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Old 11-15-2010, 11:44 AM   #1
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Propellor Guard

This past weekend, I was merrily cruising up the ICW between the Treasure Island and Madeira Beach Causeways participating in a Veterans Day Boat Parade in west central FL when I hit some kind of submerged obstruction.* No idea what it was, but I suspect possibly a waterlogged piling that had broken loose.**All I got was a loud bang, and then excess vibrations in my starboard shaft.* I limped back to my slip and dove on the boat, and found three of four blades on my starboard prop severely damaged.* Two had about 1.5 inches of the blade tip completely sheered off, and one was ripped and curled over.

I was in the center of the channel in about 10 ft of water, going about 10 kts, and I didn't see anything either before or after the impact.* Chart didn't show anything like submerged piles or anything, so I'm assuming it was a large piece of flotsam.* Two questions:

1.* Should I contact the USCG or Army Corps of Engineers or anyone else in case this is some kind of uncharted obstruction and not just flotsam?* As I said, I doubt it was any kind of permanent obstruction because the waterway is heavily travelled, and I was almost directly on my track from earlier in the AM.

2.* Does anyone have any thoughts on whether it would be worthwhile or effective to install some kind of propellor guard?* The boat is a Jefferson 46 with a semi-displacement hull.* One of my concerns when I bought the boat was how exposed the props and rudders were, and the fact that they are the lowest appendage on the boat when underway, and I have been pondering this question for a while.* This incident has now brought it to the fore in my mind.* My thought would be something made of tubular construction, a few inches larger than the propellor diameter, that would surround the propellor, with a bar that went forward and attached to the hull forward of the shaft that would serve to deflect any flotsam that I ran over.* It could even have a bar that went aft to the tip of the rudder to form a sort of skeg to provide additional support to the rudder.* Only major drawback I can see, and it's a big one, is if something got lodged in the guard where it could trash my transmission or engine if the key didn't shear quickly...

Looking forward to the opinions of this august group of experts!* Thanks.
Glenn

CAPT Glenn Zeiders, USN
M/V SYREN
Jefferson 46
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Old 11-15-2010, 12:00 PM   #2
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RE: Propellor Guard

There's no guarantee, but you would have been wise to have acquired a trawler having a propeller protected by a keel.* In my home waters, I shudder to think of having unprotected propellers.

All the tenders and lifeboats I've observed on cruise ships have metal cages or circular*"belts" around the propellers, but I'd guess this is to protect persons in the water rather than the propellers.
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Old 11-15-2010, 12:13 PM   #3
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RE: Propellor Guard

Propeller guards are fairly common around New England waters to protect running gear from lobster pot lines and buoys. Not so sure, unless one is stoutly made and even then, whether they would protect from a floating log or similar. I can envision a solid hit on the guard driving part of the guard into the prop. Perhaps the PNW contingent with their greater experience of such objects in their waters can speak to what, if anything, is used in their neck of the woods. And yes, if you back up into a floating line a guard can cause a heck of a mess.

A lot of boats around here, mine included, also use Drivesavers or equivalent. It seems to have saved my drivetrain on one occasion although the prop still was damaged.
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Old 11-15-2010, 12:25 PM   #4
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RE: Propellor Guard

A proppeller guard would have not helped in your situation. If it was solid enough to damage the prop like it did it would have done the same to the guard. A guard is fine for lobster or crab traps. The best protection is a keel. Although depending on the obstruction that may not protectd you a piling submnerged can be pushed down by the keel and pop back up into the wheel.
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Old 11-15-2010, 12:27 PM   #5
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RE: Propellor Guard

You could have hit anything from a Submarine to a partially submerged con ex.
Doing the*damage you indicated it sounds like more then a log.*
Images for nozzle propeller*-*Report images

If you had the cash something like this would be cool.

SD*
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Old 11-15-2010, 12:35 PM   #6
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Propellor Guard

Welcome to our world. In the PNW, stuff like this is all over the place. If what you hit was a waterlogged log or section of piling, it's what we call up here a deadhead. They can (and do) sink boats if you hit them with your hull at any sort of speed. Usually they float vertically with the upper end just breaking the surface or coming in and out of the surface so you have a degree of a chance to see them before you hit them.

I have seen propeller guards on commercial fishing boats occasionally but these are to keep nets or lines out of the props.

I have not yet seen prop guards on any recreational boats, single or twin, in our area. We have a large yard in our marina (Seaview North) and we drive past it every day on our way into the marina. We always look at what's there as we pass by--- the yard has a 150 ton Travelift so works on big commercial fishboats as well as large yachts, sailboats, and smaller boats like ours--- and I have never seen a trawler-type boat with running gear guards.

