Boat nearly threw us out - why?

[workingonit]

Hi all,

I'm new to owning a boat. Purchased a second hand 6 metre alloy plate, narrowish width, single hull, with 70hp Johnson cable steer. Hope I got the terminology right :)

Situation, moving with outgoing fairly glassy water, at speed, in Elizabeth River Darwin. However, the tide is coming in, so we start to encounter standing waves(?) at 45 degrees to direction of travel coming up river at us. We chop through that quite happily for a bit when suddenly the boat turns violently right, but tilts left, nearly throwing us out.

Anyone can advise what might have caused this? Not aware of hitting any shoals or objects.

As an aside, the bottom of the stern is finished off in some box like shape rather than a 'v'. Any reason for this? Other boating friends don't know.

Cheers.

[Tombie]

Your boat sounds like it tracked the wave which then via inertia threw it out wards...

[shining]

Just a guess but.... A large obstruction on the river bed with incoming tide rushing over it could cause turbulence not necessarily visible on the surface. Once you are slewed across the current by the turbulence the pressure on the side of the hull could pull the boat down. Were you at speed (at least relative to the current flow?). As I said just a guess.... Or a very big saltie? :-)

[workingonit]

I would say we were moving down stream faster than the out flowing water.

My impression of the standing waves, 200mm?, is that they were probably the result on incoming water (tide change) running over the top of outgoing water, and we happened upon the interface of the two forces. The incoming water created the waves at 45 degrees on our right.

I could understand if the 45 degree angle of the wave tilted us left on the long axis, but I would also have expected the boat to turn left as well. Much like a grader blade would both roll and move soil in the same direction. But in this case we were rolled left, but steered hard right. The difference is like water in a bucket. Swirl the bucket around your head and the water stays in. Make a throwing action and the water comes out - that was us. Don't tell me I have the aquatic version of the land rover steering death wobble :)

Crocodile would be a nice answer to the problem.

[shining]

I could understand if the 45 degree angle of the wave tilted us left on the long axis, but I would also have expected the boat to turn left as well. Much like a grader blade would both roll and move soil in the same direction. But in this case we were rolled left, but steered hard right.
.
The river was running out into an incoming tide. Correct?

It sounds almost like what happens when one tries to turn too hard, screw cavitates and the wake catches up and rolls the craft around.

Being pushed from the side often leads to cork-screwing especially in a boat with a shallow draught. There isn't much in the bows for the wave to catch whereas the extra mass (and less freeboard) and motor in the water at the stern give the wave more to push against.

[workingonit]

Correct.

We were travelling in a straight line, cutting the standing waves at an angle rather than straight on.

Using some of your suggestions I wonder if the outflowing water was also being directed left by the incoming tide, catching our tail and turning us right, while the standing wave rolled us left.

Next time I see this I'll just cut my speed :)

[Ean Austral]

The actoin of the boat is similar to say a car with bad suspension, turn the car hard right the body rolls to the left, the boat is the same by turning hard right your force more pressure on the left side and momentum and weight transfer will cause the body roll left.

As for why, I dont understand how you have outgoing water on an incoming tide, unless you have hit a wider section or arm where water hasnt quite turned and you have met the tide that has already turned coming around the point of land.

My guess would be we are on spring tides at the moment and that is the time of greatest water movement, the waves were likely caused by the incoming tide moving over a shallow bank and thus causing the waves, think of surf over a reef, same thing.

Knowing the river you were in its natorious for bad tide eddy's and am guessing you hit one which caused the boat to turn as it did. When we had our hire boat business we had 1 sink in that river because the guy threw the anchor over with all the spare rope just floating on the surface, the current caused the rope to wrap around the leg of the outboard and held them side on in the spring tide eddy and flipped the boat over. That was a 5mtr tinny.

Cheers Ean

[workingonit]

Thanks for dropping in Ean with your local knowledge of the Elizabeth. Can't remember if we were north or south of the Eliz Bridge outside Palmerston, but that general area.

Need to clarify - I'm assuming the tidal eddy is basically a different phenomenon to the wave form over sand bank.

I can understand your description of the boat turning hard right and tilting left. Something turned us right, from our dead ahead course.

From this discussion I certainly have a better understanding.

[Ean Austral]

Thanks for dropping in Ean with your local knowledge of the Elizabeth. Can't remember if we were north or south of the Eliz Bridge outside Palmerston, but that general area.

Need to clarify - I'm assuming the tidal eddy is basically a different phenomenon to the wave form over sand bank.

I can understand your description of the boat turning hard right and tilting left. Something turned us right, from our dead ahead course.

From this discussion I certainly have a better understanding.

Easiest wayto explain the eddy;s im talking about, think whirlpool, but without a big hole in the centre. Usully caused buy the water flowing past say a large rock, it goes around each side and causes the water flow to speed up , if the water can also flow over the top of the rock, then it causes the water to swirl and in some cases churn.

