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Old 02-09-2020, 05:13 PM   #1
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'04 Mainship 400 Speeds and RPM with Single Yanmar 370hp?

Would anyone with the Mainship 400 with the single Yanmar 370hp please share your speeds and RPM (GPH if you have it). Mine seem a little off from what I have seen online such as the Stella Blue site (http://www.scyr.org/stellablue/specifications.html)

Also before you ask. I have:
New Bottom.
New Shaft and coupler.
New PSS shaft seal.
New cutlass.
New Motor mounts.
New Trim Tabs.
Prop was sent in and trued.
Diesel is running fine all the way to WOT no overheating etc.
Thanks,
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Old 02-09-2020, 09:22 PM   #2
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Kent
Have you verified that your prop is the same as Steve (Stella Blue)?
I can't provide any meaningful data as pur MS is a 34. I can say that Steve is very thorough and has put a lot of effort into documenting his prior boat. I have communicated with him and found him helpful and more than willing to share.
Are you reaching wot rpm spec?
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Old 02-10-2020, 02:02 PM   #3
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For what it's worth I found this online...
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Old 02-10-2020, 02:18 PM   #4
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I am reaching wide open throttle at 3600-3700. I have had tach photo gauged up to 2000 rpm (at the dock) and both helms are off only 100 RPM plus or minus.

Good question about Stella Blues prop vs mine but I have what I was told standard prop was what I have 5 blade 26R by 19.5 pitch. I will see if I can ask Steve what his prop was.

Previous owner did damage prop and didn't have it repaired correctly. My prop shop did but told me there was no way they could get the pitch to 19.5. At best he said it was pitched to 18.5. Now maybe that makes a little difference but I seem to be off a knot or two.

The speeds in the table one of you provided is what I am going by. Same ones Steve had on Stella Blue site.
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Old 02-10-2020, 03:06 PM   #5
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Since you have the Yanmar 370 and not the 440 hp engine, even allowing for 185 off of your wot numbers for tach error (1.85 *100 due to the rpm being higher than the 2,000 rpm your error is based on) you are propped a little high.

Splitting the difference at 3,650 rpm and subtracting 185 gives 3,465 adjusted rpm at wot. That is maybe 100 rpm high. But propping down a hundred rpm isn't going to change much.

The figures reported above are Yanmar measured values and are based on a pristine bottom and prop and very little added weight and are a bit high, at least that is my observation with two Mainships against similar Yanmar data.

All in all you should burn about 3-4 gph at 7 kts.

David
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Old 02-10-2020, 03:20 PM   #6
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Also note on weight. I have very little on the boat. No dingy mounted. 1/4 tank of fuel.
Bottom and all running gear is fresh. Just put back in the water.
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Old 02-10-2020, 04:17 PM   #7
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I guess those figures for Stella Blue seem about right, considering hull weight and length, and bottom configuration.

You appear to be more than a little over on wide open RPM (but better to be a little high than a little low).

Our boat has twin Yanmar 370's. We are 42 feet, 40,000 lbs, with a deep v hull.

Our top speed is about 16 knots at 3400 rpm with a clean bottom. If we want to make some time, we generally cruise up on plane, at around 13-14 knots at about 2900-3100 RPM.

Otherwise, we just mosey along at about 1200 rpm and about 8 knots (or even slower), with occasional carbon burning runs.
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