2 engines or 1

[9D280]

Originally Posted by bobcheer

(Better power-to-weight ratio,

Not Necessarily - See my previous post......

Originally Posted by bobcheer

lower costs

Not Necessarily - See my previous post......

Originally Posted by bobcheer

Subscribe to Seastart,

About as much use as a fart in a spacesuit on the west coast of Scotland, Orkney.....

Originally Posted by bobcheer

make sure your VHF is ok (plus hand-held)

Absolutelty!

Originally Posted by bobcheer

the most likely problem is going to be either hitting an obstacle or fuel issues. This will probably affect both main engines.

Fuel - Separate tanks (and if the engine needs it to stay alive, two batteries) and of course two independant umbillicals taking different routes under the floor if you want to take it to it's logical conclusion.
But you could argue the twin tanks setup for a single - that way if one gets "poisoned" you stand half a chance of flushing through the fuel line & carrying on. Those of us on portable tanks have that setup already!

As for hitting an obstacle, yes, that could disable both, however I'd be interested to see the stats for debris strikes on twins killing both engines. (that's not a sarky comment - it's a genuine Question).
My thought process here is that the chances are that unless you are too busy watching the world go by you'll catch a glimpse of whatever it is, even if it's too late to avert an impact a tight turn / throttle back may limit damage to one side type scenario.

[Channel Ribs]

Originally Posted by 9D280

SeastartAbout as much use as a fart in a spacesuit on the west coast of Scotland, Orkney.....

The OP is talking about passages around and between the Channel Islands, so indeed Seastart are not a realistic option.

[cuttlefish]

what is OP (Old age Pensioner)?

[GordyP]

Hi Rupert,

I run twins on the Arctic for two reasons. Firstly if you have an issue with one of the engines you can still easily get home (demonstrated recently when one of the previous engines ate its piston rings, was able to cruise home at 18 knots on one engine). I also mainly use the boat for diving and can have up to 8 divers with kit on board, the twin props really help to cope with the load.

Even without the load issue if I was doing anything remotely offshore i would personall ygo with a twin set up. Sounds really nice too .

[bobcheer]

Originally Posted by 9D280

Not Necessarily - See my previous post......


Not Necessarily - See my previous post......


About as much use as a fart in a spacesuit on the west coast of Scotland, Orkney.....


Absolutelty!



Fuel - Separate tanks (and if the engine needs it to stay alive, two batteries) and of course two independant umbillicals taking different routes under the floor if you want to take it to it's logical conclusion.
But you could argue the twin tanks setup for a single - that way if one gets "poisoned" you stand half a chance of flushing through the fuel line & carrying on. Those of us on portable tanks have that setup already!

As for hitting an obstacle, yes, that could disable both, however I'd be interested to see the stats for debris strikes on twins killing both engines. (that's not a sarky comment - it's a genuine Question).
My thought process here is that the chances are that unless you are too busy watching the world go by you'll catch a glimpse of whatever it is, even if it's too late to avert an impact a tight turn / throttle back may limit damage to one side type scenario.

Agreed. It obviously depends upon individual intentions and preferences. I'm weighing up the pros and cons between twin 200 Verados vs a single 300. There are tangible power to weight ratio and cost benefits there. And fuel/obstacle/location problem scenarios must have numerous combinations. I suppose it's 'horses for courses' in the end.

[bobcheer]

Originally Posted by codprawn

It is a lithium ion battery - like in a laptop or leccy car - a bit more efficient than a lead acid for the same weight but that price.........

I would say these things are crap for their inteded market but they could be viable for people who already have some batteries on board.

Think I will stick with small petrol engine.

Er - would these be the same li-ion batteries that spontaneously combust in laptops, sports cars and i-Pods? That accounts for the three grand ticket - it includes a subscription to a helo-rescue service!

[9D280]

Originally Posted by bobcheer

Agreed. It obviously depends upon individual intentions and preferences. I'm weighing up the pros and cons between twin 200 Verados vs a single 300. There are tangible power to weight ratio and cost benefits there. And fuel/obstacle/location problem scenarios must have numerous combinations. I suppose it's 'horses for courses' in the end.

Absolutely, and at the top end of the HP sizes, it's more like "one lump is badged as 3 or 4 different downrates, so as you say the power - weight issue becomes more significant at the lower end of the high HP bracket when you are comparing two identical lumps at around 100 Hp difference.

[cuttlefish]

a further thought has occurred to me: is it better to mount an outboard in engine well or on a transom mount?
Pros? Cons? Indifferent? Is there, for example, more chance of fumes being swept in on occasions from a transom mount? Is there more chance of snagging by haivng the engine in an engine well structure? Or are these things my fantasy?

[willk]

Originally Posted by 9D280

Fuel - Separate tanks (and if the engine needs it to stay alive, two batteries) and of course two independant umbillicals taking different routes under the floor if you want to take it to it's logical conclusion.

But you could argue the twin tanks setup for a single - that way if one gets "poisoned" you stand half a chance of flushing through the fuel line & carrying on. Those of us on portable tanks have that setup already!

Much is made of separate tanks. My rib was previously coded for use in Scotland (c'mon the Scots lads, who is she?) and is single tanked. However, she is rigged with two main fuel lines running via twin filters and fuel taps which switch from Main to twin portable tanks.

And this is the interesting (ish) bit. If you fill twin tanks from the same fuel source (and you will, naturally) then you will likely have the same contaminants in both. I'd say that twin tanks really only protect against damage to a fuel line, tank leak etc. And... if you loose an engine and have a long run home at WOT on the other, you have only half your fuel supply and less range due to WOT consumption (I think ? )

Anyway, I try not to fill the portables where/when I fill the main and renew the fuel every couple of months leaving me with a 46 liter reserve of clean (different anyway) fuel that can be used by either or both engines. A handy backup also for the other ribs in the fleet that use the same connectors.

[9D280]

Originally Posted by willk

And this is the interesting (ish) bit. If you fill twin tanks from the same fuel source (and you will, naturally) then you will likely have the same contaminants in both.

Can't fault the logic, but realistically tho' on a rib the contaminant is most likely to be sea water or solids, which a good filter should remove.

At risk of digging up that old dodgy fuel thing of a couple of years ago, realistically how often do you get "engine killing quality" fuel from any normal outlet?

So not only is it horses for courses, it's a risk management game as well!

[codprawn]

There was a big Quinquari Humber use who posted on here - can't remember his name - who had both his engines swamped. There is a possibility an aux with a cover over it could have been used after the swamping.

Not something I had thought of before but a very good point.

Also a heavy impact could take out both props - an aux out of the way would still be usable.

[Bigmuz7]

Originally Posted by rupert

what is OP (Old age Pensioner)?

Original Poster

Originally Posted by willk

Much is made of separate tanks.

Indeed .. due to so many failures at sea being down to fuel problems, I carry a seperate tank for my aux which I refresh every year. I also have a method of extracting fuel from the main tank if I need more, and if I'm satisfied its clean enough,.. which as mentioned also gives me a 20 litre spare for the main, if I ran out on the main ,.. although thats why I keep a consumption log to avoid this.

[willk]

Originally Posted by 9D280

At risk of digging up that old dodgy fuel thing of a couple of years ago, realistically how often do you get "engine killing quality" fuel from any normal outlet?a risk management game as well!

You'd need to ask Mollers that one...

http://rib.net/forum/showthread.php?...highlight=asda