Twin or single for Ribcraft 5.3

[al40]

Hi,

I'm interested in some opinions of owners with twin engine installations...

Looking at a Ribcraft 5.3. I currently have a 50hp-2stroke, less than a year old, which I was hoping to use. I now have the dilema of whether to use this as a single engine (pretty underpowered for the 5.3) or opt for another 50hp and do a twin install. The transom would need to be lowered for a single install (it's only a long-shaft) so I'm comitted oncee I do that!

I like the idea of twin engines from the safety and security point of view but I realise the overall effective power will be less than 100HP with added fuel consumption... How much extra fuel would I burn with twins? 1.4x?

I was thinking the single plus Aux root but I've had bad experiences with this as the Aux never really gets used properly to keep it running well and I didn't find it that reliable. I guess a 4-stroke Aux (6-8hp) would be a possibility.

Thoughts?

[jyasaki]

How much fuel depends on speed, of course. At WOT, probably pretty close to twice, I'd guess. At cruise, well, I suppose it depends on how you're measuring, but for a given speed, I'd guess about 1.5 times (that's a guess, though.)

You would have much more available power, but you're also adding a lot of weight, and increasing lower unit drag by a factor of 2, so the tradeoff may not be as good as you'd think.

Most of the references I've seen say you lose about 1/4 to 1/3 the total rating going with twins (i.e. your twin 50's would net you the equivalent of a 66 to 75 hp single.)

This is all theoretical, as I have never played with twins (I do like the way you can crab the boat around with twins, however. That would make it worth it in my book. Then again, I'm not paying for it, either. )


jky

[mdt]

The club have got 2 ribs identical 5.5m bar one with a 75hp 4stroke and one with twin 50hp 4strokes.

The twin picks up quicker from a standstill but hardly night and day over the 75hp one. And there is sod all in the top speed.

Personally I would go for the single given the choice. And as you said get a new-ish 6-8hp as a back up?

[al40]

Thanks, usefull info..

[Rogue Wave]

theres a weight consideration to putting twins on a shortish rib.

if you alreasdy have the one engine find out it's weight and add the equivalent amount of water in cans to the rear of the boat and see if she rides OK.

I think you get better performance from a single and better economy but twns are kinda nifty if you can afford to run them.

I used to drive a Delta 5.5 with twin yammie 40 2 strokes and I used to take it way off shore but I always thought it would do better with a single 70 or 90

[al40]

Yeah it was the offshore aspect I was thinking about when looking at twins. I had assumed I would be able to plane on 1of2 but that may not be the case. Jury's still out!