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Old 10-07-2015, 10:04 PM   #1
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To TURBO or not to TURBO

Thought I would drop in and ask a question if you don't mind.

I am moving over from a sailboat to a power boat. My first thought was a trawler displacement hull, but then I started looking at semi-displacement hulls and heard a bunch of stories that those boats with turbo diesels could go at trawler speeds and not hurt the engines. Or, you could go slow for a while then you had to go fast. And, if you bought one from someone, you had to make sure they did it right when they had it or the engine would be used up.

I know there are semi- displacement hull boats that have naturally aspirating type diesels and that they can handle slow speeds better.

So, my thinking is that a non turbo diesel is better than a turbo diesel for slow speeds on a boat that can reach planing speed. Is this correct?
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Old 10-07-2015, 10:25 PM   #2
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Really to general a question. It depends a great deal on the motor and at what RPM it's turning at slow cruise. You will reach a slow enough RPM with just about any motor where it won't be happy regardless of turbo or not.

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Old 10-07-2015, 11:02 PM   #3
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Suppose I wanted to take a 46' Searay (27500 lbs) with a pair of 6V92 DD Turbo and run it at say, 10 knts (mind you this is for fuel economy purposes)

or

a 40' semi displacement hull like a Viking with a pair of turbo 225 Lemans running it a 10 knts all day.

Are those acceptable compared to a Bertram with pair of DD 871's naturally aspirated running at the same 10 knts?
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Old 10-07-2015, 11:07 PM   #4
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One reason I bought my boat is because it has naturally aspirated 175 hp Hinos. I didn't want the extra problems that can happen with a turbo, even though I give up some hp and they're less efficient. I believe with proper maintenance and operation a NA engine will give a longer trouble free life than a turboed unit. The reason I believe this is I've replaced many failed turbos over the years and a few did damage to the engine when they failed, I was looking for what I thought would be the most dependable.


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Old 10-07-2015, 11:14 PM   #5
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None of the the DD 2 stroke series are naturally aspirated they all have blowers to charge the cylinders and scavenge the exhaust gasses.


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Old 10-08-2015, 12:53 AM   #6
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Turbos also whine - depending on the acuity of your hearing that can be noticeable.


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Old 10-08-2015, 02:02 AM   #7
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CWC-we have a full displacement boat with twin 158 HP John Deeres w/turbos. We cruise at about 1600 RPM and seldom get above 1800. WE have never had any problems. Never have noticed any whine, but then our ER is pretty well soundproofed.
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Old 10-08-2015, 02:02 AM   #8
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I`ve had both. Keep it simple, NA, not turbo. But if you find a great boat at a good price, with turbos, don`t let it stop you, just balance everything up.
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Old 10-08-2015, 02:14 AM   #9
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Not a deal breaker for me, but I prefer naturally-aspirated to keep it simpler. My NA 80-hp John Deere meets the boat's power needs.
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Old 10-08-2015, 02:47 AM   #10
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CWC-we have a full displacement boat with twin 158 HP John Deeres w/turbos. We cruise at about 1600 RPM and seldom get above 1800. WE have never had any problems. Never have noticed any whine, but then our ER is pretty well soundproofed.

Q? would the engine be under boost @ 1600/1800 rpm ? maybe not
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Old 10-08-2015, 05:12 AM   #11
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Hi
With our current vessel which has twin Cat 3406 540 hp turbo which rev out at 2000 rpm, we cruise at 1200 rpm at 9.6 knots, so they are not ideal for load and are working very lightly.We just completed a 2500 mile cruise , and all we do is every 4 or so Hours put the hammers down for 5 mins to give them a run. We have not experienced any issues with the engines. What we do like about the engines are that when we require some additional power , in say crossing a bar etc, it's there. They are also very quiet just purring along. Depending on your gearboxes, ours are twin disc, we often run on one engine, which helps apply a bit of load, and the other windmills, you can do this for quite a few hours, just need to be mindful of oil temp in the windmilling box
You can also purchase an additive, de carboniser that may assist in keeping the cylinders clean and prevent glazing.
Our last vessel had the same overpowered approach with a full displacement hull 50 foot with a pair of cummins turbo 6bta 210 hp each , again we cruised at 1650 rpm at 9.3 knots and these revved out to 2200 rpm, and again we had 5 years of trouble free boating using the same approach, give them a run at wot every so often and at least once every time we went out.
Booth vessels we brought as used vessels.

Cheers Chris D
I see no issues with a turbo engine.
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Old 10-08-2015, 06:23 AM   #12
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IIRC the 3406 was designed for the trucks building the Alaska Highway,
they were spending long periods at idle.
Nice engines for driving.

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Old 10-08-2015, 06:45 AM   #13
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"None of the the DD 2 stroke series are naturally aspirated they all have blowers to charge the cylinders and scavenge the exhaust gasses".

True , but the blower leaves almost zero above atmosphere pressure in the cylinder by design..

The question is really do you need the extra power a turbo can create?

If you have a boat that can get up on top and go, 20-40K a turbo will be required to keep the engine light enough .

To make wakes and wallow along at SD speeds 12-15K a turbo is not required to give the under 1nm/g fuel bill.

