Construction: Week 48 - Sea Trial in Taiwan

IMPORTANT: There are two Week 48 articles.  The previous one, "Construction: Week 48 - More Finishing Touches" contains the most complete set photos to date.

The sea trial in Taiwan took place last Thursday, November 14. I received the report below on Monday. 

	TANIA YACHT SEA TRIAL REPORT
A
1.  Hull  No. : Outer Reef 63-063
2.  Date :  Nov 14, 2013
B. Engine / Propulsion :
1.  Engine :  Cat. C9 Acert / 503 BHP x 2
2.  Propeller :  D35 " x P25.5" x 4B x 0.70 (NACA)
C.  Speed /Revolution  Test :
	Ahead	Return	Average	Fuel Rate (GPH)		Engine Load  (%)
RPM	Speed (kt)	Speed (kt)	Speed (kt)	Port Eng.	Stbd. Eng.	Port	Stbd.
700	4.7	4.3	4.5	0.9	0.9	7	6
800	5.3	4.5	4.9	1	1	2	1
900	5.8	5.2	5.5	1	1	6	5
1000	6.5	5.9	6.2	1.5	1.5	8	7
1100	7.2	6.6	6.9	2	2	13	13
1200	7.6	7.1	7.4	3	3	14	15
1300	8.0	7.8	7.9	3.1	3	18	19
1400	8.7	8.4	8.6	4	4	19	20
1500	9.1	8.9	9.0	4	4	20	21
1600	9.7	9.3	9.5	5.2	5.4	22	22
1700	10.1	9.9	10.0	7	7	28	27
1800	10.8	10.4	10.6	8	8	29	28
1900	11.1	10.9	11.0	9.8	9.6	35	35
2000	11.4	11.1	11.3	12	11	40	38
2100	11.8	11.8	11.8	14	13	47	46
2200	12.0	12.1	12.1	15.9	15.5	56	54
2300	12.4	12.4	12.4	18	17	69	64
2400	12.8	12.7	12.8	20	19	80	73
2500	13.0	13.1	13.1	23.7	23.4	92	90
Max.	13.4	13.4	13.4	25.1	24.8	98	95
	1.Fuel Tanks : 100%        Water  Tank : 100%
Remark :	2.Max. RPM :  Port Engine = 2529   Stbd. Engine = 2546
	3.Person on Board : 15
	4. Boat Weight = 45.45 tons + 15 person = 46.58 tons

The boat was tested with full fuel tanks (7,800lbs - 6lbs per gallon x 1,300), a full water tank (2,400lbs - 8lbs per gallon x 300) and15 people on board (2000lbs).  The boat weighted in at 93,160lbs (46.58 tons).

The boat's empty weight (displacement) is 73,000 pounds.  This does not include fuel, water, optional equipment (e.g., a dingy and davit adds an easy 2,500 pounds) or the owner's gear.   Actually, the boat was not fully fueled and had none of our personal gear on board.  Tania simulates the fuel and gear with lead weights.

Bottom line: The boat is tested "heavy."  We should get slightly better speeds as we will not be operating with full fuel tanks most of the time. 

Explanatory Note: Best practice with regard to fuel is to keep tanks full to prevent condensation.  However, with a fuel polishing system any condensation can be eliminated by regular operation of the system.

Tania's speed readings have a high degree of reliability.  The report's "ahead" and "return" speeds indicate speed recordings in opposite directions to correct for wind and current.

What is not totally reliable is the fuel burn rate or Gallons Per Hour (GPH), which were obtained from Caterpillar's digital engine monitors.  They show the same fuel burn at several of the lower RPMs (i.e., 800/900, 1200/1300, and 1400/1500).  It is unlikely, for example, that a 4 GPH fuel burn rate occurs at both 1400 and 1500 hundred RPMs. Higher RPMs are achieved by injecting more fuel and air into the cylinders.

Also notice that the report does not list the vessel's range.  Boat manufacturers tend to avoid range representations as that number can be effected by wind, current, vessel loading and the condition of the boat's bottom.

