Bulbous bow - A good thing or bad?

[Lepke]

Some larger commercial fishing boats have the bow done, but I hear it only works best at one speed.
On anchoring, I was on a destroyer with a big sonar dome on the bow. To use the center bow anchor, we had to be moving astern. When you're assigned a specific anchoring spot, you're expected to put the anchor in the exact center. To do that pre GPS, you take a series of fixes from visual bearings, when the bow passes thru the center you back down and drop when the bow passes the center the 2nd time while making sternway. Somebody got excited and dropped going forward and ruined the dome, 3 million to fix in 1970.

 

[CNL43]

They do make for great pictures:

https://twistedsifter.files.wordpre...-stands-on-bulbous-bow-of-queen-marry-2-1.jpg

https://twistedsifter.files.wordpre...-stands-on-bulbous-bow-of-queen-marry-2-4.jpg

 

[twistedtree]

And more fun with a bulb... named "Tigger"

 

[ssobol]

A bulbous bow is designed to control wave formation of the hull. Depending on how you want to describe it, it either controls where the hull wave forms or helps cancel out the hull wave formation.

But since the bulb is a fixed object it only really works at one speed. For large ships which basically only cruise at one speed this works ok. Maybe someone will invent a variable geometry bulbous bow that will work over a larger range of speeds.

For cruisers that can travel at variable speeds the utility of a bulbous bow has limited utility. At certain speeds it is a benefit and others it might be a negative.

For smaller boats the hull wave is a smaller part of the overall drag picture and limits the benefit of a bulbous bow as the size of the boat decreases.

Using the bulb as a freshwater reservoir might be useful but only if you replace the used freshwater with something of similar density. Otherwise as the freshwater is consumed. the bulb will become a buoyancy device at the front of your boat which might cause trim problems. You could have a flexible membrane and have the bulb open at the bottom as the freshwater is consumed, the sea water could flood the bulb to replace the freshwater. Refilling by pumping in freshwater would displace the sea water back out the bottom vent. Sort of how the fuel tanks on diesel submarines work (except they don't use the membrane).

 

[BarefootViking]

Marlow & bulbous bows

I’ve run a ton of various Marlows, working for them as a delivery captain and owner orientation captain

Marlow built 2 boats W bulbous bows:

1- they built due to owner demands. They resisted BC they build high speed trawlers (18-22kts)...not good w a typical bulbous bow. Also, David Marlow wants all his boats to have a timeless & classic look.

2- is a high speed, wave piercing, ice breaking bow...it’s amazing. It’s on a ice class Marlow. I had it out in 8’ seas in the GOM and loved it. Worked great at hull speed and at planing speeds, but was expensive and built for Antarctic.

W all the new wave piercing bows on catamarans (Hayfu II) and Horizon HPPB, and now Marlow....I think we’ll see the new technology on other fast crusing boats.

 

[obthomas]

In my opinion a boubous bow has a primary purpose of extending the wetted perimeter around a boat. This then alters the hull speed calculation. More wetted perimeter more hull speed. While there may be more unintended consequences with the shape and the boat itself, the elemental relationship is to increase the hull speed.

 

[BarefootViking]

Hayfu II. 23 kt boat w wave piercing bows
https://www.marinelink.com/news/catamaran-scotia-nova329611

Marlows wave piercing, high speed bulb. https://www.powerandmotoryacht.com/boats/review-of-marlow-yachts-voyager-class-flagship-ice

 

[Alaskaflyer]

https://www.trawlerforum.com/forums/showpost.php?p=970682

 

[psneeld]

I hope that guy has some ice experience before he heads off to Antarctica. Not sure about the bow, usually specific shapes are designed as hitting ice is like constantly having collisions and/or groundings.

 

[mvweebles]

I delivered 5 Nordhavn 57s with bulbous bows. As Twisted Tree commented up-thread, there is a discernable clap in a head sea. In all fairness, there are a lot of noises in a head sea, but the bulb-boom rattled me the first time I heard it - thought we'd hit something.

The N57 is just about my perfect boat. Good size for a couple, great turn of speed, good access to gear, and was a high-end boat (even for Nordavn) at the time were normally equipped with very robust equipment. The hi-volume/capacity hydraulic trash-pump reminiscent of a fire-boat also served as an anchor wash-down comes to mind.

But I was not crazy about the bulb-bow. Despite the hype, the benefits could not be great and the down-side of boom was enough that I'd prefer not to have a bow bulb. That said, I wouldn't remove it anymore than I'd add one to a boat that wasn't purpose designed. Boats are designed with a certain amount of bouyancy and entry, messing with that just doesn't make sense to me.

Peter

 

[fgarriso]

You can't buy a off the shelf bulbous bow. They have to be custom designed for each hull, gross tonnage, draft, and desired speed.

