Hydro Design- Kneeler vs Laydown

[Dennis Crews]

I am sure most would agree that European hydroplane racing is the pinnacle of the sport and from what I see here on HR, they run 'lay-down' style hydros exclusively. This appears to be the case in the PRO / USTS category here in the States as well but not in the Stock or Mod categories, even for the classes that run boats comparable in size to the PRO classes.

It would seem that the greatest benefit of the lay-down design would be a lower center of gravity for better turning. But it would also seem that the driver would loose the ability to transfer his or her weight around in the cockpit to compensate for wind conditions or to plant the turn fin going into the corner. Obviously the lay-down design has proven to be faster than the kneeler design or the 'big-boys' of corporate sponsored racing overseas would not run them.

Being intrigued by hydro design I have some questions that I hope some of you experienced experts can answer.

1. Is there more to the laydown design that just the lower CG?

2. Does the lay-down design move the amount and location of the lift built into the bottom of the boat verses a kneeler designed for the same racing class?

3. Why is the lay-down design not more prominent in Stock and Mod racing?

4. For those of you who have piloted both kneelers and lay-down hydros, which do you prefer and why?


Thanks in advance for anyone willing to share their .02 worth on this topic.


Dennis

[Jack Stotts]

A few years ago a builder told me he had put a scale under each sponson and at each corner at the transom with the boat with him in a kneeldown configuration and then changed to a laydown. He told me that there was very little change in the readings. I do know that I don't like to be on the course, especially during milling, with a laydown out there. They seem to not be able to clear themselves or don't try very hard to do so. They tend to be a menace on the course! I can 't comment on the design differance as to how much lift is changed or even if it is necessary. I've exceeded my level of knowledge. Hope I didn't offend anyone who likes to use the laydown. I'm sure you'll get some more valuable opinions. Jack

[Guest]

What end is he talking from

A few years ago a builder told me he had put a scale under each sponson and at each corner at the transom with the boat with him in a kneeldown configuration and then changed to a laydown. He told me that there was very little change in the readings. I do know that I don't like to be on the course, especially during milling, with a laydown out there. They seem to not be able to clear themselves or don't try very hard to do so. They tend to be a menace on the course! I can 't comment on the design differance as to how much lift is changed or even if it is necessary. I've exceeded my level of knowledge. Hope I didn't offend anyone who likes to use the laydown. I'm sure you'll get some more valuable opinions. Jack

That's for SURE!!!

[Yellowjacket]

1. Is there more to the laydown design that just the lower CG?..

Yes.... Can you say "Aerodynamics...", I knew you could....

The body of a "kneeler" has a lot worse aero profile than a laydown. This is because not only is the frontal area larger, but the shape of the resulting frontal area is worse, it basically represents a cavity, the air hitting the front of the driver and then acting like a scoop stagnating in front of his body.

3. Why is the lay-down design not more prominent in the larger classes of Stock and Mod racing?

That's aero realted too. Aero drag is more important in the smaller classes since the boat doesn't have as much acceleration (or power to do acceleration) so you are closer to your top end speed coming off of the corners. Small motors mean you are looking for every advantage...

[Dave M]

Design

There is a lot more to it than simply laying down.

There is this thing called Hydrodynamics and also Aerodynamics. The two don't mix real well, and what is it we are trying to accomplish ? Both. In everything we design as a hydro or runabout pits both of these theory's aginst each other. A master design is not achievable. What we try to do is make the best of a bad marriage. To much control on one over the other and you end up with an ill handling boat. Find a happy medium and you have what most racers would consider a cadilac.

In wind tunnel tests, the slower boats, basically under 90 MPH the design is less important than it is to balance the weight to speed ratio, and also the lengths of certain features. Over 90 MPH and I noticed a big change in Aerodynamics. It suddenly becomes more important to achieve a deck design that provides the down force required for the top speed. And it is VERY important to get the this right. it is al very important to get the lengths right, and the balance right. Over 90 MPH you basically need to find a very happy balance of hydrodynamics and aerodynamics. Since our engines are required to be fixed in place while under power you can't compensate.

Laydown verses kneeler ? Whatever floats your boat. if the boat is designed correctly, it won't matter as much. But laying down does have the CG advantage. You can corner harder and tear up gearcases a lot more.

I agree with Jack, I ran a laydown in SEH (850CCMH) against the kneelers once. It was perhaps the msot uncomfortable feeling I have ever had in a boat. It was not the boat, it was me. The two simply don't mix well together. Had the whole field been a laydown, game on. When I ran Pro, 350CCH, we were all laydown boats except one. it works well, becasue we all have the same sight pictures.

Hint - if you are moving around as much as you indicate in your boat, you need to work out a set up, or get a new boat.

[Bill Huson]

faster classes - add a couple more skid fins and you can go around the corner faster! Go around corner super fast in a kneeler and G force tosses you out. No problem. Add yet another fin and laydown. Now you got WOT turns!

