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Old 12-27-2014, 11:06 PM   #1
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In defense of SD trawlers

I just received the 20th anniversary addition of Passage Maker magazine. On page 41 there is an article comparing the three major hull types which includes planning something I would not include in a trawler format. What I focus on is the comparison of the FD and SD trawler types. I personally would have thrown in the modern cruising sail boat including the catamarans since so many of these boats cruise and often under power. What got my attention is on page 43 a comparison of statistics in particular the fuel burn numbers. One of the reasons I chose a SD over FD is demonstrated by these statistics. I am not a stranger to the FD type having owned a forty footer and cruised it up and down the Mid Atlantic region of the USA. I have also done similar cruising in sail boats East and PNW. Now to the meat of the matter. The FD boat used in the article a Krogen 44 burns 1.9 gallons at 7 knots more than my previous J/44(sail) under power. At WOT a top speed of 9 knots at 7.8 gallons per hour is reported. This is where my choice of a SD hull makes fuel efficiency sense to me. My 48 foot boat with twin 330 HP motors at 9 knots where I like to cruise in trawler mode burns only five gallons per hour verses the 7.8 of the Krogen if they wanted to do 9 knots. If I still wanted to travel at 7 knots I would not have given up my sail boat . Now considering the fact that fuel costs for most boaters is not a big part of the total boat expenditure why not have your extra knots and if needed the ability to have even more knots. Thus one of my arguments in favor of SD. Boaters entering the trawler phase of boating should give serious consideration to SD and not be put off by the fuel cost. There are of course many other pros and cons SD vs FD but I don't think fuel burn #s should dominate your choices.
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Old 12-27-2014, 11:49 PM   #2
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SD needs no defense.
Nine out of ten trawlers are SD.

I agree fully. And that explains to a great extent why the majority of trawlers are SD.

Some SD trawlers have a fuel burn as good as a equally sized FD boat. Lighter displacement SD hulls are much more common than light FD. So some SD boats are as fuel efficient as some FD. For example Craig's planing boat may have a 1gph fuel burn w the same engine as is in my boat because his boat is probably at least half the weight as my Willard .... 1gph.
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Old 12-28-2014, 06:29 AM   #3
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I totally agree; and the market for second hand boats agrees too.

i was reading the stabiliser thread and thinking to myself: in a S/D boat there's no need to fit €50k (probably much more) stabilisers; if you want to stop rolling in a beam sea just go a bit faster and the boat will firm up at 12-15kts.....

Of course most owners of big planing boats of 50' and over say there's no 'hump' to get over on a big boat: it just accelerates through the low teens at the same trim angle 'as if it were a S/D hull'.

If you look at the torque graph of most modern diesels they seem to happy at 1500 revs and over so idling along at 7-8 kts shouldn't affect them too badly.

What's not to like About a S/d hull?
Do they use more fuel 'on the plane' than a proper planing boat ?
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Old 12-28-2014, 06:47 AM   #4
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Ed

Why denigrate your vessel and call it a trawler? Does Sam Devlin call it a trawler? It seems to me that your vessel, if one wanted to pigeonhole it by type, is a Downeast style.

Those of us with FD vessels are cursed with going slow and not always enthralled with thumping our chests over locked in low fuel burn numbers. Which is why Nordhavn is entering the SD market with their Coastal Pilot.

Fleming vs Nordhavn vs the Downeast designs will be an interesting contest. My bet is on the Downeast designs holding sway. No matter what one labels their vessel, the common rail engine is a game changer with both the luxury of speed and when desired slow velocities with accompanying good NMPG.

Don's Sabre is another SD that deserves mention with its rakish Downeast design, good go slow capability and speed when needed. The MJM 50 is a great new vessel too, fully utilizing low weight, modern engines, a Seakeeper and cruising speed well above 20 knots.