 

[Nomad Willy]

It would seem to me that short FD boats would benefit most from the BB.

They (being short) pitch a lot and are very limited in speed (due to their short WLL).
That could/maybe increase my cruise speed from 6 to 7 knots. Then I could actually cruise alongside more typical trawlers if the desire ever came up.

Worth the expense? Probably not. And I could always buy a longer boat but not many appeal to me. But 99% of longer boats are taller/wider also .. fat. haha

And if I went into my slip stern first other passing boat would probably crash into the bulb that would be hidden under the water.

I think I’ll pass.

 

[ssobol]

It would seem to me that short FD boats would benefit most from the BB.

They (being short) pitch a lot and are very limited in speed (due to their short WLL).
That could/maybe increase my cruise speed from 6 to 7 knots. Then I could actually cruise alongside more typical trawlers if the desire ever came up.

Worth the expense? Probably not. And I could always buy a longer boat but not many appeal to me. But 99% of longer boats are taller/wider also .. fat. haha

And if I went into my slip stern first other passing boat would probably crash into the bulb that would be hidden under the water.

I think I’ll pass.

But to get any real benefit on a short hull, you'd need a pretty long bulbous bow. My understanding of the bulbous bow is to change waves generated by passage of the hull through the water so that the bow wave and the hull wave basically cancel each other out. But they only really work at one certain speed. For a FD boat that basically only cruises at one speed they can work. For SD boats that travel at a range of speeds, they are not that effective.

 

[PacificBlue]

They can be used in a wide range, I have seen some on boats 60’ - 70’ long that went up to 20 knots to fix a few mistakes, like bad static trim, these two in particular were down by almost a foot in the bow. Poor build management and lack of a project manager didn’t help.

It just depends, what are you goals? A single speed FD bulb should be straightforward, but have to consider how anchor deployment/retrieval is managed.

 

[Benthic2]

In my opinion a boubous bow has a primary purpose of extending the wetted perimeter around a boat. This then alters the hull speed calculation. More wetted perimeter more hull speed. While there may be more unintended consequences with the shape and the boat itself, the elemental relationship is to increase the hull speed.

I think the bulb is designed to create a wave separate from the bow wave that is 180 degrees out of phase with the bow wave in order to flatten the wave along the waterline of the ship.

 

[markpierce]

Someone wanting a boulbous bow on the typical recreational trawler has been brainwashed.

 

[friz]

Don't know about a sub-80' vessel... but I had over 4 years on a guided missile cruiser with a large bulb covering the sonar dome, and can tell you in heavy seas, as the bow is coming down hard, the bulb would add a side-side lateral shimmy motion at the bottom of the downstroke (for lack of a better term).

As our berthing (sleeping) quarters were in the bow at the waterline level, I can tell you that it is one thing to be pitching vertically displacing your body 40-50' in a matter of seconds... but that shimmy at the bottom was enough to toss you out of your rack if you weren't smart enough to wedge yourself in...

Of course that boat was 533' long...

Wedge? Hey shipmate in my 22 years of Naval service I never served on a ship which did not have straps in your rack. This went from the USS Sperry AS-12 to the USS San Jacinto CG-56. No doubt we sailed in the same miserable sea states but when I "turned in" I "strapped in". Fair winds and following seas!

 

[ssobol]

Wedge? Hey shipmate in my 22 years of Naval service I never served on a ship which did not have straps in your rack. This went from the USS Sperry AS-12 to the USS San Jacinto CG-56. No doubt we sailed in the same miserable sea states but when I "turned in" I "strapped in". Fair winds and following seas!

The bulb for a sonar array is a lot different than a bulbous bows used on ships for performance or efficiency. They are designed for different purposes.

 

[FF]

I think for a displacement cruiser more bang for the buck for efficiency would come from a CPP.
Controllable pitch prop.

 

[Chrisjs]

That bulb looks kind of long from the photo. Might be an issue docking in some locations, requiring more space and/or the need to reverse in to marina slip. I would guess if it was such a great improvement, more (bigger) boats (not ships) would have started offering it or building it in as standard.

 

[Sailor of Fortune]

I’ve run a ton of various Marlows, working for them as a delivery captain and owner orientation captain

Marlow built 2 boats W bulbous bows:

1- they built due to owner demands. They resisted BC they build high speed trawlers (18-22kts)...not good w a typical bulbous bow. Also, David Marlow wants all his boats to have a timeless & classic look.

2- is a high speed, wave piercing, ice breaking bow...it’s amazing. It’s on a ice class Marlow. I had it out in 8’ seas in the GOM and loved it. Worked great at hull speed and at planing speeds, but was expensive and built for Antarctic.

W all the new wave piercing bows on catamarans (Hayfu II) and Horizon HPPB, and now Marlow....I think we’ll see the new technology on other fast crusing boats.

