Proper Prop

Inquiry****** Have you ever had your prop*damaged while under way?**
********************
******************How did you deal with it?***************** KJ

Much to my relief, it doesen't*seem like that's a problem to be concerned about.
I guess most are protected.******** KJ

How did it get damaged?

KJ wrote:

Much to my relief, it doesen't*seem like that's a problem to be concerned about.
I guess most are protected.******** KJ

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Depends on where you boat.* Up here (PNW) the water is full of prop and running gear damaging debris. Logs, deadheads, old pallets, kelp and eelgrass mats, errant crab pot buoys and their trailing lines, and so*on.* The owners of twin engine boats have to be particularly vigilant as the struts, shafts, props, and rudders are completely exposed to this stuff if you run over it.

Single engine boats at least*have the benefit of the keel in front of their prop and rudder although from the tales I hear in our marina, single engine boats (including sailboats) have as many encounters with prop fouling or prop damage than the twins.

We took the autopilot out of our boat for another reason but had we retained it we wouldn't have had much chance to use it as we are almost*constantly making small*heading changes during a run to avoid a drifting log*or piece of lumber or an eelgrass mat or crab pot buoys.* Deadheads are not as common in our area as they used to be but as you go north into BC they are much more evident judging from our experience the last three summers on cruises to Desolation Sound and the Gulf Islands.* And a deadhead can be a boat-sinker.

And I've perfected the execution of the "Titanic maneuver" which has moved our props and rudders out of harms way on many occasions, particulary in rough water when you can't see the stuff until you are virtually on top of it.

So, no, it is very definitely a problem you have to be concerned about up here.

*

So if one of your props got badly damaged you would shut that engine down and make into port with the one good engine/prop?

Yes. In our boat we'd have to tie off the shaft with the damaged prop, strut (or damaged shaft itself) because we can't let a shaft freewheel with its associated engine not running.

We've had to finish a run on one engine four times since buying the boat in 1998. None of them were as the result of external damage, however. Three times were due to cooling problems external to the engine, and the fourth time was my fault for letting an engine get a*slug of air during a fuel transfer. In all cases we tied off the shaft of the shut-down engine and finished the trip on the other engine.

Since you seem interested, as an illustration of what can happen up here, friends had their twin-engine, 40-something foot, steel hull-wood topsides*deFever named Sea Beaver up in Big Bay in the late 90s. Big Bay is a (now) former resort on an island about 230 miles north of Seattle. This area with its hundreds of islands, narrow channels, and large tidal ranges (12-17 feet or more) is notorious for its swirling currents, upwellings, and rapids.

As they were leaving Big Bay and negotiating a nearby rapids at the end of slack water, an upwelling barfed up a huge saw log and jammed it between one of the prop shafts and the hull in such a way that it also jammed the rudders. So Bob not only lost thrust on one side of the boat, he couldn't steer. The current was moving the Sea Beaver slowly toward the rocky shoreline on one side of the fairly narrow passage.** Bob, a very experienced boater and pilot who was the picture of calm in a crisis tried to free the log with*the*pike pole they carried on board but it was too wedged in. He and his wife then lowered their dinghy, a Boston Whaler suspended in davits off the transom (a good illustration of why keeping a dinghy stowed on a cabin top or boat deck is, in my opinion, a very*Bad Idea).

So they had the Whaler in the water in moments and got a line to it and Bob tried to pull the*Sea Beaver*out of danger. Even though the Whaler had a decent size motor on it all he could do was hold the*Sea Beaver*stationary--- he couldn't make any progress away from the shoreline. And the current was building. When it became apparent that the boat was going to go into the rocks no matter what, he told his wife to prepare to abandon the boat. As she was preparing to do so and as the Sea Beaver was carried slowly closer to the rocks, the log suddenly popped free on its own.

Bob quickly returned to the boat, found the rudders were free, and with the remaining engine powered the Sea Beaver into open water. It took only moments to determine that the running gear on the one side had been damaged enough to preclude using it. So they completed the run back to Seattle and Lake Washington on the other engine.* I don't remember how long it took them-- three or four days I think.

And that boys and*girls,*is boating in the Pacific Northwest.*

It's also one of the*reasons my wife and I prefer a twin engine boat over a single.* While one can speculate forever, the saw log came up into the Sea Beaver'srunning gear from below.* Had the boat been single engine, there is no guarantee that the log could not have launched up into the prop and rudder and taken them out of commission on the way by.

When it comes to stuff in the water, it's a crap shoot.* The only defense you have is a really good pair of eyes and the ability to keep your attention on the water in front of you.** And for deadheads and incidents like what happened to Bob, even that can be not enough.



-- Edited by Marin on Saturday 12th of February 2011 12:10:21 AM

Marin wrote:

Yes. In our boat we'd have to tie off the shaft with the damaged prop, strut (or damaged shaft itself) because we can't let a shaft freewheel with its associated engine not running.

