anti cavity plate or wings on outboard,,,

[vanvan450]

hello,,¡¡
any one use the anti-cavity plate or wings on outboard (on a cruising sailing catamaran),,,... any good results¡¡¡????????????????????????

[smj]

Yes, we have installed these on 3 catamarans.
http://www.powerthruster.com
Really cut down on cavitation/ventilation. Worth every penny spent, which isn't much.

[Factor]

Originally Posted by smj

Yes, we have installed these on 3 catamarans.
Power Thruster............."Accelerate your Outboard" - Power Thruster Outboard Accelerator
Really cut down on cavitation/ventilation. Worth every penny spent, which isn't much.

Which size did you use in the Yamaha 9.9? Presuming you had 9.9s on one of your boats

[smj]

Originally Posted by Factor

Which size did you use in the Yamaha 9.9? Presuming you had 9.9s on one of your boats

When we had the Seawind's with the 9.9's they didn't offer such a large selection of Power Thrusters, just small and large. I would email them as I'm sure they have done plenty of the Yamaha 9.9 HT's.

[Cormorant]

We use a PropGuard on the 9.8HP outboard on our 31-foot boat. They're supposed to increase thrust and fuel efficiency. I think they do, though the difference isn't huge.

Mainly I like it for those possibilities PLUS reducing the risk of prop-inflicted injury if you ever have to motor near a swimmer. (Granted, an unlikely event, but maybe in a rescue situation, etc.)

[hurricanehole]

Hi-I'm interested in this too. The other option is an shaft extender for an additional 4" of depth and costs about $400. In rough steep waves my long shaft 25 hp Yamaha looses grip. I suppose wings aren't going to help this since the prop is almost out of the water.

[vanvan450]

I AM THINKING TO FIT THE TWO ENTENSION PLUS THE WHALE TAIL,,,

[vanvan450]

THINK YOU WILL NEED THE TWO ,,, EXTENSION AND WHALE TAIL,,,,

[Rapanui]

Anything extra you bolt on underwater will add drag. Hydrodynamically designed, such things can add thrust by modifying the flow in or out of the prop. Which wins depends on the design but typically such things may make an improvement at low speeds but usually reduce the top speed.

They all share the fact that rarely has any rigorous scientific testing been carried out to establish their performance delta over the unmodified setup.

Tugs use nozzles to improve low speed thrust which is there key operating regime, they are less interested in top speed.

[VBsail]

I have used with and without on my Cat. The main benefit I have noticed is the prop can be closer to the surface before sucking in air and ventilating, both forward and reverse. Resulting in better thrust.

It does nothing for speed, may even slow you down depending on the drag as noted.

I recently put a 5" extension on a 25" XL Yamaha T9.9 to make it 30". This combined with a low drag foil seems to be giving good results. About as good as can be expected from an outboard IMO.

[UNCIVILIZED]

Originally Posted by Rapanui

Anything extra you bolt on underwater will add drag. Hydrodynamically designed, such things can add thrust by modifying the flow in or out of the prop. Which wins depends on the design but typically such things may make an improvement at low speeds but usually reduce the top speed.

They all share the fact that rarely has any rigorous scientific testing been carried out to establish their performance delta over the unmodified setup.

Tugs use nozzles to improve low speed thrust which is there key operating regime, they are less interested in top speed.

Yes, what you're referring to on tugboats are Kort Nozzles. I've seen a few on outboards, but never inquired as to how well they did or didn't work. Occassionally you see them marketed for outboards, & some guys DIY them. They have me fairly curious as to how well they work. Though I'm guessing that the best setup for OB's on multihulls is to mount them on buoyant hinged sleds that attach to the underside of the bridgedeck, or crossarms, at the sled's forward ends. That way the sled keeps the OB more optimally positioned vertically due to their naturally rising & falling as waves pass underneath of the boat.

[smj]

There was a Kort nozzle built for outboards years ago called The Handler. The nozzle was foil shaped and came with a custom large bladed prop that had a very tight clearance between the prop tips and the nozzle. We installed it on a 50hp Honda attached to our 35' Cherokee catamaran and the advantages were amazing. Much greater thrust, the ability to make the same speed under greatly reduced rpm, got rid of most cavitation/ventilation and reduced fuel consumption. The only disadvantages were cost and the fact Honda would no longer honor the warranty if it was installed.

[vanvan450]

[QUOTE=Rapanui;2509466]Anything extra you bolt on underwater will add drag. Hydrodynamically designed, such things can add thrust by modifying the flow in or out of the prop. Which wins depends on the design but typically such things may make an improvement at low speeds but usually reduce the top speed.

They all share the fact that rarely has any rigorous scientific testing been carried out to establish their performance delta over the unmodified setup.

Tugs use nozzles to improve low speed thrust which is there key operating regime, they are less interested in top speed.[/QUOTEOUTBOARD ARE OUT OF THE WATER WHEN SAILINGGGGGGGGGGGGGG

[catsketcher]

That looks like a nice extension VB. Where did you get it. Does the motor still works nicely?

cheers

Phil