Need a small motor for Sea Hornet

[Martin Field 1Participant @martinfield1]

Hi all,

I recently bought a Sea Hornet for 99p off ebay. Quite nicely built, but needing some delamination problems repairing.

I was going to finish it in the style of a two cockpit ChrisCraft 16' Runabout to 1/8th scale, which would suit it well. But I think we'll have to revert to single cockpit because the low prop shaft brings the motor too far forwards.

Now, I like to use vintage motors, but the built in shaft is very low and I would need something compact.

I have a mystery motor that worked off 7.2 volts driving a geared propellor in an Ugly Stik model aircraft. The gearbox shaft was bent, but the motor is fine. It has excellent magnets, is about 2" long and 1" diameter, black all over, completely cylindrical and has, oddly, "FULLY" stamped in the brush end case.

OR, I have dragged my Monoperm out of the showcase (yes I collect old model motors). That says 6 volt–3.0 amps.

Which would you use?

And any suggestions for a suitable prop?

I have a SimProp 18-08 ESC, which I assume is an 18 Amp.

Would that suit?

I do find all this electrical guff tedious and difficult to understand.

I'm looking for a "vague plane" performance, not a demented duck. So scale speed really. I actually enjoy building them more than playing with them, but it's nice to see them afloat sometimes.

Martin

[Martin Field 1Participant @martinfield1]

[harry smith 1Participant @harrysmith1]

Hi Martin

Nice buy, I am building one from the original plans with a few mods.

I did not like the hatch openings as I was planning to plank the deck.

As for motors keep them in the showcase.

These new brushless motors with Lipo batteries are far more powerful.

The Lipo batteries vary in size, so fitting these in smaller boats is far easier than Nicads.

A 2400mah NiCad is about 300 grams and the size Lipo 2650mah 3S 30c is about 250grams.

If use 2 Turnigy 1500mah 3S 25C batteries(these are 80 x 34 x 25mm) and about 115grams each.

These fit easy each side of the motor and room for Turnigy 45Amp car ESC(with reverse), no water cooling required.

As for motor a XK2845B-2000kv 28mm motor on 2S (7.2 volts(14800rpm)) or 3S(11.1 volts(22200rpm)).

Prop32mm x 1.4 pitch or 30mm x 1.4 pitch would be a good start.

As for figures I found some 135mm(5 and a quarter inch) wrestling ones in the cheap shop.

As for windscreens I have made these one piece with gold car pin strip tape for the wood look.

I have posted the build on this site is scratch builds, Sea Hornet 2015.

I have clear coated the deck, sides and stern(post pics. a bit later).

Harry

[Martin Field 1Participant @martinfield1]

Hi Harry,

thanks for the response. I have no idea what's what with brushless motors, ESCs and all that guff. LIPos scare the heck out of me as does the special charging, discharging, balancing arrangements and I still keep my special charger in its box as I can't get it to do anything.

I don't like the idea of spending big on ESCs, only to see them fry, as so many have written of. Isn't it time they were now reliable? If I could find my old Bob's Board, I'd use that!

I have a few flight packs of hardly and Un-used Nimhs which will be fine for my needs. I'm more of a builder than a sailer, but it'll look nice on the water from time to time.

My experience of model boat clubs has been so awful that I will be sailing alone anyway. I am a member of Victoria Model Steamboat Club, but tht's because my Grandad was a founder member, not because I will ever be in London (if I can help it!). It also gives me the right to use V37 on my boats. Locally, there are no clubs, despite there being water everywhere! Go figure.

Cheers,

Martin

[Martin Field 1Participant @martinfield1]

OK, thanks to an American forum, I have discovered that the motor i rescued from the model aircraft is known as a Long Can 480.

If it is capable of flying quite big kites with or without a gearbox, I reckon it should run well in a smallish boat at around 12Amps (according to the fly boys), so my Simprop ESC should work.

They also use NiMhs quite a bit still, so I have that confirmation. Weight isn't a problem with boats as most need ballasting to sit at their marks anyway.

Cheers,

Martin

[ashley needhamParticipant @ashleyneedham69188]

Martin. A 480 is quite a feisty motor and will be more than up to the job,. A plastic two blade S30 or S35 will do, or a plastic 3-blade 35mm prop. Probably will not draw 12A in all likelyhood..best use a meter once connected up.

I have some Lipo for a specific craft, but would not bother to buy some for a runabout. You dont really want to add ballast on a cabin cruiser sort of thing, wherever the waterline sits should be ok. MAY need some fore/aft balancing (battery).

Ashley.. Standard disclaimer – personal opinion on motor/prop/battery choice and waterline issue..

NB dont forget a driver to drive the craft. Looks empty/silly wothout (standard disclaimer applies)

[Martin Field 1Participant @martinfield1]

Ashley,

many thanks for your advice. I was thinking a 30 or 35mm prop too, though no idea why<G> I'm expecting to have some fore and aft balancing to do. Glad that the Sim-Prop ESC can be used.