***

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How do you tie off the shaft?

*

On the underside of the heavy main cabin floor beam above each engine there is short, heavy, aluminum angle extrusion screwed and 5200-ed to the beam directly over the shaft coupler. A shackle is fastened to this bracket.

If we have to tie off a shaft we have a line cut for this purpose that we tie around the shaft coupler and then wind it a bunch of times around the coupler in the opposite direction that the shaft will freewheel. Once this line is wound tight around the coupler a bunch of times I then run it up and tie it to the shackle. The line prevents the shaft from turning. We had the original set-screw couplers on our boat replaced with much larger split couplers, so there are bolts and other stuff on the couplers for the line to grip.

Marin wrote:

On the underside of the heavy main cabin floor beam above each engine there is short, heavy, aluminum angle extrusion screwed and 5200-ed to the beam directly over the shaft coupler. A shackle is fastened to this bracket.

*

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Did you install this set-up yourself, or was it already in place when you bought your boat?* *

*

We put it in ourselves. On the first couple of occasions we had to shut down an engine I tied off the shaft to a purpose-drilled hole in a heavy extrusion bolted to the top of the inboard engine stringer next to the transmission. The extrusion (one on each side) holds the primary fuel filters and gravity*fuel distribution plumbing from the saddle tanks. But when we had the boat's original double-Fram cartridge setup on each side changed to a Racor 500 on each side, the Racors sit higher and obstruct the tie-off holes. So that's when I fabricated and installed the overhead brackets.

It would be really nice to see a photo of your current set-up.
Maybe someday when you're down at your boat you could snap a quick pic.**** KJ

-- Edited by KJ on Saturday 12th of February 2011 02:14:36 AM

Our Christmas vacation, 1997, was 10 days in the gulf islands. on day 3, going south in Northumberland channel, just north of Dodd narrows, we hit a log, and damaged the port prop enough to preclude running it for the rest of the trip. Once we determined that was all that was damaged, we carried on and had a great trip at just under 7 knots on one engine. My hour meter was 25 hours behind on port for the rest of that meter's life. Once back home, the props both went in for service, and the spares went on. No serious damage, in fact the starboard prop needed minor tweaking and cost almost as much to repair as the port. I put a dial micrometer on the shaft to be sure there was no shaft damage, and all was well.
At that point in my experience I never gave a thought to immobilizing the port shaft, and the Velvet drive tranny didn't seem to mind. I think those trannys have 6000 hours on them so far and are showing no signs of wear.

koliver wrote:At that point in my experience I never gave a thought to immobilizing the port shaft, and the Velvet drive tranny didn't seem to mind.

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The issue isn't the Velvet Drives.* The Velvet Drive manual states that the transmission can be freewheeled at slow boat speeds, which they define as "sailing or trolling."

On our boat the issue is the packing gland and the cutless bearings in the shaft log.* These components are cooled and lubed by a water feed from its associated engine.* If this feed is cut off-- and shutting down the engine is an effective way of doing that--- the bearing, log, shaft, and packing gland get extremely hot extremely fast if the shaft is allowed to freewheel.

The first time we had to shut an engine down was on our delivery cruise from Tacoma to Bellingham.* The port engine temp started to climb very slowly and by the the time we reached the entrance to Bellingham Bay we decided to shut the engine down.* The broker who'd found us the boat was helping me run it north and he called the local diesel shop in Bellingham to ask if they thought we should tie off the shaft for the last few miles of the run.* They said no, but take it easy on speed to keep the bearing temperature down.* We did, but within that few miles the packing gland, the shaft emerging from it, and the exposed part of the shaft log were too hot to keep your hand on.* At a normal cruise speed for even a few minutes enough heat can build up to damage the shaft, the bearing, the packing gland, and possibly even the log.* This is why we tie off the shaft.

A lot of boats don't need "water injection" to cool and lube the cutless bearing(s) in the log--- some boats have one bearing in there, and some, like a lot of GBs, have two--- so there should be no need to tie off the shaft to protect them.* You still have to account for the transmission, however.* Some can be freewheeled with no limitations, some can't be freewheeled at all, and some--- like the Velvet Drive--- can be freewheeled at slow speeds.

*


-- Edited by Marin on Saturday 12th of February 2011 04:47:30 PM

Marin wrote:Depends on where you boat.* Up here (PNW) the water is full of prop and running gear damaging debris. Logs, deadheads, old pallets, kelp and eelgrass mats, errant crab pot buoys and their trailing lines, and so*on.* The owners of twin engine boats have to be particularly vigilant as the struts, shafts, props, and rudders are completely exposed to this stuff if you run over it.

Single engine boats at least*have the benefit of the keel in front of their prop and rudder although from the tales I hear in our marina, single engine boats (including sailboats) have as many encounters with prop fouling or prop damage than the twins.

