reverse jet drive

[ericrunner]

I'm about to drop engine and jet drive out of a yamaha waverunner 650 into a pontoon . Anybody has a simple way to make a reverse on it ?

[ericrunner]

i found a bit of info about a volvo gear box forward,neutral,reverse ! part number ?

[gonzo]

They already have a built in reverse. It is that scoop.

[ericrunner]

no there is no reverse on my jet ski now !

[gonzo]

How old is it?

[ericrunner]

1997 yamaha waverunner

[ericrunner]

i'm going to drop 2 yamaha engine inside the pontoon tube. 1 on each side with a reverse on each side 360 degree turning should be fine

[ericrunner]

what can i compare 2 x 55hp yamaha jet ski pushing my 26 feet pontoon . My buddy as a 115 hp 4 stroke in a heavy 28 foot i wonder if i will keep-up ? not that it matter's but

[gonzo]

You can compare HP to HP. The problem you will run into, is the impeller. As a propeller, it has to be sized and pitched for the application. A jetski is lighter and will go faster.

[Landlubber]

..they will work, but water jets are designed for high speed use, planing hulls is where they start to be good, whereas the old prop works very well at low speeds

[RivrLivn]

As mentioned already the reverse for a jet drive is a bucket or scoop that drops down over the water jet to direct the water back at the boat. The angle and direction of the flow is very important in the reverse bucket design if you want it to work well. The good reverse system allow you to adjust the amount of the bucket you drop over the water flow. This way you can get a neutral position and do 360 degree turns.

[Submarine Tom]

How would neutral get you 360 turns? And what is the point of a 360 turn exactly?

Sorry, I'm kinda thick, I don't get it.

Thanks for clarifying.

-Tom

[anthony goodson]

RivrLivn is using the correct term ,a bucket ,Early jets used a device resembling a twin Pelton bucket as used in a water turbine nowadays a "whaletail "configuration is more common .Difficult to describe but if you imagine two hockey stick heads laid side by side with the curved ends facing out you have a plan view. This bucket is lowered over the jetsream to vector its thrust ,this vectoring is infinitely variable ,one of its greatest assets. A stationary jet boat can use this to turn within it's own length .There is also a party trick involving full speed full power full bucket full helm and full trousers this is a NZ invention used to frighten tourists.
These buckets are normally mounted on the unit body and the nozzle moves across the face .the flow is split and vectored down forward and to the side .It is important to try and avoid entrained air entering the intake ,the later style buckets may be better at this. As a result of this configuration a jet boat's bow will always follow it's helm, whether moving forward,stationery or in reverse, not a disadvantage but can be confusing to a newcomer A small number of jets mount a smaller device on the nozzle these steer conventionally but have the disadvantage that there will always be a helm position where jet flow in reverse is redirected to the intake. Jet boat reverses are not good the main reason is entrained air in the intake lowering the cavitation threshhold. The jet boat "crash stop" is only possible when a solid mass of water is presented to the intake ,once the vectored thrust overtakes the boat, efficiency drops off very quickly.
As regards your pontoon ,if you can obtain a pair of buckets from jetski's that use them there is no reason you should not use them. they do not have to attach to the jets they will work hanging off brackets on the transoms.Do not expect too much from them though. If you use these buckets it is essential to maintain the exact distances and orientation as in their original application.

[ericrunner]

thanks for the explanation i'm not expecting to back-up at 10 mph but i'm sure it will beat pushing in the water

[Submarine Tom]

Originally Posted by Submarine Tom

How would neutral get you 360 turns? And what is the point of a 360 turn exactly?

Sorry, I'm kinda thick, I don't get it.

Thanks for clarifying.

-Tom

I still don't get it...