Lots happening out there for SD vessels and with fuel prices stabilized, at least in NA, strong sales looming for the specialty builders. Last but not least, buyers with money are again appearing for the SD vessels.
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Old 12-28-2014, 07:16 AM   #5
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Sunchaser so true I don't classify my boat as a trawler but the person writing the article in Passage Maker does so I used the comparison by his standards trawler to trawler. By my standards its DE Express SD vs FD. It was only the fuel burn issue that I wanted to address since it is often touted as a major reason to choose the FD over the SD and I wanted to point out why for most boaters its a none issue especially for those who find the 7+ knot limitation irksome. I did not go near the other issues which I favor some types of SD over FD since some are contentious issues on this site.
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Old 12-28-2014, 08:26 AM   #6
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Yes a FD boat weighs more and goes slower, with less fuel burn.

The SD boat MUST keep the weight down which unless a rather large boat means things like food and water and even fuel will be far less.

For cruising , say just the Bahamas where food and booze are taxed at 40% or so, the ability to bring 6 months of stores has a great advantage.

1,500Gal of fuel at US or Bahama prices will add up.

Very light weight construction adds considerably to the SD boat cost as does the larger engine.

No >best< just different style for different use.

TRAWLER is mostly deck house style for marketing , as many boats are similar underwater.
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Old 12-28-2014, 09:25 AM   #7
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Yes a FD boat weighs more and goes slower, with less fuel burn.

The SD boat MUST keep the weight down which unless a rather large boat means things like food and water and even fuel will be far less.

For cruising , say just the Bahamas where food and booze are taxed at 40% or so, the ability to bring 6 months of stores has a great advantage.

1,500Gal of fuel at US or Bahama prices will add up.

Very light weight construction adds considerably to the SD boat cost as does the larger engine.

No >best< just different style for different use.

TRAWLER is mostly deck house style for marketing , as many boats are similar underwater.
I was not opening the full SD vs FD pros and cons only wished to address the fuel issue. the chooses one makes has to include the issues you raise and how and where a boat is used no argument there. I fully agree and there are factors that would favor one over the other dependent on those issues. For example where I boat and how I boat carrying 1500 gals of fuel would be bad news but that is not about fuel burn as a factor in SD vs FD
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Old 12-28-2014, 09:37 AM   #8
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Tom,
What is it about Don's Sabre that makes you think it's a SD? For that matter what is it that makes it "down east"?
It's 100% a planing hull in my book.
Looks like an absolutely straight run aft.
Wouldn't make 25 knots if it wasn't a planing hull.
And w enough power it should go 40.

FF wrote;
"The SD boat MUST keep the weight down which unless a rather large boat means things like food and water and even fuel will be far less."
Most all the boats on this forum are SD and very few are on the light side. And most will only go a few knots above hull speed. Most all look quite heavy to me. However I agree the route to speed w planing OR SD hulls is light weight.

Ed,
"Down East" isn't a hull type IMO.
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Old 12-28-2014, 10:40 AM   #9
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Tom,
What is it about Don's Sabre that makes you think it's a SD? For that matter what is it that makes it "down east"?
It's 100% a planing hull in my book.
Looks like an absolutely straight run aft.
Wouldn't make 25 knots if it wasn't a planing hull.
And w enough power it should go 40..
Eric, you are absolutely correct on the Sabre. I do not know deadrise at stern on MJM so maybe it is a planing hull vs SD too. Regardless, planing hulls are the choice of many yachtsman and successful builders with few limitations for coastal activities.

FF, there are many SD hulls cruising the Bahamas and doing serious blue water work. Fleming, Outer Reef, OA and GB are but a few with common rail diesels permitting range only dreamed of a decade ago.
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Old 12-28-2014, 11:06 AM   #10
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Eric, you are absolutely correct on the Sabre. I do not know deadrise at stern on MJM so maybe it is a planing hull vs SD too. Regardless, planing hulls are the choice of many yachtsman and successful builders with few limitations for coastal activities.

FF, there are many SD hulls cruising the Bahamas and doing serious blue water work. Fleming, Outer Reef, OA and GB are but a few with common rail diesels permitting range only dreamed of a decade ago.
Is is true that common rail diesels just clean up the emissions, but are no more economical than the old fashioned injector pump versions?

