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Old 12-13-2021, 01:46 PM   #21
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Turbo and RPM (speed)
Every couple of hours open up the throttle to exercise the turbo under load.
"They" tell us prior to shutting down the engine, increase the speed (RPM).
I would also suggest, once docked, idle the engine a bit to cool down the turbo.
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Old 12-13-2021, 03:04 PM   #22
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Like everyone else, I have an opinion, right or wrong because I don't have any experience with that particular boat. Firstly, LWL is likely less than 34' on a 34' boat, but that's a separate issue. If you want best fuel economy, stay a little below hull speed. However if you want to go fast and can get on plane, I think you will get better mpg at higher RPMs. Again I am assuming you can plane. At 8.5 knts you are likely barely planing and not very efficient. If your boat does plane, the engine is more efficient at 3000 rpm than 2400 and you will get better mpg. "Generally" if you look at tables for turbo diesels with a planing hull you will see best mpg around 80% of max RPM (unless you are below hull speed).
There are two misconceptions presented in this post:

1. Very, very few boats increase mpg as they go faster. The 34T sure isn't one of them.

2. At 8.5 kts the 34T isn't planing. It really doesn't plane in the true sense, but the wake and bow wave do smooth out at about 12 kts which is what I would consider as planing for that hull. Below 12 kts down to about 10 kts you are pushing the bow wave and climbing "over the hump".

And yes, I owned a 34T so I have some basis for this position.

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Old 12-13-2021, 03:15 PM   #23
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1. Very, very few boats increase mpg as they go faster. The 34T sure isn't one of them.

Agreed. The only boats that tend to get better mpg on plane are relatively light weight, high powered planing hulls (that are very efficient on plane) with gas engines, where the huge drop in engine efficiency at light load out-weighs the worse drag from going faster.
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Old 12-13-2021, 03:44 PM   #24
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The AT 34 has an OAL of 34'5" and a WLL of 32'6" so unless you have a swim platform the size of a dance floor, just subtract about 2 feet from your OAL and you will be real close to WLL. I have used that 'estimate' for years and I have always been real close.

Soooo, take 2 feet off OAL (interior space) and ignore the swim platform.
IF you doubt my word, go to an overnight slip and tell the harbor master, you have no idea what the OAL is and he will grudgingly come out and measure it for you. LOL
I always tell them, it is documented as 34ft and they are happy.
Oops, I forgot to include the 2 ft overhang of the dingy.

The new AT34s are sold as AT36 (same hull), including the swim platform. So I am moving up in the boating world... I now drive a 38ft AT OAL.
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Old 12-13-2021, 03:46 PM   #25
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The AT 34 has an OAL of 34'5" and a WLL of 32'6" so unless you have a swim platform the size of a dance floor, just subtract about 2 feet from your OAL and you will be real close to WLL. I have used that 'estimate' for years and I have always been real close.

Soooo, take 2 feet off OAL (interior space) and ignore the swim platform.
IF you doubt my word, go to an overnight slip and tell the harbor master, you have no idea what the OAL is and he will grudgingly come out and measure it for you. LOL
I always tell them, it is documented as 34ft and they are happy.
Oops, I forgot to include the 2 ft overhang of the dingy.

The new AT34s are sold as AT36 (same hull), including the swim platform. So I am moving up in the boating world... I now drive a 38ft AT OAL.

It depends a lot on how much overhang you have in the hull design. My "38" foot boat (manufacturer listed LOA which excludes the bolt on pulpit and swim platform) only has a 33'6" waterline. Add the platform and pulpit and the LOA is up to 42'4".
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Old 12-13-2021, 03:52 PM   #26
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It depends a lot on how much overhang you have in the hull design. My "38" foot boat (manufacturer listed LOA which excludes the bolt on pulpit and swim platform) only has a 33'6" waterline. Add the platform and pulpit and the LOA is up to 42'4".
Dont tell the harbormaster but when you are at the bar, or with your relatives you can brag about you 42 ft boat. LOL

I added a swim platform to my N46 and presto, I was driving a 49 ft boat.

Oops again, the N46 also had a RIB overhang so maybe I had a 50 of 51 ft boat. Who was I going to impress, I don't go to bars.
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Old 12-13-2021, 03:58 PM   #27
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Dont tell the harbormaster but when you are at the bar, or with your relatives you can brag about you 42 ft boat. LOL

I added a swim platform to my N46 and presto, I had a 49 ft boat.

I generally take the attitude of "the manufacturer says the boat is 38 feet (plus dinghy and davits once I add those), but if you'd like to measure, feel free"
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Old 12-13-2021, 04:03 PM   #28
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I generally take the attitude of "the manufacturer says the boat is 38 feet (plus dinghy and davits once I add those), but if you'd like to measure, feel free"
I have never 'thrown in' the measurement for the bow pulpit nor the RIB overhang.
The only 2 people who might be interested in the 'true OAL' are the harbormaster and the tax man. Or maybe the sweet young lady at the bar.
(gravelly old man voice, "Hey there little girl, wanna come see my boat?"
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Old 12-13-2021, 04:42 PM   #29
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Good one Dan...

