Propeller protection O/B

[Guest]

Anyone had any experiance of those devices fitted to the cavitation plate and skeg of the outboard - a circular tube which protect the propeller?

Are they any good?
Is propeller damage a real threat on the River?
Are there any handling changes at river speeds?

 

[Guest]

I would not bother with these devices as they mostly do nothing to improve hydrodynamics. The enlarged rudders, etc you see help at river speeds but will make the boat over sensitive at sea speeds. There is debris in any river but the engine will kick up for anything solid - its part of the risk you run.

What size of outboard do you have as a large engine needs to be run at a decent speed to avoid plugs fouling etc. My point under slipways about an auxiliarly engine would come into its own here as a 22 footer will only require about 15hp to achieve river speeds.

Also, the low speed handling of outboard driven planing craft is not great - they tend to wander and be susceptible to crosswinds at low speeds. A bit of concentration will be called for.

In some ways, the place to learn to handle a boat such as your own is on sheltered seas where you can get the feel for what she will do at various throttle/helm settings in wide open spaces with nothing to hit - sorry if that sounds a bit patronising but its well meant.

Good luck

Nick

 

[Guest]

To clarify.... is this instance.....

The outboard is 40HP. the boat will almost certainly only be used on the river and has a long but shallow keel - maybe 8" for the full length of the hull.

 

[Guest]

Do I recall we are talking a planing hull here? If so, I am not sure what sort of performance you can expect on a 22 footer with a forty horse - it will not be a ball of fire but should manage a reasonable lick. 40hp will probably not be enough to get her on the plane but that does not matter too much for river use. If you are going to consider sea use, you probably want a bit more grunt.

Nick

 

[duncan]

So it's a displacement boat and has some inherent stability. If you can afford it the 'best' protection would be a stainless prop because whatever you put on to protect will not avoid normal river debris - twigs (some big!), nasty bail strapping stuff which wraps round prop and folds blades, muddy stuff etc. Alternative is to carry a spare all the time (basically the rebuilt one that you damaged last month..........) or the piranha type with spare blades only.
Note the circular protection thingys you mention are mainly for the specific problem of lines in marinas.

 

[Guest]

- Aren't they really to protect our delicate dangly bits from a sharp rotating choppy-uppy thing?

Anyway, with an outboard you can tilt it up to unwind rope/weed etc whereas with a shaft drive you could be vulnerable to tangles.

Cheers,
Rich.

 

[markc]

I was always under the impression that one should avoid fitting a SS prop on rivers etc where there is a higher risk of debris - due to being much harder, any impact forces would be absorbed by the gearbox/engine rather than bending a blade as it would on an ali prop.....maybe

 

[chrisbrown]

I have found that the protection ring provides a snag for junk to be wedged on when the prop is fouled, the ring is then bent by the torque of stopping the prop and the engine is unusable until repaired. A hull parts the floating rubbish as you make headway and this protects the prop on any design. Try to avoid laying or working stern to the stream and use tiny amounts of power in shallow water to avoid fouled props. Inspect the drive before starting the engine.

 

[duncan]

I would agree to a degree - this makes your alloy prop the 'crumple zone' to protect the gearbox.......

I practice it seems to be the thinngs that get wrapped round that destroy the props though - especially plastic bale ties! unless of course you hit a rock - less likely on a non tidal waterway in a smaller (low draft) boat.

Look at any boat with an alloy prop and you will tend to see a build up of minor damage as well - SS won't suffer this.

but a good point

 

[brianrunyard]

Navy divers use them, not to protect the prop. but to protect themselves.