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Author Topic: Norwegian Tjeld class MTB  (Read 44080 times)

SinWin

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Re: Norwegian Tjeld class MTB
« Reply #25 on: October 03, 2009, 07:01:58 PM »

Unfortunately, the electronic speed controllers failed completely at the first test launch. When we arrived at the test site, I found that only one of the motors were turning - I blamed this on a malfunctioning sender, but after checking we found that not to be the case. We decided to try the boat with only one motor working, just to see how it behaved - about five metres out in the water, the last ESP too failed, but fortunately it was still able to run backwards, so we got the boat in to shore.

Returning home, we tested and found that the ESPs had failed. I returned them to the dealer, and were sent another type a few days afterwards.

Pity, but I guess something has to go wrong.


Well, this was as far as it got before the remaining speed controller failed... Hope the new ones will be better.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #26 on: October 03, 2009, 10:43:43 PM »

After long consideration, I finally thought of a plan how to fasten the deck to the hull. The deck totally covers the hull, and I've considered gluing the whole deck to the hull, and cut holes here and there for access, but I can't help thinking that it will really help being able to take off the whole deck.

What I'm thinking is to drill four holes in the deck, through which I'll stick four screws. On the hull, I'll fix four nuts, which the screws can be fastened to, thus holding the deck in place. It works in theory, but it was a bit difficult in practice.

I've tried to build the screws somewhat camouflaged:

The holes where they will stand, is as close as possible to where these things stood on the original.

Underneath the deck, I once again used Meccano, glued in place and with the nut soldered on:


And finally, I was able to mount the deck on to the hull, and get an impression of how it'll look some day. I've cut small pieces of a rubber mouse pad to fit under and around the screws, so that they won't destroy or scratch the deck, and keep it watertight.




However: How on earth am I going to make this watertight? Have you any suggestions? I have to come up with something to put between the deck and the hull to seal it. I've tried some K-profile rubber used to seal windows and such, I glued it to the deck, but it did not work as intended.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #27 on: October 11, 2009, 11:41:10 AM »

Before fitting the deck, I received two new speed controllers in return for the two faulty ones. These were of some other brand, and they actually work.

After fitting them, I had to wait long to find a day when the weather was suitable for a test run - and what a test! The boat performed perfectly, going fast and making beautiful waves.


Full speed - however, this is with the original slower speed-propellers I had. I have now bought some new propellers, but I've not had a chance to test them yet. I suspect it will go even faster with the new ones.



I also took some video of it, which can be seen here: http://www.youtube.com/watch?v=eT72zrfuMpE

However, I'm still wondering how to fit the deck... any suggestions at all?
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #28 on: October 12, 2009, 10:28:09 AM »

After reading my previous posts, I see that my language is not the best, and my questions are vague and open for interpretation. I'll try to put it straight:

The hull is one separate part, and the deck is another. The deck is designed so that it will fit over the hull, the deck resting over it with about half a cm sticking out all around the hull, and there is also a downward-facing edge on the deck, about half a cm. 

I'm trying to think of a method to fix the whole deck to the hull. In order to do this, I have drilled four holes in the deck, and fitted four nuts to the hull, corresponding to the holes in the deck. Thus, I can fit four screws which will hold the deck in place.

As can be seen in the video and pictures in the previous posts, the boat makes a rather large bow spray, higher than the hull. When the deck is fitted, the bow sprays will reach up to the deck, but because of the edge on the deck, the bow spray will be directed to the inside of the hull, where it of course is not supposed to be. I have tried to fit a K-profile weather strip to the deck in the hope that it would make the connection watertight, but it did not work as intended, and the hull was filled with a litre of water after only a short time on the water.

The question is: how am I going to make the 'connetion' between the deck and the hull watertight? Any suggestions?
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rsm

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Re: Norwegian Tjeld class MTB
« Reply #29 on: October 12, 2009, 11:20:09 AM »

If I was you I would permanently bond the deck to the hull to prevent water ingress. I would then cut a lift out section around the bridge in the deck (and fit the deck with flanges)for access to the batteries, speed controllers etc..
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #30 on: October 12, 2009, 11:44:54 AM »

Thank you for your reply! It is perhaps the best idea, and I guess the only way to make it completely watertight.

