propguard improves performance ?

[ian parkes]

http://www.propguard.net/

I just folowed this link posted by Blackroady in another thread . Now i thought propguards reduced performance , but the manufacturer here claims it improves thrust and improves fuel economy .

So why don't we all use them then

[Poly]

Originally Posted by ian parkes

So why don't we all use them then

and why don't engine manufacturers build them into the engine design as standard! unless of course there is some marketing spin here.

[Locozodiac]

Originally Posted by ian parkes

http://www.propguard.net/

I just folowed this link posted by Blackroady in another thread . Now i thought propguards reduced performance , but the manufacturer here claims it improves thrust and improves fuel economy .

So why don't we all use them then

Hola Ian

Engine parts the manufacturer doesn't want to include in a current production model, will be someone else's bussiness to make a high margin profit. Inventors are welcome!

There are issues to them: (Quoted from Prop Guard Web Page)

To obtain optimal performance out of your motor with the Prop Guard® installed, (*) you may need to change your propeller diameter: 9" Prop Guard® up to 8.5" prop, 11" Prop Guard® up to 10.5" prop, 14" Prop Guard® up to 13.5" prop, and 16" Prop Guard® up to 15.5" prop.

The closer the prop blades are to the Prop Guard® rings, it will optimize your performance, handling and will not create a drag. Your motor will also have to be trimmed to a setting of optimal performance.

A matter to buy one spending between $ 150 to 200 per unit to test with/without to experiment differences + $$ to buy bigger diam prop in case yours doesnt' work properly. A prop-guard guinea pig with financial resources is wanted...

Happy Boating

[ian parkes]

I am sure there is some marketing spin , but it does make me wonder just how much difference one would make .

Anyone who can compare before and after ,

does the tube around the prop improve performance in turns etc .

They certainly don't seem to effect the zap cats too badly

[m chappelow]

i suppose the propguard could be extended by a few feet and it could then be a jet drive .

[captnjack]

They really work on slower speed displacement vessels. All the tugs use them, in this application they are called "Kort Nozzles". They direct the prop tip vortices backwards and generate more thrust. For high speed craft they add too much drag and aren't effective. That's why hydroplanes, with props spinning at 10,000rpm wouldn't dream of adding a guard/nozzle. Typical RIB performance/characteristics, being planing vessels slightly more like a hydroplane than a tug, generally aren't improved by adding a nozzle.

[codprawn]

Originally Posted by captnjack

They really work on slower speed displacement vessels. All the tugs use them, in this application they are called "Kort Nozzles". They direct the prop tip vortices backwards and generate more thrust. For high speed craft they add too much drag and aren't effective. That's why hydroplanes, with props spinning at 10,000rpm wouldn't dream of adding a guard/nozzle. Typical RIB performance/characteristics, being planing vessels slightly more like a hydroplane than a tug, generally aren't improved by adding a nozzle.

Spot on!!!

[Cookee]

Originally Posted by ian parkes

They certainly don't seem to effect the zap cats too badly

Rumour has it that a Zapcat speed record was achieved without a prop guard - I guess it was scrutineered in the water!

[alystra]

Originally Posted by captnjack

They really work on slower speed displacement vessels. All the tugs use them, in this application they are called "Kort Nozzles". They direct the prop tip vortices backwards and generate more thrust. For high speed craft they add too much drag and aren't effective. That's why hydroplanes, with props spinning at 10,000rpm wouldn't dream of adding a guard/nozzle. Typical RIB performance/characteristics, being planing vessels slightly more like a hydroplane than a tug, generally aren't improved by adding a nozzle.

Just what I was about to say.

[K&S]

Was about to say the same but you saved the bother

http://www.marinepropulsion.net/kort/nozzle.htm

Another big advantage is the ability to steer astern with lttle /no paddle wheel effect (if you have a fixed shaft) not really a concern to us outboardy types

[ian parkes]

Originally Posted by Cookee

Rumour has it that a Zapcat speed record was achieved without a prop guard - I guess it was scrutineered in the water!

Do they help with tight turns etc , by reducing or stopping ventilation. Zapcats , arancia irb's etc all seem to turn so fast with lots of power on without ventilating.
The problem with fixed trim on small boats with tiller steer is finding the happy medium between a low trim for good turning and slightly higher trim that gives better speed and cruising.
If a propguard does help then its worth losing a little bit of top to improve turning especially if you are messing about in surf and inshore a lot .

[Cookee]

Originally Posted by ian parkes

Do they help with tight turns etc , by reducing or stopping ventilation. Zapcats , arancia irb's etc all seem to turn so fast with lots of power on without ventilating.
The problem with fixed trim on small boats with tiller steer is finding the happy medium between a low trim for good turning and slightly higher trim that gives better speed and cruising.
If a propguard does help then its worth losing a little bit of top to improve turning especially if you are messing about in surf and inshore a lot .

Having had the pleasure of racing a Thundercat in Portugal that doesn't have a guard, I can tell you that although they play havoc on your forearm muscles, they do not suffer from ventilation at all unless landing a jump from miles up in the air with no forward speed on full throttle!

[ian parkes]

Cheers Cookee
i guess i shall have to play with my set up a bit more then .
What i was thinking was that a boat with power to wieght ratio such as a zapcat would maybe ventilate easily if too much power was used in a tight turn , rather like a powerful car would spin the wheels easier . Lateral thinking