Just what does a "built for the arctic" Marlow or other fiberglass vsl mean? with or without BB you aren't breaking yourself out of any ice...other than skim ice. Even if built of steel, a BB would hinder icebreaking....

 

[ssobol]

Just what does a "built for the arctic" Marlow or other fiberglass vsl mean? with or without BB you aren't breaking yourself out of any ice...other than skim ice. Even if built of steel, a BB would hinder icebreaking....

A proper ice breaker has the opposite of a bulbous bow. The fore foot of the hull is cut back. This makes it so the ship can ride up on the ice and use its weight to break it.

 

[Nomad Willy]

It’s my understanding the BB moves the bow fwd as seen by the water. The bow normally pushes the water aside as the submerged part of the bow hits the water. Then the stern channels the water back to where it was before the boat came along. Of course the water oscillates up and down and back and forth (sideways) until the wave energy is lost.

Along comes the BB and it’s form pushes the water aside before and ahead of the traditional bow. Since this happens sooner and the shock wave fm the BB and the water moves at the same rate the spot that the boat occupies on the water lasts longer and is longer. The hole the boat occupies is longer as it would be w a longer hulled boat. And thus the BB equipped hull would be faster,

So the effect of the BB is that the water acts like it would with a longer traditional hull. There in lies the advantage.
The strength of the new wave created by the BB is probably mostly a result of the ratio of the bulb diameter and the hull width fwd or fullness fwd. and if you had a longer BB one could come along and say “why didn’t you just build the boat longer. That probably is just a function of economics. A bigger boat would of course carry more weight and provide the basic advantages of a bigger boat. And (this is just a guess) but due to it’s smaller size the BB is probably noticeably less effective re how fast the boat will be w a given amount of power.

I have little interest in BB’s so my readings and observations could be in some ways wrong. But this is my understanding of how the BB works. It just moves the shock wave of the original boat further fwd thereby (to some extent) lengthening the hull and the wave (wake) it creates.

And theres lots more about BB’s like efficiency and how the BB effects the boat in rough water.

 

[South of Heaven]

Someone wanting a boulbous bow on the typical recreational trawler has been brainwashed.

Says the guy on a go anywhere, brick sh*thouse Coot.

 

[Sailor of Fortune]

A proper ice breaker has the opposite of a bulbous bow. The fore foot of the hull is cut back. This makes it so the ship can ride up on the ice and use its weight to break it.

I'm very aware of how icebreakers work...thats why I posed the question....No FG vsl is going to get herself out of a situation in other than skim ice... Not any arctic transits...

 

[FF]

"The fore foot of the hull is cut back. This makes it so the ship can ride up on the ice and use its weight to break it."

From a marine site,

Limitations of Icebreakers

While the icebreaker ships rule the polar regions and ice-waters across the world, the vessels lack efficiency outside their specific regions. The slight negative aspect of this design is that it makes icebreaker ships good enough for the purpose of ice breaking alone. They are definitely the best at their job. But their specialized design makes them highly unsuitable for normal waterways. With the rounded bow, the icebreakers are almost unseaworthy in the normal seas. When a typical hull shape can resist the waves, the design of icebreakers allows the waves to hit the vessel in full force, making the manoeuvring a difficult job.


Does not sound great for a pleasure boat.

 

[sunchaser]

Someone wanting a boulbous bow on the typical recreational trawler has been brainwashed.

A very smart cruising couple we know had a bulbous bow added to their DeFever 49. For their heavy weather use it was a real improvement as far as reducing pitching. Brainwashed or just very smart? The latter.

In walking the docks in AK the large commercial fishing boats are normally with a bulb. Improvement in speed and pitch reduction are reasons given. In very heavy weather with helm and living quarters forward pitch reduction is important. As is fuel burn reduction. Brainwashed or experienced? The latter again.

 

[Prospective]

Where's Cruising SeaVenture?? Didn't he put one on his boat recently?

 

[Alaskaflyer]

Where's Cruising SeaVenture?? Didn't he put one on his boat recently?

And subsequently posted their early data of resulting performance improvements. They were going to start a new thread when they had time, I believe he said.

 

[Nomad Willy]

A very smart cruising couple we know had a bulbous bow added to their DeFever 49. For their heavy weather use it was a real improvement as far as reducing pitching. Brainwashed or just very smart? The latter.

In walking the docks in AK the large commercial fishing boats are normally with a bulb. Improvement in speed and pitch reduction are reasons given. In very heavy weather with helm and living quarters forward pitch reduction is important. As is fuel burn reduction. Brainwashed or experienced? The latter again.

Tom I get all the pitch reduction and speed advantage but can’t see the BB as a road to efficiency? Does it happen?