impeller diameter calculation?

[Tradient]

I am looking for a basic calculation for determining the optimum diameter for an impeller. For the sake of imformation:
Medium: water, low salt content
Maximum power: 12.5 Hp @ 3500 rpm
Maximum lift: 12"
Flow: as high as possible

The reason: I'm an aircraft mechanic who builds boats on the side. I have a request for a jet boat with minimal pressure differential. Basically, push a lot of water with minimal sediment disturbance in shallow areas.

 

[Artisi]

Go to -

http://www.ask.com

- and type in - jet boat pumps - there are plenty of references.

Naresuan University
Phitsanulok
Thailand

 

[MikeHalloran]

On the intake side, I guess you could modify a regular bottom inlet jet boat pump by adding a wide shallow scoop going forward, sort of like the after half of a double bottom ... at the expense of some weight.

On the discharge side, I don't see how a fast- moving jet of water is _not_ going to stir up sediment in shallow areas.

How about an airboat with a nontraditonal (e.g. quiet, e.g. extant) muffler?



Mike Halloran
Pembroke Pines, FL, USA

 

[Tradient]

thanks for the help, unfortunately what i was thinking was a wide flat outlet (and inlet) with high volume and low pressure rather than the typical high pressure type available commercially. That's what he wanted to avoid.

the airboat idea has the flaw that the prop will always make the same amount of noise for the thrust provided unless you invest in a true laminar flow prop (which are rediculously expensive).

 

[MikeHalloran]

Propeller noise? On an airboat? Are you kidding?

I can't recall ever seeing one with a _muffler_.

;---

I suppose you could _try_ using two jet boat inlets back to back and a double bottom diffuser. I.e., instead of having the pump discharge through a nozzle, have it discharge through a diffuser. Expect a _lot_ less thrust than you get from the same pump working through a nozzle.

;---

There was an article in a recent WoodenBoat about an odd boat adapted for Florida's 'flats'. Sort of a tunnel hull with a nearly symmetrical tunnel, and virtually no notch in the transom. Sort of the same idea as above, without the double bottom. With a large slow turning prop, it might be satisfactory to your customer, and quie a bit easier to build.

;---

Or, you could go the complete opposite way, and use a high pressure jet boat pump discharging at high pressure into an array of thousands of very small nozzles. The wake would be like a rain squall hitting the surface.






Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

http://ncma.adgwebserv.net/Page_Images/AWSC_Stern_Wheeler.jpg