M.V. Sea Nass

[Dave HarrisonParticipant @daveharrison24862]

Hello everyone, I have really enjoyed reading this forum for a while now, I have always had an interest in boats, ships and scale models. I haven’t built a model boat for about 30 years, so I would be very grateful for any comments and suggestions. I am certainly going to need help along the way.

My chosen subject is the “M.V. Sea Nass” formally “M.V. Mini Luck”. The Mini Luck was the first in a series of ten small coasters built in japan. She was completed in 1970, at 65 and a half metres, around 3000 tons, a top speed of 10knots and a range of 4300 nautical miles. She was shallow draft wide beamed and designed to travel into rivers and estuaries. Originally designed to carry general cargo such as Ore, Coal, timber etc, she could also be loaded with 32 twenty foot containers.

I am using the James Pottinger plans at 1/75 ( model shipwright 119 ) which I have started to redraw digitally so I can cut the frames on a CNC router. I am still deciding on scale but leaning towards 1/48 to give a OAL of 1364mm or 53 and a bit inches.

The hull is hard chine, the frames and keel will be cut from 6mm ply and the hull skin will be whatever I have available in my workshop either 1 or 1.5mm ply. I will probably use the same for the deck and then plasticard for the superstructure etc.

[Dave HarrisonParticipant @daveharrison24862]

[Dave HarrisonParticipant @daveharrison24862]

Over the weekend I have been thinking about the displacement and ballast requirements of this hull in 1:48 scale. When the full size ships sailed unladen they sat quite high. ( see picture ) I quite like the idea of ballasting my model with water. I am thinking of a large baffled tank in the centre of the hull. First ideas are to construct a vented tank that could be filled and emptied with a small electric pump. This would allow me to control how the model sits in the water for any given day.

[Tim RoweParticipant @timrowe83142]

Hello Dave

Ballast tanks should either be empty or completely full. Anything in between and you have what is called the "Free Surface Effect" which can play havoc with the stability.

A way to reduce this would be to divide the tank longitudinally into three, ie one tank on the centre and two wing tanks. You then have the combinations of:

All tanks full
Wing tanks full centre tank empty
Wing tanks empty and centre tank full
All tanks empty.

It's then just a question of plumbing.

Tim R

[geconParticipant @gecon]

Hello Dave, my first thought is that all water should always be on the outside of a hull!

If you must 'pump water' as ballast, the deck-to-superstructure joins must be 100% watertight. You will need a high 'lip' all the way round inside of the superstructure to make sure no MORE water gets into the hull. That freeboard looks menacingly low to me!

Maybe you could fit an automatic bilge pump too?

Tanks should be very well baffelled so that water can only 'flow' very slowly from one section to another.

I see on google that many build sinkable/refloatable boats for warfare and iceberg-bashing simulation sessions, so the necessary equipment is certainly readily available.

Have fun and good luck with the project.

George

 

Edited By gecon on 12/01/2021 08:48:56

[Tim RoweParticipant @timrowe83142]

Hello again Dave and Gecon

If the tank is empty or completely full then baffles will have no affect at all. In a fuel tank where it cannot operate either empty or full, baffles are fitted to prevent the fuel sloshing around.

The danger of allowing water to flow slowly is that if there is any imbalance or wind heeling, the water will flow to the low side and tend to stay there. If the heel moment is reversed the boat can flop to the other side in a condition know as loll. This is the situation where the boat / ship is not actually stable in the upright position. It's a bit like trying to carry a tray full of water. It requires effort to keep it level.

Tim R

[Ray Wood 3Participant @raywood3]

Hi All,

Sounds like a challenge, but I would use the 2 pint plastic milk bottles filled at the lake, I imagine you will have 2 fair sized holds either side of that massive crane.

The hull doesn't actually look that deep on your drawing and loses some displacement with the chine design versus tradition round bilge design, rather like a TID tug.

