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Old 08-29-2016, 06:17 AM   #141
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Lepke - I agree with you on the maintenance issues but not sure about your statements on fuel consumption. ("The high hp turbo version of the same engine burns up to 30 gallons an hour at full power and 2.5x hp. The 12v71 natural (non-turbo) burns about 12 gallons an hour at about the same hp as the turbo 671.") At http://boatdiesel.com/Engines/Engine...-4&SC=1366.768
I found that the 671M burns 6 gal/hr at 80hp and the 671TI burns 5 gal/hr at 80hp both at 1400 rpm and I took the data from the prop hp curves. So the turbo does burn about 20% more fuel than the non turbo but not twice the fuel.

I believe that in the case of 4 stroke diesels (at least some) the turbo charged version gets a little better fuel consumption. I'll check the data sheets and post when I get more time.

Happy cruising - -
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Old 08-29-2016, 10:12 PM   #142
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Planing boat, light compared to a trawler, twin diesel 370hp stern drives.

Sweet spot: 1300 rpm, 8 knots, 3.5 gph.

Go fast: 2800 rpm, 23 knots, 26 gph.

Just got back this afternoon from a three day trip and did 80% of the trip at trawler speed.

And where did our warm water go? A very different summer than last year. I miss the El Niño.
How effective is an autopilot at trawler speeds on you boat?
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Old 08-29-2016, 10:34 PM   #143
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How effective is an autopilot at trawler speeds on you boat?
For an autopilot to be effective at very different speeds and even in different conditions, you need to fully learn all the capabilities of the one you have and the adjustments. You may need the sensitivity set very different at 8 knots vs. 25 knots. When it impacts you more at trawler speeds is in non-calm conditions. On plane you just power through in a straight line. At trawler speeds you can tend to waddle through. Also if the waves are from your stern, then at planing speed you're running fast enough that they don't hit you, while at trawler speed they may. You may have to adjust speed down or up and the autopilot sensitivity.

I recommend practicing with all your autopilot can do. Many just set it one way and never adjust it. Some have more capabilities and flexibility than others.
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Old 08-30-2016, 08:29 PM   #144
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How effective is an autopilot at trawler speeds on you boat?
Just went from Charlevoix MI to Port Huron MI ~320 miles. At 1200 RPM/6.2 Knots my auto Pilot worked very well. The PO had done the setup. We had 2' to 3' quartering seas off the bow one day and 6' following seas the next. Auto Pilot held a steady course both days.
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Old 08-30-2016, 08:43 PM   #145
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Old 08-30-2016, 10:21 PM   #146
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Just went from Charlevoix MI to Port Huron MI ~320 miles. At 1200 RPM/6.2 Knots my auto Pilot worked very well. The PO had done the setup. We had 2' to 3' quartering seas off the bow one day and 6' following seas the next. Auto Pilot held a steady course both days.
I have no doubts about Grand Banks steering ability at displacement speeds. It is 25-30 knot hulls with tiny deflectors instead of rudders that I am wondering how they manage at low speeds without having to constantly pull the throttle.
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Old 08-30-2016, 10:25 PM   #147
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I have no doubts about Grand Banks steering ability at displacement speeds. It is 25-30 knot hulls with tiny deflectors instead of rudders that I am wondering how they manage at low speeds without having to constantly pull the throttle.
I have one of those. And the answer is....not very well!!! Granted...the P29 in my signature also had a "deflector" and not much of a rudder. But it did okay!!!
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Old 08-30-2016, 10:27 PM   #148
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I have one of those. And the answer is....not very well!!! Granted...the P29 in my signature also had a "deflector" and not much of a rudder. But it did okay!!!
Interesting. Is there a systematic reason why some deflectors are better than others?
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Old 08-30-2016, 10:32 PM   #149
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Interesting. Is there a systematic reason why some deflectors are better than others?
Nope...pure physics!!! That P29 I referenced was a single engine with a ton of windage. It made me a better boat handler. But why they are that way????...I guess it is just the way they build them!!!
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Old 08-30-2016, 10:37 PM   #150
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So, is it safe to say that the class of boats that includes Carvers and Sea Rays cannot be trusted with an autopilot maintaining a course in moderate conditions at 6-7 knots?
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Old 08-30-2016, 10:49 PM   #151
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So, is it safe to say that the class of boats that includes Carvers and Sea Rays cannot be trusted with an autopilot maintaining a course in moderate conditions at 6-7 knots?
I don't think that is a fair assessment. I do not have an autopilot. But I do know that the most current generation of autopilots do an exceptional job of maintaining course regardless of speed and hull configuration. So take that FWIW....obviously not much. But I don't think an autopilot would have much issue with holding a course on my boat.

