Innovation series, episode 3: external ballast

[seansherrod]

Note that this is episode 3 so if you're starting here, you might find it helpful to read the intro in episode 1.

This idea goes back about 6 years and it originated when I was trying to figure out how to add weight to my 1998 ProStar 190 without loosing any storage or seating space. So the idea works for boats without built-in ballast but it works just as well for boats with built-in ballast that could use more. Let's get to it.

The external ballast is a tank that mounts below the swim deck at the stern of the boat. Simple, I know. Yet, it has some significant advantages:
1) It's external so there are no worries of water leakage inside the hull.
2) The location being as far back as possible serves to maximize the effect of the weight.
3) Importantly, being below the swim deck, it has no impact on buoyancy when the boat is stopped (assuming it's filled - it would provide additional buoyancy when empty).
4) Since the tank rests in the water, it's very easy to fill - just open the fill point.
5) The tank is basically hidden unless the boat is on plane.
6) This can be easily added to boats that were built both with and without built-in ballast.
7) Since the only time the tank would be weighing on the swim deck mounts would be when the boat is on plane, there would never be the weight of a person standing on the swim beck in addition to the weight of the tank (only one or the other).

My quick calculations show that about 350 lbs would be pretty easy to attain. Emptying the tank could be as easy as pumping in air through a check valve in the top. Personally, I'd like to see MasterCraft offer these for both new and old boats (1998 Prostar 190 please). It would be possible to use the same tank for a bunch of different boats just by changing the mounts that the tank uses. It would also be possible to integrate the swim deck into the tank assembly.

Now, in the interest of full disclosure, I was sufficiently smitten with this idea that I actually did a little patent search to see if I could lock this idea up and I was surprised to find that the basic idea had been patented in 2000. While initially disappointed, I chose to focus on the hopeful prospect that someone might actually commercialize it. Alas, no such luck so far (at least as far as I am aware). So my suggestion here is that MasterCraft find a way to bring this to market. Maybe the patent maintenance fees were not paid - I did not research this so I don't know either way. There are a limited number of years left to the patent so it could be bought out, licensed, or potentially designed around. I guess the last resort would be to wait it out but I'd prefer to see this sooner than later. Anyway, I've attached an image of the first page of the patent for reference:

[ski_king]

Is this your boat?
http://www.mastercraft.com/teamtalk/attachment.php?attachmentid=34960&stc=1&d=1210961700

http://www.mastercraft.com/teamtalk/showthread.php?t=23441&highlight=ballast+platform

[seansherrod]

Negative. Cool pic though - thanks for posting. Wonder where it was purchased/made? This is my boat:

[vision]

As you indicated, ballast tanks on the swim platform has been done in the past in several variations.

A down side to swim tank ballast systems has been poor weight distribution giving a poor wake shape. With most V drives, a more even front and rear distribution is required. But with a direct drive, the rear distribution of the ballast certainly would be more beneficial.

To show my ignorance of the physics of buoyancy, wouldn't external ballast tanks lose their weight effect as they touch the water, or more specifically are surrounded by water? Water ballast is neutral in buoyancy and does not sink. Inside a boat, it is adding to the weight of the boat and therefore sinks the boat. But if the ballast was external to the hull, once the ballast tank was under water it would have minimal weight as it would be neutral in its buoyancy. Or am I thinking about this incorrectly? I guess as long as the tank is never under water, its relative weight would not be lost.

[Jesus_Freak]

...To show my ignorance of the physics of buoyancy, wouldn't external ballast tanks lose their weight effect as they touch the water, or more specifically are surrounded by water? Water ballast is neutral in buoyancy and does not sink. Inside a boat, it is adding to the weight of the boat and therefore sinks the boat. But if the ballast was external to the hull, once the ballast tank was under water it would have minimal weight as it would be neutral in its buoyancy. Or am I thinking about this incorrectly? I guess as long as the tank is never under water, its relative weight would not be lost.

Yes, and I think he relayed these issues in his post.

[seansherrod]

You're 100% right about external ballast being ineffective (neutrally buoyant) when submerged. That can be good when the boat is not moving as the ballast tank would be in the water and it would not change the behavior of the boat at rest (as long as the external ballast tank is filled with water - it would actually provide buoyancy if it was empty or filled with air). However, when the boat is on plane, the external ballast tank would be lifted out of the water and that would cause it to be effective at creating a larger wake. It's possible that the shape of the larger wake would not be preferred - to your point - that I'm not sure of.

Additional comments unrelated to your reply … there would need to be clearance to allow exhaust flow and the design execution would be important so that the look of the boat is accounted for. Clearly, it would be possible to design a really cheap looking add-on. Could a good industrial designer create a shape/form that flowed with the boat? Maybe?

[vision]

That makes sense. I read the comment in your post about being on plane versus sitting, but I was not sure how tall/deep a tank on the platform was required. Thank you for the clarification.