Water ballast thoughts.

[GILow]

Hi all,

I’m thinking of fitting water ballast tanks to the new boat. The space is there, the materials are there and, to some degree, the need is there. Since removing close to two tons (metric, in case you are from a country not using metric) from the boat she’s a little bouncy at anchor and I’d like to settle her in the water.

I like a lighter boat for passage making and sailing performance but I like a heavier boat for comfort at anchor.

The boat is a Kelly Peterson 44. The tanks will be midships, against the hull on either side so can be used for righting ballast when under way.

But I’m pondering sizing them correctly. Not being one to reinvent the wheel I am looking for boats around the same size that use water ballast. Can anyone point me at some boats that do this or help me with sizing advice? I feel like half a ton either side should do it, but maybe I’m missing something?

Matt

[psk125]

Will the tanks be far enough outboard to be really helpful for righting moment under way? To get your two tons back you'll need 1000 liters (about 260 gallons) in each tank. That's a lot of water. If you fill both tanks, the one to leeward will negate the righting moment of the one to windward. If you add enough tankage to have 2000 liters on each side, so you can shift the weight to windward and empty the leeward one, you will need really hefty pumps to move the water quickly as you maneuver through a tack or gybe. Otherwise the excess weight to leeward could cause problems. If you only use the tanks to keep from bouncing around at anchor, having them midships close to the centerline should be OK. Sounds like a lot of blood, sweat and tears, adding complex systems and potential leaks for little benefit, however. Adding a few hundred pounds of lead to the keel would achieve a similar result without all the hassle, though you wouldn't be able to shed the weight on passages by pumping it over the side. Your boat, you choose.

[StuM]

Originally Posted by GILow

Hi all,

I’m thinking of fitting water ballast tanks to the new boat. The space is there, the materials are there and, to some degree, the need is there. Since removing close to two tons (metric, in case you are from a country not using metric)

To be correct, you should call it either "2 metric ton(s)" or "2 tonne(s)" unless you are referriing to the US or Imperial ton

[ejs]

Hi our last boat (Able Apogee 50) had 900L tanks on each side. We kept each about half full and pumped all the water to the high side on long tacks on passage. It made a noticable difference, but wasn't worth the trouble when day sailing. It was also a benefit to be able to fill all 1800L at the dock so you didn't need to fill as often, but we never noticed a stability difference when full.
-E

[GILow]

Originally Posted by StuM

To be correct, you should call it either "2 metric ton(s)" or "2 tonne(s)" unless you are referriing to the US or Imperial ton

I literally cannot begin to say how helpful this is.

[GILow]

Originally Posted by ejs

Hi our last boat (Able Apogee 50) had 900L tanks on each side. We kept each about half full and pumped all the water to the high side on long tacks on passage. It made a noticable difference, but wasn't worth the trouble when day sailing. It was also a benefit to be able to fill all 1800L at the dock so you didn't need to fill as often, but we never noticed a stability difference when full.

-E

Excellent reference point, thank you.

[chrisr]

we (briefly) had a volvo 60. if i recall correctly we had 2 x 2000L ballast tanks (one each side obviously...)

absolutely loved the power these gave the boat. 9ks uphill in 25kts TWS

but we had a yanmar 2GM solely for powering the ballast pump and could shift a full tank in 30 seconds.

still seemed like ages when waiting to tack...

i'm a great fan of water ballast, but make sure you design the system carefully.

cheers,

[Franziska]

If your tanks are high up close to the gunwhale where they are most effective when sailing (windward tank full), they are not in a good location to settle her down at anchor.
If they are both full they will create a pendulum effect.
To settle her down at anchor the tank should be at the center and as low as possible...
A kind of stabilizer is used for at anchor stabilisation of Megayachts.
Not sure if there are small enough and retractable units which you could use on your boat.
There are also gyro stabilizers but they are heavy and expensive.

Maybe adding some kind of retractable center board on each side, possibly with a T foil might help in your case.

[El Pinguino]

Are you looking at ballast tanks or at trim tanks?
If ballast tanks just carry more FW or FO.

If trim tanks ie 50% in each tank and a transfer pump different game.

Don't know why you would think you would need that.

I use my two FW tanks as trim tanks on long passages by closing the one on the high side and using the low side but 400 litres total makes no practical difference - more a case of knowing when I have used 50% of my water.

Why not just solid ballast low down - depleted uranium or something?

BTW its 'tonnes'

[GILow]

OK, some good feedback so far, thank you all.

So to clarify one thing... ballast at anchor. What I've found with this boat, and the same with the Swanson, is that removing weight leads to a narrower beam at the waterline. Both boats turn in quite drastically at a point close to the waterline and therefore both have become noticeably more jittery at anchor as they lifted. (Approx 200mm) Both started moving around as I walk around. (I'm not light.)

I found that filling the fresh water tanks on the Swanson (700 litres total) makes a huge difference. Settles the boat remarkably, despite both tanks being at or above the waterline and both being against the outer hull sides. I put this down to the increase in beam.

Now for the new boat the fresh water (1600 litres) will be below the cabin sole so down nice and low. And to reassure those that noted it, compartmentalised into four tanks, split port and starboard and fore and aft. Plenty of trim options there and I will plumb them in a way that allows me to shift the water between tanks if space allows it.

The logic behind the ballast tanks is that I can flood them with salt water at anchor to lower the boat and increase the beam back to close to the designed waterline. Therefore the aim is to get stability from the beam increase rather than low ballast. But if I'm going down this path I figure it is worth considering side benefits such as reduced heel and it would be good to get a feel for how much would be needed to make a difference. I'm happy to dump the ballast water from both tanks before sailing to get the speed advantage, which is considerable.

[rslifkin]

If you're that short on weight compared to design, I'd be looking for "what useful stuff can I add?" Like more batteries or other things that aren't just dead weight.

[GILow]

Originally Posted by rslifkin

If you're that short on weight compared to design, I'd be looking for "what useful stuff can I add?" Like more batteries or other things that aren't just dead weight.

Well, I’ve installed a nice front loading washing machine. [emoji16]

But no, I’d like to keep her light. They sail so much better. I’ve got a 20% daily range improvement from the same process in the Swanson.

[Bowdrie]

This site: https://www.boatdesign.net/forums/
It's populated with many who are Naval Architects, Marine Engineers, and people who have in-depth knowledge of hydrodynamics.
Those who can crunch numbers, leading to satisfactory results without guesswork.

[GILow]

Originally Posted by Bowdrie

This site: https://www.boatdesign.net/forums/

It's populated with many who are Naval Architects, Marine Engineers, and people who have in-depth knowledge of hydrodynamics.

Those who can crunch numbers, leading to satisfactory results without guesswork.

Yes, some good discussions there on the theory, but very few contributors who’ve actually sailed boats with water ballast.

[El Pinguino]

Have you considered wobble stoppers?