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I hesitated for some time before deciding to respond to this thread.* First, let me find some wood.* OK

In my 37 years of owning/operating 37-40' single screw 7.5 knot boats, and an earlier 15 years growing up/operating my*parent's 46' single screw boat,*we have never dinged a prop, or wrapped a line around the wheel.* KNOCK-KNOCK.

And this for thousands of miles in Puget Sound/B.C./SE Alaska waters.* We also tend to travel close to the beach and occasionally at night.

As Marin indicates, there can be significant hazards in these waters, but I would disagree with his statement about single screw vessels having "as many encounters with prop fouling/prop damage as twins".*

At my marina,*at any time during the summer, there*will be boats in the work yard having propeller/shaft work done.* And every one of them is a twin.* Probably only boat insurers might know for sure the actual ratio between single/twins.

The other thing mentioned elsewhere, and which I have also observed, is that there is less heavy debris such as deadheads and logs than a few years ago.

*

Jay N wrote:

At my marina,*at any time during the summer, there*will be boats in the work yard having propeller/shaft work done.* And every one of them is a twin.

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Again, depends on the area and, obviously, the boater.* There is a big yard in our marina and we see what's in it and what's going on every time we go to the boat, which is just about every weekend year round.* I've never counted, but we've seen a number of single engine boats (power and sail) having prop damage work done on them and a number of twin engine boats having prop or shaft damage work done on them.* And while I don't know that many boaters in the overall scheme of things, I actually know more boaters with single engine boats (power and sail) who have told me over the years about prop strike damage than I do owners of twin engine boats who've told me the same thing.

Not arguing your experience at all, just saying that in ours, it seems to be six of one, half dozen of the other with regard to people who have actually experienced a prop strike severe enough to damage something.* Maybe there are more inattentive boaters in Bellingham than there are in Edmonds

As you say, the insurance adjusters are probably the only ones with data to prove anything one way or the other.

*


-- Edited by Marin on Saturday 12th of February 2011 05:39:16 PM

Marin,

It may be something as simple as considering that more singles drydock in Bellingham, and only twins drydock in Edmonds.

Cheers.

Jay N wrote:

Marin,

It may be something as simple as considering that more singles drydock in Bellingham, and only twins drydock in Edmonds.

Cheers.

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Just curious--- why would that be?* We do get a lot of commercial seiners in Seaview North and they are all single engine boats.* On the other hand Seaview has a 150 ton Travelift as well as their smaller one, so they get a lot of big yachts in addition to the seiners, and the yachts are almost always twins.

But down in the blue-collar world of recreational boats like ours the number of singles and twins (if you include sailboats) seems pretty even.* Are there not many single engine boats in Edmonds?

*

Marin wrote:


Jay N wrote:

Marin,

It may be something as simple as considering that more singles drydock in Bellingham, and only twins drydock in Edmonds.

Cheers.

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Just curious--- why would that be?* We do get a lot of commercial seiners in Seaview North and they are all single engine boats.* On the other hand Seaview has a 150 ton Travelift as well as their smaller one, so they get a lot of big yachts in addition to the seiners, and the yachts are almost always twins.

But down in the blue-collar world of recreational boats like ours the number of singles and twins (if you include sailboats) seems pretty even.* Are there not many single engine boats in Edmonds?

*
I was thinking of the commercial fishing fleet in Bellingham being the source of a lot of single screw boats, something that Edmonds (and many other marina boatyards) simply don't have.

There are probably around 350 boats larger than 34' in Edmonds, I don't think there are*more than 20-30 that are singles, under 35 (10%) anyway.

*

I did have this little incident three boats ago. It looks like a modern artist sculpted the crab pot around my wheel.

Daddyo wrote:

I did have this little incident three boats ago. It looks like a modern artist sculpted the crab pot around my wheel.

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Nice pic!* Did you have a shaft cutter at the time?

When we purchased our present boat, it had a Spur's shaft cutter system, but I had to remove it due to significant corrosion.* Couldn't rationalize the money to replace it, although I continue to think about it from time-to-time.

*

someone mention kelp can damage props, please elaborate?
we have large surface kelp areas in so callifornia, whilst we do not navigate through this habitat purposely sometimes you just find yourself in the middle of one.. i usually exit at a very low speed.

Kelp is very tough stuff. It can get wound up on a shaft, create an out-of-balance condition, and the vibration could conceivably knock things out of alignment. I would be surprised if kelp would physically damage a prop, however. But we avoid the kelp mats because of the potential they have to foul a shaft or rudder. We've gotten a wad of kelp hung up on one of our rudders and it shakes the hell out of the rudder, rudder bars, etc. This sort of thing doesn't do the rudder bearings any good.

