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Old 11-22-2013, 05:09 AM   #21
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All 2 stroke Detroits have similar operating limits.

The DD get very poor when the power is below about 60%.

Thats why there are 1,2.3,6,8,12,&16 cylinder versions of many of the offerings.

Between 20 and 30 HP per cylinder they work great , have long service lives and are not bad fuel wise. 16Hp / gal

The Air Police doesnt love them tho.

Even at a slow idle the 12V71 will be thirsty , but at 240-360 HP its just fine.

The chined hull does not do well at the 8K trawler crawl , so engine replacement would hardly be worthwhile.

Sell and get a better slow speed boat.
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Old 11-22-2013, 12:24 PM   #22
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In Passagemaker, if memory serves correctly, somewhere in the last 5 yrs or so, was an article about a 53 MY Hat that the owners repowered from tired DD to JD.
They decided they didn't care if the boat planed so replaced the DD with JD 4 cylinders. New iron, economy, reliability and the boat had the living space which they valued.

Looking thgough archives may find the article. Cost, I have no idea.

In the Hatteras Forum around the same time there was a long running thread where another Hat owner kept his DD's but reworked things, depowered, but he did understand what he was doing.
Smaller injectors, smaller props so the engines would run at good revs making less hp and yet still run decently. Of course he knew that he could not run the boat at the old speeds ever untill all was put back the way it was. It was apparently successfull. But I emphasize he knew what he was doing, or at least had a heck of a good idea.

Applicable or not I won't say but it may be worthwhile trying to find these threads and articles.
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Old 11-22-2013, 12:42 PM   #23
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Here's a nice video of an 53 Repower.
http://youtu.be/EqQPlavvD5I
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Old 11-22-2013, 02:13 PM   #24
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I suspect doing nothing (other than enjoying the boat, running as economically as possible) may be the most inexpensive option.

-Chris
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Old 11-22-2013, 02:42 PM   #25
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Thanks for that great Video N4712.
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Old 11-22-2013, 02:42 PM   #26
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Here's a nice video of an 53 Repower.
Big Yacht RePower - Full Length - YouTube
that is a great video.
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Old 11-23-2013, 10:58 AM   #27
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Maybe this title is misleading, but I’m not sure what else to call this idea.

First some background: A friend has a 1989 61ft Hatteras (nice roomy, well built boat, great Bahama cruiser). Back in the day it was built to plane with twin 12v71’s. Repowering to make it a real LRC or trawler speed boat would be very expensive. Lately, he has been running it around at trawler speed. He can either run both engines just above idle, or run one engine at a time (the preferable option). Running on one engine he can get about one gallon per mile at 8kts. The boat has a modern autopilot which tracks ok under one engine.

We recently brought the boat back up from the Bahamas to New Orleans and while sitting around the pilothouse during the trip we debated the pros and cons of repowering along with other ideas to help run the boat more efficiently. We started thinking about removing one prop for the bulk of the Gulf crossing. We could pull one prop in the shallows on the Gulf side of the Keys and reinstall it in the Mississippi Sound or vice versa. Obviously, pulling a prop for the crossing would eliminate the redundancy of the main engines and reduce maneuverability (though the thruster helps in that regard). Without the deadhead prop, the boat would track better with less drag and eliminate the shaft and gear rotation (the Twin Disc people say the gear can take the free rotation as long as the engine is started and run every 8 hours).

Anyway, the idea we are now discussing is replacing one prop with a folding or feathering prop. Maxprops and other brands are available for the 2.5 inch shafts, though they are not cheap. The idea is not necessarily to power the boat with this; rather the folding prop engine would be used only as a maneuvering engine or as a get home engine. The other engine would be used as the primary propulsion engine.

So what do you think guys? Repowering would mean cutting a hole in the side of the hull to get the 12v71’s out. One boatyard thought they could do it for around $200k. The boat is probably worth $325k and may be worth no more even if it was repowered. The 12v71’s are in ok shape, but running them slow is not helping their lives. Any downsides? alternatives?
I know exactly what you're describing as I was experimenting cruising on one engine past season. My approach was slightly different. I have planing hull and great engines. My goal was simple, cut down fuel burn and the engine hours (obviously, if I'm going slow I'm adding hours). So, my idea was if I use one engine at a time I'll be cutting the hours in half.

