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Author Topic: Norwegian Tjeld class MTB  (Read 44070 times)

pompebled

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Re: Norwegian Tjeld class MTB
« Reply #150 on: November 21, 2010, 07:24:05 PM »

Hi SinWin,

An electric heat gun (for paint removal) will work fine.
Make sure to mainly heat the propshaft (stuffing tube) and not the surrounding hull, as the hull is much thinner than the glued joint and does require not a lot of heating up to deform.
I assume the hull is polyester, so once you deform it by heat the damage is irreversable, so keep an eye on it.

450 mm shaft is not a lot for the boat size, I have a 450 mm shaft in my 80 cm speedboat...
But a lot depends on the place where the shaft exits the hull and the hullshape in the aft section.

I would take out the woodblock completely and make a motormount out of 3 mm aluminum sheet.
I added a picture of what I mean;

The one on the left is a motormount that is shaped to fit into a single motor set-up, the one on the right is more universal and can be bolted into the boat on a bulkhead.
Notice the cooling slots for the motor, these are not to be blocked by the mount, as the fan inside the 700bb need to be able to draw air through the motor.

The motor should sit om the bottom with just a mm of space, no more.
The same goes for the prop, 2 mm cleareance of the hull is sufficient

Regards, Jan.


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Perkasaman2

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Re: Norwegian Tjeld class MTB
« Reply #151 on: November 21, 2010, 08:10:10 PM »

Hi Sindre, I heat the propshaft tube with a mini/diy gas flame soldering torch. I always use this method to avoid/minimise heat damage to hull or interior spaces. You will be applying intense heat to a small area of the shaft tube OUTSIDE of the hull - much safer.

1. Disconnect/remove the motors/couplings and propellors.

2. Turn the hull on its side and get a friend to hold/support the hull firmly.

3. Firmly grip/clamp the propellor end of the shaft tube with pliers/molegrips (Leave shaft in.)

4. Apply heat to the shaft tube. (pointing flame in a direction away from the underside of the hull to avoid damaging it.) The heat will build up and transfer along the length of the tube and soften the epoxy jointing.

5. Gently/slowly....... twist/pull the shaft through/out of the hull using the pliers/grips. Apply heat carefully as needed until the shaft is out.

IMPORTANT: BEWARE of fumes - do this outside or in a very well ventilated area. 
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #152 on: November 21, 2010, 09:53:51 PM »

Thanks a lot for all your help! I think I have an idea of how to do this now. I'll lend a heat gun from work, and try and get the shafts out. Perhaps I'll find some aluminium to make two motor mounts as well.

I looked over the instructions that were given alongside the hull, and I have actually followed them. I have bought the shafts that they specify, and mounted the motors like it says. Also, as far as I can see, I have mounted the shafts in the same angle as shown in several photographs! Ugh.

What I am really wondering is how to get that wooden beam out of there, though. It is a very small hole to fit a saw in, and I really don't want to remove the deck again.
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Perkasaman2

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Re: Norwegian Tjeld class MTB
« Reply #153 on: November 21, 2010, 11:26:15 PM »

Hi Sindre, The angle of the props/shafts  on the original boats was very steep and if you are happy with the performance of your boat then don't alter the shafts/motors alignment. Concentrate on your original plan ..... it's your build .... you are the boss.  :-)
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pompebled

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Re: Norwegian Tjeld class MTB
« Reply #154 on: November 22, 2010, 08:59:06 AM »

Sindre,

That's the problem when an original drawing is converted for model use; the designer often hasn't got a clue on the effect of the propshaft angle on the not scaled down water.
On 'proper'(meaning practical) mopdel plans this has been take into account and changes have been made to the propshaft angle and sometimes even tt the underwater hull to improve the performance and handling of the model.

When this is done properly, the difference will not show immediately, unless you are very familiar with the 1:1 ship.

My Italian MTB originally has two motors, but as a single motor with a large prop is more efficient, I'm going with that, as it's going to be a model for running, rather that putting it on display.

Regards, Jan.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #155 on: November 22, 2010, 04:19:16 PM »

Well, I can't say that I'm happy with the performance so far. Or - well - when it does work, it works well - but I can't live with the unreliability.

