the Stock game

[Yellowjacket]

Basic runabouts are actually very aerodynamic, with the exception of the driver and motor sticking out into the airstream.

One area of aerodynamics that I see that could provide a large potential improvement is that of a fairing ahead of the driver. More modern boats have an area ahead of the driver that effectively keeps most of his body out of the airflow. If the only thing that is sticking up into the airflow is half of your helmet you are doing it right.

As they found out on bicycles and motorcycles, if the trunk of your body is sticking up into the airflow and that presents a concave surface to the wind (think about how your body and arms look to the wind trying to get around and out of the area near your chest cavity), that is very bad aerodynamically.

If you don't have enough of a fairing ahead of the driver to hide most of your body (when viewed from the front) you are creating a lot more aero drag.

[Team B&H]

Re: aerodynamics vs hydrodynamics and drag

All you need to do if figure out the Reynolds Numbers for air and water at whatever speed you're interested in. Even considering that aerodynamic drag is affecting a much larger area, you'll see hydrodynamic drag dwarfs it. Of course, I don't anticipate that many here are familiar with Reynolds Numbers to model and compare fluid flows.

Hint: Did you ever drive your car through a pretty shallow puddle of standing water?

[Yellowjacket]

On hydroplanes, if you are riding in a nose high configuration, you are creating a lot of aero drag that isn't helping you. I know it looks cool to have the boat "aired out", but that is bad for aerodynamics.

The reason for that is that all of the air that enters the area in between the sponsons and under the hull gets trapped or stagnated under the hull. The air that leaks out the sides actually creates a lot of drag because you paid the energy to stagnate it and then it gets dumped out the sides. The more air that takes this path, the higher the drag is. Better to have the flow go over the outside of the hull and not slow down at all, as opposed to stagnating too much of it under the boat. You want and need pressure under the boat to get rid of hydrodynamic drag, but once you get the boat riding on a cushion air, you are just creating drag by getting it any higher than that.

Think about it this way, if the nose is higher you have more frontal area from the point where the air enters the area under the boat. Since that area is fully stagnated, that equals a lot more drag.

Flatter is faster.

[Dennis Crews]

Hydro's with tunnels...

Great thread,

Back in the early 70's my grandpa Andy Lowrey began building tunnels into the bottom of his hydro's with great success. They were known as 'Lowrey 4-point' hydros. His son's, Bob and Dave Lowrey ( my uncles ), won multiple championships in those boats and many of the top drivers in the midwest at that time enjoyed success in those boats as well ( Kid Smith, Kenny Bayer, Emmit Homfeld, Art Kampen etc...). The tunnel, as I remember, was about the width of the cockpit, maybe an inch deep, and extended probably 2/3 the length of the cockpit. Keep in mind these are recollections of a 10-12 year old boy (see my avatar) and not exact dimensions.

As a kid I never really though about the physics involved but now I am curious what the tunnel actually does for the performance of the boat. I remember hearing alot of converstion about how they turned better and handled rough water better that the 3-points they were racing against, but why, I wonder.

What do you experts think?

[PROPDOC]

Dennis,
The tunnel on a hydro works similar to a true tunnel hull. The tunnel allows the air to be "trapped" causing the lift needed to "fly" the boat but it doesn't let it stay there, it will allow a percentage of the air to "dump" out of the back of the boat with out losing the effects of the lift generated while at speed. This also allows the hull to be more stable because you have lateral air flow under the boat and not just "packing" a cushion of air under there and keeping it there until the boat sets for the next turn. Imagine trying to balance yourself standing on a small chair, while it can be done it is a little tippy, now place yourself on two small chairs equally supporting yourself, now it is more stable. Much the same way a tunnel works compared to no tunnel at all.

[BP125V]

the wind storm speaks!

This can take a while to properly explain. But since 30 hours a week my job entails properly fitting anyone from serious recreational cyclists to top level pro athletes on road and triathlon bikes, I will take a swing at this one.
To best explain I will break things down from a triathletes standpoint since in a triathlon there is no drafting allowed and aerodynamics is paramount.
First we will talk about the horse power/drag difference. The average triathlete that I fit can produce between 225 and 300 watts of constant power for a one hour maximum effort.(there are some less fit/less gifted athletes that will produce less and a few highly trained freaks of nature that will produce upwards of 200 more watts) A horse power is approx 745 watts. So on average a good athlete can produce about .35 of a hp once they have been biomechanically (not aerodynamically,I will go into that later)fit properly on a bike by me. Most people will see a 5-10% increase in watts through a proper fitting. The size of an athlete (height, width, weight and range of motion) will effect ones speed but on average one can maintain about 22 mph if they are producing 260 watts with no aerodynamic work done.
Most people are blinded by the cool technical features of a bike (aero wheels, tubes of the frame, helmet) as was f cliff. But in all reality the rider them self is 70 to 85% of the aero drag on the bike (85% when fit improperly). Once a rider has has his fit aerodynamically dialed in we can generally get his drag down to be in the lower 70% range. which will increase this speed at 260 watts to be about 24 mph. So a decrease in drag by approx 13% will increase speed by about 9%.
Even though from this one will assume that aerodynamics would make a dramatic difference. Daveracerdsh is spot on by saying how much more hydrodynamics makes a difference than aerodynamic due to the increased density of the watter vs. the air. Also a bicycle powered by the strongest of riders is still only dealing with about 2% of the HP of a stock Yamato 302.
It is more important to focus on decreasing hydrodynamic drag and increase the amount of time you can stay at or near full throttle to utilize the full horse power of your motor through better handling.