However, when you cut out parts of the deck, how do you make the gap between the lift out sections and the fastened deck watertight? Would a K-profile weather strip be any good there? I guess it will never be completely closed for any water ingress, but at least I want to prevent what ingress I can.
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rsm

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Re: Norwegian Tjeld class MTB
« Reply #31 on: October 12, 2009, 12:10:02 PM »

If you fit flanges to the underside of the deck for the lift out section to sit on, you may be able to use a gasket formed from a thin layer of silicone rubber to waterproof the join. It should be reasonably watertight if the lift out section is held tightly in place.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #32 on: October 12, 2009, 05:10:32 PM »

That sounds like a good idea. I think I'll try to cut the whole deck about 2-3 cm inboard from the sides, and glue what will remain as a frame to the hull. On that frame, I will fit some flanges and supports, and then use my screw-method of fixing the deck in four places, perhaps with the addition of some self-made 'sliding locks' or something. That way I can still have access to most of the interior, but will not have the problem with the bow spray.
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steve pickstock

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Re: Norwegian Tjeld class MTB
« Reply #33 on: October 13, 2009, 11:43:50 AM »

Rather than make an arbitrary cut - may I suugest you try and make the cut along a line in the deck so that the cut 'disappears'? Eg where the deck meets the superstructure.
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sjoormen

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Re: Norwegian Tjeld class MTB
« Reply #34 on: October 13, 2009, 12:25:43 PM »

Nice model, I like your video of test drive. O0 O0 It also rememmbered me to run my KNM Snogg. ok2
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #35 on: October 17, 2009, 10:12:40 PM »

Thank you all for your suggestion and nice words, and thanks for the comment on the video.

I'm still thinking about how to make the cut gentle, and will hopefully come up with a solution soon. I tried another way of fitting the rubber weather strip today, but it did not work out, so I will definately have to glue the deck on to the hull in some way.

I changed the propellers today, and I must say, this is more like it:



Comparison between the old propellers and the new ones:
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #36 on: October 22, 2009, 09:45:12 AM »

Some photos from the test drive with the new propellers:









She rides a bit heavy in the water, and proves a little difficult to control, she leans to one side and can be hard to bring over in a turn. I would think that the weight affects the steering, so I'll try to remove one of the three batteries and see how it does. Going from 21,6 Ah to 14,4 Ah will reduce the running time, however, I could bring extra, charged, batteries along anyway.
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derekwarner

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Re: Norwegian Tjeld class MTB
« Reply #37 on: October 22, 2009, 10:09:10 AM »

SinWin...yes the latest photographs suggest the hull has marginal bouyancy...however this was not 'as' apparent in the previous photographs.........

You suggest the only difference are the revised twin props?........ :o ...............Derek
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Derek Warner

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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #38 on: October 23, 2009, 01:56:48 PM »

Yes, so it seems. I should have noticed when I installed the batteries, but I then thought that the hull should manage the extra wheight. It was "only" a cm or so over the waterline I had painted. I suppose the extra weight is the main reason for the 'sluggish' behaviour in the water?


And yes - the extra speed must be due to the new props alone: they are the only thing I changed from the last set of photos/video on the water. I can't help thinking what the speed and handling will be like when I remove one of the batteries, they weigh 2,7 kilos each.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #39 on: November 16, 2009, 07:23:29 PM »

Having consulted the family's engineering expert and technician, we've agreed on where to cut the deck, and how to fasten it to the hull. With one exam remaining this semester, I'm looking forward to my Christmas holiday with time off to do some modelling. I'm still looking for cheap 40 mm computer fans, though. Perhaps I ought to scan ebay or dealextreme. Fans that size will be cooling the engines. I'm also working on an automatic bilge pump. I'm thinking of making one of the original exhaust vents double as an outlet for excess water, though I hope the pump will be redundant.
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Greggy1964

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Re: Norwegian Tjeld class MTB
« Reply #40 on: November 17, 2009, 11:51:42 AM »

Hello SinWin,

Great project.  :-))

I have studied your photos with interest and if I may I might make a small suggestion to help your boat speed through the water faster and smoother.

