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How to use PT Series Tension Gauges

 

 

HOW TO MEASURE

Figure 1

                  

 

ModelCable size
Model PT-1 Cable size 3/32", 1/8", 5/32"
Model PT-1M Cable size 2.5mm, 3mm, 4mm
Model PT-2 Cable size 3/16", 7/32", 1/4"
Model PT-2M Cable size 5mm, 6mm, 7mm
Model PT-3 Cable size 1/4", 9/32", 5/16", 3/8"
Model PT-3M Cable size 7mm, 8mm, 9mm, 10mm

 


Hold the gauge with the left hand and place the cable between the two nylon spools as shown in Figure 1.

With the right hand pull the lanyard and extend the spring until the hook on the nylon slider can be hooked on the cable as shown in Figure 2.

Figure 2

 Release the lanyard. Read the needle position on the scale. Refer to the calibration table obtain correct tension in the cable. The gauge can be left on the wire for "hands free" adjusting of the cable.

To assure accurate readings make sure that the slider moves freely in the frame slot and does not bind. Also, lubricate the slider slot frequently with silicone lubricant.

 

Note: An extra 1/4" inch hole is provided in the frame of the instrument for an attachment of a short lanyard and snap hook (not furnished) for securing the gauge to the cable. This will prevent loss of the instrument if it becomes inadvertently detached.

 



HOW MUCH TENSION?

Specific tension requirements for your application must be obtained from the boat, mast, or sail manufacturer or the manufacturer of the product on which the cable is used.

Table 1 recommends an initial tension setting, but there is no simple solution since the optimum rigging tension will be a function of the boat design, the rig (masthead or fractional, one or more spreaders, etc.), and even the cut of the sails. Many skippers use insufficient tension because of a fear of "breaking something." It should be noted that on America's Cup contenders, where electronic state of the art tension instrumentation is available, the standing rigging is set as tight as is structurally feasible.

Table 1
302/304 1x19 Stainless Steel Rigging Cable
Diam., In.Breaking Strength PoundsForestay* PoundsShrouds* Pounds
3/32 1200 180 120
1/8 2100 320 240
5/32 3300 500 350
3/16 4700 750 500
7/32 6300 1000 700
1/4 8200 1300 850
9/32 10300 1600 1050
5/16 12500 2000 1300
3/8 17500 2750 1850
*Suggested initial settings.

 

 

ONE DESIGN CLASS RACING SAILBOATS

Most sail makers who produce sails for the one design classes provide each purchaser with specific set of readings on the Loos Model A or Model B tension gauges for use when setting up the standing rigging. This assures that the sails will have the correct shape when the rig is under load.

For the convenience of sailors who wish to upgrade from our Model A or B gauges to the professional model (PT-1, PT-2, or PT-3) gauges we include below a conversion chart so that the same recommended tension can be obtained with the PT-1, PT-2 or PT-3 gauges as with the Model A or B gauges.

MODEL A
MODEL PT-1MODEL BMODEL PT-2MODEL PT-3
SCALE3/321/85/32SCALE3/167/321/49/32
5 6     10 11      
10 9     15 13      
15 12 14   18 15      
20 16 16   20 16 18    
25 20 19   22 18 20    
28 23 21   24 19 22    
30   22   26 21 24    
35   27 25 28 23 25    
38   30 28 30 25 27 25  
40   33 30 32 27 29 27  
42     33 34 29 31 39  
44     36 36   33 31  
45     38 38   36 33 6
46     39 39   37 34 7
47     40 40     36 9
        41     37 10
        42     39 11
        43     40 12
        44       14
        45       16
        46       18
        47       20
        49       25

 

 

 

 

When no specific requirements are provided by the sail maker, the following general comments will provide a basis for a rational procedure for tuning the rig.

FORESTAY TENSION

Masthead Rig On the masthead rig it's almost always advantageous to set the forestay tension as high as possible within the limits of structural strength. Generally, it's possible to use 15% of the breaking strength of the cable. Thus, a forestay tension of 1,000 lbs. is a reasonable place to start with a 7/32"diam., 302/304 1x19 stainless steel cable. Backstay tension would, of course, have to be adjusted to maintain a straight mast with the desired forestay tension. Since the backstay makes a greater angle to the mast, the backstay tension will be lower than the forestay tension.

NOTE ! ROLLER FURLING CAN ONLY BE SET BY BACK STAY TENSION.

Fractional Rig In a fractional rig the forestay does not go all the way to the masthead and forestay tension cannot be directly balanced by tension in the backstay. Therefore, some mast bend is generally accepted and the mainsail is cut to fit the bend. A forestay tension of at least 15% of the cable strength is desirable. However, if this results in excessive mast bend it will be necessary to back off a bit. On some fractional rigs, diamond shrouds are used to reduce mast bend.

 

UPPER AND LOWER SHROUD TENSION

Masthead Rig There is a simple criterion for shroud tension. The initial rigging tension should be high enough that the leeward shrouds do not go slack when sailing close-hauled in a reasonably brisk breeze. The proper value for your boat can be found by a few trial runs under sail. Once the correct tension is known, the gauge can be used to maintain the value.

