I will ensure that the leads will take full whack: 50A should do it?
Well today I did some measurements with the Minn-Kota Rip Tide 40 on the back of my Seafly which was moored to the jetty. Power was from a fully charged, fairly new, 100Ah Yuasa "Marine" battery which has deep-discharge and traction capability (whatever the latter means). The results are shown in the table below where:
"Gear" is the speed setting (1 to 5).
"Amps Measured" were read using an electronic Watt meter in series with the motor. These decreased during the relatively short test as the supply volts dropped from 12.6V to around 11.7V. This was no doubt due to pulling up to 52A from the battery at full power; on the second run it had dropped to 42A, the figures shown are a rough average.
"Quoted hours" are as printed on the top of the motor control pod.
"Ah assumed" is the implied practical capacity of a 12V 100Ah battery,for example at speed setting 1 Minn-Kota are assuming that 80% of the nominal battery capacity is actually usable.
These Minn-Kota quoted hours, or duration values, seem fairly reasonable except maybe for the higher speed settings. Drawing 40 to 50 A from a 100aH lead acid battery is not going to do it much good. However, as observed in the test, the result is to lower the battery voltage and hence the current drawn. So maybe it would go on for 1.5 hours at full power but at the expense of ruining the battery. This also implies that my estimate of 12kg bollard pull at full power would not be available for the full 1.5 hours - it is an over estimate. Of course a Lithium chemistry battery pack should be able to supply large currents more easily so in that case full performance would be maintained for longer.
I should mention that my Minn-Kota was bought a few years ago and has been used quite a bit. I don't know how it's performance compares to a brand new up to date motor (however they seem in the same ball park as those quoted on the Flover web site).
Is 50A enough? Well for my Minn-Kota 40 you would need a larger fuse than that and the wires should be rated for more current than the fuse. Looking at the Flover web site they say the 55 model draws max 45A to produce 25kg thrust "in bench tests" and 47A to produce 14kg in a "field test" so 50A is marginal. Also these figures again confirm that the thrust quoted for trolling motors is an over-estimate by 150% or more compared to what is achieved.
Sadly, and with much regret, I'm becoming more and more convinced that small electric outboards don't have the capabilities needed for use on the sea - or anywhere where there is a significant wind or current. Flover say their largest outboard will propel a 20' yacht at 3mph (2.6 kt)... that's not enough! So I'm stuck with my stinky, noisy, starts if you're not in a panic, Tohatsu!
Peter
p.s. I had't heard of Flover before - they look remarkably similar to the Minn-Kota!