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Author Topic:   Prop guards

sport15er posted 12-28-2001 09:35 AM ET (US)
Does anyone use a prop guard? I've been seriously thinking of installing one just for the protection aspect of it. Some manufacturers of course; claim that they boost performance as well. My thoughts are however, do they actually hinder performance by closely shrouding the prop?
where2 posted 12-28-2001 01:02 PM ET (US)
The claims about boosting performance are due to the lessened slip of having the prop in a duct. If the blades were squared off on the outer edges to a close tolerance with the shroud, then it might actually increase performance. (I've seen an OMC commercial division design of a ducted prop for rescue use, they said it hindered performance slightly, but was really geared toward the rescue boat that needs to get upto a person in the water w/o worries of open prop harming them).
Every time I see a new design in prop guards, I wonder how long it will be until the state of Florida mandates them in an effort to protect manatees. (I have manatees behind the house year round, I've considered the prop guards for them).
I also welcome comments from someone who has used one.
JohnAz posted 12-28-2001 02:09 PM ET (US)
(I have manatees behind the house year round, I've considered the prop guards for them).
How are you going to get the manatees to wear a prop guard ?
jimh posted 12-28-2001 02:18 PM ET (US)
In commercial application the Kort Nozzle is often added to the propeller of boats like tugs and tow boats to improve efficiency. These are not high-speed planing boats.
--jimh
triblet posted 12-28-2001 03:04 PM ET (US)
Even with a prop guard, I wouldn't want to
get it near someone in the water. The prop
isn't covered fore and aft. The ignition
should be off when there's someone in the
water near the stern.
If they hinder performance, it's probably
because they create more drag.

Chuck
Clark Roberts posted 12-29-2001 08:13 AM ET (US)
I have seen guards which bolt to the outboard's skeg only and will surely break skeg if impacted (sand bar, mussel bed, oysters, rocks etc) . Those which bolt to skeg and anti-cavitation plate and surround the prop may still damage or destroy lower unit if something hard is hit! Close tolerances between prop and anything can cause damage with the pick-up of even a small piece of wood... just some thoughts! Clark... Spruce Creek Navy Shallow Water Division
DIVE 1 posted 12-29-2001 09:49 AM ET (US)
Sport15er,
We had prop guards on some of our smaller outboards(40HP and smaller) when I was in the service. They worked well to protect the prop during transport in the back of a truck. We also had good luck protecting the prop during slow(idle) speed operations, but a strike at any faster speed would bend the prop guard into the prop and destroy both. As Clark points out, if a small stick gets in the prop guard, something is bound to break. The best guards we found attached to the cavitation plate and the skag. Then use a plastic composite prop-they are cheap to replace and you can rely on them to break when a strike occurs.
Jim
sport15er posted 12-29-2001 10:23 AM ET (US)
Good points, I can see where a guard could cause more damage to the o/b, beyond the prop protection. It appears they are more suited for slow, puttering around type boating.
btw, My main reason was for prop protection; not people protection... I shut it down whenever anyone's in the water.
Thnx for all replies as usual....
Happy New Year!
David Jenkins posted 12-03-2002 11:06 PM ET (US)
Today the Supreme Court decided to allow a lawsuit against a boat manufacturer over whether it should have installed safety cages around its boat propellers. The case involves a woman who was killed when she fell off a boat into the motor's propeller. Her husband is suing the manufacturer, which said federal law protected the firm from lawsuits under varying state laws. The justices ruled unanimously that federal law does not protect the manufacturer. Go to
http://discover.npr.org/features/feature.jhtml?wfId=864872 and click on "Listen to All Things Considered Audio."
timbaho posted 12-04-2002 11:49 AM ET (US)
History has proven over and over that to resist change is futile. You can bet your bottom dollar that this change is inevidable and will most likely happen in the near future. We can only have faith that our society has some of the finest Engineers in the world and they can develope a practical solution to protecting people from propellers that will not effect a boats high speed performance(such as some retractible protection once on plane)because at high speed, logic dictates that the impact of the lower unit will most certainly be a fatal blow.However, with the lawsuit currently pending, everything occured at low speed and it's equivalent to rolling over someone in a parking lot.... The OPERATOR should not be allowed to shove the responsibility of his/her actions off on some peice of machinery. 100% of the blame has to fall squarely on the operator.

