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| Sno' Dog Log |
| Performance Figures & Technical Stuff |
| Sno' Dog is a 2006 model PDQ 34 Powercat (Hull #87) with twin counter-rotating Yanmar Model 4JH3-HTHE Engines rated at 100 HP @ 3800 RPM (continous for 1 hr) fitted with ZF model ZF-25 Hydraulic Transmissions. Total weight of each engine/transmission is 259 kg or 571 pounds. The (Factory-installed) Propellers on our boat are (were): 17-in dia x 14-in pitch x 3-bladed - counter-rotating. |
| These numbers reflect ideal conditions. Range would, no doubt, be reduced in open sea and/or rough conditions. For an open water passage, I'd certainly want to allow a healthy safety margin. Hopefully, by the time we attempt our first long passage in Sno' Dog, we will have gained much more experience and be able to refine this chart further. |
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| Port Date Log Eng Hrs Gallons GPH MPG Ave Spd Cum GPH Cum MPG Cum Spd Whitby 5/17 10(E) 10.2 (Full) - - - - - - Ottawa 5/25 ? 40.5 83.7 2.76 ? ? 2.76 Burlington 6/13 ? 66.9 110.0 4.15 ? ? 3.42 Mamaroneck 6/17 ? 92.7 104.6 4.04 ? ? 3.61 Newington 6/27 ? 121.0 106.0 3.76 ? ? 3.65 Belfast 7/15 1289 155.6 97.7 2.82 ? ? 3.45 2.55 8.8 kts ________________________________________________________________________________________ |
| When we first chose the PDQ 34, we were a bit concerned about the fuel and water (and holding) tank sizes, but so far they've proved entirely adequate. Now that we've calibrated the gauges, we feel more comfortable using more of the available liquid before refilling. On our Maine cruise, we went 35 hours - and about 250 nautical miles - before refueling with 98 gallons. This works out to 2.6 nm/gal. At this rate, assuming a total usable fuel capacity of 165 gal, our range would be 425 miles. Since our cruising was a mixture of leisurely 7-kt runs interspersed with 16-kt sprints, there's little doubt that we could easily extend our range to over 500 nautical miles if needed. To me, this seems entirely adequate for this kind of boat. |
| What you can see from the above table is that fuel consumption does vary somewhat. Although it doesn't really show above, I know that the lower fuel consumption figures reflect the portions of our travels where we slowed down a bit, whereas the higher numbers reflect mostly fast (15-16 knot) traveling. Also, no allowance has been made for generator fuel consumption. (I think we've got just over 20 hours on the generator now). HMC 07-30-06 |
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| My best guess (engineering approximation) at present is that we burn about 2 gal/hr at 7 knots and perhaps 6 gal/hr at 16 knots. If we slowed down a bit, we could improve on these numbers. Based on experience to date, here are my best estimates: (Range assumes 160 gallons usable fuel.) |
| Speed RPM Gal/Hr NMi/gal NMi Range 6.5 kts (7.5 mph) 1400 1.8 3.6 575 7.3 kts (8.4 mph) 1600 2.2 3.25 525 15 kts (17.2 mph) 3100 6.0 2.5 375 16 kts (18.4 mph) 3250 7.0 2.3 345 |
| Port Date Log Eng Hrs Gallons GPH MPG Ave Spd Cum GPH Cum MPG Cum Spd Newington 10/04 1523 186.6 78.2 2.52 3.0 7.5 3.31 2.60 8.6 At. Highlands 10/07 1806 211.6 108.6 4.34 2.6 11.3 3.44 2.59 8.9 Annapolis 10/10 2035 233.6 93.0 4.23 2.5 10.4 3.51 2.58 9.1 Norfolk 10/14 2167 244.9 47.4 4.14 2.8 11.7 3.55 2.59 9.2 Beaufort NC 10/18 2346 262.4 60.0 3.42 3.0 10.2 3.54 2.62 9.3 Georgetown 10/22 2514 279.2 59.2 3.52 2.85 10.0 3.54 2.63 9.3 Thunderbolt 10/24 2661 291.6 57.2 4.61 2.6 11.8 3.59 2.63 9.4 Ortega (JAX) 10/27 2807 304.5 55.1 4.26 2.7 11.3 3.62 2.63 9.5 _______________________________________________________________________________________ |
| The latest Performace UPDATE - as of 11/04/06 - for Sno' Dog's Fuel Consumption and Mileage... |
| Note: All values are in Nautical Miles (Knots). To convert to Statute Miles, multiply by 1.151 |
