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Old 09-16-2016, 08:47 PM   #21
Join Date: Aug 2012
Posts: 9
Hey K Reman---
The Mainship I is a great boat, Easy to work on, economical to run, but is is the Chevy, not the the Cadillac of trawlers. It's still a semi displacement hull doing 7-8 knots economically, but being that, she does get tossed a bit in a following sea. Mine hasn't let me down in the 21 years I've owned her! As was said before, their owners love her, and they are truly worthy of the owners attention. Look to spend under 50k for a great example.

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Old 09-17-2016, 06:47 AM   #22
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City: Fort Pierce
Country: USA
Vessel Name: Florita Ann
Vessel Model: 1982 Present
Join Date: May 2014
Posts: 1,630
I think the prop and rudder being so far forward begs for at least 4" more to be welded on to the backside would help a great deal in handling. There is an articulating rudder kit available, for a cool $5k+. I thought not for me.

To any interested party, I have a 21x21 RH 1 1/2" bore balanced and tuned fresh prop, the right one for a MK I with a 250-280 Cummins. Need a bushing to drop it to 1 3/8" shaft. Make ya a deal. It was slightly over propped insofar with a 250hp I got 2450 RPM with 2600 being proper.

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Old 09-17-2016, 09:17 AM   #23
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City: Owings, Md
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Join Date: Jan 2016
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Originally Posted by jleonard View Post
I did not use a QSB, I did my repower in 2000 (pre QSB) and used a Cummins 6BTA at 270 hp.
I could cruise at an honest 15.5 knots but usually ran at around 12. I worked quite a bit with Tony A on boatdiesel, and he suggested long term cruising at approx. 1 bar of boost pressure for longevity so that's about where my boat ran. 1900/2000 rpm, 11.5/12 knots.
The boat would do 18.5 at WOT but as you know those boats get squirrelly at 16 knots due to the hull design. It's not the bow, it's the rest of the hull once the boat leans just a little one way or another. Even the huge trims tabs I had did not stop this effect.
I did document the process somewhat via a summary, but did not take many pictures.

In the 6BTA series, I would have gained nothing by upping to the 315 hp which was the next level up at the time. The 270 and 315 share the identical power curve, except the 315 adds 200 rpm at rated. So I would not have gained cruise speed only top end which really means little.
Thanks, that is really interesting.
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Old 09-19-2016, 07:39 AM   #24
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Originally Posted by Baker View Post
I think you would have "gained" a seawater aftercooler versus a coolant loop aftercooler.....if my memory serves me correctly.

It serves you correctly and that would have meant more maintenance. That was one of the factors in my decision to go with the 270. I have a friend who is a bus mechanic and there are tons of busses out there with 6BTAs and that coolant loop aftercooler and they require almost nothing for maintenance.
I also had a boating buddy with a sister ship who had repowered with a 275 HP Perkins and I knew exactly what to expect for performance.

Jay Leonard
Attitude Adjustment
40 Albin
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