From technical standpoint there are two primary items I was looking at:

1. Shaft cooling and lubrication. This is not an issue with my boat since I have crossover cooling.

2. Transmission freewheeling. This was my biggest concern. I couldn't get an official word from ZF whether my trainy can freewheel, but after consulting with few very experienced folks/mechanics I concluded that it's not "healthy" for the trainy to freewheel. So, my solution was to lock the shaft when the engine is off.

Cruising Observations:

My hull speed is 7.4kts, which I achieve at 1000rpms with both sides running. This gives me 2gph on each side (4gph total). When I shut one side down I need to bump the working side to 1200rpms and in exact the same conditions I'll make 6.5-6.9kts burning 3gph. After my initial test my conclusion was obvious. I'm saving 1/2 the hours and experiencing only minor speed loss. BTW, during my test I didn't find a difference in speed with shaft locked vs. freewheeling.

I came up with the simplest way to lock a shaft (using a line) and when I was cruising long distance it was very simple process to lock/unlock a shaft. It takes me under 30 seconds to lock/unlock it.

While cruising I'm always using AP. It has no problems staying on track with about 10-12 degree angle when running on one engine with the other side locked. The only time I see that AP is working hard is when the seas are rough. My RPMs always stay the same, 1200rpms and my speed varies depending on tides, wind and seas. In normal conditions I usually see around 7kts. But, I've cruised between 4.5 (against the tide) and as fast as 10+kts (with the tides) on one engine.

My approach is simple, I fire up both sides when I'm departing. This gives me maximum control in closed quarters. Then, when I'm out in open area I slow down and lock one side and shut the engine. After cruising as long as I need and getting within few miles from my destination, I fire up the locked side, warm up the engine, slow down to unlock the shaft, cruise for few minutes slow with both sides engaged and then jump on plane for few minutes to "clean" anything like unburned fuel and other stuff in the block and turbos on the engine that worked the most on that leg. When I approach a harbor, dock, moor or anchor both engines are engaged to give me full control. When I'm cruising the next time I just use the other engine to "catch up" on the same hours with the other side.

In my experience of running hundreds and hundreds of miles this approach works very well. I have the flexibility to have maximum control in close quarters, jump on plane when I need to (usually this happens in rough beam seas and when approaching the inlets) and save tons of fuel when using only one side.

My advice is to try experimenting as I did and I think you'll find that it's the best approach as it requires no modifications to anything, no extra expenses and having both engines available anytime gives you piece of mind and control.

Good luck,
Alex.
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Old 11-23-2013, 11:53 AM   #28
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Excellent post, thanks

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Old 11-23-2013, 01:56 PM   #29
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Nice video. It is nice when someone takes the time to make a useful video and post it. Unfortunately, the 12v71s in this 61ft Hat are a different animal. There are 3 options for getting them out 1) Cut a hole in the side of the hull, take them out sideways, rebuild the hull and repaint the boat 2) Take them out through the salon floor, cut a hole in the cabin wall, take them out, then rebuild the wall of the salon and repaint 3) Take them out through the salon floor and cut a hole in the roof through the upper deck, rebuild etc. There are no doors or windows that will accommodate the engine blocks. Every time the owner has talked to a yard, they have said cut a hole in the hull. Ultimately, that is what might be done.

Also, he has Floscans and has many hours of trying different speeds and combinations. We have locked the prop with a LARGE pipe wrench and have considered installing a real shaft lock. The point of the original post was to discuss the possibility of using a folding or feathering prop on one side, thus making that engine a get-home and maneuvering engine only.

The problem with all these forums are all the useless and inane comments unrelated to the original issue. I know it's hard to believe, but he has considered selling it and buying something else.
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Old 11-23-2013, 02:44 PM   #30
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I have sent a private message, on another subject, to your profile page.
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Old 11-23-2013, 04:02 PM   #31
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The problem with all these forums are all the useless and inane comments unrelated to the original issue.
LOL, maybe your right, Rich, although to admit that a few of the insane and unrelated ideas expressed in these forums are being incorporated into my boat right now. Somewhere between the lucidity and madness, experience and imagination, and the qualified and ridiculous is the answer to the question I'm too embarrassed to ask.
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Old 11-23-2013, 05:14 PM   #32
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So what do you think guys? Repowering would mean cutting a hole in the side of the hull to get the 12v71ís out. One boatyard thought they could do it for around $200k. The boat is probably worth $325k and may be worth no more even if it was repowered. The 12v71ís are in ok shape, but running them slow is not helping their lives. Any downsides? alternatives?

