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Old 03-02-2012, 07:23 PM   #1
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How Slow Can I Go?

I'm a newbie, but have been lurking for a while now. The amount I've learned from all of you is invaluable. And, for that I thank you ahead of time.
*
Here's my situation - My wife and I have always been boaters, but primarily on lakes, and me sailing in San Francisco bay. We've decided it's time for a real boat and after much, much research have decided the way to go is a trawler as we won't be in any hurry and they tend to have everything we want. Need to slow down and see the sights in style!
*
In order to get her even more excited about this new adventure, I asked what features she would like and she told me that she would like a pilothouse with full walk-arounds (preferably covered) and less than 15 years old (she originally said 10 but I talked her into 15 to help keep the price down). Of course, I say "no problem" (in this market I figured I could find many boats to choose from). Wrong! The only boat in the bay area (other than 60+ footers) that meets these requirements is a 2001 Offshore 48', which has twin Cummins' 450C's, and of which we were almost ready to pull the trigger on.
*
I realize that this isn't a trawler, but thought I could just drive it slow and be as happy as we would be in a real trawler (and, if I ever needed the extra power, it's available). However, last night a friend of mine mentioned that I wouldn't be able to drive slow for very long stretches without damaging the engines (of course, the broker today told me that it wouldn't be a problem). This would be a deal killer.
*
So I have several questions and already know that they can't be answered precisely without more information (which I don't have yet), but any general opinions or general thoughts would be very, very appreciated and helpful! Again, thanks in advance!

1. Is this true and something to worry about?
2. If so, could I drive it slow for periods of times and then speed up other times to compensate?
3. If so, any guesstimate as to what percentage of each?
4. My friend also thought that the recommended RPM's were probably 75% of max (I looked online and haven't found anything yet) . Do you agree or have other thoughts or opinions?


By the way, I've also looked in the PNW and the entire west coast (on Yachtworld), but the only boats that meet the boss's requirements seem to be the Selene's, which are a bit pricey for me.
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-- Edited by Nsail on Friday 2nd of March 2012 08:45:20 PM



-- Edited by Nsail on Friday 2nd of March 2012 08:45:41 PM

*MOD* Edited for font size. We're a bunch of old guys with bad eyes. Thanks.




-- Edited by GonzoF1 on Friday 2nd of March 2012 09:38:34 PM


-- Edited by Nsail on Saturday 3rd of March 2012 09:42:58 AM
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Old 03-02-2012, 07:55 PM   #2
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How Slow Can I Go?

Have you looked at the Bayliner 4788 and the Meridian 490?

These are very good boats that can spend all day, or week or month going slow.

You owe it to yourself to grab your favotite broker and take a look at one.

They have a full pilothouse
3 staterooms
2 full baths with showers and vacuflush
Well laid out engine room
800 miles of range at trawler speeds

My 2001 has a teak interior, corian counter tops, and has the look and feel that would make all but the stuffiest of yacht owners be proud to own her.

There are fancier yachts (there always is), and there are more utilitarian yachts. These are a good mid range yacht that is extremely popular in your area.

Here's a link to a video I shot of out 4788 for the missus. Not a great video but it shows the boat.






-- Edited by ksanders on Friday 2nd of March 2012 08:59:08 PM
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Old 03-02-2012, 08:49 PM   #3
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RE: How Slow Can I Go?

Jeez Kev... You and Tony with your Bayliners.. Give it a rest, would ya'? :-D (just kiddin')

Welcome to the calm before the storm, Neal. The first thing I thought of was a Mainship, but it's not a pilot house. Defever makes a lot of pilot house boats. Nevertheless, if there aren't any within spec, you know better than I. I would suggest, however, to do a YW search for boats ONLY in your area and just get out there with her and get your feet on the docks. No sense over-limiting yourself so early in the process. She might end up liking something COMPLETELY different than what you know now. Do yourself a favor... Let HER decide what boat you buy!!! I can' emphasize this enough!

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Old 03-02-2012, 09:23 PM   #4
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RE: How Slow Can I Go?

"suck in your gut Kevin"..... I laughed out loud! Nice boat, she is huge
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Old 03-02-2012, 09:26 PM   #5
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How Slow Can I Go?

Quote:
GonzoF1 wrote:
Let HER decide what boat you buy!!! I can' emphasize this enough!
* * * * Man! Does your wife pick the car you drive or the kind of clothes you wear or where you eat every time you go out? Come on! What does she know about boats? There's a lot more to it than just picking out which one looks the best! So, you pick out a boat that she isn't nuts about but you love it! What's wrong with that? I've had 8 boats since 1995 and my wife hasn't picked one! Why should she? She hardly ever goes with me anyway!

*

The boat you mentioned (2001 Offshore) is a great boat! I had a 48 Offshore in 1996 and wish I still had it. You can run those Cummins 450s slow or fast without hurting them. Next to a Fleming 55, the Offshore 48 is one of my favorite boats. Good luck with your search!