Many of the guys in my club use the lake water for ballast and put it back when you have finished boating.

Too simple??

Regards Ray

[Tim RoweParticipant @timrowe83142]

Good practical solution from Ray as usual.

Tim R

[Dave HarrisonParticipant @daveharrison24862]

Hi Tim,

Your comment "Ballast tanks should be empty or completely full" instantly reminded me of filling sailplane wings with water ballast.

It is easy to understand why water sloshing around in a void would cause instability, it was slightly harder to grasp why a well baffled tank ( slow flowing / moving water ) would create as many stability problems as it solves, but I think I've got it. So in simple terms the problem is not how quickly the ballast moves, it is the fact that it moves uncontrollably in the first place. Meaning that Ray's idea of sealed containers ( milk containers ) filled completely with water provides a almost static ballast, hence stable ballast. I have the sudden urge to read up on the design of oil tankers.

George, I agree that the freeboard looks menacingly low and one of the reasons why i wanted the ability to adjust the ballast for the conditions ( run the model low in the water on a completely still summers evening, higher in anything other than perfectly still ). I don't know why but I have always liked the look of a ship sitting low in the water. You are right about the hatch lips stopping water ingress and something I will have to remember.

Thanks for all of your comments, I think I'm going to move my attention to cutting some wood and come back to the subject of ballast once I have a hull !

[Tim RoweParticipant @timrowe83142]

Good plan Dave

And keep the build progress going on here.

Tim R

[Ray Wood 3Participant @raywood3]

Hi Dave,

My 20" TID tug made of balsa to Vic Smeeds design enlarged slighty is the same sort of hull shape as your ship and took 4.5 lbs of steel plate ballast to achieve the scale waterline.

Somebody technically minded could probably work out the displacement, not me I put it in the bath

This picture reminds me what we are missing !!

Regards Ray

[Dave HarrisonParticipant @daveharrison24862]

Lakeside in the sunshine ? That looks great Ray, I was visited Maldon in Essex a couple of years ago and there were two TID tugs moored up just past the Thames sailing barge trust.

I was looking through your photo album to see if you had photo of the tug on the water, then I saw the photo of your Myford and instantly felt regret for selling my old ML7.

[Ray Wood 3Participant @raywood3]

Hi Dave,

One can live without lots of things, but a lathe is not one of them

Regards Ray

[Dave HarrisonParticipant @daveharrison24862]

Ray, I might have to invest in another.  I think I'm going to need a lathe for this model boat building lark !

Not much progress to report today. The project has been re-named the "S.S. Timewaster" by the misses !

The cutting file for the hull components is ready and I've just realised I've got no small cutters (silly boy). 2mm cutting bits on order and should be good to start work over the weekend.

Time to think about running gear, props, rudders and a good source of plasticard.

 

Edited By Dave Harrison on 14/01/2021 12:50:58

[Ray Wood 3Participant @raywood3]

Hi Dave,

With computer skills like yours you should consider doing a drawing and sell kits of parts, although I'm on the computer all day I can't do that !! it's the old pencil, paper and flexy curve for me

Trying to think of something different to build after Oldenburg.

Regards Ray

[Tim RoweParticipant @timrowe83142]

Ray

Build a flying boat. Maybe one of those Canadair CL415 Fire Fighters.

I am sure you would be allowed to blog it on here.

Echo the computer skills!

Tim R

[Dave HarrisonParticipant @daveharrison24862]

Thanks for the comments guys.

I've made a right old mess tonight, dust everywhere a few four letter words but now I have a building board and the start of a hull ! woohoo !

It's only dry fitted together at the moment because the ply was a little warped but I'll fix that over night.

[Ray Wood 3Participant @raywood3]

Hi Dave,

That's is mighty impressive, I like the twin skegs at the stern are you going to have to notch all the bulkheads for some stringers to take the skins ?? I find it makes life easier to extend the bulkheads an inch or so to raise the whole job up for access and cut them off later.

