Newcomer with a question

[Old School]

Firstly, I am new to this site and reside in Australia. My adult son has rekindled my interest in boating and has convinced me that fast electrics are the way to go. He has a Zonda which has been clocked with GPS at the magic 160 kph, however, my direction is not to achieve a speed anywhere near this. I would be happy with around 60 kph.

Now my question. A friend recently gave me an old 70 cm shallow vee mono hull that had been set up with a brushed 540 motor, although this has been lost years ago. The drive ran through a reduction gearbox with a ratio of 0.734. The design is not surface drive and has the conventional drive through a 3 mm shaft with a basic 37 mm plastic propellor. As the shaft is firmly bonded to the shell I am reluctant to remove and replace with a 4 mm shaft. Thus the 3 mm shaft plus the reduction drive will be limiting factors.

The hull design is quite sleek so I do not think the hull design will be a problem. I have started to reinforce the shell by filleting the inside join with epoxy.

Now to the drive. Personally, I would prefer a 35 amp 540 size Leopard brushless inrunner to enable easy install to the existing mounting, however, my speed enthused son thinks that a 65 amp Leopard would be better. The ESC would be a 120 amp model, with both the motor and ESC water cooled. Turn fins and trim tabs will be fitted. A 35 mm two-blade CNC propellor is planned.

Any thoughts please, Tim

[iop65]

Picture?
ABS hull?
35amp inrunner,65amp inrunner.....?.

[Old School]

Many thanks. The hull and deck are ABS with a relatively 'flimsy' cabin although this has been strengthened. Basically, my question is would the 65 amp Leopard 36XX size be too much for this 70 cm hull considering the 3 mm drive shaft and reduction gearbox? The conservative part of me is partial to the 35 amp motor although my son wants the boat to run relatively quickly.

I realise that I am starting with an older design but the elderly part of me wants to restomod this boat.

[Old School]

These are my possible choices -

Leopard Hobby 3650 30 amp 3200kv 2 pole
3650 35 amp 3570kv 2 pole
3650 65 amp 2930kv 4 pole
3650 72 amp 3930kv 2 pole

[rol243]

with a reduction gearbox arrangement you do need a relatively high reving motor depending on the gear ratio it has. the hull in pic doesn,t look to bad but it would be nice if you could remove the drive line and reduction drive and fit a surface drive assembly which would be direct drive and the prop would be positioned at the lower rear of transom plus the rudder behind as well. doing this mod would make for a much better and more reliable boat and its not a big job to do this conversion. if your in Australia have a look at some motors and hardware from [ r/c boat bitz . com. au ] they have some nice T.P. motors . let us know what you think about modding this hull . are the Leopard motors your looking at coming from Ebay Aust ?

[Old School]

Modifying to a surface drive would be possible and achieve a higher speed, however, due the fact the drive is permanently bonded in I am reluctant to pursue this route although my son has expressed his eagerness to get me to do it. I am getting on in years and do not have the lightning fast reflex reactions a faster boat would entail. The transom is also angled so either bevelled spacers or a complete revamp of the transom is required to mount a stinger and the rudder.

The reduction gears would give a 25% rpm decrease at the prop. I was initially concerned with a high speed motor driving a reduction gear but then realised that all RC cars utilise reduction gears.

Due my son's previous experience in fast electric boats I am aware of RC Boat Bitz and am actually awaiting some water cooling items from them. The motors are from a Hong Kong source on eBay.

[Peter A]

What I am hearing hear is that you just want a boat to play with, that will be reasonably fast and reliable. I am guessing that you will run on 2S, so the 3200kv leopard motor will be enough to make that boat perform better than the original 540 did. It should also give some reasonable run times. There is no need to overdo things on this hull. The next best upgrade would be a metal prop, around the same size and no more than 1.4 pitch. You may need a new shaft to suit the prop, but I'm sure that will not be too much of a problem. Keep it simple and have fun.

[Drkrieger]

You are gonna have a lot of downward thrust with the drive set up. Will Cause a lot of unneeded load on the motor batteries and ESC

[Old School]

Many thanks for your responses. Yes, I am just after a boat that will get up on plane and sound like it is going reasonably quickly. If I get around 60 kph then I will be happy. I have sourced a CNC 35 mm 2-blade propellor to suit the 3 mm shaft (dog clutch drive).

The conventional drive is of cause going to cause issues as it will induce a nose down attitude which will limit performance, but then I am not after ultimate performance as the 3 mm drive shaft and the reduction drive will also greatly impact. At one time all boats had a similar drive until surface drives were developed. If the performance is far less than anticipated then I can resort to the surface drive option with the assistance of my Dremel to remove the offending conventional drive. As stated previously, due the sloping transom, a lot of work will be needed to manufacture a suitable surface to mount the stinger and rudder mount.

[Old School]

After more consideration I have come to the conclusion that a surface drive is the only way to get this hull performing. Perhaps a few suggestions as regards a suitable motor given that the boat is 70 cm (28 inch) in length and the shaft will be around 320 mm long. I am prepared to cut out the old drive shaft but will call a stop in removing the motor mount.

I assume the shaft would exit the transom at the base of the vee shape. The slope of the transom is evident. It is this that I feel will make fitting the hardware difficult.

[rol243]

for the shaft exiting the transon base i would go for a Stinger type which is fully adjustable up and down so all you need to do to mount this is drill 4 holes in the transon plus 1 hole for the shaft log. for the rudder which you would preferably mount on the right [ starboard side ] or buy a long mount rudder that will go behind the stinger / prop, you can modify the rudder bracket so the rudder will vertical 90 degrees to the hulls bottom keel. i am sure when you do this mod the hull will perform alot better than its original design. i am not sure on motor / esc and battery size but no doubt someone on this forum with more knowledge will let you know. nice looking hull.

[rol243]

http://www.rcboatbitz.com/images/IMG-8831.jpg this is something you want just need to drill and re set the rudder so its vertical on transom as mentioned.

[Old School]

Many thanks. I came to the conclusion that the current drive had too many limitations. The hull is from twenty plus years ago and the owner stated that it did get up on plane although its performance was most likely very mediocre.

[rol243]

nothing wrong with a 20 plus old hull, some of the best mono hulls came out in the 80,s.

[CraigP]

Some of that older ABS is suspect, especially after being in the sun (UV resistant). Just have to watch for embrittlement.