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Jun 18, 2019, 08:50 AM
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Keil Kraft Eeze-Bilt Mermaid


I've just printed out plans for the Mermaid from Dodgy's excellent website. I've never built a proper RC boat model before as I normally build aircraft.

I seem to have sorted out the necessary RC gear and hardware so I'm hoping to provide a fairly detailed build thread. I expect to have plenty of questions so please chip in with suggestions - all criticism is welcome

Jon
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Jun 18, 2019, 03:51 PM
Boaters are nice people.
Nice, looking forward to your build!

Regards, Jan.
Jun 19, 2019, 09:39 AM
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Thanks Jan


Had an enjoyable start this afternoon.

I cut the pieces for the first few steps shown on the instructions. I'm using up some hard balsa that is too heavy for most aircraft applications - man it's dense stuff and I'm not used to working with it! I stick the printed parts sheet on the balsa with Prit Stick and cut out with a scalpel and metal ruler or french curves. For the curved parts I flipped one side to make the other for symmetry.

I'm using thin CA to run into the gaps whiles holding the assembly together. A piece of parcel tape on the desk allows you to hold the sheet parts flat without sticking them to it. The parts fit so far has been excellent - I wasn't sure if the joints would be close enough for thin CA (which is not gap filling) but the parts sheet is outstanding. I've been using a little Stanley needle file to open out and square off the slots for a press fit. Really liking the self jigging Eezebilt style.

The only issue I've had is with the central bulkhead. The cutout in the deck is 1/16" too wide, easy enough to fill with scrap balsa but I will wait to see what other bits might fit there. The forward bulkhead wasn't quite right in the same area but since the error was on the tight side it was easy to cut a bit more away from the deck slot.

I haven't fitted the transom yet as I will need to set up the rudder assembly before I close off the 'stern locker' - I may cut out the aft bulkhead for access too. I haven't added the motor mount either as I have yet to decide on the motor. I'm thinking a 9V rated MFA RE140/1 on 2S Lipo?

Weight so far is about 28 grams.


Jon
Jun 20, 2019, 05:12 AM
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I've made a start on fitting the prop shaft.

I made up a 5" shaft tube and 5.75" shaft as per the Eeze-bilt site but I'm concerned that it might be a bit short. The picture shows it protruding by 4" as on the instructions but should I make another a bit longer to avoid water ingress?

Also any thoughts on the 140 motor? Will it be powerful enough or should I go for a 180 (or more)?

Thanks,
Jon
Last edited by slowmatch; Jun 20, 2019 at 05:53 AM.
Jun 20, 2019, 08:39 AM
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Made a bit of a start with the cabin and skipped ahead to 9 and 10 in the instructions. A few minor issues with parts fit unfortunately.

The 'Cabin Frame Rear End Former' is not there on the PDF part sheet, but it is on the scanned die cut balsa sheets. I'll draw up something in CAD.

The 'Cabin Frame Front End Former' is listed as 1/16" but I made it from 3/32" to match the frames.

There are one or two inacuracies for the slots in the side frames - in some cases the slot is wider than it need be as shown in the pics below.
Jun 20, 2019, 08:52 AM
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First, let me say how gratifying it is to see one of these old kits come to life, in the hands of such an accurate modeller!

These are, of course, old kits designed to introduce children to the model boat hobby, and were never designed for radio control or large lakes. The Mermaid is a great shape, but at only 14" it's a bit small for radio. A competitor company , Marinecraft, produced a range at 18", and the Kestrel would be the equivalent of the Mermaid - plans available here - http://marinecraft.tk/Mspb.html

I must apologise for the errors in the plans. The Mermaid was an early boat that I reverse engineered, and I was having to learn CAD by trial and error. You will find that the later plans up on the EeZeBilt site are (I hope) better drawn, and the 50+ range is far better suited to installing radio. That was a range designed to perform the same function of introducing modellers to boats, but with the advantage of 50 years technology improvement!