Regarding my preious post note that i did say "if you are on plane". Boats such as mine, and Back Coves and Sabres and the like, get the same or slightly better mpg at higher speeds when on plane (up to a certain RPM). Note that I am talking mpg not gph. All very dependent on the particular boat and many other factors, the fuel cost to go from 12 knts to 16 knts for example can be negligible or even slightly favorable if the engine is operating at a more efficient rpm.
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Old 12-13-2021, 07:12 PM   #30
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Good one Dan...

Regarding my preious post note that i did say "if you are on plane". Boats such as mine, and Back Coves and Sabres and the like, get the same or slightly better mpg at higher speeds when on plane (up to a certain RPM). Note that I am talking mpg not gph. All very dependent on the particular boat and many other factors, the fuel cost to go from 12 knts to 16 knts for example can be negligible or even slightly favorable if the engine is operating at a more efficient rpm.
Planing will be more efficient than plowing. But if you compare planing to an efficient slow cruise of say 6.5 kts, slow will produce better mpg. On my boat, mpg at 6.5 - 7 kts is more than double what it gets on plane at 17 - 18.
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Old 12-13-2021, 07:20 PM   #31
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I have two of these engines. They will be happy running at that RPM all day. You many not be as happy with the fuel economy as you would be at lower speeds.
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Old 12-13-2021, 07:37 PM   #32
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IF you have 2 engines you gotta sync them....
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Old 12-13-2021, 09:10 PM   #33
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...I added a swim platform to my N46 and presto, I was driving a 49 ft boat...
I really want to be eligible to join the Boat International owners club so I can hang out with outrageously rich people who wear white pants and navy blue blazers and ascots, but the eligibility for that club is a boat that's 24 meters or 78.7 feet. Somehow I need to figure out how to extend my 40' LOA by 38.7 more feet. Has crossed my mind to paint a big red 36" diameter "H" inside a circle on my bow and then use a drone to take what looks like high altitude shot of my helipad, but they'll probably see through it.
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Old 12-13-2021, 10:59 PM   #34
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I got a little sideways with the harbor master in our marina over my length. Like many I have a so called 34 CHB, a Puget Trawler. But from end to end with pulpit and swim step and the dinghy against the transom I was too long for my slip at 37', rear end into the fairway which for a time at least was a huge problem for some reason.
Not so much now but I moved into a longer, more expensive slip so I could avoid the issue altogether.
The 34 CHB is almost 34 on the waterline.
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Old 12-14-2021, 03:55 AM   #35
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I really want to be eligible to join the Boat International owners club so I can hang out with outrageously rich people who wear white pants and navy blue blazers and ascots, but the eligibility for that club is a boat that's 24 meters or 78.7 feet. Somehow I need to figure out how to extend my 40' LOA by 38.7 more feet. Has crossed my mind to paint a big red 36" diameter "H" inside a circle on my bow and then use a drone to take what looks like high altitude shot of my helipad, but they'll probably see through it.
I have a very difficult impressing me.
I sure dont want to waste my life impressing others.

I'm finished, back to the program already in progress.
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Old 12-14-2021, 08:44 AM   #36
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Planing will be more efficient than plowing. But if you compare planing to an efficient slow cruise of say 6.5 kts, slow will produce better mpg. On my boat, mpg at 6.5 - 7 kts is more than double what it gets on plane at 17 - 18.
Of course that is true. My reply started around the post about a 34' boat running at 10 knots. My guess, that is not very effcient and not worth the extra fuel to go a little faster than hull speed.
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Old 12-14-2021, 08:49 AM   #37
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I got a little sideways with the harbor master in our marina over my length. Like many I have a so called 34 CHB, a Puget Trawler. But from end to end with pulpit and swim step and the dinghy against the transom I was too long for my slip at 37', rear end into the fairway which for a time at least was a huge problem for some reason.
Not so much now but I moved into a longer, more expensive slip so I could avoid the issue altogether.
The 34 CHB is almost 34 on the waterline.
Whether we like it or not, marinas are only interested in LOA and clearly state that includes any projections including swim platforms and bow pulpits. Many of us subtract those when we can away with it, but don't blame the harbor master if your 34 footer is really 38' or more.
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Old 12-14-2021, 09:01 AM   #38
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Of course that is true. My reply started around the post about a 34' boat running at 10 knots. My guess, that is not very effcient and not worth the extra fuel to go a little faster than hull speed.
That sort of depends on the next refueling dock and the credit limit on your bank card
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Old 12-14-2021, 09:15 AM   #39
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That sort of depends on the next refueling dock and the credit limit on your bank card
True. If you want to double your fuel cost to gain 2 knots, you are free to do so.
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Old 12-14-2021, 10:06 AM   #40
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Certainly the boat is happy cruising at 2200 RPMs. Is it fuel efficient? No! What is more important to you, fuel efficiency or time? I am not very sensitive to being fuel efficient so I would be happy with what you are doing. The boat probably rides better at 8.5kts than it would at 7kts.
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My old single diesel 32 Halvorsen's sweet spot was 2000 & 8.4 knots.
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