John Palmquist
theracersedge.net

very interesting John. Nice seeing you at Wakefield, too bad we did not get to talk. I bet you got your first taste of aerodynamics on the merry go round at Lake Zurich many moons ago!

[daveracerdsh]

Drag

I have also found that a totaly smooth surface (waxed etc) on the bottom of the boat does not work....I while back I was testing my old d rig in Eastern Washington, on a day where there was no wind at all.....100% smooth...I was seeing around 78-79, then noticed a very small ripple about 1/4 mile out...I went over there at full throttle, and when I hit the ripple I accelerated immediatly to 80....One mile an hour. Does not seem like much, but it is. I leave a semi rough surface on the bottom of my boats..as well as the sponsons. A lot of people give me grief over it..but I think it helps. It is no secret...you can see it just walking up and looking at the boat. Dave.

[bill van steenwyk]

Dennis:

In addition as "PROPDOC" says, to letting air on out thru the tunnel that might otherwise "pack in" and cause problems, some folks say a hydro with a tunnel will corner better, and also is better in rough water.

My own experience some years ago, both with boats I built myself, and ones that were built to my spec by Ken Krier, led me to believe that the tunnel down the center of the hydro, usually the same width of the cockpit sides, and starting about the trailing edge of the sponsons, give or take a couple of inches or so, (had them various dimensions on several boats) is that all things being equal, the tunnel may help the boat accelerate a little quicker, because you can run a little more kicked out without going over the edge of disaster on down the straight, because the tunnel will let the excess air out thru the back. (Some also think that is not so good as it ventilates the prop)
Conversely, it may not be quite as fast by a very small amount as the tunnel provides extra wetted surface on the bottom if you take into consideration the upright sides of the tunnel as well as the flat surface of the boat and tunnel bottom. Very hard to prove that though, as water and other conditions would change from test period to test period. I did find that the boats I had with tunnels in the bottom (about 3/4" deep at the transom tapering to nothing where they started) turned a little better, possibly because the sides of the tunnel acted like the insides of the tunnel in a true tunnel boat that will come right up to a bouy and then almost turn in its own length. One more thought on tunnel depth (or the addition of one) is that it may take away some "flotation" and let the boat ride lower at slow speed, taking away from acceleration capabilities, and also be slower off the beach on a beach or LeMans type start. Flotation can also be adjusted with the "cutout" or lack of same in the location around the tower housing cutout. The less the cutout for the towerhousing the more flotation, as is the case with bottom width between the air traps. And then there is the issue of non-trip angles on the sponson and chines. I have seen them all the way from almost straight up vertical to very shallow. What worked well for me, in decent water, were very shallow angles. The boat designed with shallow angles seemed to be very fast comparatively around the corners, but not as good in rough water.

In addition boat widths between the sponsons, depending on motor/driver weight can have a noticable effect on boat performance, as can depth of the sponsons at the various places in its length, and the "lift" or angle of rise from the flat part of the bottom towards the front of the boat.

Most all of these things have been thought and tried to death, along with air trap depth, length of same, fin location and angle of mounting, etc., etc., etc.

Best way I have seen over the years to maximize performance of a boat is to either buy a boat from someone who builds boats for winners, or is one himself. Of course that way you start even with everyone else. Starting even with everyone else comes with its own set of pros and cons. If that is not possible OR you want to try your hand at building, then copy a successful design, although most builders who have been in business any length of time have learned the little tricks of hiding in plain sight what makes their design win championships. BUT, there is no better, faster way to learn what makes a boat design successful, than building one yourself. Either way you win, maybe not on the racecourse immediately, but the knowledge gained if you use your head in the design and also the testing and racing of what you built will be invaluable. At the very least it will teach you what not to do from that point on. Plus if you win with your design, you might just have found a way to pay for your hobby, or at least partially.

What individual experiences with different design boats may tell you could be entirely different from my experience, so take what I have experienced with a healthy dose of skepticism, and test, test, test. That is the best way to improve your knowledge, but the referenced information was MY experience.