...

The problem with all these forums are all the useless and inane comments unrelated to the original issue. I know it's hard to believe, but he has considered selling it and buying something else.
Sorry if my posts might not have been on the "folding prop" target, Rich. I was more responding to your first post/last para (quoted)... especially the overall idea of downsides and alternatives

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Old 11-24-2013, 05:33 AM   #33
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Chop a hole in the side may be fine for steel or aluminum.

A GRP boat would be too hard to engineer the patch layup.

Probably the boat could be run as a dock condo , but doubtfull it could ever go to sea again.
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Old 11-24-2013, 07:10 AM   #34
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Over the years I have seen a number of boats in yards with a hole cut out of the side for removing the fuel tanks. Have no information on how they handled after the repair of the hull. You have raised an interesting question.

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Old 11-24-2013, 07:18 AM   #35
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Done all the time...there's a yard that does Grand Banks fuel tanks out the bottom.

A glass boat chopped to pieces with a chainsaw can be glued back together virtually as strong or stronger if you like and the repair is done properly.

On some glass boats the sides just keep the water out. They are not really structural but on others they are....So if the repair requires additionl strength, much like doubling up lumber around a window.....it could be reinforced...but most fiberglass patches with both poly resin (preferred as same material characteristics) or epoxy will equal or nearly equal the original strength.
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Old 11-24-2013, 08:34 AM   #36
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Done all the time...there's a yard that does Grand Banks fuel tanks out the bottom...
Why would you take the tanks out of the bottom on a FRP recreational boat? Unless it was a YouTube Video? lol Not me, I'm with FF.

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Old 11-24-2013, 09:15 AM   #37
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Cutting a hole in the side seems crazy, but I guess from the boatyard's point of view it's the most direct way to get access. No one has ever said the engines can't be removed. It's only been a question of expense.

There must be hundreds of older boats in nice shape with crazy big engines in this same spot. They would be great LRC's or trawlers, but running the engines so slow presents another set of issues.

On this 61 ft Hat, we may try the feathering prop idea for a while if we can find a prop that is not too expensive. The 2.5in shafts are what's driving up the cost. The owner has a spare shaft that we may have remachined to a 2in or 1 1/2in taper end. That way we can get a less expensive prop. The shafts are two piece with a muff coupler so it would be relatively easy to change the back shaft section. Obviously cutting down the shaft reduces the strength, but remember the folding prop side is expected to only be used for maneuvering of get-home.

As someone mentioned above, having feathering props on both sides would be great. You could run either engine alone. Maybe my 48ft Defever would be small enough to make it work.
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Old 11-24-2013, 09:58 AM   #38
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understand composites...and it's not so crazy...otherwise owning a composite boat is pretty crazy....

look at how many things are glued together in all walks of life...
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Old 11-24-2013, 11:07 AM   #39
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I can't find it now but I think I read someplace, maybe on a tug yacht board, where someone did remove 6 of the pistons, rods and FI gear to a 12v71 in a tug..... I would think it would one would have to block off the induction and exhaust ports also.
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Old 11-24-2013, 07:08 PM   #40
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It's not rocket science to cut a hole in the side or bottom - remove the motors - and replace the piece cut out. Most of the expense is not the structural work. Most likely moving plumbing and electrical runs out of the way and replacing.

The cosmetic repair would eat up the most man hours.

If the hole could be positioned below the waterline, perhaps removal might be economically feasible? Think in terms of taking a sawsall and cutting a hole just big enough to drop the motor straight down cutting through the stringers as well as the bottom. Remove the motor. Move the other motor and lower thru the same hole. Move two replacements up thru the hole. Replace the cut out piece and bond in place. Mount the motors and you're ready to rock and roll. No cosmetic work necessary! Only fish will see the scar.
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