2 engines or 1 - Page 5

jwalker · 17 August 2009, 15:50

Rupert, I do my own servicing and it costs little and is simple to do, so any servicing cost you figure into your buying choice will depend on the level of ripoff factor your marine engineer is used to applying. Presuming, of course, you aren't diy-ing it.

Your choice of power, diesel/outboards, should mainly be based on what you expect from your boating. These engine types produce a very different driving experience. You need to have good, lengthy test runs in both types, go home and swither about it then possibly do it again before laying out your cash.
Availability of fuel would be my high priority, as Polwart mentioned. If you fall in love with your boat, you may find yourself going places you didn't initially consider.

cuttlefish · 17 August 2009, 15:53

Some good point to ponder on. Thanks.

r mcdonald · 18 August 2009, 11:49

A twin engine rib with an inoperative engine, will have a better chance of maintaining hull speed,than using an aux. Mainly due to the fact that the larger twin engine will have a larger prop turning slower, creating more thrust than a small aux with a smaller diameter prop turning faster creating less thrust. For displacement speeds, a large prop turning slower is more efficent and creates more thrust.
If you can get he rib on the plane with one inoperative engine what a bonus. If not at least you will have a better chance of making headway.
One thought, If you were flying over a mountainous area in a light aircraft and the engine failed would you rather another engine on the other wing be the same size or a little aux instead.
regards
rpm

cuttlefish · 18 August 2009, 12:04

If you were flying over a mountainous area in a light aircraft and the engine failed would you rather another engine on the other wing be the same size or a little aux instead.

A little aux is quite sufficient so long as it is geared to fly the craft adequately, even in adverse conditions. I live in a mountainous area some part of the year, and a large part of accidents are caused by visibility problems, so essential is also radar, etc. as Malthouse pointed out in a previous post.

Jono · 18 August 2009, 12:08

Quote:

Originally Posted by r mcdonald

....One thought, If you were flying over a mountainous area in a light aircraft and the engine failed would you rather another engine on the other wing be the same size or a little aux instead.
regards
rpm

Neither... I'd rather have a parachute....

You're analogy is somewhat flawed... never seen a plane able to "heave-to" or drop anchor.....

cuttlefish · 18 August 2009, 12:15

parachute not a great idea. Too many wind currents. A gut died last week. Delta plane got blown into electric cables.

When the the helicopter tried to save him (mountaineous area so no other way), the vortex sucked him up and he fell with the chute wrapped around him.

r mcdonald · 18 August 2009, 12:17

Quote:

Originally Posted by rupert

If you were flying over a mountainous area in a light aircraft and the engine failed would you rather another engine on the other wing be the same size or a little aux instead.

A little aux is quite sufficient so long as it is geared to fly the craft adequately, even in adverse conditions. I live in a mountainous area some part of the year, and a large part of accidents are caused by visibility problems, so essential is also radar, etc. as Malthouse pointed out in a previous post.

.

You would most probably find the little(hp) aux would have to have a very high rpm (work harder)to create enough torque at the slower prop speed for the same thrust.
As for the people crashing planes in poor visibilty, If they are meant to be flying visually
they should not be flying in those condition, or they should have an instrument rating and a suitably equiped plane.
regards
rpm

cuttlefish · 18 August 2009, 12:20

Nice quite that simple.

Channel Ribs · 18 August 2009, 12:48

Quote:

Originally Posted by r mcdonald

One thought, If you were flying over a mountainous area in a light aircraft and the engine failed would you rather another engine on the other wing be the same size or a little aux instead.

I think your argument counts in favour of single engine vehicles...

There are many single engine planes around and they rely on their engine not only for thrust but also to stay up, if your RIB's engine also kept you afloat would you need two?

Planes with one engine are maintained like their pilot's life depends on it, why not apply that thoroughness to a boat?

If a twin engine plane suffers unrecoverable engine failure it becomes an emergency, this is not always the case with boats but I think it mostly should be (see my previous post on this topic).

All of that said there is a local twin outboard boat that can quite happily get around on one, so much so I have suggested to the owner that he gets rid of the redundant one!

