Define what a Surface-Piercing propeller is

[tom kane]

From Hickmans design to todays surface-piercing propellers is it possible to define a propeller as just being a surface-piercing propeller.

[Ad Hoc]

What does it matter?

Whether it be a prop or anything else that is "designed". If said "item that has been designed", does the job, then it has been designed in accordance with the requirements for its application. It may not always be the most efficient, or the cheapest or the "best way overall", but if it works, what is wrong with it? Why reinvent the wheel if the wheel works, but if used in a different context, so what?

Words are used to describe the application to give context to "things" so that the idea/notion can be conveyed. If a normal prop is used as a surfacing piercing prop, does it make it no longer a normal prop or does it suddenly make it a surface piercing prop because of its application?

What is considered avant-garde or weird today may be tomorrows norm.

"...What's in a name? that which we call a rose, by any other name would smell as sweet.." sums it up!

[tom kane]

I am inclined to agree with you.You would need to take a close look and handle a propeller to see what it is intended to do better than another propeller.Just a casual glance can be deceiving.

[Frosty]

A Surface prop and a normal prop is chalk and cheese, the similarity is that they propel a boat through water. How that is achieved is very different.

The surface prop is half submerged for a start off thats why they call it a "surface" prop. the root and the shaft itself is larger to take the constant pounding of thrust on the blade on and off.
swapping them would kinda propel the boat,in as much as move it.

[baeckmo]

Referring to AH I would say that a spp is a propeller that is intentionally designed to operate with mainly natural ventilation from a free surface. That excludes the 200.000 ton tanker propeller that is cutting the surface in light conditions, but includes Hickman's screws, even if they did not have the camber of todays spp and scp. The outboard prop with exhaust ventilation through the hub has much in common with the spp (and scp) designwise, but there is a difference due to the ventilating gas being introduced to the blade root isof to the outer radii.

Tom, do you have more info on the boat in your pic.s? Weight, power, speed aso. From one photo it seems to have a V-bottom, or is it only my monday vision that is diffuse?

[tom kane]

Prop is a Rola with a very aggressive cup on the trailing edge.First trials 27.5 knots with 200 RPM over- revving ride was excellent and high speed manouvering was much improved but at low speed all was not well especially in reverse when the prop walked the stern sharply to starboard.
a quick look at text..12000 lbs displacement.quarter-beam buttock angle 1.75"
Hull is a one off deeply modified.Definitely capable of generating sufficient lift to justify increased power..300 HP at a quick look at text.

[tom kane]

A surface-piercing prop,so we must look at what props in the early 1950`s
caused a boat to prop-ride,not only Hydro planes but deep v hulls. They were not called surface-piercing props then but heavily worked propellers.Not only cleaver props with heavy cupping.

[baeckmo]

........all was not well especially in reverse when the prop walked the stern sharply to starboard.
.

Even a normal prop would do the sidewalking thing with this installation, even if not as sharply. The spiralling backwash from the screw during backing will hit the vertical structure (holding the shaft) and generate a force to stbd. To counteract this, a vertical fin down from shaft line (check Arneson legs!) will help. (You will notice the same effect with an outboard having lost part of its lower fin.)

The reversing backwash from props with blades designed for cavitating or ventilating flow has more swirl than a std prop for the same astern force. Some propeller designs (Levi for instance) have an appendix at their trailing edges that both strengthens the blade and improves flow in backing.

[tom kane]

Reading from the text of this magazine article..surface area of the very tall narrow rudder was increased by 80% to give more steering authority.Most of this was at the top where the rudder would be fully immersed at low speeds but at high speeds much of it would be out of the water and would not add significant drag. In Aprill 1995....returned to the water for her final trials.She achieved 28.7 knots (measured by Radar) and the enlarged rudder was a roaring success-she was easier to control in reverse,and her handling was positive at all speeds....

[PetterM]

I am inclined to agree with you.You would need to take a close look and handle a propeller to see what it is intended to do better than another propeller.Just a casual glance can be deceiving.

Looks good, who made this drive?

[tom kane]

As the info is from an old Magazine article I felt was very worthy of keeping I guess there is no harm in puting it on this forum. The Evolution Company Camden Maine. The Evolution Marine Shafting System.From the thrust bearing back to the propeller,the shaft ran in an oil bath inside back to the propeller,the shaft ran inside a sealed tube,and turned in bearings normaly lubricated by oil bath.but would continue to run safely if the seal failed...The system did away with normal slow leak system of other systems.
WoodenBoat 126 September/October 1995

[Submarine Tom]

Tom,

I'm surprised at your aversion to the starboard prop walk in reverse (Post #6).

This can be turned (no pun intended) into a real asset if handled correctly.

Cheers, Tom

[tom kane]

Hi Submarine Tom,I was not giving may opinion but reading from a magazine article about trials of the surface drive in that WoodenBoat Magazine article as stated many times.My surface drive gave me lenght of boat turning while manouvering at low speed. I do not think that many boaties realize the limitations of rudders especially at speed where a rudder can only give at best 10 degrees each way from straight ahead before the stall position is reached stall and drag sets in.