Why is the cockpit/engine off centre in hydroplane boats?

[Jake Ellwood]

Hi all and Merry Christmas!

While working on the hull I recently picked up. I noticed that the "centre" of the boat being the cockpit etc is about 1 inch further to one side than the other. I panicked initially, thinking it was a crap hull and/or my eyes were deceiving me.

Looking online though, it seems as though this is the case with the Miss Budweiser Hydroplanes (at least, not sure about the others) - it can be seen well here.

Can anyone offer any insight why this is done? I am very curious and tried to search, but my google skills failed me

TIA
Jake

 

[Hydro Junkie]

In a nutshell, it was done to help the boat corner. The theory is that, by moving the engine, gearbox and cockpit to the left, it would:

1. Help hold the left side of the boat down and the skidfin in the water.
2. Help transfer some of the load to the right side of the boat by moving it further from the center of gravity

It was first tried on the 1979 Budweiser Griffon, with some success. The boat was destroyed not long after in a blow over that seriously injured driver Dean Chenoweth due to an aerodynamic issue. It was used on both the Griffon boats that followed, as well as the second and third turbine powered Bud boats. By the end of the decade, almost all new boats had the offset engine and cockpit. It was later phased out when it was found that it wasn't as effective with the next generation of turbines. What was kept, however, was the unequal sponsons also visible in this picture. The left sponson was now 38" wide while the right was 48".
Since you're building a scale boat, you do have one option as well. Since the boats turn right, instead of left, the wide sponson will be on the left side of the boat. The cockpit, however can be on either side. If you want to keep the mirror image, you put the cockpit and engine bay on the right, along with the narrow sponson. If you want to keep more weight on the left(radio and engine primarily), you leave the engine bay on the left. If you're building one of the new style boats, such as the 0706 Oberto/Miss Madison, the engine bay and cockpit stay in the center with the wide sponson on the left, mirrored from what's shown in the picture below

 

[Charles Perdue]

One other reason....it provides a longer lever to help counter act the prop torque.

 

[Jake Ellwood]

Thanks very much for the info. It's a good talking point appreciate you sharing.

 

[Hydro Junkie]

One other reason....it provides a longer lever to help counter act the prop torque.

I thought about adding that EXCEPT the offset design was phased out in the early to mid 1990s. It was found that with the small, lightweight turbine engines, offsetting everything didn't really make much difference. When you look at the three 2-wing boats, the cockpit and engine were centered as shown in this picture of the 1994 Budweiser T4:

 

[RobertDoak]

Jerry Dunlap also explored this on his WOF 30" Tunnel hull...

 

[dschigoda]

Oval racing Indycars were using the offset for decades before the idea made its way to unlimited hydros.

Jim Clark won the Indy 500 in 1965, in a Lotus/Ford, with a huge offset of the main body of the car/engine/cockpit to the left.

This car is currently on display at the Henry Ford Museum in Michigan.

 

[Hydro Junkie]

Something else that is done with the Indy and NASCAR cars is the right side tires are slightly larger than the left when racing on oval tracks. It is not used when running on courses that have turns that go both directions as it would adversely affect turning right

 

[AzMandella]

Something else that is done with the Indy and NASCAR cars is the right side tires are slightly larger than the left when racing on oval tracks. It is not used when running on courses that have turns that go both directions as it would adversely affect turning right

Yep called stagger .

 

[Charles Perdue]

I thought about adding that EXCEPT the offset design was phased out in the early to mid 1990s. It was found that with the small, lightweight turbine engines, offsetting everything didn't really make much difference. When you look at the three 2-wing boats, the cockpit and engine were centered as shown in this picture of the 1994 Budweiser T4:
View attachment 286452

I do not know about the unlimited boats but if you do not extend the right sponson out far enough on our toy riggers it will submarine the right sponson when it is launched. By going to a smaller diameter, less pitch prop this would go away.
This was before the long sponson booms that we are running today.

Been there and done that........

 

[Hydro Junkie]

I do not know about the unlimited boats but if you do not extend the right sponson out far enough on our toy riggers it will submarine the right sponson when it is launched. By going to a smaller diameter, less pitch prop this would go away.
This was before the long sponson booms that we are running today.

Been there and done that........

And I get that. One thing you have to remember is that a Rigger is a whole different animal. Unlike a sport or scale boat, a rigger has little to no inherent aerodynamic lift and probably less than half the weight. In addition, the sponsons are much narrower so they therefore have less hydrodynamic lift than a scale or sport boat.
I was doing some fast figuring, based on my scale 2000 Elam Plus and the MHR. Using the MHR numbers and converting to exact scale, I found the following:

• the boat scales out to 21.375 based on a true width of 14' 3"
• the tunnel scales out to 11.255 based on a true width of 7.5'
• the uneven sponsons are, according to the R/C Unlimiteds rule book, given a nominal width of 48" (6" scale) for the wide sponson and 38"(4.75" scale) for the narrow When I figured the overall width, I found a 5" discrepancy so the Elam sponsons are slightly narrower than the 48/38 standard
• my scale has a 12" tunnel with the engine bay offset .5" to the right at the centerline. That tells me that the offset isn't nearly as significant as it was on the Griffon Budweiser boats. It also has a scaled 8 foot tunnel so there is significantly more aerodynamic lift than any of the full sized boat as the widest tunnel I found was only 7'9"

If you compare that to a 60 rigger, I think you will find the rigger would have a tunnel of over 10 feet with an offset of well over 2 feet as compared to my Elam's 4" offset. In addition, your rigger isn't 14lbs like my boat so the engine torque is trying to rotate more than twice the weight probably using a smaller prop since most scales use a 57-60mm prop