Vic Smeed’s Silver Mist

[Paul TParticipant @pault84577]

Captain Bob

The new deck or 'false floor' should remain at the existing waterline.

To explain:

When using a free flooding system in a model boat you have to think of the free flooding compartment as being a separate area from the buoyant surfaces of the model.

Without being over complicated it might help if you think of the model as being built on a flat plank which, in your case, the 'plank' is the top of the free flooding chamber. (the new deck at the waterline)

Everything below the 'plank' is essentially water and has very little effect upon the buoyancy.

If you now think of the model as having a wider flat bottom then you will know that the weight of motor, batteries and electronics will have far less impact on the overall waterline.

I hope that this is clear enough.

Paul

[Ian GardnerParticipant @iangardner62867]

Hi Bob,

It's looking good! I think you will get away with not having extra bulkheads with planks that thick- they seem to be following a nice line and if you follow Colin's advice and resin inside I imagine it'll be fine. I don't know how you'll manage round the stern without blocks though- that canoe stern will be tricky to plank- especially in 4mm planks. I suppose you could scribe the blocks to match the planking if you want to show the plank lines

I didn't epoxy the outside of mine and wish I had, as the planking and the blocks have moved at slightly different rates and a gap has opened up- so I need to do some remedial work- which I'm putting off.

I think a vessel like this would be most likely to be twin screw- most of John Bain's larger vessels seem to have been and Moiena (I sent you the link earlier-ADLS) is listed as having two engines. It might be worth remembering that Vic Smeed designed this as a simple, beginners model (how times change) and was designed to be built without a building board at 21''- so you might need some extra jigging etc to ensure alignment. I built mine exactly as Vic Smeed described but I remember changing the shape of the bulkheads where they met the keel to beef things up a bit. There is one photo on my website which shows this- it's in the slide show of Siver Mist.

**LINK**

I love these old motor yachts and look forward to seeing how she progresses.

All the best,

Ian

 

 

Edited By Ian Gardner on 09/04/2016 16:35:59

[Bob Abell 2Participant @bobabell2]

Thank you, Ian

It's slowly taking shape now

Planking round the stern will be tricky, but I could bandsaw slotting on the inside, to get round the bend?

Bob

[Paul TParticipant @pault84577]

Bob

Build a small steam chest and steam the planks.

[Ian GardnerParticipant @iangardner62867]

Looking back at your post re- alignment of bulkheads Bob, it's always a problem if you don't build on a board which acts as a datum- I'd always be inclined to do that now, especially with a large model.

Regarding prop tube slots, I have always cut the slot in the keel leaving a tab at each end to be removed when the tube is installed- but I think twin engines will be perfect for Silver Mist.

Good luck with the planking.

Ian

[Bob Abell 2Participant @bobabell2]

Ahoy there boys!

This being a fun packed family show…….Something for the kids now!

I`ve cast doubts and dispersions on the latest idea for a ballastless boat…….Suggesting that the hull will sink below the correct waterline, due to the weight of the superstructure and gear etc

My partner in crime, the very honourabell…..Sir Paul Thomason, reckons a 1/2" waterline plank will do the job

We shall prove the point, either way, tomorrow morning, when the plywood waterline model takes to the waters of Coniston Pond bearing a load of about 10 lb

Just a bit of fun chaps……..If things go wrong we can always raise the false floor etc or even add some bouyancy

Bob

[Bob Abell 2Participant @bobabell2]

Surprise surprise!

I weighed Brutus this morning…….Out of curiosity

And it only weighed…..10 lb all in!

Batteries, not included

This is Brutus….

[Bob Abell 2Participant @bobabell2]

Thick frost this morning, but it didn`t effect the pond

Had an interesting time, weighing samples and decided that because Brutus, a complete boat and 4 foot in length, weighed in at a mere 10 lb, the Silver Mist stuff would be about 6 lb?

Then even more fun, getting Lady Joyce to take the photographs!……..Know what I mean, `arry?

The verdict is……Not bad?…….No! Not the photo`s, the Test!

The plank submerged by about 1/2"

A few pictures to ponder and have a chat about…….

Bob

[IAN_IParticipant @ian_i]

Hi Bob..

Very interesting build.

love this stage when the planks start to go on.

This flood chamber idea …is it based on the same thinking of a model sub, where you can control the amount of flooding ?

