Motor+prop advice

[Joao FonsecaParticipant @joaofonseca24317]

I have a friend who will make me a 1.2m wooden mono-hull boat (known as the "wild thing&quot. Picture here: **LINK** The idea is to use the boat in the river / sea hoping that it will deal with small waves when they appear. I do not need it to be a fast boat, just cruising around with Ardurover for some autonomous missions that I want to install in it. Of course, a certain ability to reach a certain speed (e.g. 20 km/h) is welcomed.

Based on your experience, can you please suggest a suitable combination of Motor + Prop for this particular case? I plan to use 6s lipo batteries with it.

Any help is greatly appreciated!

Many Thanks!

[Joao FonsecaParticipant @joaofonseca24317]

[Kev.WParticipant @kev-w]

I was advised by a revered member of the model boat world for a similar sized wooden craft, that in their opinion, I should use an 'Overlander Thumper' 42/50 800kv brushless with a 55x prop on 6s lipo.

I have every confidence in the advice I was given, so purchased the above, ready for my next project.

[Joao FonsecaParticipant @joaofonseca24317]

Many thanks for your post Kev. W, much appreciated!

Indeed I'm a bit surprised that such motor is enough for a large boat like this one. I do not have the data for the weight but with all the electronics and 6s Lipo's I have imagined that a larger and more powerful motor was needed. Something like a 5065 size motor.

[Charles OatesParticipant @charlesoates31738]

Josh, the advice related by Kev is very good, and I believe is plenty for your model. 1.2 meters isn't particularly big, and the drawing you put a link to shows a narrow hull, too large a motor would be a very bad idea in that model. As long as it's made properly, and not too heavy, the overlander motor will have plenty of power.

[ashley needhamParticipant @ashleyneedham69188]

It almost develops 1Kw of power!, is Such a motor is enough for a boat like this……I think so!

Ashley

[Joao FonsecaParticipant @joaofonseca24317]

Many thanks for all of your contribution.

I'll then order that particular motor for my 6s setup (will probably use 2x 3s Lipo 10000mah in series).

Regarding the prop… 55x prop suggested accounts for 55mm diameter from what I know. What about its pitch?

[Kev.WParticipant @kev-w]

The advise to me,was provided by the late Dave Milbourn, , I am not a man to question his word.

I would state, that the above advise was for a 49 inch Perkasa with 'Submerged' drive, I don't know if this is correct for a boat running a 'surface cutter' system.

Edited By Kev.W on 24/07/2021 23:26:18

[Charles OatesParticipant @charlesoates31738]

I hope you don't mind me asking joao, how do you address the safety aspects of this model? A 1 kw boat, massing maybe3 to 4 kilos could be very dangerous under autonomous control. Do you need special insurance? It's on its own in a seaway or river, you're not in control. If a swimmer or wildlife got in the way, it could be lethal. What would the law say, would you be liable? There's a good reason most of us use radio control, we can see risks and stop the boat when needed.

Personally I've no time for ardurover type systems in modeling, especially with a quick model.

Charles

[ashley needhamParticipant @ashleyneedham69188]

Joao. The common two blade plastic props come in two pitches.

one is “S” and one is “X” . X pitch props have a very big pitch on them, 45 degrees or so, and S types much less.

Thus an X55. Or. 55X describes both its size and pitch. If you do not want to go very fast I suggest something more like 400Watts will be more than enough. As Charles has asked, if anything goes wrong, that’s a fair old missile for that weight and speed.

Charles…good question. Some people have insurance, but anything that fast needs a clear water to operate clear of people and wildlife .

although we have fastish stuff at Bushy, it gets operated at the far side of the pond normally, and there is a vertical hard bank 18 inches or so high preventing any boats leaving the water all the way round.

Normally our fast stuff is operated in “exhibition” mode…A few quick runs to prove their worth and than exhibit on the grassy knoll! Most of our stuff is powered just sufficiently to get the required look, without being silly. I took the Bluebird out the other day (after a 6 month sojourn) and was surprised by how slow it was (especially compared to Andy’s surface drive one), but it’s achieved the three-point stance and looked great without going at Mach 10.

Ashley

Ashley

[Charles OatesParticipant @charlesoates31738]

Hi Ashley, all good points. My main concern is the idea of a model not under the control of the operator, there is too much that can go wrong. I'm sure the technology works just fine, but it can't tell if someone or something gets in the way. If the model had a system to over ride the gps using radio control, and was under constant scrutiny, that would be fine, but what would be the point of doing it?

Charles.

[Richard SimpsonParticipant @richardsimpson88330]

Charles I believe that irrespective of the size or means of control of your model if you interfere with wildlife in any way you would be liable for prosecution. Obviously using sophisticated control systems helps us to minimise these risks but I think we all have to take responsibility for ensuring that third parties and wildlife do not get injured.

It is obviously also worth considering the insurance aspects of such activities. Operating with a club and on club waters during scheduled times then you would be bound by the requirements of the insurer to remain covered. If you operate on your own outside such cover then you really are on your own in the event of something going wrong.

Sending a large heavy model out onto open water with no means of control, other than pre-set automation, and with no protection of club insurance does strike me as very risky. I am assuming the automation works on GPS to take account of ambient conditions but I suspect that it might not be so sophisticated as to include avoidance capabilities, or am I making incorrect assumptions here?

[Charles OatesParticipant @charlesoates31738]

Hi Richard, I think you are spot on, it uses gps positioning. Great for research purposes, under informed aware and considered conditions. I have no idea what level of experience and knowledge the poster has, for all I know he may be a very experienced developer, with full knowledge and back up to prevent accidents. If not,……. Then the project could be an accident waiting to happen.

Charles.

[Joao FonsecaParticipant @joaofonseca24317]

Thanks for all your help.

Indeed the boat will be used firstly on a nearby lake and will be fully monitored all the time until it is behaving correctly according to what it should be. It will run missions on the lake before it will go for the first time to the sea. Several tries will be needed to perfectly tune the boat. I'll make sure it will not put anyone or anything in danger whenever it is running. I'll have friends on a boat following it to ensure it will drive and operate safely.

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