I agree with you whole heartedly about drivers. I cannot abide driverless model boats. With that in mind, I have been buying up suitably "ordinary" looking dollies at Sunday Markets and Boot Fairs and have so far got a couple of 1/8th sizes and a 1/6th scale figure for my Derby One Design.

Would I need some sort of water cooling for the motor, do you think? I could make a brass jacket for it and pass the water out of the exhaust pipe (only one on this as it has a CC 60 horse six in it.)

How does one keep an ESC cool though? And is it always necessary?

Cheers,

Martin

[harry smith 1Participant @harrysmith1]

Hi Martin

Rule of thumb<G> 1/3 the length of the boat from the stern.

Waterline on speed type boats does not apply, it's more of the <G> than is important.

To tail heavy the nose of the boat flips up and down.

To nose heavy the boat is more like a tug boat!!

This is only my thoughts!!!

Harry

PS I was scared of Lipo's and brushless motors,but, with the help from my modelling mates I love these little beasts.

Harry

[Martin Field 1Participant @martinfield1]

Harry,

alas, there are no "modelling mates" round here. One flyer who has huge aerobatic electrics, but I wouldn't be using that kind of stuff. Otherwse, another flying chum who won't touch electric! No boaty types at all. And when I have been to a near(ish) model bat club, the people were so thoroughly unpleasant, I couldn't have gleaned anything from them at all. They barely acknowledged my presence. As there were only 4 of them anyway, I had increased their number by 20%!! They seemed, if they spoke at all, to just brag about how much their latest suit of sails had cost. They got in the Honda Jazzes and new BMW estates and left without a backwards glance.

I find this wherever I go, unfortunately. I read of some pleasant sounding clubs, but they are way too far away for me to attend.

A while back, I invited the Cambridge club to attend our village fete in the Fens. They turned up mob handed and their secretary thanked ME for asking them, saying they had never considered running on a small river/canal before, but all, including the famous Miller Agnew of AMPS reported the biggest turnout their club had ever seen.

Would that they could do that now, eh?

Cheers,

Martin

[ashley needhamParticipant @ashleyneedham69188]

Martin. Should not need watercooling on this motor running on a 35mm prop on anything up to possibly 9.6v (but depends on the motor, who made it and so on). Same for the ESC, this motor should not take too much current and an esc with space around it should be fine. Measure current draw first and use an ESC that is rated some way above this. I use Mostly 15A Mtronics on the units with speed 400/480`s and they run ok. If the motor get hot (too hot to touch as opposed to just very warm) then it is being overloaded, smaller prop needed and wotnot.

I would however arrange that there was a flow of air through the boat, as otherwise even pedestrian gear can get hot in the confines of a sealed small box.

Our gathering at Bushy park is not a club and everyone gets on famously. It is a shame when this sort of thing happens.

Ashley

[Martin Field 1Participant @martinfield1]

Ashley, you're a gent sir. Many thanks for this info. I am sure I can provide a throughput of air via the vents on the engine covers.

I have no way or idea of measuring current draw. I am a complete numbskull where electrics are concerned.

Even if I had a watt meter, I wouldn't know what to do with it.

Cheers,

Martin

[ashley needhamParticipant @ashleyneedham69188]

Martin. A wattmeter is moderately essential. They are so easy to use…you simply plug them in between the battery and ESC, tab the button (on most) and the display scrolls around showing you current draw, voltage, watts and so on. Very cheap, ebay does them,. Component shop sells same…

It is possibly the best way to set up a boat, as you can see from the performance how fast it goes, and then look at the current draw to see if the currents shown are translating into increased performance or not, when trying out different props and so on.

This sort of measurement sheds light on the fact that the performance MAY be about the same with say, a 40mm 3 blade plastic prop and an X30 twin blade, but the motor may be struggling to turn the X prop and so drawing more current (for an example)

Also allows you to judge performance and current draw for better run times, there may not be much of a difference between very fast and ever-so-slightly less fast with certain batt/prop combinations, but a big difference in current draw.

Ashley

[Martin Field 1Participant @martinfield1]

Ashley,

you put the usefulness across very well. But doesn't the reading only really mean much when the boat is actually under way? I believe it's called unloading?

Or do you just hold the boat still in the pond while a colleague reads the meter?

I can't say I've ever seen one in use at the pondside.

I'll look into them.

Someone reckoned that motor i have is about 75 watts on 9.6V, but I shall probably be using 7.2V.

Cheers,

Martin

[harry smith 1Participant @harrysmith1]

Hi Martin

I have run into a number of clubs and groups with the inner circle main group, the middle group, the one's who do 90% of the main work.

If a group communities with the public, it will grow!!!

I showed an old chap the controls of a Scottish Trawler about 35 years ago.