| 03-07-07 - Powerboat Reports published a review of the PDQ 34 in their March 2007 issue. Click here to see that review. Or, view a reasonable facimile of the report simply by clicking here. If you'd rather have a copy of the full article via e-mail (incl links to the attachments) just e-mail me. Finally, if you would like to you view the Powerboat Reports Performance Tables (which agree closely with our experience to date) just click here. |
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| We were not able to activate our Distance-over-the-Ground Log properly until July 15th. |
| For this trip - tabulated above - from Newington (Portsmouth) NH to Ortega (Jacksonville) Florida, the figures are: Total Distance traveled: 1284 n mi (1478 st mi). Engine hours: 118 hr. Fuel Consumed: 480 gallons. This works out to: Average Speed: 10.9 knots (12.5 mph). Average Fuel Usage: 4.07 gallons/hour. Average Mileage: 2.7 nautical miles per gallon (3.1 statute miles per gallon). HMC 11/04/06 |
| click for larger image |
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| 06-30-08 - Update, June 2008... We've now got data from over two years of operation. Performance continues very similar to that outlined above. Looking through our complete table of Fuel Consumption, I see that the longest distance we've traveled so far between fill-ups is 345 nautical miles (397 statute miles). We have gone a maximum of 56.5 hours between fill-ups and the most fuel we have taken on at a single fill-up was 131.2 US gallons. As expected, our mileage has varied somewhat with speed. Our worst mileage (2.25 n mi/gal) was recorded when our average speed was 11.8 knots, although for this segment our fuel burn was only 4.6 gal/hr. The best milege we've seen was 3.35 n mi/gal with a fuel burn of 1.69 gal/hr, in this case our average speed was a mere 5.7 knots (See my comments below regarding powercat efficiency at speed versus a monohull design.) As of our last fill-up in Newport, RI on May 26, 2008, total cumulative Sno' Dog statistics since we took delivery on May 15th, 2006 are as follows: Total engine hours: 878 hrs Total mileage logged: 7936 nautical miles Total fuel consumed: 3,141 US gallons Computed Averages are: Average Fuel Consumption: 3.35 gallons per hour Average Speed: 9.0 knots Average mileage: 2.54 nautical miles per gallon (2.92 statute mi/gal) One final observation about cruising range Although this boat gets great mileage, I think her useful range has been exaggerated a bit in PDQ's promotional literature. To begin with, the actual fuel capacity is somewhat less than advertised. We asked PDQ to calibrate our fuel tanks when they first filled them at the factory, which they did. Their notes showed that it took a total of 176 US gallons to top off the tanks, starting with bone dry tanks. Obviously, the fuel pick-ups are located somewhat above the bottom of the tanks, so I wouldn't count on much more than 150 gallons usable. Realistically, I'd say our range - cruising at 15 knots - is about 360 nautical miles. If we reduce speed to 6.5 knots, we could likely increase this to 550 nautical miles, but that's about it. (And that assumes reasonably calm water.) On the positive side, our Sno' Dog has the ability to cruise at speed with a very minor mileage/range penalty compared to a conventional monohull. As an example, consider the Camano, a popular semi-displacement fast trawler. At displacement speed (7 knots) the Camano 31 burns just over one gallon per hour giving her a range of 800 nautical miles. BUT, if you bring her up onto a plane and run at 15 knots, fuel consumption jumps to over 9 gallons per hour - and range drops to a mere 180 nautical miles! (See Powerboat Reports test data in the May 2007 issue.) This HUGE drop in efficiency at speed is typical of virtually all monohulls when driven above displacement speed. The powercat is the only design I'm aware of that can run at speed with such great efficiency. With fuel now approaching five dollars per gallon, this is becoming a very endearing characteristic indeed! We continue to be thrilled with the PERFORMANCE of our PDQ 34. |