-- Edited by SeaHorse II on Friday 2nd of March 2012 10:41:04 PM
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Old 03-02-2012, 09:35 PM   #6
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RE: How Slow Can I Go?

Walt
Like you , I have chosen each of the boats my wife and I have owned.

Tom
Like you, my wife has picked each of the boats we have owned.

The art is each believing the other has chosen the right one. Every time the other gets too close to making a mistake on the choice, a discussion of the merits of each boat seen so far will correct that mistake (if you work well together).
My wife's criteria (undefinable to me) would reject certain types of boat. My criteria would reject others. What was left, we analyzed until we found one that worked for us both. Seems to have worked, as we have kept the present boat for 18 yrs.
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Old 03-02-2012, 09:52 PM   #7
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RE: How Slow Can I Go?

Wouldn't running diesels with too little a load on them for extended periods be detrimental to them? Isn't that one of the problems with diesel generators that are over sized for their demand?
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Old 03-02-2012, 09:54 PM   #8
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RE: How Slow Can I Go?

I may be wrong since you have had a few valuable replies, but to me your post is unreadable.

Have you considered paragraphs? Punctuation?

Both contribute to readability.

Mike
Palm Coast FL
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Old 03-02-2012, 10:21 PM   #9
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How Slow Can I Go?

The secret as I understand it is to make sure you are running at the correct temperature. If you can maintain normal temp at low rpm, you are fine. I run mine this way, and just for insurance, I run up to full cruise rpm for fifteen minutes every two hours. This method is approved by many,

And just for the record, I find your writing much better than some on our forum.


-- Edited by Carey on Friday 2nd of March 2012 11:23:10 PM
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Old 03-02-2012, 10:54 PM   #10
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RE: How Slow Can I Go?

Nsail, are you talking about the Offshore in Tiburon? If so, I know the boat and it is in very good condition. I don't know if you've talked with John Baier, President of Oceanic Yachts, the broker for the seller. If not go introduce yourself to him. He's a great guy and very knowledgable with these pleasure boats.

Carey is correct. These diesels need to run at correct temperature and most are capable of running quite slow and still maintain temp. Give List Marine a call and talk with them about diesel temperature and running under differing loads. List is in Sausalito.

I have no affiliation with Oceanic or List, just trust them. And by-the -way, your writing is just fine. Geez...!
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Old 03-03-2012, 01:07 AM   #11
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How Slow Can I Go?

Quote:
Baggiolini wrote:
"suck in your gut Kevin"..... I laughed out loud! Nice boat, she is huge
*


-- Edited by ksanders on Saturday 3rd of March 2012 02:12:52 AM
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Old 03-03-2012, 02:52 AM   #12
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How Slow Can I Go?

Carey is right on the money with this. The issue is not too low an rpm, it's too low a combustion chamber temperature. Of course on the kinds of engines most of us have it's impossible to know the combustion chamber temperature. The only sensor and gauge normally put on these engines is a coolant temperature gauge. The manufacturer has determined what the coolant reading should be in the normal operating range of the engine under load that equates to the proper combustion chamber range.

The problem occurs at lower engine rpm because the thermostat will keep the coolant temperature up even though the combustion chamber temperature might be too low. So you can be fooled into thinking your combustion temperature is in the proper operating range when it isn't.

Of course, drop the engine power down far enough and the coolant temperature will start to come down, too. But be wary at operating at a lower-then-recommended engine rpm and thinking everything is hunky-dory because the coolant temp is still in the correct range. That's just the thermostat doing its thing.

Running a diesel too cool (inside the combustion chamber) can eventually lead to a variety of problems. How long it takes for any of these problems to manifest themselves will depend on a lot of variables. But given the cost of diesel engines, and the cost of repairing them, to my way of thinking it's better to run the engine(s) in the manufacturer's recommended range than to try to second-guess a too-low setting. If you want to go really slow and really efficiently, then buy a boat with a displacement hull that is powered in such a way that you will get the slow speed and fuel economy with the engine operating in its proper temperature range.

This is my take on the subject, anyway, based on what I've read and been told by people in the marine diesel business. But I'm not the engine expert on this forum, RickB is, and perhaps he'll chime in here with some more accurate information that will help you with your decision.


-- Edited by Marin on Saturday 3rd of March 2012 03:54:56 AM
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Old 03-03-2012, 04:57 AM   #13
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How Slow Can I Go?

Wouldn't running diesels with too little a load on them for extended periods be detrimental to them? Isn't that one of the problems with diesel generators that are over sized for their demand?



YES BUT,

Ok so you find a natural (no turbo) engine and want to operate at what is basically Hi Idle for long periods of time.

Yes, the lack of load will cause blowby (the rings wont seal) and other problems to longevity will happen.

SO WHAT? The usual large truck engine will go 8000 hours to 12,000 hours in a work boat.

So your underloading eats 50% to 75% off the engine life , that's still at least 2000 hours , perhaps 4000 hours of yacht operation.

With most boats seeing 200 hours or less per year , a decade or two of operation exists .

Double the oil change frequency , install a bypass filter and you might see 4000hours , more* decades!

