Define what a Surface-Piercing propeller is

[sandhammaren05]

Surfacing props on outboards are fully submerged when the boat is accelerated from idle. Exhaust gas is not needed for planning.

Surface piercing propellers, as the name implies, pierce the surface. Only the lower blades are supposed to be in the water. That is why sometimes exhaust gas is used to start ventilation so the boat can get on a plane.

 

[gonzo]

Do you have any examples of outboards with surface piercing propellers?

 

[sandhammaren05]

All V-bottoms and tunnels raced since ca. 1965 are surface piercing! With a short shaft outboard the cavitation plate is even with the bottom of the boat with about a 17 5/8" transom height. On V-bottoms (55-85 hp) we ran closed course races at 21.5"-22" transom height. In general, on a fast pad V-bottom about 1/4-1/3 of the top of the gearcase will line up with the pad. On a tunnel there is no disturbance of the water coming into the prop, so that in that case the bottom of the gearcase is even with or higher than the deepest edges of the catamaran sponsons.

I now, for fun, run a 350 lb 'bass boat' with a 35 Johnson shortshaft (tiller handle) at a transom height 19"-19.5", the prop is a surface piercing (41.5 mph 2-way average). It isn't a cleaver, and need not be. Our fastest surfacing props on 18-20' pad V-bottoms with 235 hp outbooards ca. 1980 were not cleavers, but were high rake round eared props.

Typically, 'bass boats' are running surface piercing props.

Do you have any examples of outboards with surface piercing propellers?

 

[gonzo]

The wrongly called cavitation plate is there to prevent ventilation and the prop to be surface piercing. The photos show typical submerged propeller setup and operation.

 

[sandhammaren05]

You're wrong, it's surface piercing.

The wrongly called cavitation plate is there to prevent ventilation and the prop to be surface piercing. The photos show typical submerged propeller setup and operation.

 

[gonzo]

What makes you think it is a surface piercing propeller, and how do you define it?

 

[sandhammaren05]

It's surfacing because one blade is always above the water surface. That the out of the water blade runs through some spray thrown up from the gearcase bullet provides no thrust. I.e., at most 2 of 3 blades are providing thrust at any given time.

If you don't like my example, then you can be satisfy yourself with any outboard tunnel, where the entire gearcase runs above the water's surface.

I think that researchers who have mainly read a bit about surfacing props, and have not run high speed outboards set up for peak performance, have trouble getting the right picture. Or?

Breaking the surface is only where it starts. Without the right 'cup' surfacing props don't work.

What makes you think it is a surface piercing propeller, and how do you define it?

 

[gonzo]

Have you taken any photos of the propeller operating how you claim?

 

[sandhammaren05]

No, one can't steer a boat a photograph at the same time. but with a 35 hp motor with tiller handle, one can look back at the cavitation plate above the water.

I've watched tunnels run where, with the motor turning 7000-7500 RPM but geared 2:1, I could see the entire gearcase hub and propeller blades above the water. When the motor's jacked up to a surfacing condition, you can feel it: there's a transition from slow to fast where, suddenly (like an airfoil lifting off), the cup becomes effective, the boat lifts and gains speed considerably.
I set the record in EP Class (V-bottom/stock 50 c.i. outboard) with the waterline nearly splitting the gearcase hub (70.560 mph). Another few millimeters and the motor no longer pumped, because the water intake is located about halfway between the gearcase hub and the cavitation plate. The motor pumped adequately so long a there was enough spray from the gearcase hub. This is all well known by outboarders.

I think you should go to a boat race, see for yourself. The technology is old. Arneson didn't invent anything that wasn't known before, so far as I can see.

Have you taken any photos of the propeller operating how you claim?

 

[sandhammaren05]

Here's a shot where you can nearly see the nose of the gearcase

http://images.google.at/imgres?imgu...images?q=cees+van+der+velden&gbv=2&hl=de&sa=G

 

[gonzo]

It is a very subjetive personal opinion. Outboard manufacturers have spent large amounts of time and money to keep the propellers from ventilating. I trust their data more.

 

[gonzo]

The photo you posted show a fully submerged lower unit.

 

[Frosty]

The rear of a surface prop blade is concave the normal prop rear is convex.

And yes outboards have ran surface props for 30 years, we used to call them choppers and were big round eared props. No air was needed to get them to break free because they were so close to the surface.

They were not used for skiing just racing and flywheel weight was reduced for out of corner acceleration. The rooster tail was enormous.

 

[sandhammaren05]

After winning 2 National Championships in 1977, the chief engineer in charge of props at a major outboard co. was smart enough to ask me to do research for them. So you listen to them, and they listen to me. Actually, they're very smart. They know that racing is the real testing ground, so they're always interested in what racers are doing with props.

Photos: 2008 and 853 are me, the other
boats were run by friends/competitors.

Working definition:
A surfacing prop is any propeller, of any design, with the motor set high enough on the transom that, with say a 3 0r 4 blade prop, at most 2 blades provide thrust via circulation about the blade at any given time. With a 3 blade prop it's only 1 blade at time that provides thrust. The photos show examples of outboards running surface piercing propellers. Surface piercing setups are typical for outboard closed course racing since at leat the midince the mid 1960s, and for straightaway records, at least since the 1950s

No, one can't steer a boat a photograph at the same time. but with a 35 hp motor with tiller handle, one can look back at the cavitation plate above the water.

I've watched tunnels run where, with the motor turning 7000-7500 RPM but geared 2:1, I could see the entire gearcase hub and propeller blades above the water. When the motor's jacked up to a surfacing condition, you can feel it: there's a transition from slow to fast where, suddenly (like an airfoil lifting off), the cup becomes effective, the boat lifts and gains speed considerably.
I set the record in EP Class (V-bottom/stock 50 c.i. outboard) with the waterline nearly splitting the gearcase hub (70.560 mph). Another few millimeters and the motor no longer pumped, because the water intake is located about halfway between the gearcase hub and the cavitation plate. The motor pumped adequately so long a there was enough spray from the gearcase hub. This is all well known by outboarders.

I think you should go to a boat race, see for yourself. The technology is old. Arneson didn't invent anything that wasn't known before, so far as I can see.

 

[gonzo]

Which major outboard manufacturer?