So for my own purposes, I constructed a more detailed analysis (below) that translates Tania's raw data into information that will be useful in operating the boat and in planning cruises.

Note: The burn rates in the GPH column combines the rates for both engines.  Between 800 and 1500 the burn rates are interpolated to account for engine monitor inaccuracy. The last three columns, MPD, GPD and GPM stand for Miles Per Day, Gallons Per Day and Gallons Per Mile.  MPD and GPD are based on a 10 hour cruising day.

 

GUIDED DISCOVERY SPEED VS RANGE ANALYSIS

RPM	KTS	MPH	LOAD	GPH	RANGE	HOURS	DAYS	MPD	GPD	GPM
700	4.5	5.2	6	1.8	3738	722	30.1	52	18	2.9
800	4.9	5.6	2	2.0	3663	650	27.1	56	20	2.8
900	5.5	6.3	6	2.5	3289	520	21.7	63	25	2.5
1000	6.2	7.1	8	3.0	3090	433	18.1	71	30	2.4
1100	6.9	7.9	13	4.0	2579	325	13.5	79	40	2.0
1200	7.4	8.5	15	5.5	2011	236	9.8	85	55	1.5
1300	7.9	9.1	18	7.0	1687	186	7.7	91	70	1.3
1400	8.6	9.9	19	8.0	1607	163	6.8	99	80	1.2
1500	9.0	10.4	20	9.0	1495	144	6.0	104	90	1.2
1600	9.5	10.9	22	11.0	1291	118	4.9	109	110	1.0
1700	10.0	11.5	28	14.0	1068	93	3.9	115	140	0.8
1800	10.6	12.2	29	16.0	990	81	3.4	122	160	0.8
1900	11.0	12.7	35	20.0	822	65	2.7	127	200	0.6
2000	11.3	13.0	39	23.0	735	57	2.4	130	230	0.6
2100	11.8	13.6	47	27.0	653	48	2.0	136	270	0.5
2200	12.1	13.9	55	32.0	565	41	1.7	139	320	0.4
2300	12.4	14.3	66	35.0	530	37	1.5	143	350	0.4
2400	12.8	14.7	77	39.0	491	33	1.4	147	390	0.4
2500	13.1	15.1	91	47.0	417	28	1.2	151	470	0.3
Max	13.4	15.4	98	50.0	401	26	1.1	154	500	0.3

 

Conversion KTS to MPH					1.15
Fuel (No Reserve @ Max Range)					1,300	Gallons
Weight (full fuel, water & 15 persons)					93,160	Pounds
Single Cruising Day (MPD, GPD)					10	Hours

EXPLANATION:

The data shows that the 63 is clearly a trawler with its semi-displacement hull design.  It has a maximum range of 3738 statute miles at 700 RPMS, which gives it the capability of crossing the Atlantic ocean.  Notice, however, that 30.1 days are required at 5.2 MPH.  Still at 1000 RPM and 7.1 MPH it is possible to go 3080 miles in 18 days.  While I do not intend to cross the Atlantic, I do plan to use the boat's long range capability (e.g., the planned beeline in May from Norfolk to the Cape Cod Canal is about 500 miles).

The boat's optimum operating speeds, 9.1 to 10.4 MPH, occur between 1300 and 1500 RPM (green cells).  At those speeds the fuel efficiency (GPH) is slightly better than 1 gallon per mile (GPM).  From there, every 100 RPM increase produces a slight increase in speed with a considerably greater fuel burn and reduced range (yellow cells).  Once you get to 1900 RPM and above (pink cells), the speed increase per 100 RPM is minimal while the fuel burn is significant.  Example: Compare 1400 RPMs at 9.9 MPH to 1900 RPMs at 12.7 MPH in the MPD and GPD columns. The extra 2.8 MPH translates into an additional 28 miles of range at a cost of 120 additional gallons or $600 more at $5.00 per gallon. The problem simply worsens at the higher RPMS.

