than the bottom. Imagine removing sponsons, what is your side view shape. How does this shape affect drag;lift. What does your the leading edge/section do?..... increase or decrease lift; drag? ... increase or decrease responsiveness? How does angle of attack affect lift; drag? How will design change for CSH with the 3/4 depth rule of 2007?

[johnsonm50]

great replies

Also consider, airflow characteristics other than the bottom. Imagine removing sponsons, what is your side view shape. How does this shape affect drag;lift. What does your the leading edge/section do?..... increase or decrease lift; drag? ... increase or decrease responsiveness? How does angle of attack affect lift; drag? How will design change for CSH with the 3/4 depth rule of 2007?

My guess.. however much speed loss there is [3/4"] will easily be compensated for in no time.