PT BOATS

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PT BOATS

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22 January 2012 at 15:03 #33163
Gunboat Driver1
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@gunboatdriver1
Hi Mr. Jones…The PT boat you were given was a AEROKITS 1/24 scale ELCO PT boat (40″ long) Kielcraft in the old days only did the smaller 12-14″ MTB…Terrier…all the best…great rebuild…
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22 January 2012 at 15:03 #3798
Gunboat Driver1
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@gunboatdriver1
Gareth Jones… PT boat re-build…
22 January 2012 at 16:16 #33164
Gareth Jones
Participant
@garethjones79649
Hi Gunboat Driver,

I am glad you enjoyed the article and you may well be right about the kit manufacturer. I was never very sure whether it was an Aerokit or Keil Kraft model originally. I have been told both, and also that they were one and the same company. Somebody like Dave Wiggins could probably tell us the definitive history.

Snogg is still going strong and has the occasional outing. After the article was published I did a lot of work measuring battery, motor and propeller performance to try and optimise the combination. I eventually ended up with a pair of 9.6 v NiMh batteries and a pair of Graupner Speed 700 (Pt no 7307) motors as the best combination. The batteries are an odd pair I had in my shed, one is a 2600 mah and the other 3300 mah capacity. I have toyed with the idea of fitting a pair of 11.1 volt Lipo cells and some form of low voltage warning to prevent them being overdischarged. With a pair or 5000 mah Lipos the weight would be reduced by about 300 g and Snogg would really fly. However you reach the point where you start wondering if its worth spending another £100 or so on an old boat.

One day I might go down this route and write another article – Snogg the sequel perhaps. Now if I could persuade Paul Freshney to pay for the article it would cover the the cost of the batteries and bits……….

Gareth
22 January 2012 at 18:24 #33165
ashley needham
Participant
@ashleyneedham69188
Gareth. More to the point, is it worth spending that much money on a boat that gets used only now and then?

One of the forum chaps Trevor I had the pleasure to meet at Bushy park said ALL the boats he would be building would be powered by the same 7.2V NiMh sticks, the common sort you see, so as to standardise the battery situation, and I must say there is a lot of sense in this.

Limits your choice of motors sometimes though, and I find that gel cells are the boats own ballast to boot, especially with the price of lead being as it is.

Ashley
22 January 2012 at 19:45 #33167
Gareth Jones
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@garethjones79649
Hi Ashley,

This could become quite a philosophical discussion (or maybe its a diatribe) as your posting persuaded me to think about life, the universe and everything while cooking tea.

I find that I sail most of my boats probably no more than a dozen times a year. I only have 4 fully completed ones. My wife has lots more than me,
we went out and collected another Ebay yacht this afternoon. How do you balance the cost of materials and time spent building, against the pleasure you get from the hobby. I know people in the model boat world who are quite happy to sail an RTR boat apparently aimlessly around the pond for hours, others who spend huge amounts of money on buying the best of everything and others who spend hundreds if not thousands of hours building a beautifully detailed fully functioning model and only put it in the water once, if at all.

I enjoy sailing my models but I get the most satisfaction from building the model to the best of my ability and overcoming the problems I meet on the way. I spent my working life as an aircraft systems engineer and the systems within my models probably provide the most enjoyment. Developing the propulsion system of Snogg was particularly interesting and it reached the point where I knew I could make it better. A pair of LiPo batteries would be lighter, higher voltage and potentially longer running time with very little technical risk. I could go down the brushless route but that would mean new speed controllers and I have no experience of selecting a particular motor to match my required prop speed and size – to me its a much riskier and more expensive option, but thinking about it has occupied my mind and kept a few brain cells exercised.

As you say, you have to balance the gain in performance, a few times a year against the cost. However you also have to throw into the equations the satisfaction you get from the engineering development and the additional knowledge you gain and can pass on to other people. Unfortunately life is too short and I dont have the money to do everything I would like. How do I compare spending £100 and a few hours on Snogg against spending the same amount on Shemarah II?

Everyone’s approach to our hobby is different and we have to accept that what people want to get out of it is also different. You are probably right, especially if you look at things with an accountants head on, its not worth spending £100 on Snogg to get an extra few knots and minutes running time a dozen times a year. However it might be worth it for the satisfaction and knowledge to be gained in the process that can be applied to the next project, whatever that may be. I am not suggesting you are an accountant, I just think they have too much influence over engineering these days. At the moment, building Shemarah’s wheelhouse is more interesting so I am unlikely to rush out to buy some LiPos, but who knows, one day I might give it a go.

I hope this doesn’t sound too much like a Sunday sermon, its not meant to be, its just a few rambling thoughts on what people get from a hobby.

Gareth
23 January 2012 at 08:08 #33170
ashley needham
Participant
@ashleyneedham69188
Gareth.Not a Sunday sermon, discussions is what the forum is for.

Each to his own on the modelling front. No particular view is right, its all invidual preferance, and I would never say that one particyular view is the right one. I may not agree with it, but that would ne my own personal view!