[sam]

Jim Russell's book

Has all the physics mentioned above explained in detail.

I do not know of another source with everything in one place.

[Dennis Crews]

Thanks Bill and Propdoc for your feedback on the tunnel theory. Bill, you mentioned that some folks believe the tunnel 'ventilates the prop'. If indeed this happens, would running the prop a little deeper prevent this?

We ran mostly 4cyl Mercs and as I recall everyone 'back in the day' ran 2-blade props and ran them deeper than the 3 or 4-blade props that so many seem to run today at or near even with the bottom of the boat. If the prop-shaft is at the same level as the bottom of the boat, wouldn't the 'top-half' of the prop basically be out of the water when the boat is at speed? It would seem to the inexperienced observer ( me ) that a prop running deeper would get more consistent 'bite' as opposed to a prop 'half out of the water'. Plus, the closer to the surface the more turbulent he water...right?

I realize that many, many people that are much smarter than me have tested and researched this very thoroughly and came to the conclusion that today's setups are faster. If not, they wouldn't be running them. Just curious how this all works.

[bill van steenwyk]

Prop Ventelition

Dennis:

As I mentioned, I never had a problem with it myself, but some say it can and does happen.

I noticed some boats built with a tunnel had a "wedge", usually made from the same material as the stringers of the boat, and looking like a elongated triangle, placed lengthwise in the center of the tunnel right in line with the prop and about 6-10 inches long and starting from nothing at the front to maybe 1/2 deep or so at the back.

I never talked to anyone who put one of these in a boat, and I think they are much more common on true tunnel boats, but I always thought it was there to divert water towards the prop, perhaps to eliminate ventilation or "blowout".

ADD: Sorry I forgot to comment on your question about running the prop deeper to eliminate prop ventilation.

Just my opinion (for whatever that is worth) as I never tested to see if running the prop deeper would eliminate ventilation, because as I mentioned I never experienced it with a boat with a tunnel, just heard some others talk about it, BUT if you run the prop deeper you go backwards most of the time as you lose RPM/speed and general all round performance unless you were having a problem to start with with the prop being too high which would be indicated by poor boat handling all the way around the course and slippage of the prop. There is usually always a trade off for every change you make on a race boat, be it the boat itself, the prop or motor and a lot of changes send you the way you don't want to go. I was told when I first started messing with a tunnel, that your prop shaft center line should always reference to the "real" bottom of the boat, not the bottom of the tunnel when setting up the prop shaft height in reference to the boat bottom.

If you want to get with someone right in your area who probably knows as much about boats, props, setup, etc., as ANYONE, Denny Henderson lives in Garland, Tx I believe and if you could connect with him and spend a few hours you would be MUCH smarter about all this than before you started. He is a many time National Champ and record holder in the PRO category and also one of the nicest guys and people to talk to that you will ever meet.

As I said I never experienced prop ventilation with any boats I had that had tunnels in them so can't speak with any authority about it, although the only two boats I had with tunnels were not at all deep and ended up being covered over as I thought I lost some small amount of speed with them.

I don't know whether you remember or not, but your Grandpa built a runabout with a slight tunnel in the bottom to answer the problem of runabouts of the day having a reputation of getting upside down (blowing over). Best I remember the boat was not any faster but handled better. The end result was similar to DeSilva's experience with the Delta Runabout, both the way the boat ran and handled and also in trying to get it approved for use. Perhaps your Dad or Uncle Bob could tell you more about it. Would be interesting to see it again if any pictures still exist of it.

[Dennis Crews]

.

I don't know whether you remember or not, but your Grandpa built a runabout with a slight tunnel in the bottom to answer the problem of runabouts of the day having a reputation of getting upside down (blowing over). Best I remember the boat was not any faster but handled better. The end result was similar to DeSilva's experience with the Delta Runabout, both the way the boat ran and handled and also in trying to get it approved for use. Perhaps your Dad or Uncle Bob could tell you more about it. Would be interesting to see it again if any pictures still exist of it.

That runabout was built for Emmitt Homfeld and had a slight inverted 'v' shape to the bottom. Emmit took it to an 'alky' race where he ran his c-stocker (30 cid merc) against the alky-B's and won. I wasn't there but I heard the stories about how it did turn much better than other runabouts. The governing bodies of the day promptly outlawed it and that was the end of that. ( Guess a stocker ain't s'posed to beat no alky!! )

I was there though on the day it was tested for the first time over on a canal just on the Illinois side if the Mississippi. Emmitt had taken it out and was very happy with it. Dad then asked to drive it which Emmitt went along with. As a barge was coming up the canal Dad decided to make one more turn and in his attempt to see just how far he could push the boat he nearly spun-out and went off plane....just in front of the barge. We all held our breath as he got it back on plane and got out of the way.