You can install whatever you like for the onboard hardware - here is a Youtube video of a Mermaid running with a 2.4ghz radio, RE-180 motor, GWESC300 speed controller, and an 800mah 7.4v lipo.

Keilkraft Mermaid RC electric model boat (2 min 43 sec)



The original Eezebilts would potter around on a pond at slow speed with a small motor, a 4.5v battery, and a very cheap propeller. For my 50+range, I tend to use small brushless, build a better prop-shaft and use a commercial prop. If you want to improve the prop-shaft, probably the easiest thing to do is to use a short half-inch of sleeving at each end of the prop-tube to act as a bush, so that the shaft does not contact the tube along its length and drag excessively.

Incidentally, the original method of securing the superstructure to the hull is not very positive - you might wish to add a few magnets or use an other more reliable method... and I note that the Youtube boat has a couple of chine spray rails added to deflect the bow wave. The original would never have needed this....

Good luck! I shall keep an eye on this thread...
Last edited by dodgy; Jun 20, 2019 at 09:00 AM.
Jun 20, 2019, 09:10 AM
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Rear Former DXF and PDF enclosed...
Last edited by dodgy; Jun 20, 2019 at 09:18 AM.
Jun 20, 2019, 11:08 AM
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Thanks Dodgy! I'm afraid I managed to draw it up at the same time but overlaid they are almost identical.

The CAD work on the Mermaid is very good over all - just a few little niggles but excellent compared to many kits! I've been a fan of the range (and the site) for a long time but only just got around to doing one as I'm normally heavily involved in FF and RC model aircraft. But I broke my ankle a couple of months ago and have the time to build at the moment. Plus I can't chase flying models for a while. I've got several ideas for the 50+ range but I thought it would be a good idea to build an original first.

The size is not a problem for me as I'm used to micro RC and seriously considered building the Mermaid at 50%

Thanks for the video - I had come across it. I'm not sure he's giving it full throttle there but I'm not looking for anything too hot performance wise. I'll order a 9 Volt 180 probably and I already have 500mAh and 800mAh 2S packs.

Any thoughts on the shaft tube? Will that protrude far enough above the waterline as shown do you reckon?
I was a little concerned about the hatch closure method also - it does look like any spray will find it's way in with no coaming or seal on the join?

Cabin basics are now all cut out. The pics show them dry fitted.


Cheers,

Jon
Jun 20, 2019, 01:18 PM
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Ernie Webster, the EeZeBilt boat designer, saw these kits as an exercise in different building techniques for beginners, and put a lot of different building tricks into the different boats. On the 'superstructure hatch' front, we have removable roofs like the Neptune and Triton, superstructures which have interlocking slots like the Terrier and Curlew, removable seats on the Cresta, the Otter cabin which drops into a deck well, and the Mermaid where the superstructure just sits on top of the deck, located by raised bulkheads...

The Mermaid approach suffers if either the deck or the cabin is the least bit warped. Magnets can help, or you might like to consider the Marinecraft technique, which was to surround the deck location with thin 3/32" square balsa, and arrange a sliding catch. See section 15 of their instructions below:

I can't see how high the prop-shaft is in your model - you are correct that it should be above the waterline, of course. If you cannot manage this, you can use the trick with silicon tube pictured below to waterproof the end - with a bit of oil it's nearly frictionless. You would use that in the Beaver if you used the high motor mount...

http://eezebilt.tk/IMG_5006.jpg
Last edited by dodgy; Jun 20, 2019 at 01:26 PM.
Jun 20, 2019, 01:30 PM
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..... and seriously considered building the Mermaid at 50%

Were you going to run it in your bath? Actually, note that the spray rails at the bow, which were not in the original, seem to be essential the minute you put a bit of power into the hull. Otherwise the water will surge up attached to the hull and fill it in a minute or so of fast running....

