[PSUBS-MAILIST] Fw: Thruster position

Thu Dec 3 12:09:54 EST 2015

I talked to the engineers at M-K about that a few years back. They had no data for other props, but say the motors run just as well in reverse. Replacing the plastic scimitars would probably cost you a bit of thrust in one direction, but you'd get a lot back the other way. It seemed like on balance that might be a reasonable trade-off. I did look for props at the time, but don't remember whether I actually found one. I'm betting if someone called Michigan or somebody they might find just the ticket. That would be cool, even if you had to build an adapter for the skinny shaft. I've got a wheelbarrow load of M-Ks sitting around. Maybe it's time to look into that again. I would really love to have something with a smaller diameter, maybe 3 or 4 blade to make up the difference. They'd have to be nicely balanced, however, as the M-K bearings are probably undersized for heavy props. Hmm.
Vance

-----Original Message-----
From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Thu, Dec 3, 2015 11:43 am
Subject: Re: [PSUBS-MAILIST] Fw: Thruster position

I'm not aware of counter-rotating props for a Minnkota but that would be fantastic if anyone has a lead. As far as the motor itself, I don't know that it has any preferred direction of rotation, and hopefully the forward bias is based on the prop only with the motor not minding. 

Thanks,

Alec

On Thu, Dec 3, 2015 at 9:44 AM, via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Alec,

Can you just get counter rotating props? That is what my sub has ad I have no problem with rotating on powered decent.

Thanks,
Scott 

-------- Original Message --------
Subject: Re: [PSUBS-MAILIST] Fw: Thruster position
From: Alec Smyth via Personal_Submersibles
<personal_submersibles at psubs.org>

Date: Thu, December 03, 2015 7:14 am
To: Personal Submersibles General Discussion
<personal_submersibles at psubs.org>

Hi Hank,

I had to think about the same thing not long ago given the new sub has two vertical thrusters. The fundamental question was whether to point them up or down. What I settled on was pointing both downward. Here was my reasoning:

- I like diving the sub slightly positive, and use the side thrusters for depth control. Pointing downward, they are operating in their most efficient direction for the vast majority of the time.
- Pointing downward the wash goes UP, which prevents stirring up silt. 
- By canting them outward you can crab by running them in opposite directions, gaining an extra degree of motion.

Just two cents. If you prefer diving the sub negative you could point them both up. That would give you more power for reaching the surface in an emergency, but it would stir up silt the rest of the time. I have really huge MBTs for the emergency situations, so went for what I thought was the most convenient thruster direction in normal use.

There's one more detail that I'll just have to test. When I dive Snoopy down on the side thrusters, she can get into really fast rotation because both props are turning in the same direction. I counter that by tilting one of the side thrusters slightly off vertical, but with the permanently mounted thrusters I won't have that possibility. It may not be an issue on the new sub, but if it is, I'm thinking I might have to install a little vane in the wash of the vertical thrusters to compensate. Or I could correct the rotation with the horizontal thrusters. Maybe even program that compensation into the speed controller logic. Practice will tell.

Best,

Alec 

On Thu, Dec 3, 2015 at 8:39 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Tim,
My idea was to mount one vertical thruster pointing up and one pointing down because the props are only efficient in one direction.  This way I get full power from one and half power from the second in both directions.   Tilting them may get weird, but I can easily change things over time.
Hank

On Wednesday, December 2, 2015 8:22 PM, T Novak via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hank,

Why not cant your vertical thrusters 45 degrees out from the vertical?  Sort of like this bow on view:  /O\   where the / and the \ represent the thrusters canted 45 degrees out from the O which represents the pressure hull.  This would allow the down wash to miss the horizontal thrusters while both "vertical" thrusters are heaving the sub upwards.  And it would provide controlled translate (sidle) movement when the two "vertical" thrusters are powered  to thrust one up and one down.  Your ballast block will keep the sub from rolling and force it to translate sideways.  This works very well for the DW2000's.
Tim

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of hank pronk via Personal_Submersibles
Sent: December-02-15 11:11 AM
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] Fw:

Alec,

I was hoping the wash would go around the motor, I have no experience with this, but it makes sense. :-(  I will move it back.  My original plan was to have them up front vectored 45 degrees, but they are very heavy, over 40 lbs each and that takes away from the buoyancy for the arm.

Hank

On Wednesday, December 2, 2015 12:04 PM, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

If it were me, I'd move it just a little bit aft, just enough to leave the vertical one unrestricted. I don't think you'll have any trouble at all rotating the boat if the thrusters are not exactly in the middle.

Best,

Alec

On Wed, Dec 2, 2015 at 1:57 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi All,

This is a picture of my proposed thruster location, I am not sure if the motor in this location will interfere with the prop wash from the vertical thruster inside the can above the thruster.
What do you guys think?  I want the motor as mid ship as possible for best steering.  This location is also good for cabling to the pen plate   

Hank

On Wednesday, December 2, 2015 11:51 AM, xxx xxxxx <mp13 at live.ca> wrote:

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