Handed if over to him and for over half a hour I seen an old kid with the greatest smile!!!

To me that is model boating, not winning the best boat in show.

Harry

[Martin Field 1Participant @martinfield1]

Harry, that would be nice to do for somebody, but it ain't gonna happen round here any time soon.

It seems we have the barely findable geriatric Isle of Manners (IOM yachters, I can't see IOM and not say Isle of Man, sorry) and the distant "phone before you come, find a gate on Grid reference such and such, bomble through the woods, open another gate, shut them all before you drop to the lake and then pay a fortune each visit" that is about 25 miles away.

I guess I'm on my ownio.

Cheers,

Martin

[harry smith 1Participant @harrysmith1]

Hi all

These Watt meters go in line between the battery and ESC with a telemetry output via the receiver to the transmitter(e.g. Turnigy IA6 or IA10).

You can add a Quanum GPS logger for speed reading etc.

Harry

[Martin Field 1Participant @martinfield1]

Harry,

telemetry?? GPS??? Turnigy??

I have Acoms or Mini-Hex 27 Meg 2 function R/C for my boats. I do have a Spektrum Dx5e for my aeroplanes, which I may not use for them after all, but it won't talk to me with telemetry!!

Of course, if someone would buy me a Jeti system I would have to learn all the fancy stuff, if I could bring myself to take it out of the frame on my wall!

I've looked up watt meters and found a huge variety of things, some that would appear to travel with the boat/aeroplane and record the info, some that you must just hold onto the boat while it whacks around in the water. I would have thought the two readings would have been very different.

Martin

[ashley needhamParticipant @ashleyneedham69188]

Martin. The most current draw will be at a standstill, so holding the boat still, putting on full throttle and looking at the reading will give you the worst case highest current reading.

Once moving the water is travelling past the prop at speed and this lessens the amount of power required to turn it. Basically….. will not argue with anybody who has another idea.

Some of the meters can be left in the boat and will capture the highest amp draw, so you can look at this when the boat comes in. However, things like motor temp and also battery temp should be borne in mind when assessing all this. To be honest I think this is all a bit deep for your application, and as long as the static current draw does not wildly exceed the spec of a comparable motor (say, a J.Perkins 480) and the motor gets no more that fairly warm or even slightly hot to the touch, you will be ok.

Ashley

[Martin Field 1Participant @martinfield1]

Ashley, yes…point taken about max. draw.

But the voice of reason speaks the clearest and as you say as long as nothing gets obviously warm or hot we should be fine.

We're a way off so far as I have to fiddle and faff with the hull first to get it to a point where the pearwood veneer can go on.

Got it all epoxied inside yesterday and that has gone off nicely, so paint next for the innards, then the motor will be fitted.

Thanks again,

Martin

[BanjomanParticipant @banjoman]

Martin,

Re: wattmeters, the one I got is the SkyRC iMeter 7-in-1 multimeter (**LINK**), which does indeed go in the boat (or whatever) and which will record and remember (until it is deconnected) among other things the peak current:

This is of course handy, as it allows one to get a peak current draw figure from actually running the boat, as opposed to holding it still. It is also possible to get a reading of current draw, but only by looking directly at the meter which of course takes one back to the holding-it-still scenario where current draw will be more or less the same as peak draw.

As Ashley has already said, peak draw is very useful figure to know for configuration purposes, although I would not have minded also being able to know average current draw, as this would be a rather useful figure for comparison with peak when calculating potential run times.

This particular meter also has an optical tachometer, a battery tester, thrust calculator, temperature gauge and battery checker, the only one of which I've used so far is the tachometer. The latter is of course primarily intended for air props, but did seem to work on a boat propeller, too; at least it gave me a reading in the expected RPM range, although I did of course not have anything to check the reading against. And of course that reading had to be taken out of the water, so the value of this particular bell-and-whistle for model boats is perhpas a tad limited. I haven't yet tried painting a line on (for example) the motor-propellor axis coupling to see if I could get a reading from there, too, but will have a go at that one of these days. If that works, it would of course be possible to check RPM's with the hull in the water, too.

I'm not particularly trying to say that this thingamajig is the bees-knees, must-have, cat's pyjama of a wattmeter, and it is of course more expensive than a simpler one, but it has so far done what it says on the box to my full satisfaction.

/Mattias

[Martin Field 1Participant @martinfield1]

Matias,

many thanks for your reply. Your meter is a bit pricey, but I think I saw some that do similar jobs for less money.

I suppose I will end up getting one because I would hate to not know what a slight change in voltage or propellor size and pitch would do to batteries and run times.

I would rather not have to faff about with all these electronical things as the subject itself leaves me bored silly.

But it would perhaps be interesting to put such a metre on one of my Taycol motors to get an idea why Taycols EAT batteries!

Cheers,

Martin

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