Bulbous bow water ballast?

[tensim]

We're installing a bow thruster in our vessel and when installing the tunnel we've discovered that our bulbous bow was filled with freshwater. We're fairly sure the structure was a later addition to the vessel, not part of the original design. Any thoughts on why it would have been filled? I'm assuming for extra weight, or to reduce the bouyancy of the bulb? Thinking we should refill it once we're finished?

 

[Simi 60]

Or a deck leak down.

 

[tensim]

Or a deck leak down.

It's welded tight, so doubt it

 

[Mako]

Since it’s aftermarket, it’s sounds like you’re right in that they needed to counteract the additional buoyancy.

If you can disinfect it then consider installing a fill hose and a pump out. You can use it for additional freshwater, or pump it out if you need the additional buoyancy in the bow, like when running in heavy seas.

 

[Shrew]

Since it’s aftermarket, it’s sounds like you’re right in that they needed to counteract the additional buoyancy.

Then why not fill it with lead ballast?

 

[KnotYet]

Then why not fill it with lead ballast?

If the bulb was in fact added after the boat was built, the goal may have
been to make it close to neutral buoyancy to maintain the design waterline.

tensim, if you are able to re-seal the bulb after the thruster install,
consider adding an anti-rust additive or just antifreeze to prevent
the possibility of corrosion if you refill it with water.

 

[CharlieO.]

I believe the bulbous bow M/V Sea Venture added had a couple open holes in it to allow it to fill with sea water.

 

[OldDan1943]

Tell us about the boat..... brand and length of the boat. approx dimension of the bulb.
must disturb the bulb to install the tunnel?

If you have some pictures, that would be nice too.

 

[tensim]

Can you only post images as links?

 

[Taras]

Yes, when Sea Venture added their bulbous bow, it was designed to fill with water. The expert company that installed their bulbous bow made it that way. If it was water tight and void of water, you would probably experience a worse "hobby horsing" effect. I would refill with water.

 

[mvweebles]

Can you only post images as links?

If you are posting from a PC, below the "response" box are two buttons "Advanced" and *Preview Post." Select "Advanced" and a paperclip will appear on the status bar above the response box. This will bring up a separate dialogue box that allows you to select files from your hard drive. Once selected, you need to "upload" them (button below list of files you selected). In your response, select the paperclip again and it will allow you to insert one of all of the pictures you uploaded.

I know of sounds a bit clunky, but after once or twice it's pretty intuitive.

Apologies for not including screenshots, but I'm on my phone this morning.

Peter

 

[Nomad Willy]

Most all trawlers are said to be a one speed boat. Bulbous bow boats are said to be a one speed boat.

Having those two features together would more or less insure you had a one speed boat. But obviously even w a BB boat you’ve got all the speeds BELOW BB hull speed to choose from.

BB boats are not on my should have list.
Most people buy BB boats IMO to have the new thing. Like a fad. And the same people have nothing that could be considered old school. I mostly try to buy/have things that have real value … not just social value. But to many others social value is very important.

Peter I’m on my chair. The phone’s still on the wall

 

[GoneDiving]

I thought everyone was playing a practical joke on the new guy (me) but apparently it's common here to fill BB's with molasses to prevent porpoising. Note that I live in the centre of a sugar cane growing region.

 

[OldDan1943]

LOL, whoever told you molasses was pulling your leg. LOL

 

[ABfish]

Cannot imagine filling it with water and sealing the bulb if there is any possibility of freezing.

 

[OldDan1943]

Cannot imagine filling it with water and sealing the bulb if there is any possibility of freezing.

antifreeze and water.

 

[tensim]

I thought everyone was playing a practical joke on the new guy (me) but apparently it's common here to fill BB's with molasses to prevent porpoising. Note that I live in the centre of a sugar cane growing region.

I've heard of using molasses to clean rust (1:10 ratio with water I think?) maybe something to do with that? Thinking about it, the water that came out of our bulb was very sweet (like, sugary), hmmm, I wonder? ?

No chance of freezing in Australia, so that's not a concern

So consensus seems to be it was a deliberate act to get weight forward?

 

[backinblue]

Not to get weight forward. If this was added after the boat was built, adding water would negate the added buoyancy if it was left empty.

 

[tensim]

Here's a picture of our boat and it's bulbous bow

 

[Mac2]

A dock neighbor has a Selene that has a bulbous bow added. It has a hole so the BB can fill with water. I got the impression it is open, so it can fill/empty on it's own. I can see benefits to having it drain, or having it sealed. I think the material of your BB, or the area you cruise, would be the deciding factor for you.