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Old 24-07-2007, 16:52   #1
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Powering Large Boats - From Scratch

One of the boats I'm looking at for our next "home on the water" is a commercial ex-government boat. It is 57' long, 15' beam and 40 tons. It's a MONSTER, which is great because we can live out at anchor year round with this one even in the most harsh Maine winters.

My question is regarding powering this vessel. It's basically a bare hull. No power, no systems, nothing really to speak of. I have to install it all.

I wanted to see if I could solicit input on this possible project. I'm not 100% sure I'm going to get this boat, but this thread will help with that decision.

First, it's starting from scratch. The engine was removed. There are controls and a wheelhouse, but no engine. Also, the "living space" is already constructed and was part of the vessel when it was built.
A good dollar savings and also good for stabilty. No added top-heavy weight.

Powering Question:

I am looking at a Detroit Diesel 6-71 @ 250hp for $5500. I hope to achieve 8 knots guzzling fuel, but back off to 6-7 knots to save fuel. Is this realistic? Is it the right size engine? I'm going by a book I have that specifies engine size as a function of tonnage and desired top speed. Any diesel specialists that are on this forum are welcome to solicit me for a project here. The boat is in VA. I need to install the engine and I would imagine it's going to be tricky with the crane, mounts, etc...

Powering/Systems Question:

What about an electric system? I have to get a genset and HUGE battery bank to be able to put out our much larger power requirements. Some things we want to do living at anchor are: microwave leftovers from batts, run a small 750 watt heater for 15 mins from batts, have a semi-normal refrigerator, etc... some upgrades in convenience since we are here to work and work hard. No play, no cruising. Since we have to generate massive power anyway, I was thinking why not go fully electric (with genset as long range cruising engergy source)? What size electric motor would be correct to propel this vessel? Does anyone know?


Any other inputs as to setting up this vessel's propulsion system would be very welcome. I'm dabbling in an area I have little if any clue and need to learn pretty fast. We are expecting a closing soon on the Gulfstar and a purchase of the next vessel in fairly short order.

Thanks!
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Old 24-07-2007, 17:38   #2
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Sean

How well would a vessel of that displacement and LOA maneuver with a single engine? I would lean more towards a hull designed for twin diesels and a little more horse power when you are talking monster boats.. When the sun is shining and all is well it sounds like it all works, but I do believe that even trawlers have to power themselves off lee shores against 60 knot winds, and I wouldn't want to think about having to put that monster against a dock or maneuver in tight fairways with a single engine without a bow thruster.

Just my thoughts on the subject..
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Old 24-07-2007, 17:58   #3
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57' is no big deal.
First, DON'T even consider Detroit diesel.
Secon, how was the boat set up? single or twin? any pics?
Figure about 15kw on the generator to start, we'll get more specific later.
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Old 24-07-2007, 19:56   #4
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Now, take a deep breath and...

You are looking at another corollary of Murphy's Law.

"In the marine area events only happen at the most inconvenient time and place."

I would have to recommend that you find some alternative accomodation in the event that your boat sells.

Buying another boat is something to be done with great care and dispassionate calm.

Not to mention serious discussion with your significant other.
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Old 24-07-2007, 22:37   #5
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You are looking at a major project repowering and adding systems to a bare vessel such as that. You sound like you don't know what you would be getting yourself into. It would be many many thousands of dollars to do it right. You would be better off selling your boat if it is unaffordable, hold off and be patient. Just when you purchased another boat you can't afford then the right boat will come along and you will have regrets for once again making a hasty decision. Why not sell your boat, come down to Florida where there are hundreds of boats to choose from. I am only trying to steer you in the right direction because I think your alittle off course. Good luck with whatever decisions you make.
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Old 24-07-2007, 23:37   #6
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I'm kinda with Inthewind on this one. As a general rule, a second hand yacht will sell fro a lot less than the value of the sum of it's parts (do a quick inventory of what it would cost you to replace all the major systems/parts of your boat with reasonable quality 2nd hand gear; odds on it will cost way more than the market value of the boat. You are obviously an intelligent guy, Sean, and have probably done your homework, but personally, I am sceptical that the end result is going to cost less than buying a viable, sailable (or usable, if a motorboat) vessel. Good luck though!
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Old 25-07-2007, 04:48   #7
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Quote:
Originally Posted by never monday
57' is no big deal.
First, DON'T even consider Detroit diesel.
Secon, how was the boat set up? single or twin? any pics?
Figure about 15kw on the generator to start, we'll get more specific later.
Thanks for the input, Pat. I agree - 57' is no big deal at all. I've run a 100' megayacht without a ton of trouble, but that did have thrusters and twin screws. But still, I have 45' of single screw unresponsive boat right now. What's another 12'?

Here are more details about this specific boat. It's not a cruiser - it's an anchorer and coastal boat. So Detroit Diesels aren't as good as some say? I kept reading that they were good because the injectors were their own fuel pumps and if one fails you still have a working engine, etc... I also read the DD was a complicated beast and was more likely to have trouble if not maintained well.