He will go about as fast as he currently cruises and half his running costs. The boat used to go out in all weathers and work close in to rocks with 6 knot tides running, so the twin installation was a good idea.

codprawn · 18 August 2009, 14:42

Plenty of single engines helicopters as well - including the most common of all - the Jetranger and my favourite - the Hughes/MD Defender as from Magnum.

The smallest twin engined helicopter is the MBB105 which suffers a bit from the extra weight.

Channel Ribs · 18 August 2009, 15:26

Quote:

Originally Posted by codprawn

Plenty of single engines helicopters as well - including the most common of all - the Jetranger and my favourite - the Hughes/MD Defender as from Magnum.

The smallest twin engined helicopter is the MBB105 which suffers a bit from the extra weight.

I think this deserves a link to pPRuNe

bobcheer · 18 August 2009, 21:57

My two penny-worth for a leisure rib (you're not likely to go too far offshore) is to have one main engine plus aux. (Better power-to-weight ratio, lower costs etc.) I've had two hard boats: Sea Ray 215 and Trophy 2052 and now intend to switch to ribbing (xs 750). In the Navy I thought they were just work boats but now realise they're great leisure boats too, if you only do day-running. Considering the reliability of modern engines the most likely problem is going to be either hitting an obstacle or fuel issues. This will probably affect both main engines. Therefore a totally separate auxilliary method of propulsion makes sense. A nine hp outboard (for up to 7 or 8m) with its own fuel supply would get you home, or if you have money to burn the electric wizard from Torqeedo looks good. I saw a demo at Seawork and was impressed. The battery alone was £3K so it must be good, I suppose, although it's a want-have rather than a must-have. Whatever you get stow it down aft and make sure you can fit it when you need to. Subscribe to Seastart, make sure your VHF is ok (plus hand-held) and happy days. If there's a flaw in my thinking please advise.

cuttlefish · 18 August 2009, 22:40

Sounds pretty good sense to me, although I am sure others will also chime in with your thoughts. I suppose the most obvious question is why 750 XS? I am looking for a cabin, so Redbay and such like are obvious choices for me, but I shuld be interested to hear your reasoning, especially as you are coming from two hard boats.

Thanks,
rupert

willk · 18 August 2009, 22:56

Quote:

Originally Posted by bobcheer

or if you have money to burn the electric wizard from Torqeedo looks good. I saw a demo at Seawork and was impressed. The battery alone was £3K so it must be good, I suppose, although it's a want-have rather than a must-have. Whatever you get stow it down aft and make sure you can fit it when you need to.

This is a new one for me, do you have any contact details for them or other info?

codprawn · 18 August 2009, 23:00

You can also use a normal old lead acid. Some of the models are 24v.

http://www.youtube.com/watch?v=FnAEUFBsx34

http://www.youtube.com/watch?v=FdxrJ...eature=channel

Could possibly make sense on a RIB if you have twin batteries.

I reckon they are better suited to James Bond as they pack up into a rucksack!!!

http://www.torqeedo.com/en/hn/home.html

bobcheer · 18 August 2009, 23:09

Simple really, after looking at all the current ribs, just decided that XS ticks all the boxes for me; they're basically the same as the old Tornado, which is a proven hull. And they can fit a console with a Jabsco inside. This is important if you take children, women etc. out for the day.

bobcheer · 18 August 2009, 23:20

Don't know anything else about them. They're German and very expensive. The guy at Seawork said there are two types. The bigger ones with two batteries are not necessary for ribs. In fact their demo boat had batteries under the deck, in series or parallel, not sure. I think it was used on the Norfolk Broads for tourist trips. They're probably too expensive for most rib users but they look good. Even got some sort of GPS thingy that shows speed and endurance.

bobcheer · 18 August 2009, 23:33

Followed the 2 links in Codprawn's reply but the one I saw was orange and a bit bigger, although much smaller than a normal aux outboard. You could certainly handle it much easier; if the batteries were lashed down somewhere close to the transom.

bobcheer · 18 August 2009, 23:35

Finally, no idea why the battery is three grand. He didn't tell me the price at the time but emailed me later. I wonder why.....

codprawn · 19 August 2009, 02:37

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.