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Old 03-27-2018, 07:31 PM   #1
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8mph 8mph 8mph

My new to me 1982 Marine trader cruises at 8MPH. My friends Prairie 29 cruises at 8MPH. Several of the Trawlers I looked at in my search cruised at 8MPH. Many larger Trawlers I saw advertised said 8MPH--- these ranged from 36ft to 46ft. A K-K42 said 8MPH. I come from the sailing world where longer waterline means higher cruising speed. This does not seem to be true in the Trawler world. The mysterious 8MPH.
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Old 03-27-2018, 07:38 PM   #2
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I cruise at 7 mph, 34 foot wayerline on a 40 foot trawler...

Don't worry.... a lot more experience and you will figure it out.
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Old 03-27-2018, 07:52 PM   #3
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I don't cruise at 8 mph, I cruise at 7 knots, but then I'm not land locked.

You can certainly go faster if you're prepared for the fuel burn. I burn:

6 knots 1.3 GPH
7 knots 2.0 GPH
8 knots 3.7 GPH

Burning 85% more fuel to go from 7 to 8 knots isn't worth it to me.

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Old 03-27-2018, 08:01 PM   #4
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Many people, me included, say 8 knots because it is easier than saying 7.2 or 7.6 or 8.3.

In most cases 8 knot is good enough unless there is a specific reason for being picky such as fuel use comparsions which I have also done and apparently so has O.C. Diver.

The rule about w/l length does stand although modified somewhat sometimes for power boats depending upon planing, semi planing, full displacement..
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Old 03-27-2018, 08:08 PM   #5
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Many people, me included, say 8 knots because it is easier than saying 7.2 or 7.6 or 8.3.
+1. Saying 8 kts is usually implying a range close to that speed, in my experience anyway.
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Old 03-27-2018, 08:30 PM   #6
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I travel at 8 knots = 1800 rpms. It’s Southerlys sweet spot! 36ft. Waterline 42 ft. Overall.
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Old 03-27-2018, 08:33 PM   #7
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I think length may play into it .mine seems to be like oc's but 1/2 to 3/4 knot slower at each burn rate.
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Old 03-27-2018, 09:05 PM   #8
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I usually speak in knots when discussing vessel speed, but find I have to give a commensurate mph number when speaking to non-boaters.
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Old 03-27-2018, 09:33 PM   #9
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If you cruise at 7 knots it’s 8 mph. At about 8 knots (7.82) it works out to 9 mph. Easy math to remember.
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Old 03-27-2018, 09:41 PM   #10
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7.8 mph or 6.8 kts is where IL likes to run. You get used to it or not.
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Old 03-27-2018, 11:32 PM   #11
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I usually speak in knots when discussing vessel speed, but find I have to give a commensurate mph number when speaking to non-boaters.
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Old 03-28-2018, 12:47 AM   #12
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ASD normally cruises a 8.6kts (10mph) unless I am making the trip from Neah Bay To Astoria (or the other way) at 15kts (17mph). You tend to see more things at 8kts.......
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Old 03-28-2018, 01:07 AM   #13
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My maximum speed is eight statute miles an hour (7 knots). A wasteful speed, so cruise at a knot less.
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Old 03-28-2018, 01:08 AM   #14
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7.5 to 8 knots and no wash for us at 1150rpm on 60ft.
Faster with tide and slower pushing it.

8 knots on shorter boats will be pushing water and burning extra fuel.
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Old 03-28-2018, 01:11 AM   #15
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I travel at 8 knots = 1800 rpms. Itís Southerlys sweet spot! 36ft. Waterline 42 ft. Overall.
What indicates it as the sweet spot?
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Old 03-28-2018, 01:12 AM   #16
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I usually speak in knots when discussing vessel speed, but find I have to give a commensurate mph number when speaking to non-boaters.
You speak to non boat people?
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Old 03-28-2018, 01:15 AM   #17
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Letís be honest for a moment. If somebody seems in a hurry, Iíll tell them 9knots, maybe even ten if I want to appear as a speed demon. Someone taking it easy Iíll say 8. If they ask whether I mean miles per hour, Iíll say yes. Itís so much more polite than appearing smug and I say I donít care. Truth is that not only do I not really care, I often donít even know.

Reality is that I push the throttles forward until the engines make a sound that matches my mood. Which usually translates to about 1400 rpm, give or take. If I do give or take, I give or take from the port engine because itís throttle lever is a bit smoother.

No, but really, we get there when we get there. Only days I pay closer attention is when I need to make slack. In which case I go early to not miss it, get there early and usually run it early anyway, cause who wants to wait.

So yeah, I go 8 too.

Its really funny after awhile how little the exact speed seems to matter. Itís like asking what time it is. I donít know that either. I have a vague sense of what meal we are closest to and that also becomes the exact time, such as ďa little before our mid morning snackĒ.
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Old 03-28-2018, 01:18 AM   #18
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You speak to non boat people?
Dirt Dwellers.....
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Old 03-28-2018, 01:29 AM   #19
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We were dirt hotelers recently in Astoria. I pulled up ship finder and saw some boat named Alaskan Sea Duction on AIS just up river. You should reach out to them having a similar boat name and all.
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Old 03-28-2018, 06:55 AM   #20
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Inshore charts are frequently in statute miles , so planning in statute miles is less work.
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