For many boat designs a shroud tension of 10% to 12% of the breaking strength of the cable is adequate. Thus, for 7/32", 302/ 304 1x19 stainless steel cable , the upper and lower shrouds would be set to 600 to 700 lbs. tension. On some rigs it may be desirable to carry more tension in the uppers than in the lowers.

Fractional Rig For most fractional rigs the correct shroud tension is the same as that for a masthead rig, i. e., a tension setting that will keep the leeward shrouds from going slack. However there is one exception. On certain fractional rigs , the upper and lower shrouds lead to chain plates that are aft of the mast. The spreader is swept back. For such a rig most of the forestay tension is balanced by the upper shrouds. A shroud tension of approximately 20% of the cable strength may be required to achieve the desired forestay tension. Never exceed 25% of the cable breaking strength. (Refer to the breaking strength chart Table 1.)

NOTE ! THE INTENDED USE OF THIS GAUGE IS TO BE USED ON 302 / 304 1x19 S.S. CABLE IN APPROPRIATE SIZES. IF USED ON OTHER CABLE TYPES, SIZES, AND CONSTRUCTION YOUR READINGS WOULD BE CONSISTENT (REPEATABLE) BUT POUND TENSION VALUES WOULD DIFFER FROM THOSE LISTED ON THE LABEL. GAUGE MAY NOT READ "O" WHEN AT REST, AS THEY ARE CALIBRATED AT MIDRANGE OF TENSION.
NOTE ! IF FLAT SPOTS APPEAR ON NYLON SPOOLS AFTER EXTENDED USE, ROTATE NYLON SPOOLS 45°.

 

ADDITIONAL SCALE READINGS

LBS. TENSION

 
CALIBRATION PLATE
MODEL PT-1
CALIBRATION PLATE
MODEL PT-2
CALIBRATION PLATE
MODEL PT-3
SCALE 3/32 1/8 5/32 3/16 7/32 1/4 1/4 9/32 5/16 3/8
5 70           550      
6 80           600      
7 90           700      
8 100           770 500    
9 110           830 550    
10 125     180     900 600 320  
11 135     240     1000 650 380  
12 150 100   270     1100 720 440  
13 160 110   300     1200 780 500  
14 170 125   330     1300 830 550  
15 185 135   370     1400 900 600 200
16 200 150   420     1500 1000 680 230
17 220 165   450     1650 1080 740 270
18 240 180   500     1800 1150 800 290
19 260 200   540     2000 1220 870 330
20 280 220 140 590 320     1300 950 360
21 300 240 155 640 360     1420 1050 380
22   260 170 700 410     1540 1130 420
23   280 185 770 450 300   1660 1210 480
24   300 200 840 500 350   1800 1300 530
25   320 220 920 560 400   1960 1400 570
26   345 245 1030 630 450   2130 1500 600
27   370 265 1110 680 500   2300 1600 650
28   390 300 1240 740 550   2500 1700 720
29   420 320   820 600     1850 800
30   450 335   890 660     2000 870
31   475 360   970 720     2200 930
32   500 390   1060 780     2400 1000
33     420   1180 840     2700 1100
34     450   1300 900     3000 1200
35     480   1480 1000       1300
36     520   1680 1100       1400
37     560     1200       1500
38     610     1300       1650
39     700     1600       1770
40     800     2000       1900
41                   2100
42                   2230
43                   2400
44                   2620
45                   2850
46                   3100
47                   3400
48                   3700
49                   4100
50                   4500



 

ADDITIONAL SCALE READINGS

KGS. TENSION

 
CALIBRATION PLATE
MODEL PT-1 METRIC
Kilograms
CALIBRATION PLATE
MODEL PT-2 METRIC
Kilograms
CALIBRATION PLATE
MODEL PT-3 METRIC
Kilograms
SCALE 2.5mm 3mm 4mm 5mm 6mm 7mm 7mm 8mm 9mm 10mm
8 50                  
9 54                  
10 58           300      
11 62     95            
12 66     110     360 200    
13 70     120       220    
14 75     140       240    
15 82 70   150     480 270    
16 90 75   170       300    
17 100 82   180     550 330    
18 110 90   200       360    
19 120 100   220     630 400    
20 130 110   240       430    
21 140 120 70 260         460  
22   130 76 280 160   790 500    
23   140 83 310 180     540    
24   150 90 340 200   900 590    
25   160 100 370 210     630 370  
26   170 115 400 230   1100 680 410  
27   180 127 440 250     720 440  
28   190 140 490 270     770 480  
29   210 150 550 290     850 520  
30   220 160 620 320 220   920 560  
31   235 170   350 240   1000 590  
32   250 180   380 270   1100 630  
33     195   420 290   1240 700  
34     210   460 320   1400 750 400
35     225   510 350     810 430
36     240   570 370     870 460
37     260   640 400     940 500
38     280   730 440     1020 540
39     320     470     1100 590
40     360     510     1190 630
41     610     550     1300 680
42     700     620     1420 730
43     800           1600 790
44                   870
45                   940
46                   1000
47                   1090
48                   1180
49                   1270
50                   1360
51                   1500
52                   1640
53                   1800


 

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