Replacing an outdrive with a jet

I have a 1986 34' gillnetter up in Alaska that has a Chevy 350 and an Volvo 290 outdrive on. The boat is a bow setter and picker so going full throttle in reverse is a pain; especially in rough weather. Plus i need to be able to go in really shallow waters in order to fish (let's say 18" deep). The boat draws about 4" at the bow and 10"-12" at the stern. Can anybody advise me if is possible to throw a jet in, and how big it has to be.

Thank you,
Gabriel

 

what's your top speed at present?

 

I think it is around 15 knots at 2800 RPM; the engine will not go over 3000 under load

 

Go visit your nearest KaMeWa's FFjet supplier or Hamiltons...find the closest to you..they are best to advise since they can see your boat too. Plus you'll get an idea about cost..which is what it generally boils down to!

 

Hi Gabriel,

It's probably possible to replace your sterndrive with a jet. You will probably have to sacrifice a bit of mid-range efficiency and a fair chunk of cash to make the switch.

A Chevy 350 should be going a lot more than 3000 rpm at full throttle. Its normal redline is somewhere in the mid to high fours (I've heard anywhere from 4200 to 5000, depending on how it's set up). So your current setup is almost certainly sub-optimal.

If a jet does interest you, your application would call for one of the beefier industrial-style units (KaMeWa, Hamilton, etc.) as opposed to a jet-ski pump or an Aggressor/Jacuzzi/Berkeley style. I'd suggest dropping HamiltonJet a line ( http://www.hamiltonjet.co.nz/contact_us ). Given the dimensions, weight and power of the boat, their engineers can take a pretty good guess at what pump would work and how it would perform in your boat; they can also refer you to a local dealer who can check out your hull and determine exactly what would need to be modified for the conversion to work.

 

I wouldn't be too fast tossing out the Berkeley option. There is no way a Chev 350 can overpower one. We used to run 1200+HP through the one on drag boat I worked on. I think it was plain vanilla berkeley with stainless impeller. The rule of thumb was 650 HP before you needed the stainless impeller. What's the 350 chev put out? 300 - 350 HP?

Now, would it work at the speeds you're running? Don't know.

-jim lee

 

Jim,
the Chevy is a 1986 and puts out about 260 HP.

 

Also, i just checked Berkeley and is for boats up to 5000#; mine is at least 8000.

 

Replacing the Volvo with a jet pump will not improve your 8000 lbs boat's performance when reversing. It will probably double your fuel bill unless you spend real money on a Hamilton matched to your boat.

Before mentioning Berkeley again, read this thread:
http://www.boatdesign.net/forums/jet-drives/looking-berkeley-12jf-parts-28320.html

 

CDK, thanks for the heads up. I contacted the Hamilton guys yesterday; Gave them all the details and waiting for them to get back to me. I also left a message with the Rolls-Royce guys.

 

Well, ok.. Berkeley clone. Legend, Dominator, AM Turbine.. Kinda' like we all say PC, but how many really mean the one built by IBM? (Its their name for them)

-jim lee

 

Jim,
I think the problem with a Berkeley, or any of the similar drives, is that- for our questioner's application- speeds are relatively low and the boat is relatively heavy. Aggressor, Jacuzzi, Berkeley, etc. are all meant for relatively light boats that run relatively fast. To get a jet to work efficiently in the sub-30-knot range requires a lower rpm, larger diameter, high flow rate / low exit velocity design.

The fact that our original poster's Chevy 350 is refusing to rev over 3000 seems to me to be a strong indicator that the prop and/or gear ratio are not appropriate for his application. I would bet that considerable improvements in performance could be achieved simply by substituting a larger diameter, lower pitch wheel.

 

Matt, you're right about the gear ratio. In the very beginning i had the original sterndrive on the boat and i had it up to 4000 RPM (just me on the boat). A week later that unit broke and I replaced it with a spare i had; with the spare the engine won't rev past 3000 loaded or not; I think there were different gear ratios on the sterndrives. The reason why I want to replace the stern drive with a jet is that:
1. will allow me to fish in shallow water (currently with the sterndrive the boat draws almost 3ft of water).
2. I think it will give me better steering and a little bit more speed reversing; since is a commercial gillneter when you set the net speed is of essence.
I'm still waiting for the Hamilton guys to get back to me.

Gabriel

 

We call'em PC, not IBM PC. And it was a good design that conquered the world with over 90% market share.
The Berkeley story is exactly the opposite, lousy design, 0% market share.

 

Funny.. I just ripped a jet out and converting to outboard