You need to remember that on spring tides we have high tides of 7 mtrs low of 1mtr, its not that much today think its 6.8 to 2.0 so 4.8 mtrs of movement in 6 hrs, first hour after or before the high or low tide is not alot of movement, so really you are looking at 4mtrs of water in 4hrs, thats alot of force. Thats why I couldnt work out outgoing water with incoming tide.

I would doubt you hit something, you would have heard it, and if it was the bottom, you would likely have gone over the bow not the side.

A guess is a tide eddy of sorts, but hard to say.

Anyway, be careful on that part of the harbour, its a very tricky place .

Hope your next trip is less eventful

Cheers Ean

[Bearman]

G'day workingonit. That is a fairly big tinny for a first boat. Most boaties get a bit of experience in smaller dinghys before progressing up to ones that size. As others said there are lots of scenarios that can cause what you have described. It is hard to say what was the cause without being there. Things like tide movement, wave height, angle, speed, trim (bow up/down) wind direction, and boat characteristics all can have an effect on how it handles. Get out there often, take it steady and get the feel of how the boat handles in different situations before giving it too much.
The rear of the hull is probably shaped that way to give stability at rest. Quite a few brands have rear hulls shaped rather square so they ride good at anchor. As Ean said, big tides and lots of water movement up that way so as it's all a learning curve take it carefully until you get the hang of the handling characteristics of your boat. I am sure you are going to have a lot of fun with it. One of my favourite pastimes also:)

[workingonit]

Thanks Bearman. Was out a few times in a friends boat crossing the water to places like Gun Point, the Bottle Washer and a few other areas, fishing and crabbing. We went out on different occasions in two different boats that he owned, a Bar Crusher (?) and a more basic plate boat with welded in floor which seemed more practical for cleaning out. I used to do a small amount of scuba diving years ago so not entirely unfamiliar with boats, but still claim to be novice - having said that I do like to keep my head above water and sometimes wonder if I should have saved a bit more and got a poly boat. Before going to sea with my friend my son and I spent many days trying to fish from the shore, from the few bridges and elswhere but the mangoes midges dominate. So having experienced the freedom of boat fishing I took the plung on a second hand unit on the side of the road. The boat at the time of sale was also tethered to a second hand Disco Tdi300, something I had also been thinking of buying. Got both.

Just this unscheduled right turn at speed, but left tilt, was completely unexpected, novice or not.

By the way, you have a tag 1985 110 V8 County (soon to be Isuzued) - have you done the conversion yet? I've got the engine and matching Isuzu gearbox to put into my 82 RRC and have been watching a couple of threads where some conversion kit options have become available or will soon be available to allow gear changes and mount the transfer case. Might be of interest to you. Cheers.

[Bearman]

Thanks Bearman. Was out a few times in a friends boat crossing the water to places like Gun Point, the Bottle Washer and a few other areas, fishing and crabbing. We went out on different occasions in two different boats that he owned, a Bar Crusher (?) and a more basic plate boat with welded in floor which seemed more practical for cleaning out. I used to do a small amount of scuba diving years ago so not entirely unfamiliar with boats, but still claim to be novice - having said that I do like to keep my head above water and sometimes wonder if I should have saved a bit more and got a poly boat. Before going to sea with my friend my son and I spent many days trying to fish from the shore, from the few bridges and elswhere but the mangoes midges dominate. So having experienced the freedom of boat fishing I took the plung on a second hand unit on the side of the road. The boat at the time of sale was also tethered to a second hand Disco Tdi300, something I had also been thinking of buying. Got both.

Just this unscheduled right turn at speed, but left tilt, was completely unexpected, novice or not.

By the way, you have a tag 1985 110 V8 County (soon to be Isuzued) - have you done the conversion yet? I've got the engine and matching Isuzu gearbox to put into my 82 RRC and have been watching a couple of threads where some conversion kit options have become available or will soon be available to allow gear changes and mount the transfer case. Might be of interest to you. Cheers.

Good one, you got the daily double in one. Can I ask what brand of tinny it is.
With regards to the County, I still haven't done the Isuzu conversion yet, the V8 is still waiting patiently for me to find some time to get around to it. I have all the bits to do it but other projects like a new shed and work, sickness etc have taken precedence as far as time goes. I have done a couple of conversions before so I don't anticipate any snags although I am going the easy way with LT95A gearbox and I have a 110 chassis with the Isuzu mounts as well. So it all just bolts straight up. Most likely will have a perentie 110 project on my hands in the not too distant future as well :)

[workingonit]

The boat has no brand markings as far as I can tell - has what might be some Western Australian rego number? Plate construction. Tinny is pressed?

[Pedro_The_Swift]

surely if the boat was under power there would be no outward lean?
so whatever caused you a problem,, it was not the boat.

