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 Ballast questions please

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BrianP
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Join date : 2020-12-04

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PostSubject: Ballast questions please   Ballast questions please EmptySun Jan 10, 2021 8:39 pm

Hi could anyone give me some guidance on using ballast please.

Here's the scenario:

I am building an aluminium hull tug boat.

I am at the stage where the hull is water tight .

It is sitting very high in the water at present.

I have loaded it with temporary ballast of steel blocks and water containers.
They weigh 33.7lbs/15.3kgs

I am quite worried that the hull is displacing so much water.

Could you any share thoughts on this amount of ballast for such a small vessel and can you suggest suitable ballast for the 
finished model please.

Here is the model tug boat. Thanks for any feedback and guidance.
Ballast questions please Img_4510

jarvo and Bob K like this post

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jarvo
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Join date : 2015-02-19

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PostSubject: Re: Ballast questions please   Ballast questions please EmptyFri Mar 05, 2021 3:33 pm

Hi Brian, First you need to mark the waterline on the hull, then ballast down to the marks, that will give you the final weight to finish the hull and superstructure, motor, radio gear, batteries etc, with my tugs, i prefer to use batteries as ballast, removable to help transport.

Your worry of the weight of ballast, tugs displace a lot, so thats normal if you are on the marks, stern freeboard is quite minimal, make sure the freeing ports are clear, watch how the weight is being added to the hull, (balance) is also important

Hope this gives you a start

Regards

Mark
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BrianP
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Join date : 2020-12-04

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PostSubject: Re: Ballast questions please   Ballast questions please EmptyFri Mar 05, 2021 3:44 pm

jarvo wrote:
Hi Brian, First you need to mark the waterline on the hull, then ballast down to the marks, that will give you the final weight to finish the hull and superstructure, motor, radio gear, batteries etc, with my tugs, i prefer to use batteries as ballast, removable to help transport.

Your worry of the weight of ballast, tugs displace a lot, so thats normal if you are on the marks, stern freeboard is quite minimal, make sure the freeing ports are clear, watch how the weight is being added to the hull, (balance) is also important

Hope this gives you a start

Regards

Mark
Thank you Mark. Much appreciated.

I ended up using used lead balance weights from a car tyre workshop.
I bagged it up into convenient sized multiple food storage bags and distributed it evenly.
I am still shocked how much was needed to 'sink' the hull deep enough in water.
I learnt a lot about where placing ballast/ how high up affects stability.

Just waiting to go and try the tugboat now.
My youtube channel has all the build videos. f1pitpass

regards
Brian.
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Andrew Brown
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Join date : 2021-02-25

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PostSubject: Re: Ballast questions please   Ballast questions please EmptyFri Mar 05, 2021 4:08 pm

Hello Andy. the advice you have been given is sound , but if you wish to persue the sientific route you could find out the  block coeficient of the prototype boat and a relitivly simple calculation will get you the displacemant of your model . you will still have to distribte the ballast thoughout the hull. regards Andy.
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BrianP
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Join date : 2020-12-04

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PostSubject: Re: Ballast questions please   Ballast questions please EmptyFri Mar 05, 2021 4:32 pm

Andrew Brown wrote:
Hello Andy. the advice you have been given is sound , but if you wish to persue the sientific route you could find out the  block coeficient of the prototype boat and a relitivly simple calculation will get you the displacemant of your model . you will still have to distribte the ballast thoughout the hull. regards Andy.

i'm afraid my modelling skills don't extend to my tug boat being exact in scale...

Thanks for trying to help me tho'...

regards
Brian.
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Bob K
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Join date : 2020-08-14

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PostSubject: Re: Ballast questions please   Ballast questions please EmptyFri Mar 05, 2021 11:10 pm

Hi Brian;

Check your local sporting goods stores, and find one that sells shotgun reloading supplies.  You can buy 25 lb sacks of birdshot {size-wise I like #8 shot} for a very reasonable price.  You may not need the whole bag, but its nice to have some on hand for the next build too.

Last year I finished building a 76" offshore tugboat, "Nostromo".  After installing all of the running gear and 3 gel-cell batteries, it still needed a bunch of ballast.  I got 3 bags of shot and made up 5 lb bags from heavy plastic and 100MPH tape.  The tug needs all 15 bags to get down to its design waterline, so she ends up displacing almost 150 lbs!  Needless to say, launch and recovery is interesting and definitely not a one man show.

The other thing you can do with birdshot, is cast removable ballast blocks to fit into your hull.  Mix the shot with an ounce or two of epoxy, pour it into your mold, or, mold it in the hull with protection, and you'll have custom removable ballast that will not shift.

Good luck and have fun!
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BrianP
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Posts : 12
Join date : 2020-12-04

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PostSubject: Re: Ballast questions please   Ballast questions please EmptySat Mar 06, 2021 6:16 am

Bob K wrote:
Hi Brian;

Check your local sporting goods stores, and find one that sells shotgun reloading supplies.  You can buy 25 lb sacks of birdshot {size-wise I like #8 shot} for a very reasonable price.  You may not need the whole bag, but its nice to have some on hand for the next build too.

Last year I finished building a 76" offshore tugboat, "Nostromo".  After installing all of the running gear and 3 gel-cell batteries, it still needed a bunch of ballast.  I got 3 bags of shot and made up 5 lb bags from heavy plastic and 100MPH tape.  The tug needs all 15 bags to get down to its design waterline, so she ends up displacing almost 150 lbs!  Needless to say, launch and recovery is interesting and definitely not a one man show.

The other thing you can do with birdshot, is cast removable ballast blocks to fit into your hull.  Mix the shot with an ounce or two of epoxy, pour it into your mold, or, mold it in the hull with protection, and you'll have custom removable ballast that will not shift.

Good luck and have fun!
yep, tugs sit low and take a lottttttttt of ballast!
Yep, the finished model takes some lifting!
Good tip on the birdshot, thank you.
The 'project' seems an age ago but will soon be at the lake so tests will happen!
Thanks for the good wishes. 
Same to you Bob K!
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