Explanatory Note: The 63's "calculated" hull speed is 10.3 MPH based on her length at the waterline (LWL) of 57' 11".  Click on the link below for a full explanation of hull speed and its calculation.

http://www.cncphotoalbum.com/technical/hullspeed/hullspeed.htm

Explanatory Note: There are three basic hull designs, planning, displacement and semi-displacement.  Each serves a purpose and has advantages and disadvantages.

Planning Hull: Essentially a "flat" bottom that enables the boat to lift out of the water once a certain speed is reached.  Planning hulls run on the surface rather than through the water. The 48 Sundancer was a planning hull.  At 2400 RPM this 34,000 boat was capable of a 33 MPH top speed and a 30 MPH cruise speed (with a fuel burn of 48 and 42 gallons per hour respectively).  This was accomplished with two 540 HP engines.  If we added more horsepower the boat would go even faster (but would sacrifice living space).  A planning hull's speed is a function of its power. 

The 48's "calculated" hull speed was 9 MPH.  This was achieved at 1030 RPM with a 4 GPH burn rate (2.2 GPM).  9 MPH worked great on calm water like the intracoastal waterway.  However, as seas rose the boat's stability was compromised.  In order to obtain stability in rough seas the boat needed to be up on plane.  But this only worked in seas up to 5 feet and had limitations.  In a head sea we had to reduce speed to prevent the boat from banging. After 5 feet we had to drop to trawler speeds with the resultant instability.  Stability at the dock is excellent due to the planning hull's hard chines.

Note: Planning hulls can utilize hydraulic stabilizers.  However, the stabilizers are smaller to reduce drag and therefore most effective at planning rather than trawler speed.  They easily shave off 1 MPH due to the drag they create and do not eliminate the banging problem in a head sea.

Displacement Hull: Think of a full keel sailboat and that is a displacement hull, a rounded hull with soft chines.  Incredibly efficient with a one or two small engines at hull speed, which, again, is a function of the boat's length.  Terribly inefficient as power increases.  Essentially, you cannot get additional speed by adding horsepower.  The hull never lifts out of the water.  In fact more power simply pushes more water.  The good news is that a displacement hull can be effectively stabilized.  However, at a dock the boat is subject to greater roll due to the soft chine and rounder bottom aft.  In terms of range the displacement hull is the most efficient hull design.

Semi-displacement: The Outer Reef 63 is a good example.  A deep bow with a keel leading back to a somewhat flatter hull design aft and hard chines.  Relatively efficient at low speeds while capable of higher speeds as the hull partially planes but with very poor fuel efficiency.  Good for speeding up occasionally to make a bridge or in an emergency.  Like the displacement hull, a semi-displacement can be stabilized.  We chose hydraulic stabilizers and specified the larger 7.5 foot fins.  Larger fins equal greater stability but probably cut as much as a 1/2 MPH from the boat's speed compared to the smaller 6 foot fins.  Another feature of a semi-displacement hull is good stability at the dock due to the hard chine and flatter bottom aft.

Semi displacement hulls will go faster with more horsepower.  For example, the 63 can also be equipped with a pair of Caterpillar C12s producing 705 HP each.  This increases the boat's top speed to 20 MPH as compared to the C9s 15.4.  But that 5 MPH speed increase comes with a 69 GPH fuel burn.  The larger engines also decrease range considerably at trawler speeds.  For example, at 11.5 MPH, range decreases to 910 nautical miles as compared to the C9's 1,068, a difference of 17%.  At just above idle, the range decreases to around 1,600 nautical miles as compared to well over 3,000 with the C9s.  This shows that while a semi-displacement hull has the capability of greater speed with added horsepower it is not efficient at the higher speeds.

View of the 63's semi-displacement hull
Note the very visible starboard stabilizer

View of the 63's keel, flat bottom and hard chines (Week 18)

We traveled a total of 6,150 miles during our Great Loop adventure while only burning 5,791 gallons.  This was achieved by operating the 48 as if it were a trawler most of the time.  As a result, we grew to love the leisurely pace and quiet ride.  With the 63 we will be enjoying an even more quiet ride with the luxury of significantly greater living space.

Bottom line.  The sea trial results were just what we expected.

Written by Les.