I say this because a Diesel engine sucks as much air as it wants: there's no butterfly on the air inlet so electronic injection ain't going to make any difference to fuel consumption that I can think of...
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Old 12-28-2014, 11:45 AM   #11
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There are some aspects of common rail technology that improve fuel efficiency. One thing you won't see from a properly running common rail diesel, is black smoke on hard acceleration, (unburned fuel). The high fuel pressures and piezoelectric injectors can allow for more than one spray of fuel per compression cycle allowing for more efficient fuel burn.
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Old 12-28-2014, 11:49 AM   #12
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Is is true that common rail diesels just clean up the emissions, but are no more economical than the old fashioned injector pump versions?

I say this because a Diesel engine sucks as much air as it wants: there's no butterfly on the air inlet so electronic injection ain't going to make any difference to fuel consumption that I can think of...
Actually, the facts are clear if one looks at a diesel genset data of say 30 years ago to its equal KW version of today, about a 15% improvement per the Cat Handbook of 1985 to today's. Today a common rail diesel can operate at 15,000 feet while delivering full rated power as if it were at sea level. This was not possible 10 years ago, all due to high pressure injection systems, high speed turbos, tighter build tolerances, better materials and on engine circuit boards.

And look at the MB diesel taxis in Dublin and the fuel gains they see today vs 30 years ago. If you have owned a MB diesel car from then and compare to today's Blutec, the mpg improvement is dramatic.

In boats, a common rail in the 400 to 700 HP version can safely run at say 15% load whereas a diesel of a few decades ago does not like this light loading very much. This is why the FD discussion is possible, diesels that can safely run low and high in the loading cycle.

But, many don't and never will accept that progress can and is being made in diesel technology. Just the way it is.
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Old 12-28-2014, 12:09 PM   #13
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Eric, you are absolutely correct on the Sabre. I do not know deadrise at stern on MJM so maybe it is a planing hull vs SD too. Regardless, planing hulls are the choice of many yachtsman and successful builders with few limitations for coastal activities.

FF, there are many SD hulls cruising the Bahamas and doing serious blue water work. Fleming, Outer Reef, OA and GB are but a few with common rail diesels permitting range only dreamed of a decade ago.
Tom, the Sabre is a 16 degree deadrise at the transom with a straight run aft. With current power she will top out at 33 knots. Fast cruise is 25-27 knots.

We use the speed to cover great distances. When we get to the destination area, we slow down to trawler speeds towing the dinghy. We plan on running down to Biscayne Bay in January. If we can run offshore the 120 mile trip plan would be about 5 hrs. Then a couple of weeks at trawler speeds and anchoring. Then fast cruise back to Ft. Pierce. That is basically the way we use the boat------hurry up and slow down.
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Old 12-28-2014, 12:13 PM   #14
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Tom wrote
"Today a common rail diesel can operate at 15,000 feet while delivering full rated power as if it were at sea level."
This certainly wouldn't be true of an NA engine but I can't see how a turbocharged or supercharged engine would gather the same amount of air at 15000' as it would at sea level.
Not applicable to boats of course but ??????

Tom and Don,
Re my comments about hulls I said nothing about dead rise and it's got nothing to do w it. "straight run aft" is about fore and aft ... not athawartships. Is that word right?
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Old 12-28-2014, 12:30 PM   #15
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Actually, the facts are clear if one looks at a diesel genset data of say 30 years ago to its equal KW version of today, about a 15% improvement per the Cat Handbook of 1985 to today's. Today a common rail diesel can operate at 15,000 feet while delivering full rated power as if it were at sea level. This was not possible 10 years ago, all due to high pressure injection systems, high speed turbos, tighter build tolerances, better materials and on engine circuit boards.

And look at the MB diesel taxis in Dublin and the fuel gains they see today vs 30 years ago. If you have owned a MB diesel car from then and compare to today's Blutec, the mpg improvement is dramatic.

