FINNJET Revell - RC Groups
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May 04, 2010, 06:43 PM
Work induced time dilation...
Andrey225's Avatar
The ship is looking great so far! I never realised that it was that small compared to the QM2.

Just how much weight do you need to lose to get it to the waterline? and will it be stable enough after being lightened? My old QM2 floated about 1cm lower than the waterline and its been very difficult to get the new one to stay upright with the heavy plastic superstructure.

I would certainly recommend using a flat lipo cell in the keel to keep the weight low and low down. e.g. a 2000mah cell, 5.8x54x54mm, 36g.

As you are using fairly small motors you won't need too much cell capacity so as long as the empty model is light enough the battery should be selected to get the weight up to the desired amount.
May 05, 2010, 12:32 AM
Registered User
cos918's Avatar
Hi Andrey
She a fair bit small at only 54cms in length. I have removed as much plastic as I can up top and this has helped . I am waiting on her new motors to see how they perform. I had been looking at a lipo battery 7.4v 350mah and only 17g. once the new motors are in and tested I can see what weight I have left to use. I am thinking of repainting the hull raising the hull water line by about 1.5mm.

May 05, 2010, 10:28 AM
Registered User
Jerome Morris's Avatar
I can now see why she was an economic failure as a high speed ferry. The amount of water she is pushing ahead of her is astounding.
May 05, 2010, 11:32 AM
Damp and Dizzy member
Brooks's Avatar

A camel to raise the hull

If you don't mind adding a removable fin keel (like a sailboat), you could avoid repainting the waterline. The camel will have a slab of styrofoam at the top end (to increase hull buoyancy enough to raise it to the proper waterline depth). And it will have a weight at the bottom end to maintain vessel stability. Making one will require some experimentation, both as to the size of the styrofoam and as to the amount of weight needed&depth of the keel.

If you calculate the volume of water between the current waterline and the desired waterline in cm^3, that will tell you the vol. of styro needed (or the amount of weight in grams that you need to remove from the boat to get her to float at the design waterline) . You'll also have to add styro vol to account for the weight of the fin itself (unless the fin is wood and already floats). What you are looking to achieve is a camel unit that will float by itself with a vol of styro (out of the water) that equals what you calculated you needed to raise the hull the right amount.

The fin length and Pb will require some experimentation - their dimensions will depend on how tippy your boat already is, and the max tippiness you will accept. You can reduce tippiness and roll period by deepening the keel. Of course, the more Pb you add, the more styro you'll need to add to the basic styro vol you calculated for raising the hull. Every gram of Pb will require about 1 additional cm^3 of styro. You can refine the adjustment by accounting for the vol of Pb (or the vol of the Pb container if, like me, you use lead shot for weighting keels). For small boats, say under 3' length, the vol of the Pb container provides significant buoyancy itself, and can be subtracted from the extra vol of styro needed based purely on the weight of the Pb.

The lighter pink shows the volume of water to be calculated.

Camels have been used by steamboat modelers to raise the hull to keep from immersing the paddles too deep. If the hull is wide enough, it may be possible to dispense with the fin keel and Pb.
Last edited by Brooks; May 05, 2010 at 12:10 PM.
May 05, 2010, 11:47 AM
Registered User
FatBeech's Avatar
Hi John,

I did my Revell Finnjet in the late 80ties with some TamTech electronic and motors. She was very topheavy and you could drive without wind only. The pic was made with beginning of winter and some thin ice on the water. My model was then a fast ice crusher.

May 05, 2010, 02:07 PM
Registered User
cos918's Avatar
Hi all
well the new motors turned up to day and they weigh only 11g each. I will test them in the next few days.

Jerome she was a bit of a power house ploughing up the Baltic at 30+knots and she could hit that in under 3 min from a standing start.

I do like the idea of the foam and the keel .I will have to look in to it.

Hi Ernst
Thank you for the photo she look's nice. In your photo it's hard to tell bit is she a bit low in the water .

May 05, 2010, 04:46 PM
3 Blades to the Wind
Shaun Hendricks's Avatar
Wow, she does move a lot of water out in front of her. Also, the square in your face below the bridge doesn't do much for her aerodynamics either. If they put that kind of power into a more streamlined structure they could've gotten better fuel ratings at her cruising speed and better top speed as well.