Best regards,

Ian

[Bob Abell 2Participant @bobabell2]

Thank you, Ian

Can`t get onto the planking yet……..Need to cut out the bulkhead holes, but can`t decided on the position, until the waterline question is settled

The water filled hull is an interesting idea and I`m just curious how it will turn out

Bob

[Paul TParticipant @pault84577]

Bob

The calculated depth for the plank to submerge is 13mm so I expected the upper surface of the plank to be slightly awash, I figured the above water weight of the 4ft Silver Mist to be 2.35kg (5.2lbs) whereas you have guesstimated 2.72kg (6lbs).

All in all I would consider it to be a very successful test.

Paul

[Bob Abell 2Participant @bobabell2]

This page is for the discerning reader

When we were kids……..In the 40's

We used to make a Diver in a Bottle toy………A Lemonade bottle full to the brim with water, complete with stopper

Pah!……Some toy?

Do you mind!

We acquired a small plastic tube or phial from somewhere, with a closed top, about 1" long……And called it…….. Dave the Diver

What the dickens? etc

We gave Dave a drink of water and placed him in the bottle of water, with the closed end…..Upper most

When the stopper was screwed down…….Dave the Diver would descend to the sea bed!………By magic!

And when the stopper was unscrewed, Dave came up again!……….More magic!

We used to do this for hours on end……………We had no Telly in those days!

Ahem!……Why are you boring us with this, Captain?………I can hear you say

Certainly, Kevin……….As the hours went by, try as we may, we could never get the Diver to stay still in the depths?

He went….Up….Down…….Up……Pause…..then up again……..Ad infinitum

We will pause this very exciting story and continue shortly……….For a very good reason!………Make the Toast!

Bob

[Bob Abell 2Participant @bobabell2]

Light entertainment……Part 2

You may be wondering, what the Dave the Diver story has got to do with the Silver Mist build?

Plenty!

Referring back to the floating water line experiment, conducted by Bob the Builder, the other day…..Ahem

If you had been paying attention to the finer points…….You would have spotted the wooden waterline doing what Dave the Diver couldn't do!………Float in mid water!

What?……….I'm afraid so…….I spotted it straight away, but the reason wasn't obvious

The six pack of Camping Gas weighed 6 lb alright, but when I tried them in the water…….That had slight floatation!

Horror of horrors!

All is not lost, however

Sir Paul did calculate that a floating wooden waterline of 13 mm would be necessary to float the top section of Silver Mist

And I've only used 8mm

So Paul's right and I'm right too………..Hold it!………..Why are you right? ……..I hear you ask

Because, dear boy…….I predicted that we would need a floating water line that could support the model

Yep, you did Bob……..Murmers Dr Paul, sheepishly

That was a grand story, Captain!

Thank you, Kevin

My apologises for larkin' about……Bob

[Paul TParticipant @pault84577]

Bob

I don't know about looking sheepish……I think bemused is more apt.

I am sorry but I can't follow the logic of your comments what has two packs of gas canisters got to do with Dave the Diver and what is a floating water line?

Paul

[Bob Abell 2Participant @bobabell2]

Paul

You really have surprised me, with not understanding my little story, and you like cryptic words!……..But don`t get upset……..You are not the only one confused

I cut out the shape of Silver Mist`s waterline…..Using 8mm plywood

I placed it in the water………and it floated normally

I found a load of 6 lb, using six unopened tins of Camping Gaz

I placed the six tins on the wooden shape and it floated………But the wood sank 12mm below the water

I realised this was suspicious at the time, because wood can`t hover below the surface…….Just like the Diver

Later, you thought the test was successful, but said that 13mm was the theoretical correct wood thickness

Later, it dawned on me that the test was flawed……..So I placed the gas tanks in the water and they had some floatation, caused by the plastic wrapping

To prove the point, I later repeated the test, using a 5lb lump hammer…..and the plank sank to the bottom

Proving that an 8mm plank lacks sufficient buoyancy

Verdict…….The water line floor in the model needs to be 13mm thick or 8mm with some buoyancy adding

Is this any clearer?

If not……Add my story to your joke page!

Bob

[Ray Wood 3Participant @raywood3]

Hi Bob

If your trying to establish the displacement required to support your Silver Mist waterline with a dead weight of say 6 lbs your plank will need an upstand round the edge to measure how much buoyancy your hull needs below the waterline to not be a submarine ?

Regards Ray

[Colin BishopModerator @colinbishop34627]

Bob, this all sound very complicated and trying to calculate in advance is clearly not easy, even on a rough basis. If you are keen on using water ballast then why not simply construct two wide bore inlets in the hull, one forward and one aft. Each one to be fitted with a watertight connector. Then you could make up a selection of top vented tanks in different sizes which can be connected to the inlets and tested to see which ones bring the hull nearest to its waterline. Then just use solid ballast to make up the difference.