In boats, a common rail in the 400 to 700 HP version can safely run at say 15% load whereas a diesel of a few decades ago does not like this light loading very much. This is why the FD discussion is possible, diesels that can safely run low and high in the loading cycle.

But, many don't and never will accept that progress can and is being made in diesel technology. Just the way it is.

I'm happy to accept 15%; which poses the question: is it worth it?

The improvement in petrol (gas) cars over that period is more like 50%; from about 30mpg when I was growing up for a standard 1.6 ltr car, to over 50mpg now with the latest ecu's.

I had one of the first VW golf diesels, 1.6 ltr (non ecu) and it returned a solid 50mpg day in day out. I notice on the internet people complaining that their brand new diesel is NOT returning the advertised 70mpg, more like 55-60mpg.....!

Is all that complication, outrageous spares cost, and being chained to a specific manufacturer for parts worth the extra fuel savings?
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Old 12-28-2014, 12:33 PM   #16
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High output, turbocharged, all mechanical diesels got pretty good fuel economy before the industry went to common rail.

Ski in NC, a forum member, posted on boatdiesel a study he did comparing his mechanical Cummins 450C engine (mechanical) to a QSC (common rail) engine of the same horsepower. The fuel economy was near identical.

Older mechanical engines like the Perkins 6.354, Lehman 135, NA DDs all got significantly worse fuel economy.

And the mileage improvement in automotive gassers over the years has as much to do with weight, transmissions, tires and aerodynamics as it does with engine improvements. But lower displacement, turbochargers, port EFI all did for a gasser's fuel economy what they did for diesels.

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Old 12-28-2014, 12:48 PM   #17
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I'm always suspicious of pleasure boats called "Downeast Style". There is more to the discussion than cabin profile. I've seen a fair number of Lobster Boats and typically they have a large engine sitting squarely where Pleasure Boat folks like to have a comfortable "forward cabin". Furthermore, the Lobster Boat will have a hot exhaust tube exiting vertically from the engine, through the cabin top, to a muffler sitting on the cabin top, not an arrangement featured on ANY Pleasure Boat. Pleasure Boat folks tend to situate their engines under the sole of the bridge, or even farther aft, where the Lobster Boat would rather have the hull supporting gigantic stacks of traps.


One might be tempted, by virtue of its profile, to call my Albin-25 "Downeast". I think Swedish Motor Cruiser" is a better fit.
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Old 12-28-2014, 01:03 PM   #18
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In boats, a common rail in the 400 to 700 HP version can safely run at say 15% load whereas a diesel of a few decades ago does not like this light loading very much.
And my somewhat old (1997) electronically-controlled, but not common rail, diesel does this well too. 6-6.5 knots and 1300-1400 RPM, or 16-18 knots and 3200-3300 RPM. Little or no smoke, even at startup. BSFC said to be 5-10% (IIRC) better than its non-electronic predecessors. 6,032 hours on it so far, maybe 70% of the total at 6 knots.
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Old 12-28-2014, 01:11 PM   #19
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I'm happy to accept 15%; which poses the question: is it worth it
In several cases I'm familiar with, yes. A 750Kw genset will burn roughly 50 gph. 15% represents 7.5 gph or 65,000 gallons of fuel per year. Assume a 75% load and you easily are still above 50,000 gallons of diesel per year savings. I know of larger yachts that have swapped out older diesel gensets for the same type of reasons.
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Old 12-28-2014, 01:50 PM   #20
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What interests me about the fuel burn situation with the common rail engines is the economy that can be gained by running at low loads in a SD type on engines that can also cruise at 14-16K when so desired. This allows for flexibility yes there is always a coast but for the way I boat not so great. With a little use management the long hours of low load running will not harm the motor and probably add to its life since engine life is often measured in total fuel burn and not hours. It would be unrealistic to measure life by hours. Is 100 hours at WOT = to 100 hours at half the RPM? Even before common rail people where crossing oceans doing six knots under low load. I do not think those motors were failing because of that use. Now with common rail the low load use is even better.
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