Jet speed boat RR-M250 powered.

[camerondownunder88]

Hi,
Been on this forum for years reading a watching but not super active...

Well I have a new project I am helping with, and needed some advice before I start it.

Idea is a jet boat. Using a water jet and a Rolls Royce turbine.

I want to know every ones thoughts on coupling a trans brake between the turbine and the water jet.

If the boat was sitting in water running the water jet keep load on turbine and shut the outlet and boat wont move. So though in my head is dont bother with a trans brake.

In saying that a trans brake may have benifits..

Water jet I have is off a off shore racing boat and I got a "c" cut impeller that is better suited to a 6016 RPM input speed.



Appreciate any input.
Cheers

[BFTO]

I have seen other turbineboats put a brakedisc on the output to stay stationary in the water so that is probably a good idea.

I dont know the rotationdirection on the RR-250 and your off shore racing waterjet. The jet boats using the RR T58 needs to make a gearbox to change the rotationdirection to work with the jets made for IC-engines, that is one thing you should investigate in.

[racket]

Hi Cameron

Hows NZ and the new job going ??................heh heh , you seem to have taken the rain with you ;-)

If you close off the water jet outlet you'll unload the freepower as it doesn't take power to spin the same bit of water around and around , ...........on a big steam boiler I operated , the hot water was circulated by 50HP pumps to be used in the manufacturing process , water at 200 psi and 200 deg C , ..........during overhaul of the pumps we had to run in the plain bearings and seals, this was done with the pumps outlet closed , the amp draw was very low and the level of amps was an indication of how well the run in process was going , as soon as the valves were cracked open amps went up as fresh water was starting to be processed by the pump...............I'd use a trans brake to be on the safe side.

Cheers
John

[camerondownunder88]

Hi,
Thanks for reply.

John the weather has been...wet hahah Liquid sunshine I call it. Topped out at 15 today...Summers on the way...

Guess the rain keeps me at the drawing board working out this boat.

So I made a flange on the jet unit and have a drive shaft I can mount a brake in between so easy to add. Thanks for the advice guys .

Also BFTO direction of rotation is confirmed and is all good I can drive out the front or the rear so easy to work with

As for the brake yes agree with the 0HP to not pump water with outlet shut. Bit like you block a vacuum and the RPM picks up. Didn't think of that. Good for start up I can then lock the power turbine sort out the ship and let it go. Cant see brake being used after we let it go. Have to be a pretty big brake to absorb 400HP hahah

Cheers
Cameron

[racket]

Hi Cameron

Yep , a pretty decent sized brake , 400 hp at 6016 rpm = ~350 ft lbs of torque , double that for a stalled freepower with the gas producer N1 at 100% and we we have ~700 ft lbs .............but , if I remember correctly from one of our discussions at the kitchen table , the gearbox is torque limited , so maybe no full power stalled conditions :-)

Ground idle is ~50 HP say , so a brake to hold that shouldn't be too difficult to fit , a motorcycle disc brake should be more than adequate .....................the rear brake on Anders bike is probably holding >500 ft lbs of torque at the rear wheel prior to "takeoff".

Cheers
John

[smithy1]

Hi Cameron,
You haven't told us which model RR M250 engine you're using but the most common will be the RR M250 C20B. For the C20B the engine's main rotor gearbox "drive shaft" will turn anticlockwise as viewed from the front or compressor end of the engine, there's also a drive from the rear for the tail rotor which which obviously turns in the opposite direction as they're a common internally geared shaft.

The output shaft's rpm is 6000 @ 100% N2.

Hope this helps you out a bit.

Cheers,
Smithy.