The guy that taught me how to build boats when I was a young lad sailed motor torpedo boats using glow plug internal combustion engines.

The under side of the hulls were painted and then sanded with progressively finer wet and dry glass paper until they were highly polished.

Then on top of this he used car wax polish. :-))

All this effort made his torpedo boats ride over the water very smoothly and fast making beautiful clean bow waves.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #41 on: November 18, 2009, 06:23:32 AM »

Thank you for your interest and kind words. Your proposal sounds like a very good idea. My paint now is not very smooth, so sanding it and using car polish just might do 'a', if not 'the', trick.
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derekwarner

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Re: Norwegian Tjeld class MTB
« Reply #42 on: November 18, 2009, 06:35:39 AM »

SinWin....I understand & agree with the reduced water slip as offered by Greg.....but  as %% as it may sound lets think

1) what happens if we consider that the hull is not travelling faster .....but the water covered per given time is greater  O0....one may argue that these two comments contradict :-))
2) the result is for any given body of water.....is that technically the hull will sink "marginally" lower in the water  :embarrassed: .......fact......Derek

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Derek Warner

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Illawarra Live Steamers Co-op
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www.ils.org.au

SinWin

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Re: Norwegian Tjeld class MTB
« Reply #43 on: November 18, 2009, 10:59:40 AM »

Perhaps - but would not the decreased drag make up for that? Or would it kill the speed, and make for worse handling in the water?
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Perkasaman2

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Re: Norwegian Tjeld class MTB
« Reply #44 on: November 19, 2009, 10:07:02 PM »

Hi SinWin, I like your model ;) 
How long/wide is the hull?  Are your (3) batteries 12v 7Amp/hour rated? Are your 2 rudders to scale?
I may be able to help with the speed/handling problems but the questions above are important and your answers would help members.  :-)
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #45 on: November 19, 2009, 10:16:21 PM »

Hi, Perkasaman! Thank you for your comments.

*The hull is in 1/20 scale, which makes it 122 cm long, and 37,5 cm wide.
*I'm going to take out one battery to help weight problems, leaving two 12 V 7,2 Ah lead-acid batteries. They weigh 2,7 kilos each.
*My two rudders are slightly larger than the original, as far as I can see from drawings and pictures. They are, though, those recommended for me by the museum I bought the hull from, and replicate the shape of the original rudders rather well. 
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Perkasaman2

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Re: Norwegian Tjeld class MTB
« Reply #46 on: November 22, 2009, 08:27:36 PM »

Hi SinWin, My Vosper 'Perkasa' is 124 cms long and very similar to your mtb. I put  a lot of information/photos on the forum and it may be helpful.
Forum Section: DRY DOCK
Category: WARESHIPS & MILITARY
Thread: 'Perkasa restoration'
A member was restoring a 124 cm Perkasa model and we exchanged ideas/information.  :-)
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #47 on: November 26, 2009, 10:38:33 AM »

Thank you so much for showing me that thread. I think many of your hints and tips there might help me. However, first I have to try the model with only two batteries and deck fitted, and see how it does.

That said, I'm sorry for my late reply, I'm currently enganged in preparing for my last exam this semester. Luckily it will be over soon.

For future reference, the thread in question is http://www.modelboatmayhem.co.uk/forum/index.php?topic=18030
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #48 on: November 29, 2009, 09:39:49 PM »

I'm currently scanning the web for a small continious rotation servo, which will be used for turning the radar. I've tried modifying three small servos myself, and it works, but they make a lot of noise and do not move even, so I think I have to go with a servo that was made to rotate all the way around.

Does anyone know of a reliable webshop who sells servos like that? Preferably one who ships internationally (i.e. Norway). The local shop where I live once again turned out to be useless...
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rsm

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Re: Norwegian Tjeld class MTB
« Reply #49 on: November 29, 2009, 10:21:46 PM »

How about this instead of a servo?

http://www.action-electronics.co.uk/pdfs/M7G.pdf
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