Burn Rate for 2000 42 Aft Cabin with Cat's

[jmunro123]

I am considering a 2000 42 Aft Cabin to use for dock condo and longer distance cruising. Seems like a great boat. What would reasonable cruising speed be and what would the burn rate be Cat's.

Thanks

 

[fwebster]

Which engines?

350hp 3116 = 11.3 gph @2400 rpm which is max rated cruise
385hp 3126 =11.7 gph @ 2400
420hp 3126 =13.0 gph @ 2400

All of these engines have a "sweet spot" at about 2200 rpm where the fuel burn is 9.0 gph, 9.1 gph and 10.0 gph respectively.

I can't help you on the speed as this boat tends to be load sensitive and everyone loads their boat differently, but figuring in the 18 to 22 kts area would be safe, depending upon which engines are installed.

 

[jamesv]

I have the 420 hp and Frank is right on with the burn rate. At 2400rpm I cruise around 20-21 kts.

 

[Alex D]

Which engines?

350hp 3116 = 11.3 gph @2400 rpm which is max rated cruise
385hp 3126 =11.7 gph @ 2400
420hp 3126 =13.0 gph @ 2400

All of these engines have a "sweet spot" at about 2200 rpm where the fuel burn is 9.0 gph, 9.1 gph and 10.0 gph respectively.

I can't help you on the speed as this boat tends to be load sensitive and everyone loads their boat differently, but figuring in the 18 to 22 kts area would be safe, depending upon which engines are installed.

This is the PER ENGINE fuel burn Frank, right?

 

[fwebster]

Yes..........I forgot to add that as Cat tables are published per engine.

 

[Alex F]

Recently my wife and I were having conversation on the same topic and were analizing the advantages of Aft Cabin model comparing to Sedan Bridge and Sundancer. May be a stupid question, but I mostly see GPH vs. MPG numbers. I thought it's easier to have MPG info to determine the range you can get out a boat. What's the formula to translate GPH to MPG?

James, what's the realistic cruising range you get considering you're cruising at her sweet spot or close to that?

 

[Alex D]

Recently my wife and I were having conversation on the same topic and were analizing the advantages of Aft Cabin model comparing to Sedan Bridge and Sundancer. May be a stupid question, but I mostly see GPH vs. MPG numbers. I thought it's easier to have MPG info to determine the range you can get out a boat. What's the formula to translate GPH to MPG?

James, what's the realistic cruising range you get considering you're cruising at her sweet spot or close to that?

Well you would have to know what average speed you are running at the rated rpm (which is ehavily influenced by water and weather) and fuel burn and then it is a simple division/multiplication calculation.

You can pretty much bank that running on plane you will get somewhere between 0.5 to 0.9 mpg for any 34 to 45 footer with a relevant engine package - diesel or gas. You'll be on the low end of this range on large boats with gassers (like a 420 DA with gassers) and will surpass 1.0 to maybe 1.2 mpg on smaller boats with diesels in this size range (like a 380 with diesels)


For example we average about 15.5 Gal. per engines hours annually for our 340DA ... that's for all three engines (mains and genny) ... but it of course includes running on plane, idling around the docks and running at displacement speed. We get just below 1 mpg running on plane at 3400 rpm and about 27 mph

 

[jamesv]

I figure 25 gals for 20 miles at cruise rpms(2300-2400). This keeps me on the safe side. I always run the generator and I figure about 1-gal/hr on the starboard tank and it usually come close to that.

 

[fwebster]

To show the wide range of results and why I don't get excited about lengthly discussions on who's boat or what engine is most efficient, I just topped of my tanks last weekend.....165 gal. My average consumption was 8.9 gph for the 165 gal.

I have a heavy boat with 3116's and we transit a long no wake area and have to watch our wake due to all the tourists in pontoon boats and on jet skiis. Most of our running during this period was at about 1500 rpm where we could control our situation.

But, this is summertime running in our local waters.

 

[Alex F]

I figure 25 gals for 20 miles at cruise rpms(2300-2400). This keeps me on the safe side. I always run the generator and I figure about 1-gal/hr on the starboard tank and it usually come close to that.

This makes it 0.8MPG, which is what I'm birning with my boat. Concidering the wait and shape this is pretty much what I was thinking. I guess, the biggest dissadvantage you've got the need to run genny to keep your fridge going. I was looking at 380 Aft Cabin and it had dual voltage fridge. So, if I'm not mistaken it doesn't require running genny when off dock. On the other hand I also saw that 420AC has optional 3rd cabin. That's a huge difference I'd say space wise.

Dom told me he's burning 1.1MPG on his 410DA. That's an impressive number for boat of such size.

My average consumption was 8.9 gph for the 165 gal.

Frank,

8.9gph is very nice but I think you're trolling at 1500RPMs (my guess is around 7-8kts). What do you birn at cruising speed, the usual 0.8MPG we see on most boats or does your boat performs better?

