nzjetboating Web Board. Forums => Projects => Topic started by: Chris Gutsell on April 07, 2021, 20:32:19 PM

Title: Trim Nozzle Advice
Post by: Chris Gutsell on April 07, 2021, 20:32:19 PM
Evening, I'm after some advice, pros and cons, experiences with fitting a Southern Jet Trim Nozzel to my mini jet.

It's a 3.1m with 15f and 155mm pump, Saco Dual Row.

I'm finding that at slower to medium speed, it has a hop in the corners, also if powering into a turn or midway through it gets abit bouncy and rather interesting. At faster speeds it's not so evident and feels like it's actually sitting lower in the nose and driving/drifting around the corners.

Title: Re: Trim Nozzle Advice
Post by: Ross Goldsack - JBNZ Immediate Past President on April 07, 2021, 21:59:56 PM
Yes a trim nozzle will probably help those issues, but it's really a bandaid fix as there must be something wrong with the hull.
Title: Re: Trim Nozzle Advice
Post by: Chris Gutsell on April 08, 2021, 07:25:16 AM
Hi Ross, the Hull has a 10mm delta and as far as I can see from inside and out is pretty straight, no dents or big warps. It has a plastic strip which at the rear has stretched and bulged a little. Is this likely to have a big effect? There's no stakes on the Hull either. Is this sort of issue somthing common with these smaller hulls, hard to get the right balance across the entire speed range? What are the benefits of a Southern Jet nozzle other than trim? More thrust? Sizeable nozzles? Better turning thrust?
Title: Re: Trim Nozzle Advice
Post by: Henry on April 08, 2021, 15:04:44 PM
If its a typical 3.1m with a chine width of about 1200-1300mm then the relatively big engine and total weight in a small hull can make it porpoise at slow speed.

Try adding a ride plate under the pump that extends the hull and adds a bit more planing surface in the rear.

Also try a trim wedge in the pump tail cone to give a little bit of down trim. They can be had from the 140mm 900cc Kawasaki pump and bored out to 148mm.

The trim nozzle will also help but may rob a little bit of thrust
Title: Re: Trim Nozzle Advice
Post by: Jeff B on April 12, 2021, 07:10:26 AM
Your hull sounds like it's set up ok, little boats do hop around a fair bit. A lot of little boats will hop in corners (and big boats) if trimmed up a touch too much. You can trim the factory nozzle down with a wedge that will reduce the hop at lower speeds but will suck nose down more at higher speeds.
The southern jet trim nozzle will help a lot in your case. The advantages are,
Trim (obviously)
Changeable inserts to fine tune (not that they need changing, right size stays in forever)
Lighter steering input
More thrust during hard lock steering, some people report a lot better thrust in corners.

Bigger, some reverse buckets wont fit,
Some will jamb with sand/grit in shallow water,
Some loss of thrust/top speed, hard to measure but some people report no loss of performance, some report more slippage and down on top speed.
Title: Re: Trim Nozzle Advice
Post by: Chris Gutsell on April 14, 2021, 20:31:03 PM
I havent heard many people regret putting them on, but have heard of several reports of steering jam ups. Does anyone have experience or knowledge of wild water jet new trim nozzles?