Twins Or Single

mikesyam · 07 May 2009, 07:24

Hi
Good chance of going up to a 8.5m rib in a couple of months and fancy a couple of 175 Suzukis on the back, opinions please on whether they would give the same performance as say a single 250 or a 300 and % wise how much extra fuel would they use over the single,
Thanks Mike

Chris · 07 May 2009, 07:31

Fuel use, I think the suzukis are generally pretty frugal however I would imagine you would be looking at around 50 to 65% increase in fuel consumption by running twins.

Andy Moore · 07 May 2009, 11:40

Go for a single. Twins are too much weight, IMO.

Andy

willk · 07 May 2009, 11:50

I use a pair of 90s. I'd agree with suggestions on here that this setup "looses" about 25-30% overall power compared to a 180. It feels like about 130hp. Running at 3000 rpm they burn a little under 1.4l/Nm combined.

Chris's figures would suggest (if I'm using 55% more gas) that a 135Hp Etec would burn 0.9L/Nm at 3000 rpm. Someone else on here may be able to verify this?

Anyway, your 2x175hp rig should feel like 250-275hp max.

Chris · 07 May 2009, 11:52

Quote:

Originally Posted by willk

Chris's figures would suggest (if I'm using 55% more gas) that a 135Hp Etec would burn 0.9L/Nm at 3000 rpm. Someone else on here may be able to verify this?

I would say you are spot on there my old 115 etec used to run at about .9 l/nm at around 3-4000rpm.

JSP · 07 May 2009, 12:03

All the above can comment much better than me regarding fuel use etc but I'd be in favour of twins as the manoeuvrability is 10 times better. My idle RIB would have twins on.

codprawn · 07 May 2009, 12:50

A single suzuki 300 only weighs 50kgs more. Singles are much better on fuel. Also twin engine RIBs are pretty stern heavy.

You will prob get about the same performance with 2x 175 as a single 300. Obviously safety is also a concern but you could carry a smaller aux outboard to get you home.

For the same money as the twins you could get a single Verado 350hp - that would be my choice!!!

jyasaki · 07 May 2009, 15:41

Quote:

2 strokes are my favourite.

Quote:

Originally Posted by codprawn

For the same money as the twins you could get a single Verado 350hp - that would be my choice!!!

Hmmm....

jky

mcolston · 07 May 2009, 16:05

Twins will always use more fuel, increase servicing etc.

What twins offer you though is a sense of safety as you have two engines and as above a twin engine boat is far more manoeuvrable than a single. Twins will also give you more torque.

It depends what you want to use the boat for.

If you are in a busy area, with help nearby and in a leisure environment then a single is the way forward.

codprawn · 07 May 2009, 16:13

Quote:

Originally Posted by jyasaki

Hmmm....

jky

IF someone made a 350hp 2 stroke it would be different.

A modern version of the Evinrude V8 400hp 2 stroke would be ideal - they did one in the 1980s!!!

Downhilldai · 08 May 2009, 00:16

Quote:

Originally Posted by codprawn

A modern version of the Evinrude V8 400hp 2 stroke would be ideal - they did one in the 1980s!!!

Fuel tank not included.

John Kennett · 08 May 2009, 08:46

Quote:

Originally Posted by JSP

All the above can comment much better than me regarding fuel use etc but I'd be in favour of twins as the manoeuvrability is 10 times better.

Maybe a boat-handling course would be more cost effective?

Seriously though, on most twin-outboard RIBs the motors are too close together to be much use for manoeuvring anyway.

willk · 08 May 2009, 10:24

Quote:

Originally Posted by John Kennett

Maybe a boat-handling course would be more cost effective?

Seriously though, on most twin-outboard RIBs the motors are too close together to be much use for manoeuvring anyway.

Interesting enough, the rib that I did my L2 on had twins, the instructor was a big fan, said the boat was easier to manoeuvre...

That has been my experience too.

You're not suffering from EE (Engine Envy) Mr. K, by any chance?

BogMonster · 09 May 2009, 01:34

Quote:

Originally Posted by mcolston

What twins offer you though is a sense of safety as you have two engines

It doesn't bother me as there are no trees for about 1000 miles but what are the possibilities of hitting a log or similar in the water and trashing both engines at once? That seems to be one benefit of single + aux to me - at least you won't break the leg off the aux if you hit something solid?

My ideal boat would be twins too but I always wondered what the probability was of damaging both when they are relatively close together - whether its a rope, net, log or whatever.

codprawn · 09 May 2009, 02:28

Quote:

Originally Posted by BogMonster

It doesn't bother me as there are no trees for about 1000 miles but what are the possibilities of hitting a log or similar in the water and trashing both engines at once? That seems to be one benefit of single + aux to me - at least you won't break the leg off the aux if you hit something solid?

My ideal boat would be twins too but I always wondered what the probability was of damaging both when they are relatively close together - whether its a rope, net, log or whatever.

Bloody good point and one I hadn't thought of.

Also if a boat is swamped it could easily take out both engines - an aux could have a decent cover fitted until it was needed.

John Kennett · 10 May 2009, 21:50

Quote:

Originally Posted by willk

You're not suffering from EE (Engine Envy) Mr. K, by any chance?

Absolutely not. I've got two engines too!

BogMonster · 11 May 2009, 00:04

Quote:

Originally Posted by John Kennett

Absolutely not. I've got two engines too!

So have I come to think of it. One 115hp and one 6hp

Screaming04 · 11 May 2009, 04:06

In open water, I'd prefer twins....powerful enough to plane on one of them... Can't do that with 6 hp. If you can't plane with one of the pair, big single and an aux.

willk · 11 May 2009, 08:40

Quote:

Originally Posted by John Kennett

Absolutely not. I've got two engines too!

Now now, if we include car engines, this is going to get silly

JSP · 11 May 2009, 10:11

Quote:

Originally Posted by John Kennett

Maybe a boat-handling course would be more cost effective?

Seriously though, on most twin-outboard RIBs the motors are too close together to be much use for manoeuvring anyway.

Back at ya JK.

I've used an open boat with twins close together and they managed to spin the boat nearly on the spot like any other bigger twin screw I've used.