Full-Sized Outriggers??? Why Not?

[Dr. Jet]

In the model boat world, it is an accepted fact that 'riggers are faster and corner better than scale or sport-scale hydros. Some of the modern composite riggers are stunning examples of state-of-the-art engineering and advanced construction techniques. They are also less prone to blow-overs as they capture far less (virtually no??) air under the hull. So my question is this: Why haven't the full-sized guys gone to this concept? Now I know there was the Winston Eagle that was about as close to an outrigger that you can get. Is it the power to weight issue and being stuck with a Viet Nam-era helicopter turbine engine that simply wouldn't power a 30-foot outrigger at a decent speed? Is it because you'd need a REALLY big dude to give it a hand-launch?

I fly gliders, and in the glider world, the only thing that establishes one class against the next is wingspan and/or flaps. There's a reason they all look similar and that is called a wind tunnel. In the "Unlimited" hydroplane class, is it the regulatory agency that determines the hull shape, or is it physics/aerodynamics/hydrodynamics?

[srislash]

The drag boat guys have gotten close. But there may be something to the not enough power to planing surface ratio in the unlimited world. The drag boat guys can easily’POP’ the hull clean out of the water and onto plane. A little tougher to accomplish with a 30ft’r

[NativePaul]

In "unlimited" hydroplane racing i think there has only been 2, the '69 pay n pak and the '90 winston eagle, but there have been a bunch being that Donald Campbell is a national hero to me, Bluebird K7 springs to mind.

It is just the rules, with the limited amount of power available unlimiteds need to get aero lift to reach the speeds that they can, and the turns are wide enough that there is less to be gained from a wider stance than would be lost down the straights.

It used to be the same for models here, when I started racing with brushed motors and Nicad cells there was a mixed field of semi scale boats and riggers, with no real advantage to be had either way, riggers were a little more optimised for rough water, and scales a bit more so for smooth, but either could win on any given day. Now we have three times the power in a boat half as big again that weighs the same, a rigger is in a different league.

[Dr. Jet]

Seems to make sense. We can spin proportionally larger propellers at higher RPMs with many times the power-to-weight ratio.

Let's see: A race boat weighs 6750 pounds and produces about 3000hp = 2.25 MW (2,250,000 Watts) or about 300 Watts per pound.

Now just pulling some numbers out of thin air (I'm sure most of you can provide better numbers) I'll make a wild-a$$ guess at weights and Wattages. Let's say a 5-pound boat running 4S (14.4V) and drawing 150 amps would be 432 Watts per pound or nearly 50% better. That same boat drawing 200 amps would be 576 Watts per pound or nearly double that. Now, say a 7-pound boat on 6S and 200 amps.... 617 Watts per pound. Well over twice that of a full-size boat. I guess that answers my question.

[sammyha]

All things being equal, wouldn't a full size outrigger have the lowest prop slip factor like in the OSE calculator? And therefore be faster than a hydro? If not, why?

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[Dr. Jet]

All things being equal, wouldn't a full size outrigger have the lowest prop slip factor like in the OSE calculator? And therefore be faster than a hydro? If not, why?

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I do know that the Unlimiteds are limited (oxymoron?) to a single 16", three-bladed propeller. That's 4.44% of the hull length. If a 36" boat has a 48mm prop, that's 8.05% of the hull length. The associated thrust cones would probably be a cubic function of the prop size, so not only do we get more power per pound, we probably get more thrust per Watt. This is all just a guess on my part, but it seems logical.

https://www.youtube.com/watch?v=sghncnGkFAo

[sammyha]

By all things being equal I mean full size outrigger to full size hydro. How come a full size outrigger doesn't benefit and get the 5% less prop slip over a full size hydro?

I have a thought on it.

Air. Our models are running in a medium that doesn't scale down. A model outrigger benefits by having less drag than a model hydro has moving thru air.

Because an outrigger with rear shoes actually has more surface on the water than a hydro, right? Where else can there be a 5% gain? Lower frontal drag?

Maybe that benefit is just not there for a full size outrigger running in a much thinner medium.

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[Dr. Jet]

I really don't know (that's why I asked ). Srislash and NativePaul made a lot of sense. I did some "thought experiments" on what they said and it seems their analysis is logical. I suppose it would be informative to sit down over a few beers with some full-size hull designers and see what they have to say.

[Fluid]

....How come a full size outrigger doesn't benefit and get the 5% less prop slip over a full size hydro?

Who says it does not?

...Because an outrigger with rear shoes actually has more surface on the water than a hydro, right? Where else can there be a 5% gain? Lower frontal drag?

Most truly fast outriggers only have the prop in the water in the straights, the sponsons only touch to keep the prop unloaded at lower speeds and in the turns. Less aero lift and less frontal area means less chance of blowovers and less parasitic drag. Riggers also weigh less than full-bodied hydros do. So, less frontal area/drag and less weight: to have to lift, to have to hold in turns, or to have to accelerate out of the turns.

Strength is a limiting factor full size, scale up an R/C rigger and keeping the same strength costs a lot.
.

[Dr. Jet]

Strength is a limiting factor full size, scale up an R/C rigger and keeping the same strength costs a lot.

I can see how that would be a major factor indeed....... The structure to hold the sponsons in place would have to be substantial, and if you streamlined it, you would have a wing. Kinda like what the Unlimiteds have....

[srislash]

Cause I’m a fan I’ll put this here:



Gotta love it

[sammyha]

Cause I’m a fan I’ll put this here:



Gotta love it

YESSS! I'm a fan too... [emoji106]

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[Brushman]

hello,

hydroplanes are really using air to float above the water, in the 90's, I had a Graupner Taifun with 16 x 1000 scr Sanyo pushed/matched, a webra 15/7 motor, a 828 hv Novak esc and a poor Robbe 35mm hydro prop. this hydro was faster than all gas boats, and the run time was 3 minutes and 30 seconds, Speed was above 80 km/h. I know that an outrigger with this limited power would not go as fast , but electric outriggers were not popular in Europe at this time. I am still thinking that RC US outrigger design is really influenced by the race forrmat, only a few turn of an oval at full speed, and this is not what we have in Europe. Our riggers have a wider fuselage, and the rear is flying aerodynamically. Full sized boat should take this approach. May be the drivers could not endure the"bumps" on the water, because an outrigger is not always flying above the water.
I think, that an outrigger fitted with 2 marine props and a 8000 hp helicopter turbine could beat Ken Warby's record.