The smaller the boat, the worse the scale effect of water becomes...
Jun 20, 2019, 04:13 PM
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Quote:
Originally Posted by dodgy
..... and seriously considered building the Mermaid at 50%

Were you going to run it in your bath?
Yeah probably! But I take your point about practical running.


Continuing with the cabin, I used parcel tape on the hull to avoid it sticking and glued up the cabin frame with thin CA. You could do this on a flat surface but there is a slight reverse sheer on the fore deck.

I cut out the cabin sides from hard-ish 1/16" balsa (#14 lb/cubic foot.) As I mentioned, I like to stick the parts sheet to the wood with glue stick and cut them out. The paper peels off fine if not left on too long but if not a dab of water soaks it off. Cutting out the windows and portholes before the outlines gives a little more support. The radius edges and portholes are done with the little Stanley needle files, a 1/4"/6mm half round does most of it.

The sides where 'cracked' or at least bent over the edge of the desk and CA's on while lined up on the flat, again on a strip of parcel tape. It's come out pretty square and flat but the hull has the tiniest sheer at the moment so there is a half a mil gap. I may be able to sort this when I sheet the hull.

One more little error - the rear cabin former looks too low by 1/16" but I can add a strip to build that up.

Next, I need to get on and sort the installation of the prop shaft tube and make a rudder.

Quite pleased with the look of it, starting to look like a boat anyway and it's gone together pretty quickly.
Jun 21, 2019, 02:51 AM
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I made up a 5" shaft tube and 5.75" shaft as per the Eeze-bilt site but I'm concerned that it might be a bit short. The picture shows it protruding by 4" as on the instructions but should I make another a bit longer to avoid water ingress?

The shaft would have been the standard item available to the designer for all the EeZeBilts in 1959, and he would have had to work with its limitations. If you have the option to make a longer one, I would go for it. Webster would have greatly preferred to have been able to specify an appropriate shaft for each design and place the motor where he wanted...
Jun 21, 2019, 03:03 AM
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I can see where the errors have crept in - the die-cut lines are drawn from direct measurement from a scan of the original balsa.

When I design my '50+' series I make an overall drawing and then take measurements directly off that. The only errors then are in my cutting, or in any modifications I make which are not properly reflected back into the plans.

For the original EeZeBilt boats, I did not build a test boat or make an overall drawing. Consequently, any distortion of the original balsa, or any measurement error I made, are just transferred direct to the cutting lines with no check.

Your accurate build is very useful - it has shown up all sorts of issues which need correction. I must do this - and may I put an abbreviated version of your build log on the web site? I will send you the draft for checking first, of course...
Jun 21, 2019, 03:49 AM
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I have enough tube to make up a longer shaft and I can use this one in some other model.

Just looking at the baffling array of brushed motors on Ebay. The 180's seem to mostly be the flat sided version.

Quote:
Originally Posted by dodgy
Your accurate build is very useful - it has shown up all sorts of issues which need correction. I must do this - and may I put an abbreviated version of your build log on the web site? I will send you the draft for checking first, of course...
Sure, no problem - happy to help. I hope you understand that my comments are intended as useful feedback rather than criticism

Jon
Jun 21, 2019, 05:07 AM
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I hope you understand that my comments are intended as useful feedback rather than criticism...

Not a problem at all. I appreciate the work you are going to in documenting your build and itemising the points where the published lines are not what the designer originally produced! More power to your elbow...

It was quite a learning experience doing the reverse engineering, and I should have spent more time on it. There are a host of places where errors can creep in apart from my poor drawing skills - the old balsa can shrink, it can be hard to determine where a line is from a scan of the die-cut sheets, and the die-cutting itself may be incorrect.

I did the first kits drawing the lines by measurement straight from the scans of the sheet. Only towards the last few kits did I realise that it might be better to extract all the measurements, construct a full drawing, and then re-create all the dimensions assuming that the designer used standard imperial measurements between points like 1/8", 3/16" and 3/4". I tried that on some drawings, but found it was very time-consuming...


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