Mangusta 72 - Arnesons

I don't care how experienced someone is, if an autopilot causes a boat to veer 90 degrees at 35 knots then something is clearly not set up right or it's a bad choice of autopilot or something. That's not normal.

You don't want to use an AP, that's your choice.

Ok, let me try to put this differently.

1) When we did the big trip, the AP was not really needed. We were merely testing systems.
2) I did not experience this type of event in this particular boat. Maybe it doesn't have that issue.
3) If it happens as the other guy said, it should be investigated. Although he put it as a normal thing to happen.
4) We shall see in the future what happens with my boat. I think the Mangusta story is a success case anyway, so the stuff they're made of is good. Anyway, as previously suggested, BCS/Arneson and Simrad are not trademarks of Mangusta. I think, Pershing, Baia, Leopard, Itama, Sunseeker, Jaguar and probably Magnum to name most, all use the same systems. So if there is a hardware issue with this one, the others must have the same type of issues. But I can't see anybody giving out so much info on their boats and attitudes on the web.
5) I think this thread is about the interest in the purchase of a Mangusta 72, and the possible drawbacks of ASDs. So maybe we should not veer away from the subject by dwelling into details that can hardly be scientifically answered at this stage.
Alternatively, if ASDs are a pain, there used to be an AB Yachts with 75 feet. That was called the Follio 72. A nice boat with Hamilton Jets and CAT engines. But a bit older.
Good luck.

Well, what you're describing is not a drawback of ASD's. They may not track as well as some, but it's not a normal characteristic of them when using Simrad autopilots to suddenly veer 90 degrees. That is being characterized in this thread as a normal issue and it isn't. The reason you don't read about it all over the place is it doesn't happen to all these boats mentioned normally. You're the one spreading the rumor from hearsay.

We installed a Simrad AP-25 with virtual rru to replace a Robertson that came with the boat originally.

One of the challenges in an autopilot installation on Arneson Drive equipped boats is that there is no easy way to tell an autopilot what the "rudder position" is. The virtual rru eliminates the need for rudder feedback to the pilot, the pilot actually "learns" the characteristics of the boat and gets better and better as time goes on. It did a great job for us at anything above planing speeds, but couldn't hold a line in displacement mode.

With that being said, the only time we used the autopilot was on offshore deliveries to reduce fatigue for the helmsman. The helm was NEVER unmanned, even for a few seconds.

I believe it is the same, AP-25. I will check when possible.

You need a software update for your Simrad.

This was a common problem with Simrad autopilots and had nothing to do with the type of propulsion installed.

I did encounter a problem with a new Simrand fitted to a shaft drive Cayman 58 which used to go zig-zaging at anything below twelve knots.
Fixed this year with the update.

Other similar updates are one I had on an old Raymarine on a small Atlantis 42 which had the same problem and needed a rudder sensor to improve at slow speeds.

As for surface drives I sold a Pershing 52 which goes well with a new 2014 Raymarine system but with the old set up from 2001 had the same problem AGP22 encountered.

I am not an Autopilot technician but these are problems I remember out of my head. Both our local Raymarine and Simrad techs are friend and clever so when I meet them I will try to ask some feedback from there side.

Liam, you and Kilbride are verifying what I'm saying. It's not an Arneson issue. It's simply poorly set up or performing Autopilots that need to be fixed or adjusted and adapted properly to the installation.

That's what I thought.

Anyway, in an attempt to provide the info initially requested by the thread starter, I don't know what issues arise with MANs that power M72s if you sail at 12 or 15 kts for a long while.

As far as keeping a straight line, the M80 does it fine at these speeds as long as you are on it, and if you can adjust the MTUs so as to keep all turbos on, pressures, load and temps within limits, you should be fine for a good while.

12 or 15 knots is a really bad speed to run it though. You really would want to run slower or faster. At 12-15 knots it's going to be well below plane and beyond hull speed and just not a good speed for that boat. Probably can stay on plane around 17-20 knots although might have to go a bit faster to plane and then pull it back. So either a bit faster or just pull back to idle speed.

It's not an engine problem, but it's a drive and design issue that limits the feasibility of running at in between speeds.

There are quite a few tests of Mangusta's and Pershing's online although not for that specific boat, but for someone not familiar with surface drives, I'd recommend looking at them. Most of the ICW one could run 17-25 knots and be fine. Obviously with all the no wake zones in South Florida that's not something one can do.

I'm not familiar with the ICW. Are there very long no-wake zones ?

Not long in Palm Beach and Broward counties, just over 30 of them. Longer in Miami-Dade. Those are the three counties of the area.

Any planning hull 72' boat is going to be at maximum plow at 15 knots, bow pointed at the sky, burning a ton of fuel. And an Arneson boat will be cavitating like crazy. Either run 10-12 knots (whichever it likes) and 26 knots or better.

On the M80 I guess so, but you can do the adjusting with the foot on the tiller, AP style inputs. I did it standing up on the helm. For close to two hours.

As previously mentioned, we were on tall and long waves for close to two hours at avg 14kts. I can't recall the fuel burn, and it was obviously not the ideal one. But perfectly manageable within the general average. Also I'm not sure of the boat's pitch during that sector (I don't remember it being that bad of an angle). But it can be done for quite a while without killing the engines or exhausts at it and that is the point I wanted to get across.

It's an AP20 and J300X junction box. The rest is already mentioned here.

Humphrees do help them ride better and they provide stern lift. BUT, Arneson boats DON'T have an issue with tracking. I've run several and they all run straight at cruise, slower speeds etc. Fins don't generally work well with surface drive boats......they would steer them all over the place.

Each one does react differently though. Most take a lot of skill in docking because bumping one engine in forward for 2 seconds and the boat jumps 20'. Reverse has very little thrust, so it takes a long time to recover the length you just went forward. Each boat is unique. Some are pretty good at docking, some are pretty good at all RPM's although generally it's hull speed or on plane/cruise, in between it's just a whole lot of caviation. Others, not so much.....Arnesons are made to go fast. Very efficient, one of the ones I manage has 1% prop slip at cruise.