Multihull in Fast Flowing Water

[Fanie]

I've never sailed in fast flowing water ie like in a river.

How does a multihull behave in this ?

The motorised boats have a problem going upstream since they have to gun their motors to go upstream.

Logic tells me if there is wind a sail boat is going to have less of a problem, am I right and what can one expect ?

[TeddyDiver]

Of course it depends of the river but they have a turbulent water flow and that tends to turn boats (also mono's) suddenly to unexpected directions. With a cat this affect is more than disturbing..

Originally Posted by TeddyDiver

Of course it depends of the river but they have a turbulent water flow and that tends to turn boats (also mono's) suddenly to unexpected directions. With a cat this affect is more than disturbing..

Just to add to that:
for this reason you do´nt see any cats on the Amazon river for example.
And for a given displacement and hull form there is no difference between motor and sailing vessels, both need the same power to go upstream.
On the other hand we have some sailing cats on the river Elbe in Germany and they do as well or weak if tide and the rivers current add against their heading.


Regards
Richard

[Fanie]

The amazon doesn't have wind if I'm not mistaken. Too many trees and structure ?

I agree the water drag on the hull would increase, but shouldn't a sail have an advantage over a prop in this case ? The sail propultion is out of the water while a prop is greatly affected.

In fast flowing water one should experience the same feeling or effect as when you sail fast, right, so steering may be more sensitive ?

[CatBuilder]

The cat will behave in a nearly identical manner to the mono, except that it will be pushed around slightly less by the eddies owing to the fact that it doesn't have a deep reaching keel.

As to your original question of motor vs sail, they behave identically with respect to the effects the current has on them.

Both cats and monos require a lot of extra power to the prop to overcome the current when motoring.

When sailing, you also require a lot of extra "power" from the sails to overcome the current. One thing that makes it different to sail up a river with a lot of current is that the strong current can change your apparent wind direction, sometimes very abruptly if you turn the boat in the current.

Source: Just spent a season in a river the USA's 2nd strongest navigable current.

[Richard Woods]

When I was last up the Amazon river (I've been longing to say that) it was very windy some days. One thing we didn't expect in the upper Amazon was to be affected by sandstorms, but we were.

We were on a 98ft motor trimaran - so there is a multihull connection.

Tides can run fast anywhere, here in the Pacific NW the strongest tides run at 15 knots, 17 at springs.

A friend with a 20ft monohull was becalmed in the Alderney race (part of the UK's Channel Islands). He anchored. But then, as the tide runs at 8 knots, he had to hand steer until the tide changed.

He said it was the "fastest" his boat had ever gone and at the peak of the tide the boat was out of control and broaching. Not really surprising, few 20ft cruising monohulls can sail steadily at 8 knots.

As others have said, it is the whirlpools that cause problems in strong currents. So multihulls don't fare too well in that respect

Richard Woods of Woods Designs

www.sailingcatamarans.com

[Chris Ostlind]

Originally Posted by apex1

... for this reason you don't see any cats on the Amazon river for example.

Could you explain this a little more?

Thanks

It was all said above, turbulent waters aka whirlpools or neerstrom.
And as I remember we had that discussion already at the "Amazon river loadumup" thread!?

Regards
Richard

[Chris Ostlind]

Originally Posted by apex1

It was all said above, turbulent waters aka whirlpools or neerstrom.

And as I remember we had that discussion already at the "Amazon river loadumup" thread!?

With all due respect, Richard, simply making a statement that says whirlpools, etc...., does not address the issues as they may exist for catamarans as opposed to monohulls in the same waters. For statements such as this, there would be some kind of data, some kind of substantive, provable issues, etc. if the statements have any veracity.

As you remember, the discussion we already had, also did not address any substantive, or quantifiable data. It was more of the floating commentary kind of stuff that didn't really get to any causal realtionship as it may apply to multihulls. As you know, one guy restating that which he has heard over and over does not make for a reliable source.

If you know something that you can put before us, I would love to read it and give you due credit for supplying the data. I'm not looking to bust your head on this, just looking to get to the bottom of why these kinds of statements are made so casually.

Way back when in that other thread, I indicated that if the problem is uniquely about cats in turbulent waters, why then do so many river running cats exist suuccessfully in rivers just as turbulent as the Amazon, if not more so?

These are both human powered, as well as engine powered setups, so the issues can not be neutralized simply due to the power source. Why do so many catamaran ferry boats operate in highly turbulent tidal waters, such as those in and around British Columbia if the type is so fraught with vulnerability issues?

Personally, after running a lot of big water rivers in the Western US, I have seen a remarkable number of cats of all sizes being used on a regular basis. These guys do not just a buy a boat because of fashionista statements. They get them because they work well and make money for the operator. The key word is money for the commercial river guys.

Chris please, before we go into a endless debate just forget about river rafts in this comparison as well as purpose built commercial craft.
We run Catamaran ferries here in Istanbul on the sometimes very violent Bosphorus, with a average current of 4kn and some tricky "corners". But have no significant difficulties compared with the monohull ferries.
Does that mean we can assume the same for recreational craft?
A cat in turbulent water is more difficult to handle than a mono. Et basta
And you know that!

Regards
Richard

[Chris Ostlind]

It doesn't have to be endless.