| I wish we had FloScan gauges so we'd know our exact fuel consumption at various speeds - I'm seriously considering installing them (but they're quite expensive and complicated for twin diesels). What we do know is average fuel consumption. Here's what it looks like to date (07/30/06): |
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| The "canoe stern" design of the PDQ yields excellent efficiency at speeds in the mid teens. |
| Click on photo for larger image |
| PS: Feedback from PDQ owners on this subject is appreciated - how do your numbers compare? |
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| Our starboard propeller upon haul-out in NH in June 2008 |
| On our trip North this spring, starting back in the Chesapeake Bay on May 21st, we noticed a vibration. When we hauled out in New Hampshire to check the zincs, this is what we found (photo on left). I'm sure our mileage for the last 10 days of the trip might have been better without this rope wrapped around our prop! If the weather hadn't suddenly turned so cold, I might have been more inclined to dive down and check it out, I wasn't quite prepared to deal with 48-degree water (see Page 4). |
| Rope around the prop! (Click for larger image) |
| Note: I have moved the older entries from this page to the bottom. Starting here, are the original entries dating back to July 2006, a mere two months after we took delivery of Sno' Dog. |
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| 07/06/08 UPDATE - Being an engineer, and prompted by recent posts on PDQ Forum, I decided it was time to update the figures on this page. Although we still don't have exact fuel burn data, we do have two years of information on Sno' Dog. Using data from our log, combined with Yanmar and Powerboat Reports fuel burn data, I was able to construct the table below. The numbers shown apply to Sno' Dog with a reasonably clean bottom, nearly full fuel and water, and a moderate amount of cruising gear aboard. High-end performance is noticeably weight-sensitive, our top speed increases by about one knot when fuel gets down to 1/4 full. Also, we try to use fuel in our forward tank first as this improves performance. |
| Note: I have moved the tabulations of our earlier data - going back to May 2006 - to the bottom of this page. |
| To better visualize the data in the table above, I plotted it in graphical form - here's the picture... |
| Looking at this graph you can see that boat speed increases fairly linearly with with engine speed up to about 7 knots (1600 RPM) then it starts to level off. Fuel consumption, however continues to increase steadily with RPM causing in a drop-off in milage (and range). But, once the boat reaches 10 knots or so (2400 RPM), she begins to plane and speed picks up resulting in a flatening of the mileage curve. Clearly, there's not much point in cruising in the 8 to 12 knot range as there's little fuel saving to be had here. This is something we noticed qualitatively early on. The boat accelerates easily to 7 knots at a mere 1500-1600 RPM. (At this speed - which feels like a fast idle - the boat is so quiet we're always surprised to see a 7+ kt reading on the GPS.) But, much like a planing, or semi-displacement monohull, increasing the throttles from 1800 to 2800 RPM increases the wake size but does not to offer a commensurate speed increase. Once above 2800 RPM, however, the boat feels as though she's planing, the bow actually comes down a bit and the wake gets smaller. For this reason, we normally avoid extended cruising in the 2000-2600 RPM range. For Sno' Dog, our most economical high-speed cruising occurs at about 3000 RPM which, depending on load, produces a speed of 14 to 15 knots. Speeding up to 3200 (about 16 knots) however results in a very modest milage penalty and we do this often if we are in a hurry.