A turbo would be fine with a small enough engine that it was required for normal cruise , but these are rare.

The turbo must have positive boost to run clean, and in many cases that is faster than you wish to pay for in diesel.

If its a must for boat speed they are worth the extra expense , otherwise , what is not there cant break.
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Old 10-08-2015, 07:28 AM   #14
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Originally Posted by River Cruiser View Post
None of the the DD 2 stroke series are naturally aspirated they all have blowers to charge the cylinders and scavenge the exhaust gasses.


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A blower is not a turbo. Indeed there were "N" model Detroits without turbos.

As for the OP, there is probably more internet lore and dockside legend on this subject in general than even, dare I say, anchors.
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Old 10-08-2015, 07:47 AM   #15
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I was happy to find out from a diesel mechanic that our Volvo TMD 31A could have the turbo removed if it ever became a problem. Also he commented that that model Volvo is a great engine, always good to hear.
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Old 10-08-2015, 10:12 AM   #16
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With but rare exception, the only way to get a legal non turboed diesel engine is on the old boat used market. Keep those old Lehmans and 4 cylinder JDs running if you wish to keep the distinction of being turbo free. The comparison to the anchor debate best be phrased " do I really need an anchor?"

Heck even the almost perfect VW 2 liter TDIs in cars use them, to great success if one is to read a different thread on TF. Millions of gas and diesel turbo charged engines are produced every year with nothing but benefits.

Why the debate over a successfully used engine intake design approaching one century in use? A bit of historical research on the subject may be helpful CWC.
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Old 10-08-2015, 10:32 AM   #17
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Thanks everyone, and I am trying to do as much research as I can. Most of what I find is that, by manufacture design, most engines match the hull design. Displacement hulls, older ones that is, come with lower HP NA diesels. But when you get to planing hulls the engines increase in HP, needing turbos, to match the hull design for speed. Trying to determine if a fast boat can economically (fuel wise and part wise) operate at slow speeds is rather hard. There are engine specs for newer boats and engines but, I have to look at older boats to be in the game.

I don't need to operate at ski boat speed. Having a boat that can get on top some of the time would be nice, but that would be on occasion. Most of the time trawlering along would do me just fine. Finding that boat and engine combo is pretty hard.
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Old 10-08-2015, 11:16 AM   #18
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Trying to determine if a fast boat can economically (fuel wise and part wise) operate at slow speeds is rather hard.
No, it's not hard. But first you need to define what "economically" means. Some depends on the engines, a lot depends on the boat.

My big fat Hatteras was designed to run on "plane", (theoretically about 14 knots) but we virtually never did. 8-9 knots wuz us. We ran it up at the end of the typical day for about 10 or 15 minutes. Engines surveyed out beautifully after 2000+ hours of running that way. I know a lot of other Hatteras MY owners, and all but one run it the way I described.

Sunchaser described the whole turbo issue quite well. You could subscribe to boat diesel.com for more detailed info.
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Old 10-08-2015, 01:44 PM   #19
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Sun chaser, do some research on the Cummins 6.7 used in the Dodge Ram, EPA and others total screwed up a great Diesel engine. DPF clogging up, turbos destroyed by recirculating exhaust gases to meet requirements. Now new big trucks required to have DPF causing break downs on the big rigs and repair bills in the thousands. I also have heard new boat Diesel engines have to be equipped with DPF. (Diesel Particulate Filters) Sure glad I have this old Volvo TMD 31 A !!!
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Old 10-08-2015, 01:49 PM   #20
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Thanks everyone, and I am trying to do as much research as I can. Most of what I find is that, by manufacture design, most engines match the hull design. Displacement hulls, older ones that is, come with lower HP NA diesels. But when you get to planing hulls the engines increase in HP, needing turbos, to match the hull design for speed. Trying to determine if a fast boat can economically (fuel wise and part wise) operate at slow speeds is rather hard. There are engine specs for newer boats and engines but, I have to look at older boats to be in the game.

I don't need to operate at ski boat speed. Having a boat that can get on top some of the time would be nice, but that would be on occasion. Most of the time trawlering along would do me just fine. Finding that boat and engine combo is pretty hard.
There are quite a number of older 35-45' semi-planning boats with non-intercooled, but turbocharged engines that were realistically sized for the 13-15 knot speed range. Ocean Alexander built a lot of them....Grand Banks in the mid-years...the tugs are another example. When the push for more speed began in the late 80's and early 90's, many manufacturers added intercoolers to the same engines to squeeze out a few more knots. Given that you're thinking in terms of a slow plane capability, these overpowered semi-planning or full planning hulls might not float your boat....more complex and truly operating way off design spec when run in the hull speed plus range. I'd recommend that you look at the prop curve for boats under consideration and compare power required for your desired operating speed range to the installed power. If it takes 300 HP to cruise at 14-15 knots and installed power is 750 HP, the boat has too much engine for your needs...especially since it's going to spend most of it's life blubbering along at 65 total HP at hull speed. Of course the same argument could be made for NA engines....but realistically, they don't exist as the physical size and weight are prohibitive. Modern engines with sophisticated fuel controls (NA or turbo) are another animal.
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