RE: [PSUBS-MAILIST] Kort nozzle

Kort nozzles,

There is a company called Propguard which have an improved version of the Kort nozzle for small boats. I read somewhere that a Kort nozzle has a pressure build up problem somewhere and the ring is best split into two, fore and aft, with a gap between which is what the propguard does.

http://www.getaprop.com/content-categories/cat-896/prop_guard_hydrofoil.html there is an 11 inch version which could be modified. I am wanting to get a small cheap one so I can get to see the engineering behind it.

Kort nozzles are no good above 10 knots which is fine for subs. There is also an improved version called a Rice Speed nozzle which has a modified profile with reflex built in.

If anyone has seen or knows of the paper referring to the pressure spike I would love to get hold of it. I found it once and now cannot find it again. Hugh

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brian Cox
Sent: Wednesday, 10 February 2010 8:27 a.m.
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Kort nozzle

Frank, It seems like it would be pretty easy to fabricate a prop out of a piece of flat plate steel. Cut out your shape with a plasma cutter and them turn each prop the desired angle. A multiple blade prop with say 8 - 10 blades would give you a lot of torque if your RPM was low enough and the motor was the right power.

On another note I'm starting to lean twords a connecting pontoon arrangement with an outboard engine for powering to dive locations. This would solve an imediate problem for me until I develope a true diesel electric that could submerge. In the meantime I could get my sub running with just batteries and attack that problem at a later date.

Brian

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of ShellyDalg@aol.com
Sent: Tuesday, February 09, 2010 11:08 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Kort nozzle

Minnkota has a couple of new products out. There is a newer motor rated at 2-1/2 HP coupled with trim tabs and electric actuators. The site I read said the dual motor set-up would run a standard pontoon boat at 5 knots.

I too will be using the regular Weed Wedge 2 props for now but would like to use three or four bladed props as an upgrade later on the two rear thrusters. They have 3/16" thick stainless prop rings on them now, acting as kelp guards and rudders. I think I could fiberglass a Kort nozzle shape onto the SS rings so adding multi blade props could add more "push". My side thrusters will need to keep the "Weed Choppers" as they have no guard rings.

I was thinking it might be possible to fabricate some props from FRP. Balance would be an issue and longevity too as the FRP is soft making it wear quickly. For sure you couldn't run into anything with them.

Could it be possible to buy aluminum props without the hole and machine the correct size hole for a Minnkota shaft ?

Another thought is to fabricate a new replacement end section that fits a Minnkota with a magnetic coupling so no pressure compensation would be needed. Bolt it on in place of the factory end section.

The overall diameter would need to be larger than the Minnkota housing to accommodate the mag coupling but if the shaft was extended a few inches a taper could be used to clear the area directly in front of the prop.

I mentioned this to my machinist son-in-law and he said he would be glad to make something if I could draw it up. ( maybe later )

I know Minnkota spent a lot of expertise designing their props for the motor but I wonder if having it designed for chopping weeds has reduced it's thrust output.

True, I don't know shit about props, but there may be room for improvement here.

I finished the drop weight/carriage yesterday, except for some tabs to attach the lead bricks and a little finish polishing. It's freakin' heavy already. It has 6 steel rollers rated at 1500 LBS. each and two smaller rollers so the sub will "teeter" on the main rollers. Should make it easier to move the sub around on the shop floor and will be used when loading/unloading on the trailer. Once installed, the sub will be MOBILE !

One step closer to Florida !!!

Frank D.

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