Hmm, more of an axial roll really
Weather is perfect again today so may head out to Big Pond if I have time, perhaps tomorrow after the club meet, there's about a 200m run available there, it's just a hack to get to with all the gear, the guys including me are rigging golf trolleys to carry our gear the 1/4 mile over boggy moorland to get to it :-) . GPS's are notoriously inaccurate for speed over short distances, which for the benefit of anyone reading this I'll explain. Generally a GPS will tell you how accurate it is from any given position, my Garmin Etrex usually tells me it's about 15 -17 feet. If the boat then travels, say 50 feet at full speed, if the GPS updates every second it could see that as only two points, if we take it as 15ft accuracy for ease each point could be plus or minus that amount, so as much as 80 feet travelled [2 points x maximum '+' error for each therefore distance travelled+(15x2)] or as little as twenty feet [2 points x maximum '-' error for each therefore distance travelled-(15x2)]. So, if the GPS error sees 80 feet it's going to give a max speed reading which would probably make one smile a great deal but would be as useful as breasts on a fish. There are so many YouTube videos with folk proudly showing the speeds obtained but I'm sorry, if the distance travelled is short it's not reliable and you're kidding yourself. Hence why Radar is the only way speed readings can be used to declare formal records etc. One of my other hobbies is Parakarting, using foil 'powerkites' to propel buggies, and there's loads of debate about this so it's well known to me.
However, my view is that GPS readings give something of an indication, and it's fun seeing what can be gained and I'm happy to join the party on their use, it just won't stand up in court as it were. So yes, I could strap my Garmin to the boat and see what I get. I estimate that at the moment I'm doing about 35 mph around the pond, I see it as being 40-45 in open water which was the target for the build, and I reckon the curved fin is robbing it of maybe 5-7 mph, the thin fin perhaps 3-5.
I set the fin to neutral to start with, then after some runs tweaked it to give a little bit of pull down to aid keeping that inner sponson held down. Tiny amounts though, too early to draw finite conclusions.
On the motor front I have a direct comparison, my son's boat has the same engine with lots of run time and his is audibly revving far more than mine, but he has a Master Airscrew 12x6 on his, mine has a APC 12x8, so that's all very well but it's thrust that matters and it would be wise to measure that rather than RPM. My gut feeling is that there's more to come on mine. I add ZX1 to my fuels as I'm a complete convert on the stuff, but it does mean running in takes much much longer.
By the way I've been thinking about the rooster tail differences. We must take into account that the finer tail coming off the thin fin could be the result of greater speed, it's not necessarily indicative of the holding power of the fin.
Unfortunately one of the niggles with all of this is that getting reliable video is tricky, I have the gear, but I need someone to operate it. The vids above are simply off a phone rigged to the transmitter, and the wide angle lens on phones crucify the perception of speed due to perspective issues. What's really needed is a long focus lens, a stable mount, and a smart operator to follow it. I'm seriously seeing if the 'Soloshot' system can be used, this rig automatically follows a transponder on the subject, I don't know if it's fast enough though, I'll see. I like making videos (check Jes437 powerkite vids on YouTube), and to date there is not a quality video of one of these boats, there's plenty of fun vids like my current ones which are great, but it would be good to have a properly produced version some time.