Looking back at my post, I see I may not have been clear on the systems/powering section. When I was speaking of the large house demands, I was thinking "why not power with an electric drive and genset combo, using spare power as my house power?" I have seen 100HP electric motors for sale (3 phase) for reasonable amounts of $$. (100hp electric SUPPOSEDLY corresponds to 250hp diesel)

What would you drop into this beast to power her? I am awaiting some more details on the boat and they may be slow coming since it's the govt. May not know then until Monday, when go to VA to have a look.

Ok, boat pics:
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Old 25-07-2007, 05:24   #8
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Here's a Plus for this Vessel

As it turns out, it's a little more seaworthy than I had been thinking. Here is the Navy description of the service class vessel:

Patrol Combatant Type

Combatants whose mission may extend beyond coastal duties and
whose characteristics include adequate endurance and sea
keeping providing a capability for operations exceeding 48 hours
on the high seas without support.

Patrol Ships

Patrol Combatant
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Old 25-07-2007, 06:17   #9
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If all those valves go to the bilge pumps, I'd say that's a red flag!!!

Sean, If you buy this, I think you're going to find out first hand about the "Not in my backyard" syndrome that some people with older boats experience.
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Old 25-07-2007, 07:17   #10
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The only reason I've found that older Detroits don't leak oil, is because the are out of oil.

I'd look for a Cat3208. Cheap, plentiful, and alot of bang for the buck.
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Old 25-07-2007, 08:53   #11
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sean, if you are going to be working all the time to save/make $$s, (not easy/probably impossible in maine where pay is terrible and jobs scarce), i think you should check out land dwellings. maine has cheap rent and some great little cottages empty all winter. to compare a winter in boston to one in maine is folly; its much, much more severe up here. just the dinghy ride back and forth would be horrible. i also don't think any town wants that eyesore in their harbour. i can't imagine what you see in this vessel or in this plan. sorry to be negative.
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Old 25-07-2007, 09:09   #12
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Jeez... thread babysitting

Listen, people.

I feel like a thread babysitter again. How many of you live on your boat 27/7/365? How many of you have worked on boats professionally as captain or mate? Better yet... how many of you are offering your "advice" from an office chair, your living room, or some other place on land?

I don't need to hear all of these opinions about what you think is right or wrong. Frankly, I don't care. I live at sea and most of you don't. Your advice is theorectical at best.

I am looking for real advice such as Pat just gave regarding powering this vessel and setting up a possible electric propulsion system. Looks like traditional engines are more affordable.

I realize this is way WAY over your heads since many of you are land dwellers and haven't worked in a professional capacity at sea.

Sorry to go off, but I'm tired of people chiming in about "I think your plans stinks." I'm not asking you to live with us on the boat. I'm asking intelligent people for opinions on repowering and the potential to repower this vessel.

One thing I do for a living is re-finish interiors of boats. You have seen what I did with the Gulfstar. I am going to do a similar thing to this vessel, but with a Manhattan loft apartment style. Anyway, I really don't need all this "advice." I need practical information on powering a vessel of this size, tonnage and hull shape.

I think I might be on the wrong forum. I know there are some very smart folks on here who understand boats (Pat included). Unfortunately, it's getting harder and harder to weed through the chaff to glisten any knowledge from this board.

Maybe my question should have been:

"Does anyone know of a good, active commercial marine forum?"

I know this forum is for cruisers and wannabes, but this is getting a little ridiculous.

I'm sorry I asked this here....
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Old 25-07-2007, 09:14   #13
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Quote:
Originally Posted by never monday
The only reason I've found that older Detroits don't leak oil, is because the are out of oil.

I'd look for a Cat3208. Cheap, plentiful, and alot of bang for the buck.
Ha ha ha!! Good one, Pat. I'll check out the Cat 3208s. Do you think that's an adequate size engine for the dimensions of this vessel?

Also, I know you're a busy guy... lines of people out door and such, but if you would like to PM me and look into repowering this vessel as a project for your business (even sending an employee), I'd be happy to discuss. I could buy the engine through you as well... Just let me know if you'd like to look into that.
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Old 25-07-2007, 10:08   #14
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Looks like a neat project Sean! And probably better that she's already stripped down - will save lots of time.

Having disposed of a couple Navy craft like this during my career - I know with absolute certainty that hull maintenance was not a big priority on these craft. Not sure what the history is on the commercial use of this one - maybe they put some money into the steel below the waterline, maybe not.

The last craft I disposed of had hull plates so weakened by rust that from within the tanks you could see the bulkheads "panting" with the wave motion outside the hull while the ship was dockside. Made me want to spend as little time below the waterline as possible I have also seen where new plates were welded to stringers that had rusted away at the joints and were essentially suspended in space.

Buy a good audiogage or find a surveyor who knows how to use one.

Good luck with the project - I hope it comes together for ya!

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Old 25-07-2007, 10:10   #15
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"... Does anyone know of a good, active commercial marine forum?"
Professional Boat Builder Forum:
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SNAME ~ Naval Architecture/Marine Engineering/ Ocean Engineering Forum:
The Society of Naval Architects and Marine Engineers: Public Forums

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