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Author	Topic: Prop guards
sport15er	posted 12-28-2001 09:35 AM ET (US) Does anyone use a prop guard? I've been seriously thinking of installing one just for the protection aspect of it. Some manufacturers of course; claim that they boost performance as well. My thoughts are however, do they actually hinder performance by closely shrouding the prop?
where2	posted 12-28-2001 01:02 PM ET (US) The claims about boosting performance are due to the lessened slip of having the prop in a duct. If the blades were squared off on the outer edges to a close tolerance with the shroud, then it might actually increase performance. (I've seen an OMC commercial division design of a ducted prop for rescue use, they said it hindered performance slightly, but was really geared toward the rescue boat that needs to get upto a person in the water w/o worries of open prop harming them). Every time I see a new design in prop guards, I wonder how long it will be until the state of Florida mandates them in an effort to protect manatees. (I have manatees behind the house year round, I've considered the prop guards for them). I also welcome comments from someone who has used one.
JohnAz	posted 12-28-2001 02:09 PM ET (US) (I have manatees behind the house year round, I've considered the prop guards for them). How are you going to get the manatees to wear a prop guard ?
jimh	posted 12-28-2001 02:18 PM ET (US) In commercial application the Kort Nozzle is often added to the propeller of boats like tugs and tow boats to improve efficiency. These are not high-speed planing boats. --jimh
triblet	posted 12-28-2001 03:04 PM ET (US) Even with a prop guard, I wouldn't want to get it near someone in the water. The prop isn't covered fore and aft. The ignition should be off when there's someone in the water near the stern. If they hinder performance, it's probably because they create more drag. Chuck
Clark Roberts	posted 12-29-2001 08:13 AM ET (US) I have seen guards which bolt to the outboard's skeg only and will surely break skeg if impacted (sand bar, mussel bed, oysters, rocks etc) . Those which bolt to skeg and anti-cavitation plate and surround the prop may still damage or destroy lower unit if something hard is hit! Close tolerances between prop and anything can cause damage with the pick-up of even a small piece of wood... just some thoughts! Clark... Spruce Creek Navy Shallow Water Division
DIVE 1	posted 12-29-2001 09:49 AM ET (US) Sport15er, We had prop guards on some of our smaller outboards(40HP and smaller) when I was in the service. They worked well to protect the prop during transport in the back of a truck. We also had good luck protecting the prop during slow(idle) speed operations, but a strike at any faster speed would bend the prop guard into the prop and destroy both. As Clark points out, if a small stick gets in the prop guard, something is bound to break. The best guards we found attached to the cavitation plate and the skag. Then use a plastic composite prop-they are cheap to replace and you can rely on them to break when a strike occurs. Jim
sport15er	posted 12-29-2001 10:23 AM ET (US) Good points, I can see where a guard could cause more damage to the o/b, beyond the prop protection. It appears they are more suited for slow, puttering around type boating. btw, My main reason was for prop protection; not people protection... I shut it down whenever anyone's in the water. Thnx for all replies as usual.... Happy New Year!
David Jenkins	posted 12-03-2002 11:06 PM ET (US) Today the Supreme Court decided to allow a lawsuit against a boat manufacturer over whether it should have installed safety cages around its boat propellers. The case involves a woman who was killed when she fell off a boat into the motor's propeller. Her husband is suing the manufacturer, which said federal law protected the firm from lawsuits under varying state laws. The justices ruled unanimously that federal law does not protect the manufacturer. Go to http://discover.npr.org/features/feature.jhtml?wfId=864872 and click on "Listen to All Things Considered Audio."
timbaho	posted 12-04-2002 11:49 AM ET (US) History has proven over and over that to resist change is futile. You can bet your bottom dollar that this change is inevidable and will most likely happen in the near future. We can only have faith that our society has some of the finest Engineers in the world and they can develope a practical solution to protecting people from propellers that will not effect a boats high speed performance(such as some retractible protection once on plane)because at high speed, logic dictates that the impact of the lower unit will most certainly be a fatal blow.However, with the lawsuit currently pending, everything occured at low speed and it's equivalent to rolling over someone in a parking lot.... The OPERATOR should not be allowed to shove the responsibility of his/her actions off on some peice of machinery. 100% of the blame has to fall squarely on the operator.