Add cruising prop and EGT meter ,you might get almost back near the 8000 hours .

And of course at the end of each prolonged hi idle cruise try for 30 min of heavy load.


-- Edited by FF on Saturday 3rd of March 2012 06:00:48 AM
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Old 03-03-2012, 06:02 AM   #14
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RE: How Slow Can I Go?

From a Feb. 5th post:

"Actual combustion temperature within the cylinder is nearly impossible to obtain outside a lab style setup and even then the temperature varies from above the melting point of steel to relatively cool near the cylinder walls and even there the gradient is quite steep and varies with location.

The best place to measure and obtain useful information is immediately after the exhaust valve on each cylinder. That way you can determine power balance among cylinders and the quality of combustion in each. Even there though, it is just a relative temperature that is far below the core of the combustion chamber. Turbocharged engines use valve overlap to cool the exhaust valves so the EGT probe is cooled at the end of each exhaust stroke as well. We don't really care though because we only need relative temperatures to see what is going on.

There is a lot of mythology around the temperature of combustion in our little engines. Regardless of the load, the actual temperature of the combustion event is about the same. The amount of heat released varies a great deal and is directly proportional to the power produced.

Low cylinder wall temperatures created by smaller heat release at low power can create conditions which lead to increased wear. So, bottom line, there is a difference between combustion temperature and exhaust temperature and engine temperature. The difference is cause by the amount of heat produced vs the engine's capacity to remove it."
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Old 03-03-2012, 06:30 AM   #15
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RE: How Slow Can I Go?

I can't say one way or the other...BUT...

The more I read... my understanding is this,

Main propulsion is proportional...low speed, low temps but proportionally loaded.* Not enough wear difference to worry about after the engine is broken in...if running really cold the short burst at high rpms/loading helps.

Generators have more issues because they are forced to run at a higher rpm for frequency but the loading varies greatly and therefore not proportional.

I know not very scientific but seems to be the layman's explanation that I'm seeing in many different forums from boating to trucking to RVing.....
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Old 03-03-2012, 06:37 AM   #16
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RE: How Slow Can I Go?

Maybe I should have been more specific, Walt, but now I get it. You guys don't boat together. Fine. But you didn't have to be so condesending about it.

Bess and I are a team and this is our second home. We narrowed it down to a few boats that made the final cut, but ultimately SHE picked Skinny Dippin' (or maybe SD picked her). However it happened, if you want to get the most out of this experience, she has to be in on the decision. We are planning on going cruising in a couple of years and this needs to feel like OUR boat. Otherwise, she's just a guest on my boat and she won't be nearly as emotionally invested in it. Where is the fun in that?

Tom-
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Old 03-03-2012, 08:56 AM   #17
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RE: How Slow Can I Go?

Thanks everyone for the replies. I'm already feeling better about the boat.

Kev - We've looked at several Bayliners and really liked the layout and such - but no full walk -around decks

Tom - we've been on 35+ boats already and like many of them, but they just don't quite meet everything on the future Admiral's wish list. Also, I tried to change the font size a couple of times, but it wouldn't take. I wondered how it majically changed.

Seahorse - We love the Flemings also. in fact they are one of the few boats that have everything we want, but like the Selene's, a bit too pricey for us.

Mike - You are right about lacking paragraphs. I thought about that in the middle of the night and just changed it. However, I think my punctuation, while maybe not perfect, is decent.

Ray - Yes, we know John. In fact, he's sick of looking at us! We've been to see the boat 5+ times. (I forgot how many exactly). Great guy!
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Old 03-03-2012, 10:16 AM   #18
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RE: How Slow Can I Go?

Quote:
koliver wrote:
Walt
Like you , I have chosen each of the boats my wife and I have owned.

Tom
Like you, my wife has picked each of the boats we have owned.

The art is each believing the other has chosen the right one. Every time the other gets too close to making a mistake on the choice, a discussion of the merits of each boat seen so far will correct that mistake (if you work well together).
My wife's criteria (undefinable to me) would reject certain types of boat. My criteria would reject others. What was left, we analyzed until we found one that worked for us both. Seems to have worked, as we have kept the present boat for 18 yrs.
*Wow, this post has more wisdom in it than even most technically "expert" posts. Well, at least from a lifestyle perspective. Oh, and reality, too...

Good one, Koliver!
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Old 03-03-2012, 11:46 AM   #19
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RE: How Slow Can I Go?

Quote:
Nsail wrote:
Kev - We've looked at several Bayliners and really liked the layout and such - but no full walk -around decks

The walk around decks are an each to his own thing.

I really wanted walk around decks untill I saw the difference in salon width between the two designs.

Take a 15' wide boat and you can get 14' of salon width.
Add walk around decks at 24" per side and you have a 10' wide salon.

Boats are all a compromise.
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Old 03-03-2012, 11:57 AM   #20
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How Slow Can I Go?

My 13-foot-wide trawler with 16-inch-wide side decks leaves enough interior space for our needs.

*


-- Edited by markpierce on Saturday 3rd of March 2012 01:00:01 PM
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