Just tell us why a cat is more difficult to handle in turbulent waters. (some supporting documentation would also be nice, if it's handy)

And since you agreed that cats are being used successfully in very turbulent and commerically busy waterways, perhaps a note, as to what may have driven the owners decision making when they, too, should be aware of the poor handling issues.

Where does the insurance business step in and tell them loudly... "cats suck in turbulent waters. There's no way I will write any paper on your enterprise."

[Richard Woods]

There are too many Richard's here!! And sorry, I only speak English, so don't know what "Et basta" means

Last time I white water rafted I used both a conventional raft and a catamaran raft. The catamaran was easier to manouver.

Having said that, in my experience, the two catamaran hulls can be caught in two whirlpools (one per hull) rotating in opposite directions. Which is why I said monohulls have it easier. Of course monohulls have other problems, but then no small boat is really ideal for use in strong currents (meaning over 10 knots)

Richard Woods of Woods Designs

www.sailingcatamarans.com

[TeddyDiver]

Originally Posted by Chris Ostlind

Just tell us why a cat is more difficult to handle in turbulent waters.

Once more.. Two hulls both having different and differing water flow means you need constantionous steering/propulsion adjustment to do. Doable but considering the fact that on rivers you don't need a cat due stability issues so you insted take only one canoe hull, maybe somewhat bigger, and have the benefit of reduced drag and mono-ease-of-steering thou it's a bit tricky still sometimes.
Data? It's obvious to anyone done some river boating.. so we don't need the data..
Rivers big enough to ships to navigate are a different thing. Deeper water reduces eddies, or they stay deeper, closer to surface causing them (the bottom)
Drafting and raft's have nothing to do in this issue..

[TeddyDiver]

Just one more thing to consider.. How you going to land on a bank when other hull stops on to shore and other one is having heavy drag in the deeper water.. cant' stop the propulsion before the boat is secured.. Sailing is not an option and propellers get damaged.. Ultimately you end up rolling along the shoreline every hull tip bounching against the rocks in their turn..

[Chris Ostlind]

Originally Posted by TeddyDiver

Once more.. Two hulls both having different and differing water flow means you need constantionous steering/propulsion adjustment to do. Doable but considering the fact that on rivers you don't need a cat due stability issues so you insted take only one canoe hull, maybe somewhat bigger, and have the benefit of reduced drag and mono-ease-of-steering thou it's a bit tricky still sometimes.

So, where's the argument for fuel efficiency, Teddy? All that boat traffic that gets to go down river, has to go back up if they expect to do more work on said waters. Up river means propulsion requirements. Tell me about the relative cost per mile traveled upriver with a monohull and a catamaran?

As for steering ease, I see cats as having splendid potential for precise steering with twin engines. Can a monohull turn around in a very tight circle? When a cat applies power forward to one engine and reverse power to the other... guess what happens? Can a mono perform such a feat in close quarters without a huge array of independently rotating engine pods and very potent bow thrusters?

Originally Posted by TeddyDiver

Data? It's obvious to anyone done some river boating.. so we don't need the data..

So, what does a person do who has never done some river boating? How do they make a proper decision as to type and potential without some kind of properly derived data? Word of mouth data is but one kind and remarkably susceptible to all the various foibles that can be sprung by the human mind.

Originally Posted by TeddyDiver

Drafting and raft's have nothing to do in this issue..

If raft's have nothing to do with this issue, Teddy, then I guess we need to describe them differently than we do "boats". Is that your position... that rafts are not boats, as well? That they do not behave with the same constraints and design requirements that we place upon "boats"?

You're going to experience some very tough sledding, there, Teddy, if you want to put that argument before a body of naval architects.

Originally Posted by TeddyDiver

Just one more thing to consider.. How you going to land on a bank when other hull stops on to shore and other one is having heavy drag in the deeper water.. cant' stop the propulsion before the boat is secured.. Sailing is not an option and propellers get damaged.. Ultimately you end up rolling along the shoreline every hull tip bouncing against the rocks in their turn..

Teddy, you suggest that you have river boating experience in your commentary. I'm quite sure, then, that you have knowledge of the interesting phenomenon in which a counter current develops along the shore of fast moving body of water? How about the inner shore of a turn in the river? Is the current as strong over on that side? How about the relative speed of water in the carved channel of the main flow as opposed to the speed of the water at the areas that are not main channel environments? Still the same speed of flow?

What makes you think that a cat can not simply park side-to the dock and/or shore just as a monohull does? What makes you think that the only method for doing so is to take it bow-on? In the situations when bow landings are preferred, what makes you think that the cat's hull side exposure is any greater than is a comparable monohull?

All this stuff you guys are putting out here is convenient and it looks very much like there are no proofs at all save for something less than a rigorous testing process.

Apex Richard suggested that I know this stuff already. He's correct in that I have a great deal more background on the topic than the typical guy with a passing interest in boating. I get that Apex Richard would like me to stop stirring the coals in this cozy campfire topic. Unfortunately, there are way more interested readers here than guys who "supposedly know" why catamarans will not work on a river. There's a whole huge body of readers who never post and they come here to learn about boats. Some are experienced, some complete novices.

From my perspective and experience, I can't see a single substantive reason that a catamaran could make for a truly fine river craft. The fact that nobody has been able to produce anything more than shop talk against cats, further illustrates the problem.

How about we take the time to expand our thinking, rather than confine it?