Tim Chance had an article about that boat in an issue of his magazine where he was expressing his displeasure at the governing bodies for outlawing what he saw as a significant advancement in safety. I found it at Boatsport.org a while back and I will see if I can find that article and post it here. I will see if Bob or Dave have any pictures.

Unfortunately I can’t ask Dad about it as he passed away back in February. I am taking Mom to the NBRA nat’s in Sept though. She is VERY excited as it will be the first race she has seen since the late 70’s. I can’t wait to see her face when she hears a 4 cyl merc light ‘em up again!

Now if I could just find someone who has an old Lowrey hydro that would be willing to bring it to that race...wow..how cool would that be for Mom to be able to once again see a boat that her Dad built. Ahh, but that would take a miracle.

[bill van steenwyk]

more info on props and tunnels

Dennis:

If further interested in the previous subject see my "ADD" to my previous post.

I am sorry to hear of Lynn's passing. Please accept mine and Eileen's sympathy.
He was a very nice person, and I know you miss him.

The article you reference as being written in HQ, I think was actually a letter to the AOF BOD or Racing Commission that was a letter to the editor written by me. In it I was critical of the Commission for banning your Grandpa's boat for as was the "official ruling" at the time, "violating the spirit of the runabout rule" as written at the time in the AOF rule book.

As I stated in my letter to the editor, "the only part of the rule that could be construed as a violation would be the use of a tunnel effect to "assist planing".

I stated that "to the best of my knowledge, NO TESTS were ever performed
with a competitive boat of CONVENTIONAL DESIGN, to either prove or disprove the reason for not allowing the boat to compete" under the rules at the time.

I went on to state that "this smacks of prejudice before the fact, and it is just such arbitrary rulings by other associations that led to driver dissatisfaction with other sanctioning body's and the recent forming of the American Outboard Federation." (times don't change much do they?)

I further stated "that if this boat was even 1/10th better handling and it was not given the chance to prove that, then this type ruling can do our sport no good. Boat racing is in a difficult state of affairs at this time and a step forward in boat design to improve handling and safety is sorely needed no matter the manufacturer or sanctioning organization. Rulings such as this one by the racing commission can only, in my opinion, further polarize the members of our sport. Rulings must and should be made but not on emotion and a desire for our sport to remain 20 years behind the times." END QUOTE.

Some things have not changed, and neither has my thinking about certain aspects of the sport, since that time. There is an old saying, "the more things change, the more they remain the same"!!

Those comments were in the Fall 73 issue of HQ and the publication stopped not too long afterwards. I was sorry that Tim was not able to continue on with it, for whatever reason, as we needed then, and do now, an independent voice for Boat Racing, besides the sanctioning body propaganda, especially an outlet for racer's opinions, although if you can type, HR and BRF aren't bad.

Regards your comments about Emmit beating the "B" Konig with his 30H C motor:

"Back in the day" when St. Louis ODA and KC Speedboat were active and together had probably 20 races during the season between them, both clubs ran a combined program that included "alky" "Super Stock or Am Pro" (what now would be MOD) and even some OPC classes in the case of KC Speedboat. It was not unusual for the "gas burner" guys to step up and run with the alkys as the next larger size Am Pro was a legal motor for the next smaller size alky class. In that time period, the courses were fairly small, maybe 3/4 mile around, and in a lot of cases small radius turns. Put a gas burner on the same course with an alky motor of the next smaller class, take into consideration in that time frame there was not as much difference in HP between the two as there is now, and if the gas burner got a good start it could be very hard to get around him if the alky boats started behind. Just about the time the alky would catch the gas burner, it was time to turn again, and then the next straight-a-way was spent catching up again. Add to that Emmitt being a heck of a driver and the result could very easily be what you describe.

I hope you are able to find some pictures of the runabout. That is a part of our history and it would be nice to have it here. Hope your Mom enjoys the races.

[Dennis Crews]

Legacy

Bill,

Yep, thats the article I was referring to. Sorry to miscredit it to Tim. You did a great job on that letter.

You are so right when you said ...'I went on to state that "this smacks of prejudice before the fact, and it is just such arbitrary rulings by other associations that led to driver dissatisfaction with other sanctioning body's and the recent forming of the American Outboard Federation." (times don't change much do they?)'. And unfortunately for the sport we love so much this statement is a valid today as it was in 1973.

You are also correct that no 'official' testing or research was done on the boat before it was banned. I remember Grandpa reconfiguring the bottom of the boat (at no cost to Emmit) to meet the ruling that was made. I wonder what that committe would think of today's flat turning runabouts with turning fins mounted on the side of the boat instead of on the bottom?

It is really nice of you to take the time to share your thoughts on Grandpa's contribution to boat design.

[raceright]

So Duck toooooooooooo much wind rightLOLOLOLO