Propellor guard s

TIMO · 15 May 2011, 21:40

Hi guys,,, what are your thoughts on propellor guards,, i want to fit one to my twatsu 40 hp on my sib,, what are the pros and cons? thanks ,, nige

Matt · 16 May 2011, 04:50

Prop Guards mess up all the flow over the prop and gearcase, plus add a lot of drag - the faster you go the more pronounced the reduction in performance will be.

They are good at avoiding blunt object impacts on the prop, but if you're travelling at speed, the gearcase and guard impact will still be non trivial - depends on the object which ends up worse off.

They are poor at small object deflection, hands, feet, ropes, sticks, etc. Whereas normally these objects sucked into the prop might get cut and then ejected, a prop guard does have a tendency to trap the object in, rendering it more like a food blender.

In shallow water running they do improve the protection of the prop from rocks etc, but not fully since stones, sand, mud etc will still get through.

IMVHO, (with very few exceptions) if you are in a situation where you need a prop guard, you either need to plan your boating more carefully to not get into that situation, or you have the wrong boat. (e.g. Get a waterjet, or don't try running amongst rocks, or swimmers etc).

willfinch36 · 16 May 2011, 08:58

Just out of intrest, what are the RYA guidelines on support boats and prop guards?

Will

willk · 16 May 2011, 11:11

Quote:

Originally Posted by Matt

IMVHO, (with very few exceptions) if you are in a situation where you need a prop guard, you either need to plan your boating more carefully to not get into that situation, or you have the wrong boat. (e.g. Get a waterjet, or don't try running amongst rocks, or swimmers etc).

Seconded.

Poly · 16 May 2011, 12:14

Quote:

Originally Posted by willfinch36

Just out of intrest, what are the RYA guidelines on support boats and prop guards?

Will

http://www.rya.org.uk/sitecollection...d%20policy.pdf

Cypman · 16 May 2011, 12:18

We were "forced" to fit them at our RYA Training Establishment and the resulting loss of power was considerable (75hp and 90hp O/Bs).
We eventually discovered the RYA guidance letter on the subject, which basically said "not recommended" and quickly persuaded our H and S gurus to let us remove them.
Safe operations and training is the best solution.

Matt · 16 May 2011, 12:22

As is often the case with H&S, they clearly didn't know the first thing about the subject they were being asked to advise on.

TIMO · 25 May 2011, 18:39

When you tug the pull cord , does the prop stop spinning immediatly ? Also does it stop spinning immediatly when you change to neutral ?.. thanks Nige

ashbypower · 25 May 2011, 18:57

Quote:

Originally Posted by TIMO

When you tug the pull cord , does the prop stop spinning immediatly ? Also does it stop spinning immediatly when you change to neutral ?.. thanks Nige

No and No, additionally water flow over a prop when in neuteral can cause the prop to spin

TIMO · 25 May 2011, 19:00

Quote:

Originally Posted by ashbypower

No and No, additionally water flow over a prop when in neuteral can cause the prop to spin

OK but , does it slow dramatically in either scenario, as not to be powerful enough to hurt someone? Ie would the water create enough friction/resistance to slow the prop right down . My concerns are particularly in a man overboard situation TBH Brian

ashbypower · 25 May 2011, 19:44

You have to remember the engine does not stop immediatly and has a heavy flywheel which containes energy and therefore will take time so slow down, anything the propeller touches will therefore sustain damage to some degree

TIMO · 25 May 2011, 19:47

Quote:

Originally Posted by ashbypower

You have to remember the engine does not stop immediatly and has a heavy flywheel which containes energy and therefore will take time so slow down, anything the propeller touches will therefore sustain damage to some degree

That confirms my thoughts then . i have a polypropelene propguard but am in two minds on fittting it , it also means removing my doel fins .

TIMO · 25 May 2011, 20:55

Quote:

Originally Posted by TIMO

That confirms my thoughts then . i have a polypropelene propguard but am in two minds on fittting it , it also means removing my doel fins .

Am i being cautious ,overcautious, or downright paranoid

TIMO · 19 June 2011, 20:21

Ok,, so i bought one ..
Tried the sib on friday and went from tewksbury to gloucester ,, around 22 miles.. and used a full25 litres to get there (one way)

Couldnt believe it ,, when i got to gloucester lock i had to fill up again to come back ,, i couldnt wait to get back to take the sodding thing off , it made the boat handle like crap and actually increased fuel consumption by 50% .
I took it off this morning and put the doel fins back on and it all handled great again ,,, never use one again!

CJL · 19 June 2011, 22:35

Timo - Very interesting thread, confirms my long standing suspicions!!

Polwart - Many thanks for posting the link to the RYA doc. London CG have in the past asked me to provide 40 safety boats with prop guards for some of our events and I had to laugh

, getting 40 safety boats is hard enough!!!

It's nice to see the RYA taking a risk based approach in it's advice rather than universal precautions.

Chris

Smithyyy · 20 June 2011, 20:38

Apparently there's just been one of those ridiculous American court cases in whiich someone who managed to get themselves injured by a propellor sued anyone and everyone they could think of and the jury decided to find the propellor manufacturer at fault for designing a propellor without a guard - and as the only company involved and hence having the deepest pockets they got hit for a few million. Which risks meaning it'll get pretty hard to buy a prop WITHOUT a guard in the not-too-distant future unless a blast of common sense gets inserted from somewhere.... and there don't seem to be many obvious sources of that... :-(