Feel free to ask more direct questions because I feel your are kind of beating around the bush???
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Old 08-31-2016, 04:54 AM   #152
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Better autopilots have a speed input or have manual selection for high and low speed. My boat would do 14 to 16 knots with the original motor and displacement cruise 6 to 8 knots. Parameters are very different for those 2 ranges. The Robertson (Simrad) AP20 has a high and low speed selector and 2 sets of programmable parameters. It took a little while, but my boat now tracks like it's on rails at 7 knots. Autopilots are one of those instruments where user fine tuning is everything.

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Old 08-31-2016, 06:01 AM   #153
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Correction on turbo vs naturally assperrated engines

Quote:
Originally Posted by DonF View Post
Lepke - I agree with you on the maintenance issues but not sure about your statements on fuel consumption. ("The high hp turbo version of the same engine burns up to 30 gallons an hour at full power and 2.5x hp. The 12v71 natural (non-turbo) burns about 12 gallons an hour at about the same hp as the turbo 671.") At http://boatdiesel.com/Engines/Engine...-4&SC=1366.768
I found that the 671M burns 6 gal/hr at 80hp and the 671TI burns 5 gal/hr at 80hp both at 1400 rpm and I took the data from the prop hp curves. So the turbo does burn about 20% more fuel than the non turbo but not twice the fuel.

I believe that in the case of 4 stroke diesels (at least some) the turbo charged version gets a little better fuel consumption. I'll check the data sheets and post when I get more time.

Happy cruising - -
Looking more closely at the plots it appears that they both burn about the same amount of fuel for a given HP. If there is any difference it will probably be with in the error bands of the data. As said above I used data sheet from Boatdiesel.com.

I apologize for posting the incorrect info.

Don
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Old 08-31-2016, 07:41 AM   #154
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So, is it safe to say that the class of boats that includes Carvers and Sea Rays cannot be trusted with an autopilot maintaining a course in moderate conditions at 6-7 knots?
Not at all. We have a Meridian 459 which will cruise at 20 knots but 90% of the time we cruise at 7 knots. The Raymarine ST6001 autopilot does a sterling job in heading hold or tracking a course through the chart plotter at anything above 5 knots.

I have found the sweet spot for best economy for us with twin 6bta's is 1200 rpm on both engines equals 98 hp using the torque curve and that gives us 7 knots and 12 to 14 litres per hour depending on the sea conditions. Haven't try single engine cruise yet.
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Old 08-31-2016, 07:47 AM   #155
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Feel free to ask more direct questions because I feel your are kind of beating around the bush???
I will, thank you. Should probably start another thread.
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Old 08-31-2016, 07:59 AM   #156
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So, is it safe to say that the class of boats that includes Carvers and Sea Rays cannot be trusted with an autopilot maintaining a course in moderate conditions at 6-7 knots?

I don't think so. Our boat would be in that "class" and our autopilot (Furuno Navpilot 511) tracks well at 2.5 kts (our trolling speed), at 7-8 kts (our "trawler" speed) and anywhere between 15-24 kits (planing speeds).

There was a set-up and training regime, installer did most of that before we did sea trials and final "training" -- but otherwise it didn't seem like anything special was required.

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Old 08-31-2016, 09:23 AM   #157
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So, is it safe to say that the class of boats that includes Carvers and Sea Rays cannot be trusted with an autopilot maintaining a course in moderate conditions at 6-7 knots?
No, not only is it not safe to assume, that's a totally erroneous assumption. Autopilots have adjustments and can be tuned for conditions. in fact, the autopilot, properly adjusted, will maintain the course far better than one can manually.
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Old 08-31-2016, 09:27 AM   #158
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No, not only is it not safe to assume, that's a totally erroneous assumption. Autopilots have adjustments and can be tuned for conditions. in fact, the autopilot, properly adjusted, will maintain the course far better than one can manually.
Even a poorly adjusted autopilot can keep a better course than I can...something to do with A.D.D I assume...
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Old 08-31-2016, 09:52 AM   #159
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Even a poorly adjusted autopilot can keep a better course than I can...something to do with A.D.D I assume...
Bruce
I don't know if you've ever watched auto racing, but looking at the drivers in the cars, you'll see one whose turning of the wheel is so smooth and another who seems to be moving it back and forth every second. I think that's how many of us are manually steering, as we'll overcompensate and try to be too fine and precise. Now, I've also known people to set their autopilots like that and work them to death.
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Old 08-31-2016, 10:17 AM   #160
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You must be listening to some salesman. Boat brands are not that important. Not all Hatteras or KKs are good and not all Bayliners Are bad.
My Carver was heavily built and the AP worked well at all speeds even on one engine.
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