Low Speed Surfacing Propeller

[dgruenwald]

We have a need for a very low speed surfacing propeller design. The application will be in the top speed range of 23-30 mph. Does anyone know where we might go for expertise in this area?

[cyclops]

I would love to see the horsepower and fuel savings at that speed over a completly submerged propellor of a cruiser.

[gonzo]

Yes, talk to Sonny Miller. He makes the CAL500 drives
229-776-6015

[dgruenwald]

There will probably not be fuel or horsepower savings although that remains to be seen. So far we are at parity with submerged propellers. But there will be significant draft improvements.

[bananas]

The U.S. Navy developed some high speed surface propellers that were tested at low speeds in a cavitation tunnel. They achieved efficiencies of about 80-Percent at pitch ratio of about 1.5. The tunnel tests were in the speed range of 11 to 25-Feet per Second.

These propellers had nothing in common with current surface propeller designs. A half wet surface propeller needs about the square root of 2 more diameter to match the thrust of a fully submerged propeller. In most current surface propeller designs I have seen, this thrust deficit is made up with extreme cup. The cup kills low speed performance. So current surface propeller designs perform best with very fast, low disk loading installations.

A surface propeller will also produce much bow down force, with peak force at about 50-Percent wet. This often gives significant trim problems.

If the design is executed well there will be efficiency gains. But it is easy to loose the advantage with small design errors.

[tom kane]

According to some experts a Surface Piercing propeller may look very little different to a conventional propeller.Conventional propellers on race boats at speed ran on their hubs and showed racing people just what speed could be gained by lifting propellers closer to the surface and avoiding drag.A 30 percent increase in propeller diameter is now suggested for changing to Surface piercing mode.There is debate about increasing prop size (increasing drag) and operating a prop in less dense water,(less efficient).The trend for S/P props now includes more cup and more blades,preferably odd mumbers of blades.An on-going saga of experimentation.Props can be designed to suit the speed rang rquired.Most of the fastest boats in the World still use small diameter props on angled shafts.

[dgruenwald]

Thank you all for your comments. Bananas, do you know where I could access the Navy data that showed such high efficiencies at low speed? I was not aware that such testing existed. We have a lot of experience with the Power-Vent Surface Drive system but generally the speeds we operate in are 40 mph to about 65. In these systems both types of propellers (round eared or cleaver) seem to work fine as long as we have the "right" pitch progression, cup, rake, diameter, ratio, tunnel shaoe, etc. etc. It's all of this refinement that we would like to minimize.

[bananas]

Hi dgruenwald

I have some of the Navy data.

Don Smith's Power-Vent is the best solution I have seen for the low speed to high speed Surfacing propeller transition problem. I have driven his boat and the system was superb.

The refinements you quoted to get a satifactory installation are typical. The boat manufacturer does this for you. As an individual, the expense and complexity can be overwhelming.

I have had three owners of different surface drive systems on large expensive boats (75 to 90-Ft) for which the propellers would not transition to surface mode. I am working with one of the owners now.

At speeds above 10-Knots speed becomes a first order parameter in propeller design. This is because cavitation effects vary with the square of speed and have a first order effect load capacity.

A low speed surface drive propeller, without cup should be easier to size and tune.

I think that a low speed surface drive system could be very simple mechanically and deliver very efficient performance. Especially in the case that diameter is not severly limited.

I would like to know more about your requirements. Since you have quoted a speed range, Horsepower is all that is required to look at a size constraint free design.

[dgruenwald]

Bananas, glad to hear that you had a positive experience with the Power-Vent system. I too believe that it handles the transition speeds superbly. I believe that the Power-Vent surface drive system is an excellent system. This is what we are developing for slower boats (under 30 mph). Please contact me at the following e-mail address: dgruenwald@ingeniumpd.com so we can discuss.

[xrudi]

Hi,

Our drives LD 170-150 performs well with speeds around 22 knots. We have put some pictures of a working unit on the web (inside this forum). Please visit our webpage www.levidrives.com for more information. There is also a use group MSN Levidrives with some pictures.

Best Regards

Rudi

[RANCHI OTTO]

Contact

Rolla, switzerland (www.rolla-propellors.ch)

Rolla Group is one of the best manufacturer of piercing propeller

[yipster]

http://www.well.com/user/pk/SPAprofboat.html also discusses slow speed surface props

[tom kane]

I am inclined to think that many boaties forget that surface piercing propellers can be run in a variety of configerations,small diameter and spun fast like high speed racers with smaller bore shafts and running gear, or large diameter (compared to standard size) with deep gearing (which most people know) which can only be run in s/p mode.

[u4ea32]

I talkes to Paul Kaman, gave him some design information.

I'm looking for a very efficient propulsion system to achieve 3 MPG at 12 knots for 10000 to 13000 lbs displacement. Very easy theoretically, but then you need to add the constraints:

Trailerable
Works on rivers (run over stuff, shallow draft)
Allows a 20-30 knot sprint with little efficiency loss, if any.

Looks like surfacing props work great, but they do need to be big, with a big reduction gear.

Instead of trimming, the location of the prop and steps near the transom "automatically trim" such that less of the prop is in the water the faster the boat goes. Very easy, really. As the boat goes faster and less of the prop is in the water, then the stern lift goes away too.

[tom kane]

I have been using similar to that since 50`s ,but there are many configerations you can use. search Surface drive Subsurface Drive all in one CAM.A.PROPULSION or PIVOTAL DRIVE on site.The usual Surface drive using big props means bigger heavier more expensive shaft props and running gear which means more drag and weight expense when you don not need them for efficient slower speeds.Surface props do not need to be realy big,take a look at outboards running S/Ps no room for big props there,also most high speed racers have relatively small props and push tons at high speed.