Define what a Surface-Piercing propeller is

tom kane: "Buying a Surface Piercing propeller is just like shopping for Alternative medicine there are plenty of cures available but do any have any real value other than creating an income for some speculator businessman.
There are options on things to buy on everything; not just Alternative medicine. There are even more options for underwear

Science is at a stage where answers can not be proven so we are expected to just accept Theory as fact form all those who put them forward.

You need to take the time to study what the scientific method is and its difference from faith and politics

If you think your knowledge is the only right way forward I am happy for you and thank`s for your discussions on this thread topic.

If you don't think that knowledge is the right way forward in technology, can you tell us what you believe is?

www.freeradicalsbook.com

 

This conversation is getting extra-terrestrial....

tom kane: "Buying a Surface Piercing propeller is just like shopping for Alternative medicine there are plenty of cures available but do any have any real value other than creating an income for some speculator businessman.

Seriously? I am sure that is what was said when the first turbine engine was unveiled.

I am glad to see that Dave Arneson is considered a spectacular businessman; others have honored him as a maverick with significant contributions to marine propulsion.

I have yet to see high performance offshore racing boats running inboard gear....maybe they just like "alternative medicine" because the "standard medicine" is not the best option for high speed.

 

You have got it all wrong Chris67 I have not associated Arneson with any of my comments but you have,he is not the only one in this great big field.

Everything will have it`s critics which as you can see of this forum but some are just vindictive.

 

The French Invention..the long-tail-boat is a good application to see a propeller being used as a S/P prop and also as an conventional propeller and the design follows Hickson`s principle, some people say you can not do that.

Some long-tail-boats also use a rudder combined in the drive shaft. There does not seem to be any rules or specific designs about running a boat propeller in S/P mode.

 

People use house fans at the end of a broom stick too. Nobody says it can't be done. We say it is inefficient and unreliable.

 

There are no Rules to boat design or building you can do what ever you want. Just build what suits your purpose. There is always something different even if if it is not understood by some. http://youtu.be/woredF1FAis

 

I am not familiar with New Zealand, but in the USA, Canada, Brazil, Uruguay, Argentina and the EU, there are rules.

 

Good Afternoon You all, would like to revive this old thread and get your opinion/recommendation on prop size/pitch for my 11000 lb +(without humans/gear/water/fuel etc.) so ~6 ton Catamaran with Honda 50hp 4stroke 20" shaft outboard single drive. She will cavitate in medium to heavy seas so I was wondering if I should use a jack plate to get 25 inches down or pursue a Surface-Piercing propeller option. I am looking for maximum and continuous thrust as can be obtained. My read on Surface-Piercing props is that they are cupped, however, is there any additional size/pitch changes and requirements/concerns other than over heating the engine (lack of water) and keeping the RPMs below 6K ? So should I just use a large small pitch prop and cup it so it will grab on the way up ? How much cup ? Is there a spec on cup ? Thoughts/Recommendations/Experience...

 

First concept to swallow is all outboards are designed to work on planning hulls.
Next you now have to get over all these design issues to get it to work as best as is possible on a non planning hull.

Basically your prop is too small of a diameter and is revving too high for a displacement hull
Your engine has a rev range of say 5000 rpm which covers a boat speed of zero to 8kts?
plenty of compromise there not to mention what happens in reverse.
You need it buried as deep as you can get it but it will still cavitate when the drive angle is suddenly change like in a rolling sea due to the high blade load, only more diameter, more blades and lower rpm can fix this.
Saying that some of that cavitation might be exhaust being sucked back onto the suction side of the blades, another problem to solve

 

Hi folks, My understanding of surface drive benefits is that their benefit starts at about 30 knots where drag starts to become a serious impediment to speed.

 

its all about drag, how fast does a ice boat sail?

 

From the book Power Boat Speed. Kevin Desmond.
Back in the 1930s,whenever power boats like Horace Dodge`s Delphines had lifted up their back end and thrown up a roster tail,the crew would place more weight on the back to put the propeller back in it`s rightful place,under the water! Only that independent thinker,Albert Hickman, had evolved the concept of surface piercing props for his sea sleds, and perhaps Jean Dupuy with his Soriano Six outboards.
Then after or during the War,the Champion Boat Company of California had accidentally fitted 135-cubic-inch engines some six to eight inches to far forward, only to find that not only did their power boats throw up a larger rooster tail,it also ran much faster.

Image shows April 1923 Claude Grahame-Wites sea sled at 45 MPH.
Hulton [picture Library.

 

A rooster tail is wasted power although hard to not have one at all with a surfacing prop

 

Is it not just possible that the rooster tail is the propeller lifting the water into the lower pressure off the atmosphere and driving it backwards faster because of less resistance like a water jet? But doing it more efficiently than a jet?

 

Sure Tom thats why its happening but a record winning boat has a very small rooster tail, we say in the outboard world, no higher than the engine