Fuelconsumtion and speed with 1 vs 2 outboards?

[joakimhansson]

Revenger 29 or Scorpion 8,1-8,5 with stepped hull.

With 200-250hp (1 or 2).

You have different props when you have 2 engines so lets say in 45 knots the rpm must be much lower with 2 engines. At top speed it must be close to 2 times fuel consumtion?

And speed diff?

What to expect in speed with 2 engines?

[codprawn]

I would go for a single 300 - either Suzuki 4 stroke or Mercury 300xs 2 stroke. Both very light for their power.

If you do a search on here for Fjordrafting you will see he loves Revengers. They run a 29 stepped hull and reckon it's better in the rough than even a 34 or 26' boat. They get over 60kts with 2 engines - with a single 300 they reckon about 54 kts.

Obviously flat out 2x engines will use 2x the fuel - say 2x85l for 2x250 and about 95lph for a single 300. Cruising is different of course -0 they may work out the same but I doubt it.

I prefer a single engine as the boat is much better balanced for wave jumping etc. Unless of course you are carrying loads of passengers and they are sitting forward.

My hull is the same as the Revenger non stepped and it is awesome in rough water - very gentle ride.

[Idrian]

Hi Joakim,

in a german boat magazine was a test where they compared one Yamaha F 225 and two F115 at the same boat.

http://www.dk-content.de/boote-magaz...en/MT-7021.pdf

Top speed and acceleration with two engines was better and fuel comsumption nearly the same.

[Paul F]

Also on twin set up you have engines to service at same time. That could be costly
Paul

[codprawn]

Originally Posted by Idrian

Hi Joakim,

in a german boat magazine was a test where they compared one Yamaha F 225 and two F115 at the same boat.

http://www.dk-content.de/boote-magaz...en/MT-7021.pdf

Top speed and acceleration with two engines was better and fuel comsumption nearly the same.

Very interesting test. Having said that I suspect the difference in top speed could have been closed with a better prop on the 225 - maybe a 19".

[pathalla]

two motors on a boat are like two breasts on a woman, two are ALWAYS better than one....

[pathalla]

Originally Posted by joakimhansson

Revenger 29 or Scorpion 8,1-8,5 with stepped hull.

With 200-250hp (1 or 2).

You have different props when you have 2 engines so lets say in 45 knots the rpm must be much lower with 2 engines. At top speed it must be close to 2 times fuel consumtion?

And speed diff?

What to expect in speed with 2 engines?

If you go with two motors you likely never want to run a single engine setup again given you can afford the fuel. If cost of gasoline was not an issue many more people on this forum would be running twins imho. The performance will be much better. Holeshot with twins is a blast, my boat is very heavy and it comes up on plane right now, fuel consumption is not that bad if you keep your foot out of it. I have had as many as eighteen people on my boat at one time and it comes right up on plane with no problem whatsover, try that with a single. This is not knocking boats with singles, I ran many single engined rigs over the years and had lots of fun with them, a twin setup will give you better overall performance as I see it.
When you start looking at larger boats... you'll need two motors....or three... there are a few triple (675 hp) ribs running around over here. Speed is going to depend alot on hull design and power, I get somewhere between 50 and 60 knots with my boat and I would tend to believe it's closer to 50, but then I have a much heavier boat than most. ( it sure busts waves) Performance on a 30 with a couple of 250's would probably put you safely in the low sixties or high fifties I'm guessing...

[ribit]

Originally Posted by codprawn

I prefer a single engine as the boat is much better balanced for wave jumping etc. Unless of course you are carrying loads of passengers and they are sitting forward.

Mmm so a single engine race craft is better balanced than it's twin engine counterpart... try telling that to FB design, Cougar marine, fountain worldwide, Donzi marine

my hull is the same as the Revenger non stepped and it is awesome in rough water - very gentle ride.

Did not realise that Revenger boats had done a deal with any Channel island rib builders to utilise there design work please enlighten

[Cookee]

Top speed a bit better, hole shot much much better, fuel consumption considerably (double) worse at WOT but not so bad at cruising speeds (still worse than a single), if you drive a boat hard a twin rig is much better at taking off and landing as far as roll stability is concerned - but you have to balance the boat fore and aft (I think this is what Codders was referring to?). Servicing is double.

Other factors are the look of the boat, the noise of two outboards synchronised is fantastic, and the "get you home" factor of a twin rig. You will also need more fuel capacity!

Hope that helps?

Ps - twice the price!

[codprawn]

Originally Posted by ribit

Did not realise that Revenger boats had done a deal with any Channel island rib builders to utilise there design work please enlighten

The Prosport moulds were bought from a company on the mainland I think. The design is based on the BWM RIBs which owe their design to Revenger. The Revenger hull has spawned many clones over the years - some very well respected RIB makers are using hulls based on someone elses design.

Then again as I have said before there isn't much new in this wsorld. I wouldn't be suprised if the original Don Shead design was pretty similar to some other boats around.

The name Paul Lemmer also keeps cropping up whenever this hull is mentioned......

As far as my boat is concerned the wetted area is pretty much the same but there are bigger overhangs and a fuller bow which gives a very dry ride and less chance of stuffing.