Outboard Hydroplane Dimensions

[Al Peffley]

I always wondered if anyone has developed a table of optimum dimensions for each class of outboard hydroplane (pro, mod, and stock) that we race. I realize that successful designs vary by size of driver, weight & power of motor, method of mounting the motor (clamp or bolt-thru plates), kneeler or laydown, sponson design, bottom design, structural materials selection, lift control characteristics, etc.; so I assume that each boat dimension set for a class has somewhat of a range of acceptable dimensions (including overall boat length.) Does anyone out there have a table of dimensions, by hydroplane class (APBA/UIM), for the latest hydroplane designs? I would like to use this table as a reference to either order a new boat or buy a good used hydro through this website. I am especially looking for dimensions data on the faster class mod and pro boats (hydros larger than the CSH/OSY classes, but not excluding C-mod). I would like to include cockpit dimensions in the table. Any help in obtaining or developing this "typical" mod and pro hydro dimensions table would be appreciated.

Al Peffley

[pops67g]

Science is wonderful but...

You might find the task of choosing a new boat a little easier if you just found out who builds the boats that have won championships in the class you are interested in. Number crunching is cool, but real world results probably are more reliable. I am pretty sure I know what is best for the classes I run, but I will refrain from advertising at this point. Good luck in your quest.

[Bill Huson]

Yeah, buy a running rig to get started . . .

As for dimensions, save for the J class, there are no rule RE dimensions/class for hydroplanes. And overall length isn't all that important, but the distance betwixt the sponson back and transom (afterplane) IS important. Faster you plan on going, more afterplane inchs needed.

The former is a gross simplification as there's dozens of measurements and angles involved in building a boat. Not to mention every year some boat builder *tweaks* a number that worked great the year before and has a boat that works better. Hydro design is art in motion :-)

[Al Peffley]

First Responses Comment

Hey Guys,

I realize that the afterplane dimension is very important, and I do keep track of who wins at major races and who the boat manufacturer was for that winning driver and boat. Hopefully, some the builders will be willing to share some "non-tweek", general information with me without me having to go to multiple races measuring every boat design per class (assuming the boat's owner might allow me to measure his hydro.) I'm looking for a ball-park figures table here, not one developed from aerospace lift and marine development technology science. One of my current boats is a hybrid of two boat builder's special "tweeks", and that hydro and I have done well in the past (if the motor runs well, with the right prop, and if I lost a little weight.) LOL - You can have the best hydro in the world and mate it with a driver that can't control that hydro as well as the consistent winners in our sport; I know that I don't match the winning driving capabilities of a Chris Helsten or a Jamie Nilsen. Obviously, I am not as knowlegeable about hydros as some of the members of this forum. Keeping insider information on boat characteristics is the edge one needs for winning? I already know the "tweeks" that I don't want in my next boat! I always want to pick a boat's design characteristics that are stable and safe, as well as being fast and at least placing in the finish.

Al Peffley
15-R/R-25

[Al Peffley]

More info please...

Does anyone out there know a website address for some of the European 250ccH boat builders???

Al Peffley
15-R/R-25

[Dan M]

Al,

Try signing up on Formula Series, http://www.formulaseries.net/main/. Hopefully you can get the European builders to give you what you want.

Dan

[ZUL8TR]

Some dimensions and thoughts

As a start realize that water drag is about 780 times greater than air drag all else being the same (same average velocity, surface area, drag coefficient) because water has a much greater density (62.4 lbs/cubic foot) than air (0.08 lbs/cubic foot @ 70 degrees F at sea level). Therefore shoot for less water drag as the best target. The angle of attack for best drag to lift is about 2 to 3 degrees from the water level as a base line to the rear portion of the hull planing surface. Greater angle than this results in increased air drag and water drag due to the greater wedge angle of the rear planning surface to the water. Ideal is to get the boat as low of an angle of attack as possible while keeping the sponsons off the water unless touching water needed in turns and keep water off the non trips under non turn conditions.

For stock hydros bottom widths at rear range from 32 to 36" at the non trip chine break. Less water drag for narrow but heavier engines require wider widths. Non trips are typically 45 degrees at the rear.

Afterplane lengths vary from about 1/2 to 2/3 of the lifting chord length. For pickles this is the length from the straight inbetween edge to the rear planing surface (not from the tip of the pickle). For round nose designs the length is from the tip of the round.

