......."but these days there are some awfully good solid state units that we ought to be able to adapt"
Vance,
Are you referring to standard single axis autopilot units that use a fluxgate compass for input? Or is there something else you have in mind?
I had a Raymarine SportPilot on my boat that held course beautifully, and could talk to the GPS via NMEA so that you could pre-program waypoints.....hands off trolling! All of this was so waterproof that i would spray it with the hose regularly.
The fluxgate however, was really sensitive to extraneous ferrous metals or at least, where i placed the portable radio.
Joe
From: vbra676539@aol.com
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Maneuvering
Date: Fri, 17 Nov 2006 10:34:12 -0500
Alec,Some has to do with the mass (light boats get knocked around by surface wave action more than their heavier sisters) and some has to do with all that equipment dragging through the water, but the simple fact is that if you have control surfaces (ie. rudder and dive planes) the boat will track better. This is not a guess, it is empirical. I've run both types. The question is do you need that ability? It's all trade-offs, like yacht design. I told Joe the other day that there is a simple formula for boat buyers. You may choose two of the following parameters: speed, comfort, economy. You CANNOT have all three.The little Aquarius was simple, small, lightweight and maneuverable with its single, hydraulically pivoted Hymak 5 hp thruster, and it wandered--no control surfaces. Pisces type boats with side thrusters, wandered a bit--no control surfaces. My K-350 has both side and stern thruster and it wanders, too--again, no control surfaces. They were all designed that way. It doesn't mean that you can't drive in a more or less straight line. It just means that the vehicle needs constant inputs and adjustments from the pilot (or autopilot) to do so. And you were going to do that, anyway, right?I figure that little Idabel is dandy going down the wall at Roatan, and comes home just fine, being steered with thrusters, not rudders. Karl put a lot of thought into that boat (not to mention time and money) and his choice of multiple drive and maneuvering units is deliberate. But I'm betting a big old barn door rudder out there in back would make life a lot easier on the surface. However, that's not what he does. His job and the vehicle's design is to work the wall, carefully and delicately. Transits are secondary.The Perry boats could be run hands off for longish periods on transits or pipelines (say, while pouring coffee or, with minor oversight, peeing in a bottle) but would still swing around on you if you didn't pay attention. Mind you, I've had them trimmed up with just the tail of the skids kissing the bottom and balanced so well that I could make minor course adjustments just by leaning to one side or the other).Keep in mind that Vickers ran Pisces class boats for years doing the same stuff we were doing, and managed very well, too. Of course. the autopilots were INVALUABLE for these things when they became available, and we used them a lot. If you running a pipe or going somewhere on the bottom then you could fire up the Iron Mike and make fine course adjustments with a bias pot on the PCC.And, of course, I agree with Carsten that a gyro autopilot is expensive and complex (and heavy, and did I say expensive?)--but these days there are some awfully good solid state units that we ought to be able to adapt. I'm voting for one of those.Vance
-----Original Message-----
From: Alec.Smyth@compuware.com
To: personal_submersibles@psubs.org
Sent: Fri, 17 Nov 2006 9:50 AM
Subject: RE: [PSUBS-MAILIST] Maneuvering
I think the difficulty with tracking straight is not related to the thruster configuration but to the dynamic stability characteristics of PSUB hulls. Very few subs have clean lines or anything resembling a keel. To take a K boat, for instance, there must be all kinds of strange turbulence going on in the MBT openings and the various underbelly appendages. Snoopy is equally unstable running on the stern thruster or the side thrusters.This is just a theory, I have no way to substantiate it.Alec
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Emile
Sent: Friday, November 17, 2006 6:17 AM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] ManeuveringThe contents of this e-mail are intended for the named addressee only. It contains information that may be confidential. Unless you are the named addressee or an authorized designee, you may not copy or use it, or disclose it to anyone else. If you received it in error please notify us immediately and then destroy it.Another issue with side thrusters alone is that it is virtually impossible to drive the boat in a straight line. I spent a season operating Leo, and it was quite a lesson after all the years with that big, dependable Perry wheel chunking around behind you. What you end up doing is setting both motors for transit, and then varying the power on one to hold the compass course.It is the same with the sgt, Peppers with ist fixed 4 thrusters and 1 main engine. On surface transit it looks like youâ??ve drunk way to much; especially with wind and waves.A gyro autopilot is complicated but should be nice. Without ,too much of your attention just for keeping coarse.Regards, Emile
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