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Old 10-02-2018, 07:28 PM   #1
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Experienced boater, rookie Trawler

Ok wrote this long winded post about my project. But don't know what became of it. So.
1. I have no power. Cost of rebuilt Perkins diesel 165hp 256 ft lbs of torque was going for 14k with 1.9:1 gear.
2. I already owned a low hours 6.5 optimizer that needed a marine adaptation which is already well underway.
3. HP is 6.5 Optimizer is 190hp 385 ft lbs of torque , I am going with a borg warner 1:1. while built on the Detroit 6.5 platform the optimizer was recast by AM general to eliminate the overheating and head and cylinder cracking. I chose to go naturally aspirated to eliminate complications.

Where are my potential issues at?
1. Physically this will fit.
2. At765lbs it's weight to HP is great and lighter than original.
3. I already owned it. and the motors have been used in trawlers before. 28 AlbinTE.

What questions do you have. What suggestions do you have? Has anyone ever done this? Go from a straight 6 diesel to a V8 diesel. The famous words what could possibly go wrong.

So I own and still own an outboard 24 ft 60 plus mph offshore performance boat.
I have owned I/O before and hate them. So unfriendly. And I’ve owned jet boats. My new to me boat is a 1978 Mainship Trawler MK1

I have never owned a straight inboard or diesel boat new I chartered territory for me. I have figured out and sourced all things for this motor. And have the 1:1 gear but am unclear. So I’m here, picking the minds of the veterans.
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Old 10-02-2018, 08:41 PM   #2
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I can't add anything constructive as of yet. Most was said in your intro thread about the conversion being very involved.



Now I'm along for the ride.


BTW, I like Mercruiser I/Os, but only them, because I grew up working on them in the 80s and 90's. The rest can go away now.
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Old 10-02-2018, 10:49 PM   #3
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I'm not overly familiar with the Optimizer, but I hear there have been many different variants which have improved considerably over the early models.

Izzy, I'm wondering what the rated rpm is on your Optimizer. Some were 3600 rpm which may not suit a 1:1 gearbox on a heavy boat like a trawler. It seems to me that it would be considerably overpropped with anything but a very flat prop with minimal pitch. This may not be very efficient.

I would think a 2.5 or 3:1 may be more suitable, but it would be worth speaking to a good prop shop about it.
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Old 10-03-2018, 07:00 AM   #4
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The 1:1 gearbox is a good choice for something light like a skiboat. The Boatdiesel calculators should be helpful. The goal is for the engine to reach rated WOT rpm with an efficient prop. My guess would be 2.57:1.
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Old 10-03-2018, 05:26 PM   #5
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The prop diameter is limited to 20" on that boat. Some may have gone to a 21" but that's pushing it. I'd expect a reduction gear of around 2:1 would be about right given that constraint. Original boat had 2.1:1 with the Perkins 165.
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Old 10-03-2018, 07:36 PM   #6
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The prop diameter is limited to 20" on that boat. Some may have gone to a 21" but that's pushing it. I'd expect a reduction gear of around 2:1 would be about right given that constraint. Original boat had 2.1:1 with the Perkins 165.

That's good info. Draft must be around 36 to 40 inches loaded.
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Old 10-03-2018, 07:46 PM   #7
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Has a normal draft of 2ft 10 in. I imagine with 750lbs less motor I should gain some draft.
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Old 10-03-2018, 08:09 PM   #8
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Has a normal draft of 2ft 10 in. I imagine with 750lbs less motor I should gain some draft.
I was about right. With less weight, that means more goodies can be added without affecting the draft.


I say more tankage for fresh and waste water. More fuel tanks.



Lets do the loop nonstop.
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Old 10-03-2018, 08:26 PM   #9
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I’m dealing with a Repower and your focused on “goodies” unbelievable! Focus! Hahahhhahah
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Old 10-04-2018, 06:31 AM   #10
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With a 1:1 gear ratio and a 20 inch prop you will likely get vibration in the hull directly above the prop.
I went thru a repower several years ago with a 78 M1. I used a 1.5 ratio and got the vibration that was expected. Easily solved if you can do some simple fiberglass work.

I repowered with a Cummins 270 hp, but I do know of a person who repowered with a Cummins 210 hp and a 1.5 ratio. He ended up running a 20 x 16 prop if memory serves me. He had vibration and I'm not sure if he dealt with it or not.

I posted in the past what I did for the fix, if you can't find it in the archives send me a PM with your e address so I can send some pics.
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Old 10-04-2018, 06:51 AM   #11
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I’m dealing with a Repower and your focused on “goodies” unbelievable! Focus! Hahahhhahah
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Old 10-17-2018, 02:27 PM   #12
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Ok time for a quick update. After doing the math the 6.5 wasn’t saving me any money or gaining any efficiency or power. I did source a decent range 4 200 TD which is the 185 HP variant of the 6.354. It has some blow by but runs great. So auxiliary issues like a broken bracket the seller didn’t disclose but I think my local fabrication shop should be able to square away. Should be rigged and dropped in the hole this week. You guys were right I was a salmon swimming upstream. The cost of the engine was a fraction of the cost of parts for the conversion. Now need that 2:1 trans to make sure this thing goes back as designed.
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Old 10-17-2018, 03:14 PM   #13
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Good choice!
BTW your old trans should bolt right in unless there was something seriously wrong with it. Consider replacing the damper plate with new while everything is apart.
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Old 10-17-2018, 03:45 PM   #14
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I bought the hull with zero power. Start from scratch. So yes the old would have worked.
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Old 10-17-2018, 03:55 PM   #15
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Now need that 2:1 trans to make sure this thing goes back as designed.
Do you have a prop and shaft already? That might influence your transmission choice.
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Old 10-17-2018, 06:50 PM   #16
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The blowby would be better dealt with now. Even if you only put in a new set of rings. It's a lot easier to do any engine work while it's out of the boat. Existing blowby will only get worse. Once the engine is in the boat it's a major job.
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Old 10-17-2018, 07:38 PM   #17
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I do have the prop shaft and am most likely going with the 2:1 as for the blow by I'm not willing to invest that type of money until I figure out if I'm in love with the boat or not. The R&I isn't overly complex and the engine has a good 5 years or more left on it.
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