It should be possible to find and adapt suitable plastic containers and plumbing fittings to construct the tanks. Obviously you need a wide bore inlet otherwise the boat will take forever to drain when lifting it out of the water. Then again you could be cunning and incorporate a stop valve in the tanks to shut off the inlet so you could use an electric pump to remove the water and the boat will rise to meet your waiting hands…

The possibilities are endless.

Colin

[Paul TParticipant @pault84577]

Bob

I am sorry

I have misled you with a false impression about supporting loads on a flat board as the plank experiment was just to show you that a moderately thin flat surface can still float whilst carrying what seems to be a disproportionately heavy weight.

The physics of free flooding hulls is complex and totally different to a simple floating plank and I worry that if we continue with these comparisons everyone will simply become more confused.

I propose that if you want to continue with the free flooding hull concept I could either send you masses of calculations showing how your 4ft model would work explaining the interactions between closed & open systems and how using ambient air pressure will prevent hull roll or you can just trust me in that I do know what I am doing and follow the instructions on basic drawing that I sent.

Kevin

I apologise for misleading you, please don't go and build a flat bottomed model on the basis of my plank ramblings.

Paul

[Bob Abell 2Participant @bobabell2]

To all concerned

This is getting far too complicated, so I've decided to abandon the water filled hull idea and for the present, continue building a standard hull

Many thanks, chaps

Normal service will be resumed as soon as possible…….Breathing a sigh of relief!

Bob

[Colin BishopModerator @colinbishop34627]

With regard to water ballast, people might find it worth revisiting my article on the Britannia Naval College **LINK** and in particular the section headed Tank Testing with its associated photos featuring a frigate model constructed for damage control testing purposes which has the facility to flood any of the vessel's compartments to explore the effect on stability etc.

Colin

[Bob Abell 2Participant @bobabell2]

Water filled hulls seem to be the norm these days, with full size ships

I was talking to a knowledgable chap at New Brighton, overlooking the ships entering and leaving Liverpool, last year

It seems, the ships pump sea water in and out all day long for various reasons

What an interesting idea for a model?

Bob

[Colin BishopModerator @colinbishop34627]

Bob, ballast and trimming tanks have been in use virtually ever since the introduction of iron hulls in the 19th century. They are used to compensate for cargo being loaded and unloaded to maintain the stability of the ship.

In model boats, except of course for submarines, they are used to reduce the out of the water weight of the model which is what you are attempting to do.

But you have to be careful when scaling down. Full size ships have their ballast water contained in a series of tanks either in the double bottom or along the bilges where it helps stabilise the vessel. In models you tend to have a 'wodge' of water occupying the space where the cargo would be on a full size ship and it is frequently in a proportionally large 'tank' which means that the hull can rotate around it rather than having to lift it as when a full size ship rolls. This means that a model can be relatively unstable unless care is taken in stowing the internal water. Your intention of a false bottom inside the hull with presumably free flooding below sort of replicates full size practice except that the water will not be confined in small tanks as it is in a full size ship, will occupy a proportionately greater space and will, I rather suspect, have an adverse effect on stability.

The other issue of course is that while the water ballast won't weigh anything when afloat as it is essentially part of the surrounding pond, it will still have plenty of inertia when it comes to steering the boat as you are lugging a big chunk of pondwater along with you which still has its full mass.

Colin

[Bob Abell 2Participant @bobabell2]

Thank you, once again, Colin

Wouldn't it be nice to just switch the pumps on and watch the model react?

Worth a thought

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. I think that as you have decided, water ballast would be more trouble than its worth. Far easier to have ballast that can be easily put in and taken out. For our D-Day event, Trevor`s 2 metre long corvette had nothing more sophisticated than 2 pint plastic milk cartons, filled with pond water. There was loads of space to stack them and there was loads of space to load them through the main hatch. Easy to fill at the pond and just as easy to empty.

​I recon if you used 12V SLA batteries, you would not go far wrong for the bulk of the ballast, and use something else to trim out.

I can understand the attraction of water ballast though, but I think the aggro at the pond side would not be worth it. Perhaps if you were building a 2m or 3m freighter, then it would be a must, but….

My 5 foot by 14 inch lander was made to be a no-draught vessel, (again for D-Day) to negate any ballast issues or worries. It floats in about 1 1/4 inches of water at the stern and an inch forward. I dread to think how much weight I would have needed to get it to even sink to two inches depth.

Planks…already done that.. Glorious, Nelson.

Ashley

Edited By ashley needham on 11/04/2016 15:14:18

[Bob Abell 2Participant @bobabell2]

Thank you, Ashley

Have you got a picture of your successful planks, please?

Bob

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