The deck should be as flat as possible at 90 degrees to the length of the hull to reduce the tendency of air to roll off the deck. Air guides are used to help keep the air aligned in a fore aft direction. The max curvature of the lifting wing section is generally forward of the aft of the sponson and needs to be balanced to get the angle of attack of the hull to be 2 to 3 degrees.

Air traps are generally full length to rear and ar about 3/8 to 1/2 " below bottom.

As you note there are many other dimensions to consider but remember the water/air drag difference.

Post what ever else you get from your research

[Al Peffley]

Technical Info Feedback

A big "Thank You" to the HydroRacer.net member in Florida that responded with the engineering technical information in the last response. I am also getting some technical boat characteristics information from the European race circuit -- I will share what information I get, with the permission of course of the information sources. Boat design information has been addressed on this website before I joined, but under a different venue title and discussion approach.

Al Peffley
15-R Mod/R-25 Pro

[ZUL8TR]

Hydroplane dimensions followup

Al

you might look into this site by Jim Russel who is an aero engineer and also races large outboard tunnels and knows a lot about hull design and operational performance rules that are applicable to most boats. Although the hydros we race are a bit different there are alot of similarities and a look at other approaches will not harm. He sells books with computer software on hull design and has lots of free tech articles that are worth reading.

http://www.aeromarineresearch.com/index.html

[Al Peffley]

Reference Material - Website Location Feedback

Thanks for the website reference to read up on hydroplane/marine design information.

I will check it out!

Al Peffley
15-R/R-25

[ram95]

Don't overlook the 'airspeed' factor

You've probably already thought of this but here goes... A lot of performance boaters (tunnels, hydros, etc) get a blank look on their faces when you mention airspeed. Fact is, when you're honking along 6 inches off the water at 68 mph with a breeze blowing at you of say 10 mph, your 'airspeed' is 78, or close to it because a hydro is fairly clean aerodynamically. Though your speed over the water is 68, your speed thru the air is 78! And when you're discussing AOA (angle of attack) you are concerning yourself with the speed of your boat thru the air. The fact that your boat is in what's referrred to as 'ground effect' , essentially the cushioning effect of the air compressed beneath your hull, there are further changes to the equation as to how the airfoil (your hull) will react, should that 10 mph breeze increase momentarily to 15 in a gust.

Then, to screw things up further, when you turn 'down wind' and run with the wind, your boat water-speed may increase slightly (to 69) due to the tail wind but your 'airspeed' is going to be slower (59 ), meaning less lift will be generated at the sponsons. But, the engine/prop sensing less resistance may well try to lift the transom area creating a different handling situation/surprise. Ya gotta love it!! Best of luck,

Alex
Richmond Aero Marine
Mad Russian Racing 8A, 12A

[Al Peffley]

Speed and Boat Dimensions

Yes, this new discussion sounds like real aerospace design talk. You are right about the design dimensions and lift/airspeed considerations in rougher water and potential windy conditions. Stern bottom design features (steps, tunnels, and width) can change the lift, ride stability, and airspeed (wind tunnel effects) in a shorter afterplane boat (like my Karelson 250ccH composite hull pro boat which has an 84-inch afterplane, and is only a total of 11 1/2 feet long! ) This boat will do close to 100 mph with a healthy motor, the right setup, and a good driver in a straightaway. Ed makes a great boat!

I started racing with a Furnel Flyer in C-stock. The boat was Lee Furnel's personal racing boat (that he built in the 1980's with John Stone); it had a lot of lift for a long hull (the hydro was 11 1/2 feet long; it had a long afterplane with a shallow hull and relatively wide sponsons.) I raced it with our local APBA club in Olympia, Washington at Capitol Lake in 1996 (the year after I placed with it in OSY at Depue.) I knew the boat packed a little more air in a head wind, as I could see the lift effects from a side view photo at Depue heading into the wind just before turn one there. A head wind came up quickly in turn one of a C-stock heat at Olympia where I was starting in second place on the inside of the pack with no one in front of me. There is a water lock at the end of the lake near turn one where the north wind is tunneled by the shape of the small highway bridge over the water lock. As soon as the north headwind increased with a clear air gust of about 10 mph through the narrow hole between the small bridge span and the lock, my boat bow came up to a clean 90 degrees and the hull went ballistic (about two stories high ) before it hit "apogee" and I bailed out at "tip-over". ALL of the boats in the corner behind me went by before my hydro came fluttering upside down like a leaf with a dead weight motor at one end -- the airtrap hit me on the helmet, as I could not tuck down any lower in the water with my life vest on (I came staight down faster than my boat did!) I began to worry about having too much flat bottom "exposure" in gusty conditions, and I wanted more speed and control in the corners. The Karelson does this with more speed than the Furnel had and the two boats were the same overall length and tunnel widths (within an inch), but each had very different bottom designs and afterplane lengths.

