A ballast question or two

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A ballast question or two

Postby ManInBlack on Sun Sep 05, 2021 1:08 pm

So my build is going quite well (I think), and I'm making good time too. The hull is finished and we are making good progress on the spars. (I'm actually welding a custom trailer to carry my PocketShip now.)

I'll be trying a first water test soon, although it will probably take a few months for me to source all the various sailing hardware needed to actually go out sailing. But I have had a few lingering questions about the additional ballast in the bottom of the hull that I was hoping those with more experience might help me answer:

1. I live in a floating house that I built myself, and a while back, we used steel rebar as a sort of ballast to level the house. Later, we switched to strategically placed sealed large diameter PVC pipe pontoons for this purpose. So now I have about 200kg of 1" diameter steel rebar sitting around, and since PocketShip needs about 90kg (200lbs) of extra ballast at the bottom of the hull, does anyone have thoughts about using steel instead of lead for this purpose? Due to steel having a lower density than lead, it will take up about 40% more space, but it is under the floor boards and there looks like there is the space there for it, I didn't think it was an issue. I can cut the rebar down to lengths that fit between the bulkheads, and weld them together in clumps of 3 or more to reduce "rolling around". I can also apply a soft coating to reduce scratching of the hull. Since I literally have it in storage and didn't know what to do with it, I was wondering if this would have any flaws I'm not considering.

2. This one is a bit more involved. I built my own electric outboard motor a number of years back for a canal boat that I use to cruise around the back canals on the outskirts of Bangkok, and I bought about 5kWh of reliable large capacity lithium ion cells (LiFePO4) to power it. I have them packed into four packs of about 14kg each. I'd like to use an electric outboard on PocketShip, and since it needs about 90kg of ballast anyway, I'm wondering if these 4 packs can safely be placed two in the front cabin storage compartment and the other two at the foot of the sleeping area (probably by cutting a rectangular space out from the floor planks at the foot of the sleeping area to get them as low as possible). Thus balanced left/right and front/back, and weighing about 56kg total, can I then reduce the additional hull ballast to about 40kg? Or are there reasons to keep the steel or lead ballast weight up in addition to the batteries? These packs are about 20cm tall, and I'm planning on placing them on the bottom of the hull. Due to their height, and being in the front/back, their weight will sit a handful of centimeters higher in the boat than the lead/steel ballast would. But I wouldn't have thought those few centimeters would have made so much difference.

Does anyone have any thoughts or suggestions with regards to replacing the ~90kg (200lbs) of lead ballast with a combination of about 55kg of batteries front and back and 40kg of steel rebar in the normal ballast section toward the center of the boat? Assume that I will package the steel in a way that doesn't roll or scratch the hull.
ManInBlack
 
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Joined: Mon Jun 14, 2021 5:22 am
Location: Thailand

Re: A ballast question or two

Postby craig on Tue Sep 07, 2021 7:51 pm

I would feel comfortable switching out steel for lead. All else being equal you would need more of it to balance its lower density, but I don't think the "200 pounds" was carefully calculated and I don't think any builder carefully weighs it out, anyway. Sail with it and add/subtract if you feel unhappy with the results.

As to your second question, I would think about your most common expected crew size. I usually sail with a lot of people on board, so my pocketship tends to squat in the stern. I would definitely not want more weight behind floor 4, and in fact I've moved some of my ballast forward of floor 4. If its usually just you or one other person, you might feel differently. The plans call for a battery in front of bulkhead 2.
Titania, launched January 2015
craig
 
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Re: A ballast question or two

Postby ManInBlack on Tue Sep 07, 2021 9:04 pm

Thank you so much for your reply. It really helps.

Like every first time builder, I'm deciding things based only on seeing the boat on dry land and on the pages of the manual. It is really helpful to get feedback from someone who has actually sailed one. :D

So in my case, I would rarely sail with more than 2 people aboard including myself. In my imagination for the batteries, the two blocks of them up front would be in the compartment designed for it in the manual, and the two in the back would be removable "spare power", and inserted only when I really felt I needed it. They are too big to fit under the floor (and I want to keep the tops where the terminals are up above any water that might seep in anyway for safety). Are you saying that, if I can fit them, I might consider putting all four blocks up front (55kg/120lbs), and adjusting the ballast under the floor to compensate, if needed?
ManInBlack
 
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Joined: Mon Jun 14, 2021 5:22 am
Location: Thailand


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