[PSUBS-MAILIST] Gamma's diesel engine

Fri Aug 11 18:04:37 EDT 2017

Greg,At full power with all thrusters going, Gamma tends to nose dive a bit.  I think the bow wave sits on top of the sub and pushes it dow.  It is no big deal but it does happen.  I figured the nose would drop but I could compensate by lowering the  stern.I too will keep it simple.Hank

On Friday, August 11, 2017, 3:45:40 PM MDT, james cottrell via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hank,
Too bad we don't have the captain around to answer questions anymore- he did it all. George was an expert at building simple things that worked really well.
Don't worry about 6 hp being too small- it will be plenty. George was working on another diesel boat for himself before he passed. I think that the engine was 7 hp. The hull is now on display in South Thomaston ME. as a memorial to him.
Ideally, a high thrust motor needs to be pushing at the metacentric point (average between center of buoyancy and center of gravity) This point is usually very low on a shallow diving sub. There are a couple of guys around that mounted high thrust engines at the mid point on the stern and found that the subs would nose dive at full power. You can get away with a center mounted prop when the thrust is low.
George also ran the engine with the intake open to the inside of the hull and the hatch open for simplicity. He used flexible stainless exhaust hose through a ball valve at the bottom of the hull. The "skeg" was a thick piece of steel angle welded to the bottom (pointing down and back) ahead of the exhaust outlet with the "V" pointing forward.
Greg C.

      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Friday, August 11, 2017 5:14 PM
 Subject: Re: [PSUBS-MAILIST] Gamma's diesel engine

Hi Greg,Thank you for the input.  That is good to know that the captain liked the diesel model.  I have been torn over the idea, but since I have an actual engine room with insulated door, it should be fine.  My 6 hp motor sounds small now, I can get a bigger one.  My problem is it has to fit through a 18 in dia opening with ease so the escape pod can still be an escape pod.  Gamma had a 2 hp electric originally with the prop in the centre of the height.  I figure the 6 hp diesel should be double that and spin the prop twice the speed.  I will take the transmission advice, I have one so no problem there.Hank

On Friday, August 11, 2017, 6:31:48 AM MDT, james cottrell via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hank,
Captain Kittredge built three diesel subs and liked them very much. He used 7-8 hp yanmar diesels with a transmission. He highly recommended using a transmission and considered reverse a necessity. Exhaust existed at the bottom of the hull just behind a makeshift "skeg" that created cavitation (vacuum to reduce back pressure). 
The prop should be below center on a sub due to the low center of gravity. If you place a powerful prop as high up as the middle it will lift the stern.

Greg C

      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, August 10, 2017 5:14 PM
 Subject: [PSUBS-MAILIST] Gamma's diesel engine

Hi All,I have just purchased a 6 hp diesel for Gamma.  The plan is to use the original prop assembly that can jettison.  The only thing I am not sure of is will I have cavitation problems.  The prop will be about 12 inches from the occupant sphere, mounted in the centre of the sphere (equator)  Will I have to put a spacer between the sphere and prop assembly to move it further away?Hank

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