My current OSY boat that Jon Steen built for me to my specs just before the Furnel was retired is shorter, has a shorter afterplane, and does not ride as well as the Furnel did in rough water on long courses like Depue sometimes gets. However, it turns the corners much faster with less effort. Two feet and a different sponson design can make a big difference in lift, cornering, and stability. Both hydros had about the same top straight-away speed at 68 mph+. Speed performance is good, but speed AND hull stability in long AND short course rough water racing is better. The trick is to find the balance through the right afterplane and tunnel features between the sponsons to attain the best straight-away acceleration & desired top speed in "typical" wind/water conditions.

Jon Steen and I have talked about the impact of speed on afterplane length selection considerations and designer lift controls built into a hull. There is a fine line between a little loose (fast) and too loose (blow-over.) Wind at certain angles is not our friend, but must be considered in hull lift design.

I wonder what the blow-over rate difference is (if any) between a UIM European Formula hydros and similar US-class pro designs??? The Euro-OSY pro boats, in general, are a little longer and they seem to have a shallower hull for the Lemans starts and the perceived rougher water in river racing they do over there. I am very interested in the newest European designs (like Kala OSY-125 hydros) for a new, combined OSY/C-mod/125ccH laydown boat.

Thanks for the thoughts on airspeed, lift, and ground speed. I wonder if anyone has measured the airspeed inside an outboard hydro's airtraps? If one is truely "flying" and "prop riding", would the airspeed sensor interfere with boat's control and stability???

Al Peffley
15-R/R-25

[drbyrne55]

Italian Boat....

Al,
I just contacted the owner of a OSY European boat. It took second in OSY400 Worlds in 2005 and 2006. It is a laydown made entirely of an air core materal and carbon fiber. It is for sale at $4300 fully rigged US plus shipping .... it would be a fun experiment ....
Dan

[Al Peffley]

Italian Boat Opportunity

Dan,

I'll bet the shipping to Puget Sound from Europe would be almost as much as the boat is worth in his asking price in US$, but I agree that it would be a great experiment. I would like to start with a Euro-design wood boat first that has a few composite features before I try a more radical, all-graphite composite hull design... Thanks for the input (too bad I couldn't trade him straight across for my pro boat and motor! )

Al Peffley
15-R/R-25

[ZUL8TR]

hydroplane dimensions continued

At bottom is part of a site for Ken Warby the present Aussie world speed record holder in a jet powered hydroplane at about 318 mph. He is trying to break his own record that he set back in 1978 with a home built hull (good show mate). He presents a very interesting set of calculations (link below) for the drag forces on the hull he has designed and the required power needed to propell it at 500 km/h and 600 km/hr (300 and 360 mph). The calcs are all metric so get out the conversions.

http://www.onlineconversion.com/force.htm

Although they are for a straight line run the procedure is informative to determine the relative amount of the drag components to the total drag force once various values are known. For example the rudder is a significant part of the total drag about 52% and can be likened to the lower unit portion of the engine with appropriate values. I am in the process of calculating various forces involved for my hull set up and will present here when done.

Note that Ken has a 5 degree angle of attack of the planing surface to the relative wind factored in for his calcs. I thought rather high for such a high speed hull? Also note the small hull area in contact with the water and the relatively large amount of hydrodynamic pressure lift the hull has compared to the weight of the hull which is adaquate to lift it at 500 km/hr. Need to convert Kg to kN = 1000N, N = newtons, 1 Kg = 9.806... N)

Also note the relative power increase he calculates is from 1880 Kw to 3280 Kw to go from 500 to 600 km/hr and is approx. equal (as expected from physics) to be the cube of the velocity ratio i.e. (600/500)^3 = about 3230/1880 = 1.72. So get out the calculators and see what power increases are needed to go faster in our boats. For ex. to go from 65 to 70 mph will require (70/65)^3 = 1.25 or 25% more power or a similiar reduction in drag. So with engines fixed in stock classes all that is left is drag reduction.

http://www.kenwarby.com/calcs_page.htm

Here is the lead page for additional info.

http://www.kenwarby.com/

If questions on the terms in the equations and other information not to clear in the calcs I will try to assist, just ask.