# Tank testing for amateurs

Discussion in 'Boat Design' started by Alwaysthinking., Oct 30, 2019.

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### TANSLSenior Member

Check your calculations, if you don't mind.

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Can you explain what this means please?...in relation to the reply from DC

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### TANSLSenior Member

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No he is not.
Eric was/is RCNC and RINA President at one stage, and used to sit on the Lloyd's Maritime Academy board, but i don't believe he does any more.

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So how does DC/readers to this thread know what you mean, if you wont explain this statement further?

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### DCockeySenior Member

TANSL, you appe
TANSL, please explain where you believe the algebra I showed is in error.

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### DCockeySenior Member

Example of speed for same Froude number with scale model testing using formulas from post #30.

Full size length = 8 m
Full size speed = 3 m/s.
Full size Froude number = 3 m/s / sqrt (9.82 m/s^2 * 8 m) = 0.338

Model length = 0.5 m
What speed for same Froude number?

Scale factor = Scale model / scale full size = 0.5 m / 8 m = 1/16
Square root of scale factor = 1/4

Model speed = square root of scale factor * 1/4 * 3 m/s = 0.75 m/s

Model Froude number = 0.75 m/s / sqrt ( 9.82 m/s^2 * 0.5 m) = 0.338

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### TANSLSenior Member

Álgebra is correct but scale factor is "SQR(L1/L2)", not L1/L2

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David,
You are not in error nor the understanding of scaling and geosims. The error is with Tansl.

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### rxcompositeSenior Member

I read somewhere that Eric's name is on the board of Westlawn. But that was a long time ago when Westlawn was being reorganized. He must be the same author of my book.

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### bajansailorMarine Surveyor

Eric Tupper is also the co-author (with K. J. Rawson) of the standard textbook for students in the UK in the 80's, 'Basic Ship Theory'.
It was in 2 volumes - I did have both, but I can only find Vol I now.
Mine is the 2nd Edition; I bought it in 1980 for GBP 7.50. Amazon UK have a copy of Vol II of the same edition for sale, for about the same price as I paid almost 40 years ago.
https://www.amazon.co.uk/Basic-Ship-Theory-Dynamics-Chapters/dp/0582445248/ref=sr_1_5

Or you can buy a combined volume (of the 5th Edition, from October 2001) for GBP 122.
https://www.amazon.co.uk/gp/offer-listing/0750653981

Also available from Amazon in the USA for approx \$125 -
https://www.amazon.com/gp/offer-listing/0750653981

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### DCockeySenior Member

Eric Tupper was the course director and co-author of a training course about naval architecture from Lloyd’s Maritime Academy. " The Certificate in Naval Architecture is a 14-week course which provides the essential tools and knowledge needed to understand this absorbing discipline, for anyone who works with ships or is interested in their design."
RINA Endorses Distance Learning Certificate in Naval Architecture https://www.maritime-executive.com/article/rina-endorses-distance-learning-certificate-naval-architecture

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### Squidly-DiddlySenior Member

interesting, but the one I posted looks safe enough and about 2ft deep. what is skill/agency level of drowning victims? I could see how larger ones with several feet of steep banks and fast flow and smooth sides could be a problem. Also hear they can be still then "turned on" pretty fast, so by the time you realize what's up your in the current and walls got higher.

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### BlueBellAhhhhh...

Clean water out the side of a tender has always worked fine for me.
Using a windsurfing mast with a pulley on the end to route the tow line to the spring scale.
It's a little subjective reading the analogue display, a digital with memory might work better.

However, the larger the scale model, the more accurate the results...
So, just build the full scale version, and put a motor on it,
or tow it and measure it's resistance at varying velocities.

Nothing better than tinkering with boats.

"Believe me, my young friend, there is nothing – absolutely nothing – half so much worth doing as simply messing about in boats."

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### portacruiseSenior Member

Squidly, those canals can be slippery to get a grip with hands trying to hold on to dirt and wet muddy feet slipping, depending on how tall you are and the rate of flow. If you get washed down to where the area of deeper gates is, some Gates release water from the bottom so there could be a large hydraulic Force pulling you down under, possibly wedging you there.

From BB : However, the larger the scale model, the more accurate the results...
So, just build the full scale version, and put a motor on it,
or tow it and measure it's resistance at varying velocities.

I do get useful information by testing my one man boats using a full-scale model powered by an electric motor and measuring adjusted watts while I drive, but I'm not sure it would work for everyone. So it might be possible to use different carved RC boat hull measurements to successfully test different boat hull designs.

With my target speed being just a low three knots, even tiny variations of wind /water currents, voltage, propeller design (Rick Willoughby), boat wetted area, etc. have to be controlled. The difference in efficiency measured can be quite significant as a percentage- compared to testing at fast speeds. Also, It gets more costly to build full size test models as the boats get larger, especially if the losing model is to be discarded.

Just my humble experience.

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