[roverrescue]

Ean is onto it, but out of interest does you outboard have a fin of any flavour bolted to the anti-ventilation plate?

You mention cable steering which for all intents and purposes is direct 1:1 attachment to the motor. If you hit a tidal eddy and the load is then amplified by a fin on the leg you will never be able to resist the reefing on the wheel... A fin amplifies any differential load one side of the leg to the other. Hydraulic steering may indeed have helped with the issue at hand combined with more river knowledge.

In my experience what happened to you is not that uncommon in narrow boats (think wahoo/hooker dories) Spend a few years in one and you read the water very differently to something with more beam. BUT narrow beam is why you can get away with minimal horsepower and still have good performance. Everything in boating is a compromise. Which is why you need at least three boats probably more ;)

Steve

[workingonit]

Good guess, yes, has a fin 400 wide at its end just above the prop. Should I surf the Elizabeth without it :)

Beam is 1800mm or 6 foot.

[roverrescue]

It is my opinion and many others that know their shizzle that a properly set up boat has no need for a fin. They are a crutch... Just to keep it landy oriented they are like a "return-to-centre" steering damper. Fix the underlying problem and end up with a better result.

Issues to look at are motor height, prop size, pitch and cupping, and weight distribution.

1800 is the same width as a 'dory' and as I mentioned above you will learn how to surf it with time ;) Nothing more fun than running home with an angry building sea, 25kn from the SE in the 5m waho, 60yam on the tiller... must be the surfer deep within me! Just gotta make sure that if you mis-time and punch through a green one that first your passengers dont panic and grab your arm and also that you keep headway and keep the scuppers working!

Anyways, my guess is that being a territory rig it is a relatively heavy, and you carry pretty good weights (esky, ice, beer, camping gear etc etc) and that the fin was put on to give some lift in the tail. With some planning and experimentation you should be able to lose the fin and end up safer in the current. Or put in some non-feedback steering such as hydraulic. Or upgrade the donk to a 140zuk, that way the only thing in the water will be the prop hitting every thrid pressure wave and you wont have a chance to bog in and get broached.

Steve

[LandyAndy]

Any chance of a pic of the boat???
Andrew

[workingonit]

Steve. The fin came with the boat so don't know if there are any underlying issues that previous owners might have been trying to remedy.

Found a WA rego sticker expiring 2005 on it so may be a WA construction? So its likely to have been in the Territory in various hands for many years.

Andrew. Will try but no promises (it needs a clean)

[dero]

I had exactly this same situation happen to me a few years back .
Coming back into the boat ramp at Exmouth , past the Naval jetty , strong tide running against a strong current , low chop .
Broke a collar bone & the lid of the esky .
5.8 M Westerberg [ well made ] .
I could only put it down to experience .

[workingonit]

Being nearly thrown out illustrates the value of having the ignition attached to your belt to kill the engine - we didn't :(

[ozscott]

What was the trim of the boat like...sounds like classic steering with the forefoot of the hull with too much downward positive trim when hitting a wave the forefoot bit in and steered from the bow? No feedback helms are great. I fitted a Teleflex NFB cable helm to my Vagabond a few years ago and love it.

Cheers

[workingonit]

Earlier on I said the boat had cable steering. My mistake. It is hydraulic.

Without being able to walk on water to make the observation (in which case who needs a boat) :) , I would have said the nose was up and we were planing on the rear. But I could be entirely wrong. Reviewing all comments it does sound like nose digging in and wake pushing the rear. Or as Ean indicated, maybe eddies.

Boat is not going anywhere at the moment as I believe the fuel lift diaphram may have a split. Got a new one on hand.

[NavyDiver]

Any boat or ship can change course or swing significantly off course. Trailing sea makes it really had to stay on course and If you get the right sequence of waves, swell and wind keeping a warship on course is almost impossible. One ship I was on the helm of moved 90 degrees off multiple times. For our smaller boats it doesn't take a lot to get shunted. It happens seldomly for most so most of us never expect it to happen. I dropped my dad out of my boat into the drink while taking a fairly slow turn in inshore waters.

If you sit by a big flat rock in nice flat oceans here every now and again a big one come over, Thats way rock fishing is our most deadly sport:eek:

[workingonit]

Thanks weakestlink. My 'warship' will be in dry dock for some time to come, due to land based activities.

[NavyDiver]

Thanks weakestlink. My 'warship' will be in dry dock for some time to come, due to land based activities.

LOL my Warships are now dive wreaks or museum toys. Funnily enough our little boats last longer.

Dry dock is no place for a fishing boat:)

[Roverlord off road spares]

Do a Google on CHINE WALKING, it might provide some answers

[workingonit]

An interesting read.

I suspect it was not chine walking as we did not experience oscillations before the 'main event'. But then the boat is a narrow 'v' with what appears to be a rise pad, reckoned in the article to be the most prone to chine walking.