Every year our club run a four hour challenge event. The rules are pretty simple the boat (for practical reasons) needs to be reasonably small and agile. Must be battery powered. And well thats about it really. A course is laid out that must be followed and if you exit the course you must re-enter at the same point. ie: if you come inside a bouy then you must circle it to rejoin. Bty changes are allowed and the trick seems to be to have a good lick of speed along with good longevity of battery. the winners usually change bty’s about 6 times.

 

Despite notching up 300 laps last year with a rather fast ish tug I came nowhere the winner (a 500 mm copy of a huntsman.( well designed DM.)) notched up over 400. So for this year I thought I’d set out my stall (so to speak) a little earlier and build something specificly to address the challenge. I chose a 435mm x 145mm(120 on water line) grp hull as the low beam to length ratio should reduce drag and make her a little slippy in the water. Max displacement is 726g so reasonably light and a 385 low drain motor on 8.4v  should provide enough grunt without draining bty’s to quickly (my aim is only 4 bty changes max) electricery will come from some 2450 Mah (or possibly bigger) AA NiMh  cells (7 per pack)

 

The pics are of progress so far

Nice thought Ashley however, and DM will no doubt confirm or otherwise, modern esc’s do not create significant power loss, and certainly not in the order of the mech ones that used to, still do for some, warm the inside of the boat. Plus yes the course requires some level of control esp in the tighter corners, and there’s the other boats to avoid, so a reasonably  good level of speed control is a must. Technically without an esc its an rg boat (radio guided) and  the rules do state RC I can just hear the mutters of Bloody Hooligan from here and the challenge is in Sept lol and hey I’ve never been that much of an “all or nothing kinda guy” just don’t tell any one

Hi Rick. I think what we do is pretty much on those lines, we don’t have a max size or bty definition in the rules yet but the possibility is there. Although we do compete for a trophy it is still very much an informal event aimed at allowing as many in the club to compete/have fun as possible. The length of the event does tend to self regulate the top speed of the vessels as to get “hooligan” speeds tends to mean high amps so producing short bty life/multiple changes which in turn defeats the gains made by the high speed, also the tightness of the course makes it near impossible to go to fast. About 400/500 mm seems to be the norm usually of the “swordsman” style. ie: quick and nimble, the big trick seems to be to get it real light thus saving huge mounts of bty power pushing it round. Last years winner displaced a measly 800g hopefully mine will come in well under 700g (currently weighs less than 200g but  still has superstructure btys esc rx and servo to be fitted) the other criteria I perceive is survivability as collisions are somewhat inevitable so a level of swamping must be acceptable hence I’m building with large airtight cabins fore and aft. Also the centre area will need to be easily accessible for speedy bty changing. A little secret weapon in case of a bump against the bank (Concrete in parts) is the front 50mm of the bow is a solid GRP plug with strengthing bars glassed into the inside of the hull running fore/aft back to the midpoint. Some rubber along the gunwhales should help too

Some more WIP pics! only 3 days on this so far and its sure taking shape the weights looking too with only 30g off ESC 20g off RX and bty’s to fit she now weighs a spritely 420g so if the rest of the superstructure and bty’s come in under 240g (which they will) she will be under design weight (a good thing ) The bty’s will be fitted on the cockpit floor with a box over possibly held to steel strips with magnets to allow them to be shifted forward/aft to trim and making them easily accessible for rapid changing. the rest of the superstructure will be minimull (to keep weight and aerodynamic drag down)

Hi Bob sorry to hear about the potentially duff P98 I take it they’re both running on the throttle channel and one of the RX plugs isn’t reversed??

 

The heat sink should be good esp as I have a self adhesive heat transfer pad between it and the motor. (The sort of substance that you will find in between esc fet’s and their heat-sink) I’m going to risk and air scoop on the deck with spray deflector of course and a vent rearwards between where the windshields are to go. sort of inspired by the cowl on your Slo-Mo-Shun.

I’ve just ordered the ESC and Batteries for her and so now its sit back and wait for the snail mail to fetch my goodies. given one item is coming from hong kong it could be 10 long slow days  however for applications such as this I rate the ESC I’ve ordered slightly over kill as its rated 50a fwd and 20a rev With  a Voltage range of 6-12V having said that once had one in an off road buggy and it never failed despite my grandson constantly stalling it (Prob 80A’s) trying to climb rocks, also they are 100% waterproof and testement to that was the same buggy (a 1/8 scale 4wd job) driving through many puddles, often slowly sometimes quickly, that where deep enough to completely submerge it. the esc was strapped to the chassis so no protection there. finall testement is the fact that said abused esc is still performing faultlessly in the SS Tonendale So yes a good piece of kit well worth the £20 average that I spend on them on ebay generally they just won’t let one down and this one will be my fourth, I’ve got 2 others powering tugs.

 

 

Phil (looking for his patient head)

The ESC arrived from hong kong today and so it’s full steam ahead on sunday.

 

 

Personally I feel the performance, speed wise, will be satisfactory, and duration wise prob a little disapointing. this is based on the fact that I’ve exceeded the target weight of 726g by nearly 150g, ooh er thats a lot, however in the domestic tank her response to a 1/2 throttle blip is to jump onto the plane in about a foot, swiftly caught by my waiting left hand I might add! So I’m hopefull all is not lost, and she may even stand a prop  size reduction to extend bty life.

 

If nothing else I’ll have a fun little boat and some valuable experience under the belt.

 

 

Phil (praying for dry weather this Sunday)

Here we go then in a moment of bordem I took this one off the backburner and ripped the heavy balsa/grp deck and the forward bulkhead out and replaced it with depron. basically styrene foam. I also moved the esc back to just forward of the rear bulkhed. all this has reduced the weight to a tad over the target weight.

 

The effect on performance isn’t stunning. she still sits a little low at the rear and top speed aint sparkling. edurance is though nearly 45mins at 80% throttle on one bty before any serious degridation of speed. so to lighten her further I’m looking for a lighter esc (current one weighs in at 50g) and then add a cell to the bty packs and then fingers crossed eh

 

Phil