Vintage Gentleman’s Cruiser

[Bob Abell 2Participant @bobabell2]

Paul

I`ve had an idea!

In order to determine the amperage of the required ESC……And knowing that the VGC won`t fit the bath

Why not construct a special test rig?

One Abel Drive mounted on a board with a 50mm prop coupled up and an Amp reader and battery connected?

Any further suggestions before I start the build?

Bob

[Paul TParticipant @pault84577]

Hi Bob

Unfortunately the amp test needs to be done in the hull as the motor/shaft set up has an important bearing on the result.

The angle that the motor is fixed at, the drag resulting from the shaft and connections all add to the amps being drawn by the motor.

Unless you have a paddling pool or garden pond the only option will be to test the boat at Etherow.

Paul

[Bob Abell 2Participant @bobabell2]

Thank you, Paul

You are probably right, but I would think that a test rig will give us a fair idea on the loads

Will do it anyway……Have ordered a 100amp Watt Meter

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob.Test rig would be more trouble than its worth. When you get the 100A meter, that will be all you need.

You really need to try some other props as well but at the large size you have thats a bit difficult

I have ordered not only a replacem,ent watt meter (100A) but also an optical tachometer, hopefully I may be able to check out not only amps but revs as well..

Ashley

[Paul TParticipant @pault84577]

Sorry to Pooh Pooh the idea Bob

The drag from a long or incorrectly fitted propshaft could add a theoretical 2amps to the load, add to this misaligned or tight propshaft connections ………………..the load increases.

With the Lady Joyce you have two pairs of motors to take into consideration and the way that they are wired will play a big part in the final outcome.

Paul

[Bob Abell 2Participant @bobabell2]

Thank you, Paul for your Doomsday scenario…..lol

Got an idea!

Ashley

When you've got a few minutes to spare, will you run one of your largest boats, with the Watt Meter attached……In the water and out the water?

The results should be very informative!

That should put the cat amongst the pigeons!

Bob

[Bob Abell 2Participant @bobabell2]

Paul…..I`ve managed to disentangle the gold lettering with a scalpel

Many thanks and kind regards to Jane….xxx

And played about with the furnishing arrangement

Bob

[BanjomanParticipant @banjoman]

Oooh … now that is what I call pretty! Very, very nice lettering indeed!

/Mattias

[Bob Abell 2Participant @bobabell2]

Thank you, Banjo

Have to confess, the lettering was put on, a bit …"Cock eyed" for the photo, but Photo Shop put it right!…..Ha! Ha!

Bob

[Paul TParticipant @pault84577]

Hi Bob

The lettering looks ok (despite your attempts with photoshop lol) The fitting out of the rear cockpit is coming along very well and I do like your use of redundant lock fittings.

Sorry to throw another spanner in the works but testing the amp draw on a big model should also include the mass of the boat.

Paul

[Bob Abell 2Participant @bobabell2]

Well spotted, Paul

Those Yale Lock rings are difficult to find these days

You seam to be over subscribed with Spanner's at your house!

The 130amp Watt meter should arrive today…..Goodness knows, what I'll do with it?

Bob

[Gareth JonesParticipant @garethjones79649]

Paul,

Why is the mass of the boat important? The worst case measurement is with the boat static in the water so I don't understand the significance of its mass (or dimensions)

The key thing you need to know is the current drawn – to make sure you are not exceeding the rating of your ESC.

Its also useful to know the prop speed/motor speed to check that you are somewhere in the region of 70-80% of the free running speed of the motor and therefore operating in a resonably optimum area of the motor performance chart.

Gareth

[Ralph PinchParticipant @ralphpinch41762]

Hi Bob.

Just skipping around the forum waiting for some glue to dry hmmmmm and found you latest pictures, love that checkered flooring, looks fantastic, if fact it all does, the lettering is very elegant.

Ralph.

[Bob Abell 2Participant @bobabell2]

Thank you, Ralph

I'm pleased you like the build

Weren't you asking Paul about the plans, the other day?

It would be very interesting to see your build…..It's very simple, but a little on the large size

Just build it as drawn….Never mind my mods?

Bob

[Ralph PinchParticipant @ralphpinch41762]

Sorry Paul, just realised that I am on your post not Bobs, sorry to cross talk it was an error, hope I did not break any rules.

Ralph.

[Bob Abell 2Participant @bobabell2]

Ralph

I think you are ok on this thread

Anything to do with the big VGC is ok here

Bob

[Paul TParticipant @pault84577]

Hello Gareth

The peak amp draw will occur when the boat moves forward from the stationary position and the mass of a boat as large as the VGC has a direct bearing upon the amount of amps required.

Paul

[Diede van AbsParticipant @diedevanabs87670]

I actually think peak amps will occur when going from astern to full ahead, the mass of the boat is still pushing the boat in the opposite direction of what the props what it to go. Next worst peak when holding the boat stationary while running full ahead, and moving forward from stationary coming in third.

Bear in mind though that these are only worst case scenarios; you should calculate your ESC's and motors to keep up with it for good measure but the situations themselves should be avoided during normal operation.

[Bob Abell 2Participant @bobabell2]

I think you've hit the nail on the head there, Diede!……..Lol

Bob

[Dave MilbournParticipant @davemilbourn48782]

the mass of the boat is still pushing the boat in the opposite direction of what the props what it to go.

Sorry, Diede, but Isaac Newton says not. Force = Mass x Acceleration. Mass can't exert a force on its own. The only forces acting on a boat going astern are the thrust of the props and the resistance of the water to it. These balance each other out if the speed of the boat is steady.
You will need a larger acceleration to go from a reverse speed to a forward one than you would from a standstill – speed and acceleration both being vector quantities – and, for a given force, the larger is the mass of the object then the smaller will be the acceleration which will be produced.

DM

[Bob Abell 2Participant @bobabell2]

DM

Inertia = Mass x Acceleration………….not……….. Force = Mass x Acceleration

Bob

[Keith LongParticipant @keithlong89920]

Sorry Bob as a physicist I do not recognise that equation that you've put up. Inertia is the resistance to change of momentum NOT the product of mass (inertial mass) and acceleration.

Force=mass x acceleration is the correct relationship.

Rearranging – mass (inertia) = force / acceleration

[Bob Abell 2Participant @bobabell2]

Thank you, Kieth

What about the units?

Lb ft per sec squared = lb x ft per sec squared

Bob

[Dave MilbournParticipant @davemilbourn48782]

Bob

Force = Mass x Acceleration is written as

1 N = 1 kg⋅m/s2
Where the units are expressed as follows:
N: newton
kg: kilogram
m: metre
s: second.

Inertia is a measure of how much an object resists rotational acceleration about an axis. Unless you were swinging VGC around your head on the end of a piece of string (!!!) its inertia isn’t something which would affect the situation.

I think you are getting confused with momentum, which is the product of a body’s mass and its velocity. A force is required to change the momentum of a body and because it is a vector quantity then a greater or more prolonged force/acceleration will be needed to reverse its direction of travel than would be simply to bring it to a halt.
This is probably only a fancier way of saying the same thing as Diede said but, like Dr Thomason, I seldom let an opportunity to nit-pick pass me by!

Come on, Gareth – your turn.

Dave M

[Bob Abell 2Participant @bobabell2]

Are we talking about the same Newton?

I Newton = 0.22lb

How can 0.22lb = lb ft / sec2 units?

But I think I meant Momentum not Inertia

Bob

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