I love seeing a ship move that much water but man, the fuel needed to make it do it is another thing!
May 05, 2010, 07:19 PM
Cheif Bottlewasher
more coffee's Avatar
She's a nice ship bad she met the breakers in Alang..

Cos..really like the work you put into this ..

One thing though guys ..Finnjet sported two gasturbines and was also a Class1 A Super Icebreaker..hence the bow wake under full power....What i know off breaking ice is a kin to Elmer Fudd's knowledge of hunting wabbits...Im guessing you cant have both and not scarifice something..besides fuel was cheap in the late 70's at the time of her birth..

Last edited by more coffee; May 05, 2010 at 07:29 PM.
May 06, 2010, 09:57 AM
Damp and Dizzy member
Brooks's Avatar
Comparing the bow shot on the beach with the on-the-water shots, it looks to me like maybe the real ship ran deeper than designed :-). The blue part of the hull should not have been such a water-shover as the photos reveal, to my eye.

Do modern icebreakers have the bulbous bow? Used to be the point was to have the hull ride up on top of the ice so that the weight of the boat could then break it (for any ice too thick to be broken just by the forward motion of the icebreaker). A bulb would prohibit ride-up, I think.
May 06, 2010, 11:19 AM
Registered User
cos918's Avatar
HI all
More Coffey thank you .
Finnjet had 2 gas turbines and 2 Diesel engines. That is what gave here her power. She is NOT an icebreaker. What she has is a super class A1 Ice hull diffrent to an Ice Breaker . This means she can work in thine ice were she can punch through it. I was on Silja Symphony this Feb in the bad ice. We were on the bridge talking to the captain. He said in the old day when the got stuck they just waited for Finnjet as she had the power to punch trough 3 foot of ice. The problem was after wards for the other ferry to keep up .
Icebreaker do not have bulbous bow as the ride up on the ice to break it,this can not be done with a bulbous bow.Finnjet plating on her bulbous bow was over 50mm thick if I remember correctly.
Brooks Finnjet has a very deceptive hull from some angels it looks very slim to a fine point other angels it look's very blunt
that a look at this 2 site they have loads of photos of her.

May 06, 2010, 11:21 AM
Cheif Bottlewasher
more coffee's Avatar
In this case though Brooks with the two ferries here ..that are both Class 1 A ..the bulbous bow serves as a fulcrum..the ice rises up onto it and fractures under its own weight
Dont forget that a ship will "squat' in the water under an extent more noticable in shallower water however..

Take an envelope,seal it then run a knife underneath the sealed edge..similar principle.

Class 1 A is really just a reference to icebreaking capability..not really classed as a purpose built icebreaker

Edit..exactly cos ..thats what i was eluding to in a previous post..
Last edited by more coffee; May 06, 2010 at 11:30 AM.
May 06, 2010, 11:33 AM
Cheif Bottlewasher
more coffee's Avatar

The bow wake under Caribou at service speed of 22knots ..put 8-10 more and you can fathom the similarities to Finnjet's wake
Both are Class 1 A icebreakers and have quite similar bow design

Sorry Cos ..not meaning to Hijack your thread..
May 06, 2010, 12:20 PM
Damp and Dizzy member
Brooks's Avatar
Thanks guys, answered my questions. Neat boat, Cos, I am sure you will figure out something to make her perform the way you want.
May 16, 2010, 03:14 PM
Registered User
cos918's Avatar
Hi all
well the new motors are in and I remade the prop shafts out of tube as the old one were solid rod. This has helped in the weight dept new motors 11g each new shafts 5g each old shafts were 10g each. The new motors work well and make a fair bit of power on 4.8v,one of them is running a bit tight so this will require some work.
Done some more testing in the Baltic (bath) on her weight. As there is no more easy to remove weight I have come to accepted she will run about 2mm deeper than her water line. This does have the benefit of increasing stability. All so her hull is blue/black above the water line and black below so it is hard to determine were the water line is. Next job is to order a nice light weight Lipo battery of ebay as this will help clocking in at 30g.


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