stopping water spray ingestion

[waynep712]

i have been thinking about water ingestion in boat racing for a bunch of years...

why do boat builders still let the ram air be directed into the carbs or throttle bodys

i would think that there may be enough room for a large enough air box with baffles to stop any water or spray ingestion into the carbs or intakes.. this would prevent the engine failure that seems to happen. without restricting the airflow and ram air pressure into the motors....

this box would be designed into the hull of the boat.. one for each engine...

another thought.
i cannot understand why nobody has put a tiny scoop on a set of ladder bar type framework the transom... out of the rooster tail... but just above the surface 6 or 8 feet back... so if the boat starts to blow over... this scoop is dipped into the water and drags the hull back down to the surface before it can go all the way over...

this could work on drag boats and hydroplanes..

offshore racing boats it would need to be higher above the surface.. and less effective..

[seattle smitty]

Many years ago some OPC (tunnel boat)racers experimented with a cockpit controlled water brake. This involved (didn't see it myself) a pneumatic cylinder on the transom with a 1/4" steel rod; when the driver hit the brake pedal, the rod would be driven several inches into the water. Maybe they had a pair of these, one behind each sponson. They were reportedly very effective; the earliest experiments used longer or thinker rods, and when they were deployed, the poor driver was nearly thrown through the cowling! I don't know if anyone uses them today. One of the Unlimited camps experimented with a driver-controlled drag chute to arrest incipient blow-overs. I think they concluded that between the driver's reaction time and the chute deployment time, the whole operation would be way too late to help.

You're on the right track in your thinking about ram-air scoops. The supercharging affect of ram-air is a mere 4% at 200mph. A big slug of water in the engine will certainly keep you from going 200, or maybe even 2mph.

[CarbGuy]

Most of the Offshore Race boats (unless the rules dictate a specific scoop opening size) have a trap door system so that the water opens it to dump the water into the bilge, only allowing fresh air to get into the carburetor(s) or throttle body(s).

[Ol' CW]

Originally Posted by waynep712

another thought.
i cannot understand why nobody has put a tiny scoop on a set of ladder bar type framework the transom... out of the rooster tail... but just above the surface 6 or 8 feet back... so if the boat starts to blow over... this scoop is dipped into the water and drags the hull back down to the surface before it can go all the way over...

this could work on drag boats and hydroplanes..
..

They do have that on racing airboats (these things can reach 100MPH in 400 feet)

usually shaped like the Greek letter Pi turned upside down and connected to a foot pedal operated by the left foot

Also used to shower your opponent after dogging them LOL

[seattle smitty]

CW, do those guys have a website? Pix of the brake??

[Ol' CW]

[DavidVizard-GFN]

I am going to stick my neck out here.

Some years ago I got to drive a class winning off-shore power boat. In the process I nearly killed myself and the boat's owner.

My conclusion here was that apparently not one offshore power boat designer has a single clue what they are doing. Anyone that designs a race vehicle with a huge negative feedback loop (inherant instability) without black box control should be made to drive it themselves until death.

I remember looking at Donald Campbell's jet boat 'Bluebird' a few weeks before his attempt on the water speed record. My comment was the it was inherantly unstable and was a death trap. My fellow co-worker in the lab I worked in at the time (an older guy of 32 and more set in his ways) asked if I thought I knew more about boat deasign than Leo ??? it's designer. My arogant youthful answer was 'obviously so' Three weeks later Camnpbell was dead!!

My contention here is that just about all hi-speed boats are designed backwards. What is needed is a whole re-think in the field of hi-speed boat design

DV

(Wonder if this post will change my life!)

[seattle smitty]

Come on, DV, you're not sticking your neck out far enough to give us speedboaters room to hang you! How about some specifics?

My thought on the Bluebird, then and now, was that Campbell had a nice 200-225mph boat (smooth water only), but that both the engine fairing and the tops of the sponsons had enough curve to create a lot of aerodynamic lift which could cause trouble given how light the boat was. He needed to spoil some of that lift, and he needed a way to make the lifting effect over the top of the boat be spoiled instantly whenever the bow started to rise. There is a way to do this. Imagine a standard light aircraft wing, say on a Cessna 150. This is designed to work across a good range of angles of attack until the stall. Now, if you were to attach a piece of stiff sheet aluminum, 8" wide and running from wingtip to wingtip, sticking straight forward into the airflow as the airplane is sitting on the ramp, you would have a pitch-spoiler. The plane could make its takeoff run, building lift over the wing, with no effect from the spoiler, which is parallel to the airflow. But when you start to rotate, increasing angle of attack, that 8" of sheetmetal is now at an angle to the airflow, which trips over its sharp edge, and goes turbulent before it gets to the wing . . . spoiling lift.
The one guy I knew who built some boats (outboard hydros) with this type of spoiler (thirty years ago) was Ron Anderson. Ron said the first version of this anti-blowover spoiler was TOO effective and made the boat excessively pitch-sensitive.

But I'm curious as to what YOU have in mind, DV. I hope its not yet another "backwards-boat." Over the years, many would-be improvers have looked at our three-point hydros, with the two sponsons and most of the aerodynamic lift apparently well forward, and seen them blow over backwards. And they said, "Why don't those fools have one step forward, and the two sponsons and all of the lift aft, lifting the weight of the engine, and they won't blow over?!!" And every fifteen years or so someone builds such a boat, and a driver dies when it stabs its pointy nose into a roller like a spear looking for a place to land. I've only seen a few old photos of the British "Crusader" of the early '50s, and don't know the name of the unfortunate pilot of that craft. But I've seen good home-movie footage of the Dave Karelsen bat-wing drag boat augering-in with the late Chuck Skaggs at the wheel. Ron Anderson was running some of the timing equipment when Lee Taylor was killed by his backwards boat. The "Circus Circus" unlimited hydro was abandoned before it killed anyone, but I stood in the pits in Seattle and watched it come by on a test run, all alone in the straightaway and in good water, when for no discernable reason it violently swapped ends. Driver Ron Armstrong, who was rather skeptical about the craft anyway, was heard breathing hard on his radio until he recovered enough to exclaim, "Holy Hell!!!!!"

But I'll just bet there is another "backwards-boat" on somebody's drawing board right now.

[seattle smitty]

Thanks for the photos, CW. I googled racing airboats and found some YouTube footage. Looks like the thrust line is so high that it keeps the bow down. That means they are getting their speed with sheer horsepower. If you want to go 100mph with a 250cc outboard, ya gotta have it light and loose . . .

[Ol' CW]

Oh trust me real race airboats are light and loose. Under 1000 pounds and the shape of the bottom is very important if you want to win. They are skimming right across the very top of the water, probably less than an inch of hull in the water.

They will fly, but you're right about the thrust helping them stay down. The brake is used when they let off the throttle as the lift is still there but not the thrust

Most aircraft/race airboat engines are 350 HP or less but the car motor boats get way up there.