Conversely, better mileage can be obtained by slowing down, but to realize significant improvement, we have to slow down to about 7 knots (1600 RPM) . If we really want to maximize mileage - and range - it appears that we should run below 6 knots (1200 RPM). At this speed we could theoretically go 620 nautical miles on a single fill-up. Finally, there's been an ongoing discussion about the possible fuel saving of single-engine operation. The PDQ is quite capable of running on a single engine. Even though the other propellor will freewheel, I am told that the cutlass bearing will fare just fine (which is not true of all twin screw designs). So the question is, how much fuel might we actually save by doing this? With all the data shown above, it is now possible to comment on this. The only missing information is speed and RPM for single-engine operation. Fortunately (being an engineer and all) I just happen to have some data on this. Plugging in the fuel burn numbers from the table above, we can generate the following mini table: Twin Engine Performance Single Engine Performance 6.5 kts - 1400 RPM - 1.70 gal/hr - 3.9 n mi/gal 2000 RPM - 1.5 gal/hr - 4.3 n mi/gal 7.0 kts - 1500 RPM - 1.85 gal/hr - 3.8 n mi/gal 2400 RPM - 2.0 gal/hr - 3.5 n mi/gal As I suspected, the numbers come out awful darn close! It looks as though a small saving might be had if you keep your speed below 6.5 knots. I gather the consensus in the powercat design world is that variable pitch (feathering) propellers are necessary to realize meaningful savings from single engine operation. But it does appear that, at least at slow speeds, we might be able to save a little bit with our PDQ - and certainly we'd cut down on engine time and associated maintenance. I'm sure this discussion will continue, but that's my two cents for now. HMC 07/07/08 |
| ENGINE SPEED FUEL BURN MILEAGE RANGE (150 Gal usable) RPM in MPH in Knots Gallons/Hr Stature Miles Nautical Miles Stature Miles Nautical Miles 800 4.4 3.8 0.8 5.5 4.75 820 710 1000 5.6 4.9 1.1 5.1 4.45 765 665 1200 6.7 5.8 1.4 4.8 4.15 715 620 1400 7.5 6.5 1.7 4.5 3.9 675 585 1600 8.3 7.2 2.0 4.2 3.65 625 545 1800 8.7 7.6 2.3 3.8 3.3 570 495 2000 9.2 8.0 2.7 3.4 2.95 510 445 2200 9.9 8.6 3.2 3.1 2.7 465 405 2400 10.8 9.4 3.7 2.9 2.5 430 375 2600 12.7 11.0 4.3 2.9 2.5 430 375 2800 14.6 12.7 5.1 2.9 2.5 430 375 3000 16.6 14.4 6.0 2.8 2.4 415 360 3200 18.0 15.7 7.1 2.5 2.2 380 330 3400 19.4 16.9 8.4 2.3 2.0 345 300 3600 20.6 17.9 9.7 2.1 1.85 315 275 3800/WOT 21.8 18.9 11.0 2.0 1.7 290 255 |
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| 04-17-10 |
| ENGINE SPEEDS RPM in Knots 3-BLD PROP 4-BLD PROP__ Difference__ 800 3.8 3.9 +0.1 1000 4.9 5.0 +0.1 1200 5.8 6.0 +0.2 1400 6.5 6.8 +0.3 1600 7.2 7.4 +0.2 1800 7.6 7.7 +0.1 2000 8.0 8.0 0 2200 8.6 8.6 0 2400 9.4 9.4 0 2600 11.0 12.5 +1.5 2800 12.7 14.3 +1.6 3000 14.4 15.6 +1.2 3200 15.7 16.9 +1.2 3400 16.9 18.2 +1.3 3600 17.9 19.4 +1.5 WOT 18.9 @3800 20.4@3750 +1.5 Test cond's: Main Tank 5/8 full, Fwd Tank 3/8 full, Water 1/2 full, Temp 78 F, Seas: less than 1 foot, Bottom: clean (freshly painted). |
| 04/17/10 - New 4-Bladed Propellers - Test Results: |
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| New 4-bladed prop installed on Sno' Dog. |
| The new propellers feel smoother at all speeds, but there is a slight vibration noticeble around 2000 RPM. (We seldom cruise at this speed anyway.) Speedwise, there is a substantial improvement once the boat comes onto plane. At our normal (fast) cruise setting of 3000-3200 RPM, we have gained over a knot of speed. At wide-open-throttle (WOT), the boat runs 1.5 knots faster than she did before. WOT engine speed is 3750, a bit less than our previous 3800 RPM. |
| Needless to say, we are very happy with these results! |
| Props are 17" dia x 14" pitch (same as the 3-bladers) |