We also get large eel-grass mats up here. They can just about stop an outboard motor--- we've had this happen a few times--- because the long grass blades wind up tight around the prop shaft in the gap between the prop and the lower unit. The only danger it poses to boats like our GB is that the long, slender, and tough blades can thread themselves up through the holes on the external strainers over the raw water through hulls for the engines. They can then tangle up and clog the raw water intake hoses. While rare, our diesel shop tells us that the blades can even snake themselves though a sea strainer and end up in the raw water pump. So we drive around the eel-grass mats, too.

I hit something under water once several years ago.

Going along nice an calm then, Bang.**Never knew what it was but it sure did nick up the prop.

Had to hire a diver to remove the prop and have it repaired.

*Single engine. All*I could was drive the boat home.

*Quite a vibration for 20 or so miles.

Yet when I think about it doesn't take much of a ding to cause a lot of vibration.

Because it wasn't really that bad a ding. In my opinion.

SD

This happened to a friend of mine (Cliff) several years ago.
He was returning to home port. Mystic, Ct from a 2 week trip to Maine in his single screw 35 Duffy.
Just off of Block I he saw nasty weather ahead and decided to pull into Block I to anchor till the tx storm passed. On his way toward the harbor he suddenly felt a bad vibration. His son dove and discovered a blade missing from his 4 blade prop.
He limped into the harbor (3 or 4 miles), found us and we (my buddy and I) rafted him. Lucky for him, my buddy had a prop that was close to his, and I had a prop puller. We both had dive gear.
His prop had simply fatigued and a blade broke off. 3 other blades had cracks near the hub.

Bertrams used to be famous for losing propeller blades. More than one would end up sticking in the bottom of the hull.

jleonard wrote:

Lucky for him, my buddy had a prop that was close to his, and I had a prop puller. We both had dive gear.
*

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It sounds like (for obvious reasons) that folks with twin screws can get their boats into port with one damaged prop.*For those with single engines, do you normally carry a spare prop and gear and could you change a badly damaged prop while*underway? If you were*in a remote area or quite a distance from a tow or in danger of a lee shore and*your prop was useless, what would be your plan of action?**** KJ*

ps* this is in way meant to reignite the eternal "single vs. twins" debate.*

*


-- Edited by KJ on Tuesday 15th of February 2011 06:01:13 PM

KJ wrote:

what would be your plan of action?

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Around here where being blown or carried ashore generally means going onto the rocks as opposed to onto a mud or sand bottom, the often-recommended practice if your boat loses power where you are in danger of being*pushed into the shoreline*is to first let your anchor all the way out to the end of its rode and secure the rode.* The water is often very deep almost up to the shoreline around here, so letting your anchor all the way out increases the chances of it catching on something and holding before you end up against the shoreline.

Marin wrote:


KJ wrote:

what would be your plan of action?

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Around here where being blown or carried ashore generally means going onto the rocks as opposed to onto a mud or sand bottom, the often-recommended practice if your boat loses power where you are in danger of being*pushed into the shoreline*is to first let your anchor all the way out to the end of its rode and secure the rode.* The water is often very deep almost up to the shoreline around here, so letting your anchor all the way out increases the chances of it catching on something and holding before you end up against the shoreline.
Yes, I am aware of the recommendation to let the anchor out and hoping it catches before landfall.* In fact*I had to do just that*when the engine in my sailboat crapped out on the lee side of Angel Island.* No wind, late in the evening, radio not working, current setting me to shore.* Fortunately,*my anchor grabbed not too far from shore (just happened to be a designated anchorage), and*I spent*a* pleasant night on the hook.* In the morning I was able to get the engine going (replaced the stupid water impeller) and had a nice cruise back to port.
Anyway, part*of my original inquiry was kind of like if a singe engine boat suffered severe damage to the prop (and dropping anchor was not an option, say like crossing the Gulf Stream),*would*the operator (skipper)*be capable of changing the prop themselves.***KJ

*

KJ wrote:

if a singe engine boat suffered severe damage to the prop (and dropping anchor was not an option, say like crossing the Gulf Stream),*would*the operator (skipper)*be capable of changing the prop themselves.***KJ

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If the boat was set up for it, sure, assuming someone on the boat was an experienced diver.* Famous (and true) story about a GB42 owner who wanted to move his boat from Hawaii to the mainland under its own power.* He removed the prop from one shaft and went half the distance to the mainland on the other engine and prop.* At the halfway point he dove on the boat, removed the prop he'd been running on, installed the other prop on the other shaft, and ran the second half of the trip on the other engine and prop.

I believe Carey of this forum had a prop replaced underwater by a diver in Nanaimo or some such place up north.

From what I have observed in the boatyard in our marina, the trick is going to be getting the prop off because they can jam themselves on pretty tightly.

*

A properly designed, single-engined trawler should have a full keep to protect shaft, propeller, and rudder.* What proportion of twin-engined boats are similarly protected?