I might give it a try on the water, though, before adjusting the shafts. With 5 kgs missing it should draw less current? Perhaps I'll mount the wattmeter I bought and place a camera to record its readings on a little run, to see how many amps it does draw now.
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Perkasaman2

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Re: Norwegian Tjeld class MTB
« Reply #156 on: November 23, 2010, 08:41:29 PM »

My pair of 700BB TURBO motors were running (often continuous at max power) with twin 30/40(burst) amp Mtronik speed controllers with a Futaba Skysport 6 (40mhz). I would now choose 40 amp min esc's.
Your video, posted earlier in the thread, shows the hull planing well and making a good speed and your new lighter,high capacity nimh packs should increase performance. Your hatch access in the deck may enlarge if you extend  the opening forward to include the bridge (base area) and remount the bridge on an extended hatch. You could fit a raised 'combing' to locate the bridge at it's base and prevent spray from entering the hull. This larger opening in the deck could improve access for repairs/alterations.
I hope the test run shows that the electrical issues are solved........ I understand your frustration..... I've been there! %)  :} 
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pompebled

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Re: Norwegian Tjeld class MTB
« Reply #157 on: November 24, 2010, 07:18:29 PM »

With 5 kgs missing it should draw less current?
Hi Sindre,

Less weight means less work for the motors, so that's a 'yes', unfortunately a lighter hull will suffer more from the steep propangle shafts, meaning it will allow the motors to lift up the rear more easily, making the boat run very wet, which in turn causes the ampdraw to go up, as the hull will not get on the plane.
Now I'm not certain this particular type of MTB is supposed to plane out, but with shallow propshaft angles and the power you installed, it most likely will...

Regards, Jan.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #158 on: April 23, 2011, 11:10:28 PM »

Finally the temperature has risen above freezing, and after months without any open water to test the boat with the new batteries installed, the day finally arrived.

After initially bringing the wrong receiver battery pack, and struggling with a servo cable that would not sit tight in its receiver socket, I got the boat on the water - and it ran beautifully!

Now, it has done that before, I admit, but this time I was able to run at full speed - or rather 80 % of full speed, due to me limiting the "servo travel" for the proper channels - for long periods of time. When I had the lead acid batteries fitted, I would most certainly not have been able to do that for more than a minute - by then some fuse would have blown, or an ESC.

I'll let these photos, taken by a very clever photographer accompanying me this day, speak for themselves:







When I took the boat out of the water afterwards, I was able to hold my fingers against the motor casings, without feeling any excessive heat. The ESCs were also just moderately warm. Before, the motors would be so warm I could smell burnt wood when I opened the hull, and the ESCs were so hot you could really feel the heat from them. I guess this shows that I'm really on to something - thanks to all the very kind people on this forum!
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #159 on: April 27, 2011, 05:58:20 PM »

Here is a short video as well of the test run, with some on board footage as well: http://www.youtube.com/watch?v=RFab0jQZMcU
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An Pham

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Re: Norwegian Tjeld class MTB
« Reply #160 on: June 24, 2011, 02:58:27 PM »

Some photos of the Nasty which is being buit. I am not sure that one is the same of Norwegian Tjeld class MTB.
An Pham
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pompebled

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Re: Norwegian Tjeld class MTB
« Reply #161 on: July 06, 2011, 05:07:05 PM »

Hi Sindre,

My appologies for the late response, I couldn't find this thread...

The pictures and the video clearly show the running attitude issues caused by the 'catastrofically' steep propshaft angle, ruining the handling , specially in the turns.

If you want to be amazed by your own boat running attitude and handling, change the propshaf angle to as shallow as possible.

Regards, Jan.
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SinWin

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Re: Norwegian Tjeld class MTB
« Reply #162 on: August 06, 2011, 10:21:24 PM »

That looks like a very impressive construction! Looks like a very detailed model.


I still haven't started on the operation of changing the shaft's angle. It seems like quite a task, and I must admit my motivation for removing the deck etc. is not very high. One day, however, I guess I'll do it.

For some reason the batteries I bought for the boat have died. I'll buy new ones, but that will have to wait a few months. I have also started building the forward 20 mm Oerlikon, but, alas, I haven't gotten very far yet.
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An Pham

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Re: Norwegian Tjeld class MTB
« Reply #163 on: August 12, 2011, 05:48:54 AM »

Complete model. This model is belong one of my friend from Norway.
An Pham

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