[Dominc24Q]

I have raced Kneelers most of my life. A couple years ago we bought a Euro style laydown Hydro. I don't think I will ever race another kneel down hydro. It is hands down the best ride and the most fun I have ever had in a Hydro. If you are looking for a great driving fast boat check out the Trombetta hydros out of Italy and the Kala boats out of Estonia. I have driven both and they are Awesome. With the right laydown design, I believe you could be very fast in stock and mod. Just my two sense.

Dominic DiFebo
Feby's Racing Team

[Sonny]

Design

Great topic. I am curious about something also. It would seem as though there are fewer accidents and significant injury's in the pro's. It would be interesting to know if that can be attributed to most drivers graduating up to that skill level, or the impact of the lower center of gravity as most hydro drivers are laying down? Is a lay down in fact a safer ride?

[david bryan]

you might think a bout this some what the gps taught me was were to set in the boat be for gps i allways thought the the further back the better

[Mike Schmidt]

Laydown or kneeler....

I did 25 years in kneel down hydro's. Most stock classes, some mod. classes and all the pro classes. The reason I switched was that I lost a Title Series race because I could not pull the pipe in on the last lap of the final heat. I had Bill Giles build me a laydown 250, so I could use a foot operated pipe puller. One of the best decisons of my life. Went from mid pack to being on the podium for the next several years at Depue.

In a kneeler, you use a large amount of of energy holding on and trying to stay in the boat. In the lay down you can use 100% of your energy racing. Your able to do things in the laydown that you would crash and burn in a kneeler. I want to say that there is a speed that you need to run to make a laydown work around the race course, but after seeing Ron Frances ASH, I can't....

Most of the American laydowns in the last 20 years or so were conventional hydro's with the cowel and steering moved. The boats that the Europeans developed were anything but that. Dom hit it on the head. We have a GSC copy for 125. It works good at upper 70's. We have a Mostes 250 boat that runs real well over any type of water. Check out the video of Mikey in the 250 hydro at Winterhaven. The water was very bad. You would have not have made a lap in a kneeler.

Mike Schmidt D-1

[Dennis Crews]

As I suspected there are varying responses but the consensus appears to be that the laydown is indeed faster in the turns. Interesting though the thoughts on mixing kneelers with laydown rigs together in a race.

Dave, you mention wind tunnel tests. I would think that would be very expensive and probably not too many builders/designers have access to something like that. Would it be asking too much (don’t want to reveal any trade secrets) to know who, what, where, when on the wind tunnel testing?

[raceright]

laydowns

Laydowns are something special--youth is even better Mike lololo
every driver has a preference and reasons he likes laying down,kneeling and sitting. but my take is this.
The speeds and age of driver dictate what style.
under 75-80 kneelers
0ver 80 to 100 laydown
over 100 sitdown

swallow that

Pat Wright

[Bmwbob]

Laydown vs kneeler vs another idea

From a purely visual appeal standpoint, I happen to prefer the kneelers.
Having only one afternoon session in one, it seems that you really have to work to get the cockpit fit right for you to limit the amount of wrestling and gymnastics you go through to get the darned thing to turn the way you want.
NOT to mention the practice of tightening the friction damping on the steering to the point where a couple of heats back to back wears you out!
What's up with that anyway? Has no one ever experimented with a simple hydraulic steering damper and backing off on the friction?
From a practical standpoint for us older (and/or injured) folks, the lay down is obviously going to allow us to enjoy the sport for more years.
Now here's another thought: How about a SIT DOWN driving position, with the seat base on a slider track (similar to what they use in a rowing boat) with toe loops you could hook your feet into?
This way, you could pull yourself fore and aft as needed, if that sort of weight shift is beneficial.
I REALLY want to be into this by next season, and am hanging on every word that comes forth about the evolution of OSY400 and the proposed 302 spec motor/prop class.
So. what do you think about the steering and seating ideas?
It is obvious that a seated position puts your CG higher ("roll center" for you circle track guys!), but would that really be that much of an issue?
Or should I just go straight to a lay down boat and suffer the glares of the angry kneelers that think I won't see them cutting each other off in the milling circles?
Of course, depending on how things turn out this November, we may all be limited to attending races within the range of our electric powered cars!
Bob

[Jack Stotts]

One of the guys in the midwest has configured his kneeldown hydro as a sit down which has been necessitated by recent knee replacement surgery. He's been testing with it and will probably enter the fray with it shortly. It'll be interesting to hear his comments and those of the competition. Jack

[bill van steenwyk]

Several years ago before Dan Kirts retired from driving, he drove 500 hydro in a sitting down position, although best I remember it was NOT a capsule type boat. I seem to remember he had some type of injury that was no longer conducive to lying down, as he drove that way (lying down) for a number of years, although I could very well be mistaken about the injury part.

Anyway, he drove that way for a short time, don't think it was more than a season or so, and had barrel rolled in a corner, I think at DePue, although again I could be mistaken about the location. I never saw him in a sit down, non-capsule boat again.

As someone who built a few boats years ago, I would have to be strongly convinced that just putting a seat in a conventional kneel down hydro and the attendant higher center of gravity would be the way to go without some modifications to the boat to better help to keep the sponsons off the water while cornering and eliminate a tendency to hook the outside of the boat and broach and barrel roll, or be tossed out.