Regards Ray

[Dave HarrisonParticipant @daveharrison24862]

Hi Ray.

Thanks for your kind words, to be honest with you in my enthusiastic haste I have made a few school boy errors. The top of the bulkheads are notched to take stringers to support the deck, however I stupidly didn’t cut these into the base board. So can’t put them on until the hull is skinned. My initial thoughts were that the 6mm bulkheads on a hard chine hull would give enough support for the ply skin, and the ply skin once covered with light cloth and epoxy give support to the bulkheads. I’m starting to realise that stringers to the underside of the hull would have greatly increased strength and as you say make my life easier. I’m fairly confident it’ll be ok, I really don’t want to notch all those bulkheads by hand.

The skegs are just full size spacers / blanks for the time being. These will need to be cut formed and laminated with the prop-shaft tubes running through them.

Can I ask where you got your propellers and propeller shafts for the Oldenburg ?

I need to think about what motors to use. There is scale space for 1.5 inch / 38mm four 4 blade props. The model will be quite heavy so I’m thinking reduction gears or belts to keep the amps down and the torque up. I’d really welcome some help in this area as motors and speed controllers are worlds away from the rs540s and bobs boards that I knew in the 90's.

Cheers Dave

[Ray Wood 3Participant @raywood3]

Hi Dave,

I take the view the next boat will be the really good one, well that's my excuse

My Oldenburg running gear was bought from my local boat shop in Chatham Dockyard alas closed at the moment.

I'm sure Cornwall Model Boats can sort you out mail order

The stern tubes were JP Accessories 10" M4

Propellers are Raboesch 30mm 3 blade brass left & right hand

Make sure your sitting down when you look at the price !!

With 2 motors you won't need a lot of horsepower I'd use a pair of 385's or 400 brushed, as she is relatively long she will be easily driven in my view. My 20" TID tug with a 30mm prop & 400 moved a 14' tanker

Regards Ray

[ashley needhamParticipant @ashleyneedham69188]

As it’s a largish boat then a pair of Como 540/1 motors gets my vote, and these will turn a 40mm prop ok.

I am happy with the 385’s up to say 35mm brass or 40mm plastic but perhaps if you want 4 blades then the 540s may be better. Some might argue that those props are a bit big for the motors but with the very small current draw,a bit of overloading goes unnoticed and I have never had an issue. Even 385s on 40mm props would be ok but a bit of extra oomph from the larger diameter motors will help.

Nice frame, you can see the width/flatness ratio like that !

Ashley

[Dave HarrisonParticipant @daveharrison24862]

What do you think of these…. mfa como 385LN they are advertised as low noise 385's ( 5 pole ) with a slightly higher torque and lower RPM per volt than the standard standard 385s. on 12v they produce nearly as much as the 540/1 on 6volts. The other option I have is gearing the motors to drop the RPM and gain more torque. I only really need to achieve a hull speed of no more than a slow walk.

[ashley needhamParticipant @ashleyneedham69188]

Dave. What size props are you going to use?

385s on 12v May be pushed with 38mm 4 blade brass props.

A 555 motor would be just the job, on 12v with the larger prop.

Ashley

[Dave HarrisonParticipant @daveharrison24862]

Hi Ashley I can't seem to find a 555 are they in the 540 family, do you know what rpm they run at ?

I managed to get a little bit more done this evening after work. I cut the decks and tried a new glue out which was recommended by a friend ( RhinoBond – I hope its not made of rhino's &nbsp. I have also made a note to invest in some more clamps.

Being flat bottomed i might not even have to make a stand for it !

[ashley needhamParticipant @ashleyneedham69188]

I bought some 555s from “model motors direct”, ages ago, to put in my 57” T42 destroyer. On 12v they did about 6000 rpm, but would turn probablya 60mm prop like that. Very torquey.

Had a v quick search and as you say can’t find them now? It was about the size of a 600.

Ashley

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