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How to use RT Series Tension Gauges

We offer a series of gauges to measure the tension in rods from .172 to .375 inch in diameter over a range of approximately 5% to 25% of the breaking strength of the rod and provide an accuracy of + or - 5%.

HOW TO MEASURE

Figure 1

ModelRod Diam
Model RT-10   Rod diam. .172, .198, .225, .250, .281
Model RT-10M   Rod diam .4mm, 5mm, 5.7mm, 6.3mm, 7.1mm
Model RT-11   Rod diam. .281, .330, .375
Model RT-11M   Rod diam., 7.1mm, 8.4mm, 9.5mm

 

 

Hold the gauge with the right hand and place the rod between the two nylon spools as shown in Figure 1. With the left hand pull the lanyard and extend the spring until the hook on the nylon slider can be hooked on the rod as shown in Figure 2.

Figure 2

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

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

 

HOW MUCH TENSION?

 

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
Nitronic 50 Rod
  Breaking StrengthForestay*Shrouds*
Diam,. In.Lbs.Kgs.Lbs.Kgs.Lbs.Kgs.
.172 4700 2140 705 320 470 214
.198 6300 2860 950 430 630 290
.225 8200 3730 1230 560 820 380
.250 10300 4680 1550 700 1030 470
.281 12500 5680 1880 850 1250 570
.330 17500 7960 2630 1190 1750 800
.375 22500 10230 3380 1530 2250 1020

 

ONE DESIGN CLASS RACING SAILBOATS

It is suggested that you contact your sail maker for the recommended initial settings for the rod rigging on your boat. For larger boats it may be prudent to check with the designer of the boat.

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 rod. Thus, a forestay tension of 1,550 lbs. is a reasonable and conservative place to start with a .250 diam. Nitronic rod.

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 rod 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 rod is adequate. Thus, for a .250 diam. Nitronic rod the upper and lower shrouds would be set to 1000 to 1200 LBS. tension. On some rigs it may be desirable to carry different tension in the uppers than 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 rod strength may be required to achieve the desired forestay tension. Never exceed 25% of the rod breaking strength. (Refer to the breaking strength chart Table 1.)


GAUGE MAY NOT READ "0" 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°.

 

 

RT10 & RT-10M TENSION GAUGE - FRONT LABEL

 

RT-10
POUNDS (LBS.)
RT-10M
KILOGRAMS (MM)


 

RT-11 & RT-11M TENSION GAUGE FRONT LABELS

 

RT-11
POUNDS (LBS.)
RT-11 METRIC
KILOGRAMS (MM)

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