Everybody here just keeps as sharp a lookout as best they can while they're running.

If the obstruction you hit is attached to the bottom I suppose it would be a good idea to notify the USCG about it. If it is a "floating" object, albeit underwater, there's not much anyone can or will do about it. Occasionally on the radio here we'll hear a boater in Canada, usually in the Fraser River or in one of it's entrances, or in Vancouver Harbor, reporting a big deadhead to the Canadian Coast Guard. They will ten broadcast an advisory about it.* But since deadheads drift with the currets, which up here are generally pretty strong, an advisory is only good for boats in the immediate area at the time.

Interestingly, the instances I've heard of of boats hitting a deadhead or floating log or pallet or whatever and suffering running gear damage are split pretty evenly between single engine boats and twins if you include sailboats. Twins are certainly more vulnerable in theory, but I get the impression that they don't actually suffer any more problems in this regard than singles. While there is always the chance of hitting something totally unseen--- I know one boater who had a huge log jammed between a shaft and the hull while traversing a rapids (he came home to Seattle on the other engine)--- I believe the helmsman's vigilance is the most significant factor. When passing through patches with a lot of "stuff" in the water, whichever of us isn't driving comes forward and provides a second pair of eyes to scan for things.

Not that this would have made any difference in your situation since whatever you hit was totally submerged. But you never know if a prop guard would have made any difference, either. It you hit an object hard enough or at the right angle, the guard itself could be damaged and shoved into the prop, or you might hit the object with a shaft or V-strut.




-- Edited by Marin on Monday 15th of November 2010 01:40:14 PM
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Old 11-15-2010, 02:32 PM   #7
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RE: Propellor Guard

Nozzle propellers - very cool

Don't be so quick to jump to a nozzle. Nozzles are designed to direct thrust on tugs and other work boats in specific applications. They are very good at that-supplying about 30% more
forward thrust than "open Wheels". But it is not all shrimp and grits! logs and other debris
have been known to get between the nozzle and the wheel causing a traumatic shut down
to the engine. This happened to a tug at a former employer of mine. End result was a broken crank
totalling about $1ooooo plus repair, not to mention the lost revenue of a boat out of service for
several weeks.
These boats will suck rugs and tires off of the banks in canals and narrow rivers (ask me how I know this!).
The boat handling characteristics are effected also, you lose your side forces in maneuvering
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Old 11-15-2010, 02:57 PM   #8
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RE: Propellor Guard

Isn't this the same thing that is known as a "Kort (sp?) nozzle?
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Old 11-15-2010, 03:52 PM   #9
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Propellor Guard

I think what you are referring to is a form of rudder in place of a regular rudder. The whole thing turns around the prop directing the force as if it were in a tube.

Images for kort nozzle

similar in concept and design just not in the function.

SD

-- Edited by skipperdude on Monday 15th of November 2010 04:55:59 PM
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Old 11-15-2010, 07:56 PM   #10
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RE: Propellor Guard

Shrouded propellors are generically refered to as Kort nozzles. The benefits and problems are the same weather they are "steerable" or not. s
Some have 1,2 or three rudders behind them, and some the nozzle does the work of the rudder by turning.
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Old 11-15-2010, 09:27 PM   #11
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RE: Propellor Guard

I'm sure there are others, but the only twin skeg trawler I can think of right now is the Mirage Great Harbor 37 and 47 N and GH series, but their nearly flat as a river boat at the stern. *It makes for a huge spacious engine room, but it must be hell in a following sea. *Nice live-aboards though.
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Old 11-15-2010, 10:23 PM   #12
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RE: Propellor Guard

Like this
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Old 11-15-2010, 10:42 PM   #13
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RE: Propellor Guard

One thing to consider is how much water turbulence will be created by a cage-type prop shield, and how much this turbulence will reduce the efficiency of the prop.
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Old 11-16-2010, 04:03 AM   #14
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RE: Propellor Guard

"One thing to consider is how much water turbulence will be created by a cage-type prop shield, and how much this turbulence will reduce the efficiency of the prop."


The folks in the NE that use cages are the lobster guys that flood the area , including the channels with lobster pots.

The loss of "efficiency" is minor compared to clearing the prop 40 times a day , or loosing gear from spur cutters.

Most of the smaller boats have 350 Mouse Motors , the larger some truck take out in the 200+ hp range.

Sure the cage costs a bit of fuel, but they still run 15-20K all the time.
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