 

[fwebster]

Alex,

I included the low burn numbers to illustrate the wide differential based on use. At 1500 rpm we run 14-15 kts, just where the bow is beginning to lift, but not on plane. That speed and condition is slow enough to get a 30,000lb boat stopped, without damaging the transmissions when a tourist idiot cuts in front of us on a PWC or a pontoon boat.

We run 22-23 kts.......25 mph burning 22.6 gph @ 2400rpm but normally cruise t he boat @ 2200-2250 rpm burning 19.0 gph making 20 kts or 23 mph which is 1.28 mpg.

 

[jamesv]

Alex, I also run the generator to keep the a/c's going. I like the cabin to be cool when we get to our destination. I also feel it's a good idea to run the generator and the cost is minimal all things considered.

 

[twyant]

Have 420AC cruising speed 20k 2350 RPM 23 gph w/ 3116 350 hp but have did some prop work also 1200 hr on motors with out putting a wrench on them other than maintenance. And does have a lot of room it has the three cabin layout. Alex is wright fridge and freezer are 110v so gen set must run a/c units are 220v so you must have a 50A 220V hookup. frank was right on with the burn rate.

 

[Alex F]

Alex,

I included the low burn numbers to illustrate the wide differential based on use. At 1500 rpm we run 14-15 kts, just where the bow is beginning to lift, but not on plane. That speed and condition is slow enough to get a 30,000lb boat stopped, without damaging the transmissions when a tourist idiot cuts in front of us on a PWC or a pontoon boat.

We run 22-23 kts.......25 mph burning 22.6 gph @ 2400rpm but normally cruise the boat @ 2200-2250 rpm burning 19.0 gph making 20 kts or 23 mph which is 1.28 mpg.

Frank,

I totally hear you in regards to tourists, we 've got a good number of locals that are wost than tourists.

Those are impressive numbers. Doing 14-15kts @1500RPMs is awsome. If I do 9kts @1500rpms I'll be happy. I guess, the huge torque from diesels and bigger props makes all the difference for you. The 1.28 mpg makes your 450DA almost twice more economical than my 320DA. No wonder Turtle Tone is getting 450DA skipping 320s-340s :grin:. It's interesting that 450 is also more economical than her smaller sisters like 410 and 420. Is it just better design between hull and power packedge? I hope it's not year specific.

Alex, I also run the generator to keep the a/c's going. I like the cabin to be cool when we get to our destination. I also feel it's a good idea to run the generator and the cost is minimal all things considered.

James,

Having such a luxurious floating condo you’ve got to have all the comforts including the cooled cabins. I totally agree that running genny is minor expense all things considered. Based on the numbers comparison I think that wind plays a huge role for AC and DB models. So, one must really outline all the factors and understand what’s more important and how the boat would be used. I think it’s no brainer that AC/DB give you more boat for the money (at least in the used market), but it’s going to cost more to keep it moving.

 

[twyant]

Alex the 420ac is 45.5 long and 31,000# M/T w/ diesels

 

[fwebster]

Alex,

The "secret" is in the Cat engines. A supremely efficient fuel system and huge torque. But, understand, these boats are not fast. Current models have more horsepower and burn more fuel but that also run in the 27-30 mph area for speed.

 

[jmunro123]

What is the very best economy this boat with the 420 Cats can do?

Lets assume I had as much time as needed to travel 150 miles and could go at hull speed or some other low speed. What would be best burn to Knots speed be with the larger Cat's?

 

[Gimme Time]

Just returned last week to Deltaville after cruising to St Michaels, BIH, Annapolis & Herrington Harbor South for 10 days. Great trip with two other Sea Rays and average burn rate with gen set on for cooling & other uses ran 26.7 GPH. Cursing speeds ranged from 15- 21 knots with wind on our bow through out the entire trip with some 3-4 foot conditions. We ran out front to break the waves for the 370 & 340 that we traveled with to improve the rough water ride.

Love the 3126 Kitty Cats with 420HP :smt038as yes there may not be as fast but love their reliability.

 

[Out2win4U]

First hand info on 2001 420 Aft Cabin

My wife an I are also considering upgradint to a larger SR 420 aft cabin. We are particularly interested in the 2001 model. I now that structurally they differ littel from previous 1998 and later. I would like to hear advice from owners of 420 AC

 

[Lake Erie Boater]

Alex,

The "secret" is in the Cat engines. A supremely efficient fuel system and huge torque. But, understand, these boats are not fast. Current models have more horsepower and burn more fuel but that also run in the 27-30 mph area for speed.

Frank nailed it...........again. :thumbsup:

Everyone around me seems to think that my boat is a rocketship when they see all the iron in the ER. Truth is, we are the last to arrive, but boy is it fun doing so.

My personal equation is 2200 rpms gets me 22 knots and I burn 22 gallons per hour (combined). I have no scientific proof other than the CAT chart and use this as it is a simple to remember estimate.