As with so many things in the boating world, we often run into people who have strong opinions about the different adjustable oar towers that are available to go on raft frames. To get some facts, we decided to do a couple side by side tests to compare two types: Speed-Rail fitting/stanchion & a NRS frame oar mount.
For these tests we needed a raft frame. Alex Miller, one of the guys here at Eddyline, made up one out of 1.25” pipe. Speed-Rail fittings need to be placed on the frame before final assembly. Once that was done and the frame hoop was finished, a 1.25” oar stanchion was put in the Speed-Rail fitting and an 8” NRS frame oar mount was attached to the test frame.
Static load testing
The first set of tests were done to see how each unit held up under a static load.
Our testing frame, with the oar towers slightly off the edge, was clamped down to one end of a welding table. Then, for an anchor, we threw a climbing sling around the legs at the other end of the table. Next, we looped 7 mil cordage around the oarlock of the tower we were testing. To this cordage we attached a dynamometer to measure the load. From the dynamometer to the sling/anchor on the other end of the table, we hooked a ratchet strap to generate the force.
Two tests were done on each oar tower unit. The first with the unit tightened down only 2/3rds in torque and the second with the unit as tight as we could get it.
With this system we generated up to 700 lbs. of constant tension, which proved enough for both oar towers.
Dynamic load testing
The next set of tests were done to see how each unit held up under a dynamic load.
Our testing frame was clamped to a welding table in a vertical position, with the oar towers about 4’ off the ground.
Using a sling, we attached a 62 lb. chunk of railroad rail to the oarlock of the tower we were testing. With this setup we tried to simulate a grabbed oar or rock hit by dropping the chunk of railroad rail and shock loading the oar tower.
We generated approximately 1200 lbs. of force with this system.
Speed-Rail fitting with stanchion performance and results
When attaching Speed-Rail fittings, some frame builders choose to add additional screw sets by drilling and tapping the fitting. The fitting comes with 2 set screw holes, and it’s common to see 2 more added for a total of 4. For this test we split the difference and just added one, for a total of 3.
The first static load test showed that if the Speed-Rail set screws aren’t really torqued in, the fitting will slide and yield to less than 175 lbs. of force.
For the second static load test, we tightened the Speed-Rail set screws using a technique recommended by companies like Downriver. First, they were tightened all the way in, then they were backed out, and then they were tightened all the way back down again. After doing this “double tightening” technique, the Speed-Rail tower held tough all the way up to 650-675 lbs. of force before it started to slip.
When we examined the pipe where the Speed-Rail was attached after these two static load tests, we noticed it was marred by the set screws. After seeing this we believe if the frame had been repeatedly stressed like this, it would ultimately affect the strength of the frame where the fitting was placed.
In the dynamic load tests, the Speed-Rail fitting system held slightly stronger than the NRS mount. If the Speed-Rail tower moved, it was just barely.
NRS frame oar mount performance and results
The first static load test showed when the NRS frame oar mount wasn’t tightened as tight as we could get it, it started to slip at about 200 lbs.
For the second static load test, when the NRS frame oar mount U-bolt was really torqued down, the NRS unit held until about 625-650 lbs. before it started to slide.
When we examined the pipe where the NRS mount was attached after testing, there was much less damage to the frame, and it would be more likely that after continued usage that there would be less long-term wear on the frame.
Also worth noting, Alex, who was operating the ratchet strap during the tests, mentioned it seemed there was a greater amount of continued tension/resistance on the NRS oar mount.
In the dynamic load tests, the NRS oar mount slipped about 1/8” per drop but, overall, the unit stayed tight.
Our tests made it clear how important it is to have your oar towers, no matter which type of system you’re using, as tight as you can get them. If you’re running a Speed-Rail system, make sure you’re getting a good grab on your pipe. If you are running NRS mounts, you might want to have an extra U-bolt in your repair kit, just in case you over tighten and break the bolt.
For Speed-Rail style towers, it may be worth figuring a way to through bolt the fitting, to keep it fixed over long term use. This could help reduce damage to the pipe/mounting area, which would be a good thing, as once this area becomes worn it will continue to weaken. Weakening of this sort could become an issue if the frame has a lot of different users.
For NRS oar mounts, it might be worthwhile to always check the torque on your U-bolt at the beginning of every trip and before any big rapid day.
Overall, the two oar tower systems we tested were much more similar than we originally thought they’d be. So, which oar tower system is best for you seems to come down to your personal preference.
Thanks to Alex for coming up with the idea for this set of tests & Bego & T-Berry for rigging and camera work.
See you on the river!
- Aug 23, 2019 Oar Tower Testing: Speed-Rail fitting with stanchion vs NRS frame oar mount Aug 23, 2019
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