Weather: Amazing! Cool and dry, very little wind. I launched just after 6:30.
Plan:
- 4 x 2500
- 5′ active rests
- rate target: 26
- pace target: 2:15
I am pretty darn happy with this workout. I would have been happier if it was faster, but I executed this workout to the best of my ability. No theatrics, no bailing out.
There was one weird thing with today’s workout. I was seeing a persistent difference in pace between the speedcoach and the GPS. Now, over a short span, I don’t expect them to read the same, but for basically the whole row downriver, I was seeing the GPS based numbers giving a pace 2 to 5 seconds faster than the impeller. Must be flow, you might be thinking. At least that was what I was thinking, but right now, there is essentially no flow. The water level is so low that basically nothing is going over the dam. And when I saw the same thing going up river, I decided that something was fishy with the speedcoach impeller. Either the cal was off, or there was something fouling the impeller.
Here is a comparison of the paces for the four pieces.
GPS — Imp –> Delta
2:12.0 — 2:14.6 –> 2.6
2:14.9 — 2:17.4 –> 2.5
2:16.1 — 2:18.7 –> 2.6
2:16.7 — 2:19.5 –> 2.8
I saw nothing on the impeller when I pulled the boat, so I will do the comparison again tomorrow and update the cal if there is still a difference.
Here’s the (slow) speedcoach data.
For comparison, here are the first 3 intervals based on TCX data from RIM. The pace data is a lot noisier, but the eyeball average is about 3 seconds faster. I had a glitch with the phone and the data for the 4th interval ended up in a different file.
Here’s the TCX data for the fourth interval.
Here are the tabulated results.
TCX Data from RIM
|Start|Dist_|Time_|_Pace__|_SPM__|avg HR|DPS_|Remarks
|00019|01203|07:11|02:59.1| 18.7 | 117 |09.0|Warming up
|01250|02496|10:59|02:12.0| 26.2 | 159 |08.7|rep #1 – downstream
|03746|00474|04:59|05:15.4| 16.1 | 125 |05.9|rest
|04269|02498|11:14|02:14.9| 26.2 | 167 |08.5|rep #2 – upstream
|06767|00424|03:53|04:34.8| 19.9 | 135 |05.5|rest
|07219|02501|11:21|02:16.1| 26.2 | 170 |08.4|Rep #3 – downstream
|00020|00280|03:22|06:00.7| 13.1 | 128 |06.4|rest
|00300|02498|11:23|02:16.7| 26.5 | 170 |08.3|rep #4 – upstream
|02798|01492|09:50|03:17.7| 19.7 | 139 |07.7|cool down
|—–|09993|44:57|02:14.9| 26.3 | 167 |08.5|Main Set
Impeller Data from Speedcoach
Start_|_Dist_|_Split_|_Pace_|_Strks__|_Rate_|_DPS_|_AvgHR_|_Remarks
00020_|_1188_|_06:46_|_2:50.7_|_122___|_18.0_|_09.7_|_117___|_warmup
01220_|_2501_|_11:13_|_2:14.6_|_292___|_26.0_|_08.6_|_159___|_rep #1
03720_|_0389_|_02:59_|_3:49.8_|_052___|_17.4_|_07.5_|_126___|_rest
04093_|_2508_|_11:29_|_2:17.4_|_300___|_26.1_|_08.4_|_166___|_rep #2
06610_|_0299_|_02:15_|_3:45.9_|_039___|_17.3_|_07.7_|_128___|_rest
06900_|_2512_|_11:37_|_2:18.7_|_304___|_26.2_|_08.3_|_169___|_rep #3
09420_|_0302_|_02:35_|_4:17.0_|_039___|_15.1_|_07.7_|_134___|_rest
09700_|_2493_|_11:35_|_2:19.5_|_306___|_26.4_|_08.1_|_170___|_rep #4
12210_|_1364_|_08:20_|_3:03.2_|_166___|_19.9_|_08.2_|_136___|_cool down
Dist__|_Time__|_Pace___|_Strks_|_SPM__|_DPS__|_AvgHR_|_Remarks
01188_|_06:46_|_2:50.7_|_122___|_18.0_|_09.7_|_117___|_warmup
10014_|_45:54_|_2:17.5_|_1202___|_26.2_|_08.3_|_166___|_Main set
Tomorrow: 75′ Steady State, 20 spm, HR cap at 155.
Quantified Rowing 
There is also a significant difference in total time. Do you switch both devices on/off simultaneously?
LikeLike
Both RIM and Speedcoach were continuously running. The summary is calculated after the fact using the excel spreadsheets. The differences in time and distance reflect the use of specific start and stop records for the time and distance point. I just went back and resliced the data so that I used identical time spans for each interval, since that would be consistent across the two instruments. The error would be in how the the speedcoach turns impeller spins to distance. When I did that, the total time matched within 0.4 seconds, and the total distance was 181 meters longer on GPS data. That is a -1.8% error in distance logged by the speedcoach.
LikeLiked by 1 person
The noisier the GPS data, the longer the tracks because of more zig-zagging. Was the data more noisy than on other days?
LikeLiked by 1 person
Not at all. But a good point. I hadn’t thought of that.
LikeLiked by 1 person
For courses that are relatively straight compared to the GPS accuracy and data collection frequency, the noisier the data, the more GPS overestimates the course length. I think this is the case for rowing with crewnerd.
LikeLike
So, I posted about this last November. Over 50 minutes, the overestimate of distance is about 2.5m. What I am seeing here is about 181m of error over 45 minutes, so I suspect the speedcoach mis-calibration is swamping the error from gps overestimation.
LikeLiked by 1 person