Yamaha Jet Drive

[Francis]

I was talking to a buddy of mine today and he had mentioned that yamahaa has put out a new motor that is a power thruster fuel injector instead of using a prop. He said that he thinks it is a 40hp. Has anyone heard of this???

[Mac Ziggy]

These engines are rated HP at the jet pump. They require much larger HP at the head to produce the power. So a 40 HP jet is really a 50/60 HP engine. They are priced accordingly with about 1K added for the jet drive.

http://www.yamaha-motor.com/outboard/pr ... /home.aspx

[jasper]

Yamaha has a Jet power conversion guide which converts Prop shat HP to Jet Pump HP
Prop/jet equivalents are 40/30, 60/40, 90/65
The fuel injection is Multi-post precision fuel injection, not power thrust injection.
I have the Thrust 25Hp with power trim and tilt and think it is great. At max throttle it should bet about 12-13kts as I am getting 9.6 kts at 3/4 throttle

[Francis]

So, do you guys think it is worth going to a motor like this, or staying with a prop???
How heavy is a 50hp prop motor compared to the 40 or 60 yamaha? The 60 was 268 lbs. and the 40 was 201lbs.
I'm not sure of what the price is on these.

[mallardjusted]

Francis, the jet outboard setups were developed for specific applications. For example, a lot of duck hunters and fishermen that run rocky, shallow rivers find them to work well. But they have disadvantages in a lot of other applications. The weight to hp ratio, as mentioned, is higher. Therefore, they use more fuel to do the job that a prop will do. They also tend to be noisier (at least every one that I've heard!), and the cost (initial outlay and maintenance) is higher. If you're exposed to a lot of seaweed or mud, the jets tend to clog up, and are a pain to clean out.

So unless you're going to be doing some duck hunting in a rocky river with your Mac, you're probably better off with a prop!

[Sleepy]

Down in POC a lot of people use Jet OB's on johnboats and they all complain about low speed steering control being lousy with them. Plus a 30% power loss from the head. They use them for fishing the flats.
So stick with props!

[Francis]

Thanks for the info. I think that is a good suggestion.

[Phillip]

I have never seen an Jet O/B...seems a very interesting concept.

I use to know a lot about Jet Boats, (ex Kiwi 20yr back). New Zealand is the home of the Jet Boat. I had a Hamilton Jet 32 for years.

It had a 2 stage Jet unit: I 'think' I had a motor called a Granada V6 (alloy...made in Germany....used in a car we had called a Zephy Zodiac Mk iv....don't think it was very sucessful in the car....but fantastic in the jet application). My mate had the Jet 73

Here is a site on jet boats. If you want to know what is going on in Jet Units, go thru it. I have always found it interesting, but that's because I am an ex Kiwi.

http://www.hamiltonmarine.co.nz/index.c ... Boats.html

Jet boats as we had them were very fast, highly manuvourable, and good in the sea, on lakes, and up shallow rivers. Very little maintanence, very reliable. And we gave them an absolute hiding. We were never critical of the prop boats, but they just weren't in the same class.

Those not owners of Jet Boats were the only ones critical of them, almost with a passion....once you owned one, it was hard to go back to a prop.
As for an O/B Jet Unit ... I have never seen one ... but if it is as efficient as a traditional Jet unit it will be fun.

But I am a bit biased.

Cheers
Phillip