I prefer variety and lots of it. Not for me choice of only 3 perfect boats to take out time and time again (or not). Nor do I have hours to spend on the minutae of boatbuilding, so all of my models are “stand-off” scale. They are all much too fast to boot (when the throttle is opened fully). But thats how I like them. A fair few of my models have been made of course for my son, to keep him interested, and as anyone knows, these have to be either what he likes (the flying boats) or fast.

To LiPo or not? who knows. Only you know, ultimately.

I am considering applying to participate in the Amberly working museums “small steam day” later this year , which has featured a model boat display (not steam I hasten to add) as there was only one chap on his own this year for some reason. I have never done a show before, and I would wow them with a boot-full of my eclectic collection…or not ?? will be interesting to see the reaction considering there will be shed loads of model makers there. After all, the boats are made purely for my own enjoyment first and not as display items.

Ashley
23 January 2012 at 21:00 #33174
shipwright
Participant
@shipwright
Hello Gareth,

I’m a new member on this site. I was interested in your comments about choosing motors, props and batteries.

I have constructed a Nautical Marine kit – HMS Dark Biter 1:24 scale fast patrol boat. A point raised by an experienced modeller at Gloucester & District Model Boat Club caused me to investigate motor and propeller rpm-torque relationship. He said that my boat looked a bit “slow” for that scale. I investigated and found that the scale speed is 8 knots whereas my boat was doing about 4 knots – I fitted a different set of props (both the original Caldercraft and the replacement Raboesch are 35 mm diameter) and obtained 6 knots approximately (with Graupner 600 Speed ECO at 7.2 volts – motors are somewhat overloaded but don’t get too warm). Since then I have experimented with various props and motors using a small water tank. Obviously the measurements are “static” which is equivalent to the boat roped to the quayside and 100% slip. The cost of sophisticated data logging equipment (which would record actual rpm and amps in the boat and moving on the water) is rather expensive!

One thing that I have found that is indispensable is Mark Beard’s Excel Workbook which computes the motor performance using only four simple input parameters (no load rpm and current, stall current and nominal motor voltage). In October 2010 there was a thread “method for choosing the right prop and motor” with Mark Beard and yourself amongst others. No posts since Colin Bishop’s post of 18/11/2010. Has anyone had a contact with Mark since then – I wanted to contact him to discuss his Excel application and I have sent him a message but no reply to date.

Ian
23 January 2012 at 21:03 #33175
Gareth Jones
Participant
@garethjones79649
Hi Ashley,

I am sure your models would go down very well at an open day/exhibition. My wife and I attend quite a few regattas and displays, both as exhibitors with our club or just visiting enthusiasts. My wife has built a number of quite innovative Springers as next months Model Boats magazine should reveal. Some of the ‘serious’ modellers are very put out when the public show more interest in a Mouseboat than an accurate scale model of a warship. I think many people are a bit intimidated by highly detailed scale models especially when there is a row of grumpy looking old men sat behind a stand with ‘dont get too close to my model’ looks on their faces. A bit of lighthearted fun will appeal to a wide audience and, if our experience is anything to go by you should have lots of interesting conversations with a wide variety of people – I think you should give it a go.

Gareth
23 January 2012 at 21:26 #33176
Gareth Jones
Participant
@garethjones79649
Hi Shipwright

Mark Beard did participate in the forum a couple of months ago. His spreadsheet is very useful, I would recommend it to anyone wanting to understand motor performance and use it as a selection tool.

There have been more recent posts on the topic of Colin Bishop’s Motor/Prop survey in the All things Floating section. The last thing to be added was the data on my latest project Shemarah II which I posted in September last year.

Instrumentation is not that expensive. I use a Wattmeter to measure motor voltage and current and it calculates power – cost around £20. I use a set of digital fishermans scales to measure thrust by tethering the boat to the pondside – cost around £10. The most useful tool is a laser tacho to measure prop speed, again only about £10 and if you were only to buy one thing I think this should be it. You can measure prop speed in and out of the water and get a good idea where the motor is running on the performance curve. Once you have grasped that key point you know how well your motor and prop are matched.

I have a spreadsheet of all my model’s performance, some with several different motors and props. My PT boat would be a fairly close match to your Dark Biter but has smaller props, only 30 mm diam. If you would like a copy e mail me your address and I will forward it to you.

Gareth
6 January 2015 at 23:09 #54917
Dodgy Geezer 1
Participant
@dodgygeezer1
I was never very sure whether it was an Aerokit or Keil Kraft model originally….

Keil Kraft designed and made most of their own aircraft, but also acted as distributors for a few other small companies, such as Contest.

For boats, it was the other way around. Keil Kraft made a small range of galleons, and their EeZeBilt starter boat kits, but they mainly distributed several other companies boats – MarineCraft, for instance. I think that they had a sole distributorship for Leslie Rowell's 'Aerokits' range for quite some time. So an Aerokits box would have the words:

"Aerokits, distributed by Keil Kraft"

written on it. Which, I suppose, gives both of the companies a claim to it…

Incidentally, the KK Terrier was 10 3/4" long – quite diminutive! Anyone who wants to reproduce one can download the plans from my EeZeBilt site for free – at **LINK** Where you will also find free half-size EeZeBilt 50+ plans for the PT Boat and the Sea Princess (a half-sized Sea Queen), at 20" and 23" respectively….
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