Twin yamaha 90hp

ALANT · 15 March 2007, 13:47

Just got the chance of twin 90's what fuel consumption can I expect running about 20-25 knots with 8 divers? Boat 7.3m Northcraft, Don't need to go any faster just need to be able to get on the plane with reasonably ease

Nasher · 15 March 2007, 14:43

Alant

My honest opinion is that you are better off with the single 150HP.

You may get up on the plain slightly quicker but may even struggle to get 25knts with that set up and all that weight.

I believe the rule of thumb is twins give performance about equal to 70% of their joint power.
ie two 90s is @126HP

Somebody will probably shoot this down in flames though.

Nasher

ALANT · 15 March 2007, 14:54

It already has a 150 johnson on it. Looking at the atlantic 75 about the same weight does 32knots with 75's.

How do you rate your suzi know of a 99 200efi, does it have a fuel return line form the engine?

Nasher · 15 March 2007, 15:07

Alant

The Suzi is in my opinion a great engine.

Its very light for a 200, and has a built in oil reservoir and fuel swirl pot.
So no fuel return line or seperate oil line/tank is required.
Codprawns 225 is a better, but more complicated version of the same engine with twin plugs etc.

My 6.5 Ocean is a heavily built boat with a sea-keeping hull rather than a fast hull. With the old Johnson 150VRO on it did around 30knots max using about 2.5 to 3l of fuel a mile.

The Suzi gives me a comfortable crusing speed of 25-30knts at just over half throttle, and with a very light load I've seen 52knts.

Depending on the sea state I get between 1.6 to 2l a mile out of it cruising, but as expected this goes up stupidly doing 40knts+, towing, or at displacement speeds. This is the area where I believe an Etec etc would beat it. Bear in mind however that they can be picked up in prime condition for @£2K

Nasher.

ALANT · 15 March 2007, 17:06

Is that 1.6-2 litres a mile or 1.6-2 miles a litre? presume the former.

Anyone anyother oppinion on the twin setup? I think it would give me more torque but 25 knots at wot to slow

would want that at about 3/4 throttle.

J S · 15 March 2007, 18:30

Quote:

Originally Posted by ALANT

It already has a 150 johnson on it. Looking at the atlantic 75 about the same weight does 32knots with 75's.

How do you rate your suzi know of a 99 200efi, does it have a fuel return line form the engine?

The atlantic 75 will do 35kts with twin 70 evinrudes

James

codprawn · 15 March 2007, 18:47

Quote:

Originally Posted by Nasher

The Suzi is in my opinion a great engine.

Its very light for a 200, and has a built in oil reservoir and fuel swirl pot.
So no fuel return line or seperate oil line/tank is required.
Codprawns 225 is a better, but more complicated version of the same engine with twin plugs etc.

Depending on the sea state I get between 1.6 to 2l a mile out of it cruising, but as expected this goes up stupidly doing 40knts+, towing, or at displacement speeds. This is the area where I believe an Etec etc would beat it. Bear in mind however that they can be picked up in prime condition for @£2K

Nasher.

Couldn't agree more - I am SO pleased with my engine - as far as economy goes though my engine seems to give the same sort of figures as an etec or Suzuki 4 stroke etc. Maybe it's the twin spark that makes it more efficient?

benc · 15 March 2007, 19:58

Quote:

Originally Posted by Nasher

Depending on the sea state I get between 1.6 to 2l a mile out of it cruising, but as expected this goes up stupidly doing 40knts+, towing, or at displacement speeds. .

Hmm, thats interesting..

Doing WOT in mine, about 55knots, uses about 120litres and hour, so about 1.9l/mile

Doing 40knots, it uses about 60l/hr so about 1.3 litres to the mile...

I think those calculations are about right - if so, I guess the fuel consumption isnt all that bad!

ALANT · 16 March 2007, 23:50

So anyone going to give me a top speed and consumption for twin 90's?

benc · 17 March 2007, 00:00

I agree with Nasher, you may struggle to get 25 knots with all that weight.

With a light load, low fuel etc... I managed to get 43 knots from my boat, with twin 115's, with 5 people on board, and full tanks, I was lucky to get 35.

Pete7 · 17 March 2007, 00:19

Quote:

Originally Posted by ALANT

So anyone going to give me a top speed and consumption for twin 90's?

At speed, about 8 gallons an hour, each.

Pete

Dunc · 18 March 2007, 19:34

I had a 7.5m humber which we used for Sea Safari trips. We had 2x 80hp Yamaha 4 strokes on the back. With 10 adults she would plane quickly and cruise at 19-20knots at 4200 revs burning about 20 litres an hour. Top speed with 10 was 28 knots. If you wanted to cruise at 24 knots the engines were running at about 4700 revs and the fuel consumption went up. The 90hp two strokes you are thinking of would probably give you higher speeds but I would imagine the fuel consumption would go up.

Donnie144 · 20 March 2007, 20:56

I'm running twin 90's on a 6.5M Mako. With 4 divers, gear and 12 tanks with a 12x21" prop i'm burning aprox. 8 gallons an hour doing 25 MPH @ 3,000 RPM. I can open it up it will burn 18 gallons an hour and do about 42. Empty the motors wil turn 5,600 RPMs burn 18 gallons an hour and give me 53-56 MPH. On that big of a boat and with 8 divers 16 plus tanks i would think you would need about a 17" prop and with that my RPM's max me out at 35 MPH burning the 18-19 Gallons an hour.
I'm running the newer fuel/oil injected Tohatsu's i hope this helps a little bit. If you are looking at a carborated motor then i can't help you other then tell you to at least double the fuel consumption.

Donnie144 · 20 March 2007, 20:58

Quote:

Originally Posted by Donnie144

I'm running twin 90's on a 6.5M Mako. With 4 divers, gear and 12 tanks with a 12x21" prop i'm burning aprox. 8 gallons an hour doing 25 MPH @ 3,000 RPM. I can open it up it will burn 18 gallons an hour and do about 42. Empty the motors wil turn 5,600 RPMs burn 18 gallons an hour and give me 53-56 MPH. On that big of a boat and with 8 divers 16 plus tanks i would think you would need about a 17" prop and with that my RPM's max me out at 35 MPH burning the 18-19 Gallons an hour.
I'm running the newer fuel/oil injected Tohatsu's i hope this helps a little bit. If you are looking at a carborated motor then i can't help you other then tell you to at least double the fuel consumption.

one more thought. DO to the weight of the outboards the top of my transum is only about 3" out of the water. Given this i question the wisdome of going with the twins and wounder if i should have gone with a single 200 got more speed and shaved 180 pounds on the transome.