Bulbous Bow - Anyone Done One???

[DieselTrawlerGuy]

Has anyone on this forum ever put a bulbous bow on a trawler? I'm rebuilding a 38' custom fiberglass trawler based upon a Ron Rawson hull, doing a 4' hull extension under the swimstep, changing the superstructure from a tri-cabin to a Europa style, etc. I'm going to add a bulbous bow using a 20" diameter sono-tube and I was wondering if anyone had any plans, specs, formulas, calculations, etc.

 

[Keith]

Not me, but all the reading and tests I've seen say it won't do you any good, nor harm.

 

[DieselTrawlerGuy]

Some of the stuff I've read says the boat has to be about 42-45' long before you see much of a gain - I'm 38' but I'm doing a 3'6" hull extension under the swim step so I'll end up about 41' approximate. The other thing that I'm also hoping to gain is more flotation in the bow as I've always been just a little heavy to the bow and I'm also going to an all-chain anchor rode which is going to add a few hundreds pounds right on the nose - which the bulbous bow would offset.

 

[psneeld]

Really get some use out of it by putting a sonar in there...

 

[DieselTrawlerGuy]

Yeah - don't think I haven't thought of that - I'm already putting a bow and stern thruster on. And for a few thousand more......

 

[RickB]

A bulb is only effective for efficiency enhancement within a very narrow speed range, outside that range it only creates drag and you lose more than you gain by having it.

Maersk, the world's largest containership operator is making drastic modifications on the bulbs fitted to their ships because they discovered this after instituting what the industry calls "slow steaming" to save fuel.

They look cool though and everyone who sees the bulb will be impressed and it may add some bouyancy but is is worth it? You won't know until you either tank test your hull before and after or find out by experience.

 

[koliver]

Rick:
I would think he would need to do the stern hull extension first, find out what effect that has on performance, over a few hundred hours of use, then do the bulbous bow. To do it all at once will completely confound any ability to know the effect of any one component of the modifications.

 

[Nomad Willy]

Yea I got one last month.

 

[koliver]

Eric:
Complete with forward looking sonar and a thruster (doors closed in your picture) I presume.

 

[Phil Fill]

I have look at them more for protection of the hull as most on the long range boats especially from Alaska have some bow damage at the water kine. As for performance most say they have not noticed much. I have also looked at them as the RW 58 bow is a little light with the wide flare, I been told by other 58, so maybe to weight it down. Anyway if I was going to added it would be to protect the bow and to make the Eagle look meaner/uglier.

 

[hollywood8118]

Phallic Bows

This is the bow on the N57 I was on for almost three weeks... the dolphins LOVED thething and would spend hours eying the thing. I had the forward cabin and noticed the thing made noise both ways when the boat bobbed in waves at anchor. The water normally makes noise ( inside the hull ) when the bow goes down in a wave.. this actually made more noise on the upper motion. From what I had read in the past they only make a difference in a very narrow speed spectrum. Nordhavn has not installed them on their new 64's so they must have not made enough difference to warrant installation.
HOLLYWOOD

 

[Phil Fill]

This is the bow on the N57 I was on for almost three weeks... the dolphins LOVED thething and would spend hours eying the thing. I had the forward cabin and noticed the thing made noise both ways when the boat bobbed in waves at anchor. The water normally makes noise ( inside the hull ) when the bow goes down in a wave.. this actually made more noise on the upper motion. From what I had read in the past they only make a difference in a very narrow speed spectrum. Nordhavn has not installed them on their new 64's so they must have not made enough difference to warrant installation.
HOLLYWOOD

that looks cool!

 

[Nomad Willy]

Actually I think my bulbous bow extension would be better spent at the stern if the propeller didn't come out of the water and in Willy's case I don't think it would. My knowledge of BBs is limited but it would seem to me the issue is the effective length of the hull so why not the stern ... or bow and stern.

As I usually say about extended OB mount brackets ... why not just extend the whole boat? And that's what I'd like to do w Willy. But it's already been done. The 32' Fales boat is a lengthened Willard. Lengthened by adding a 2' section to the middle. Probably more effective that my BB 30'.

 

[BaltimoreLurker]

Nose art on the BB's is definitely the way to go. The Flying Tigers shark face would be my first choice.

 

[markpierce]

Marshall Islands-registered, 374-meter, 12-knot crude oil tanker Melodia shows its fat/tall bulbous nose after unloading in Martinez:

Is the shape dependent upon hull shape or what?

 

[Tom.B]

That's quite a lump!

 

[bobofthenorth]

Its fun watching those big guys when they leave Vancouver loaded and get up a head of steam heading south for Juan de Fuca. They push up a huge bump of water a long ways ahead of them.

I've tried to capture it in pictures but it never looks as impressive in the picture as it does in real life.

There was a fishing boat at Platypus this spring that they had stretched and added a bulbous bow. Maybe that is justified on a commercial vessel although I'd have to see the numbers. On a toy boat I think we'd be better off to sell and replace the vessel rather than getting into that kind of major renovations.

 

[O C Diver]

Interestingly, there is a shipwreck off Virginia (ethanol tanker "Bow Mariner") with a pair of bulbous protrusions that resemble a women's breasts. Only double I'm aware of. No Idea if they were a success or not.

Ted

 

[skipperdude]

Wait a Minuit. They resemble a womans Brest only double??

I Have yet to see a single.

Sd

 

[THD]

Maybe the owner of the tanker was a "Boob" man!

 

[RT Firefly]

Greetings,
Or keeping abreast of the newest technology.

 

[Marin]

Maybe the owner of the tanker was a "Boob" man!

Apparently so as he ran aground.

My question would be even if a bulbous bow made a measurable difference on a 40-50 foot boat, would it be enough to make it cost effective to add one?

My initial feeling is no.

 

[Tom.B]

Maybe the owner of the tanker was a "Boob" man!

Who isn't?

 

[markpierce]

So, should we classify these bow shapes between phallic and mammalian?

 

[O C Diver]

Apparently so as he ran aground.

Actually they had a smoking problem. Ship was in transit and part of the crew was cleaning a couple of ethanol tanks while someone was smoking (you can't make this stuff up). A fire starts and all but 6 of the crew come on deck to fight the fire. It's late in the afternoon and a fishing vessel (some miles to the west) sees the Sun setting in the West and the remaining ethanol (3.5 million gallons), diesel (48,000 gallons), and fuel oil (193,000 gallons) tanks explode in a massive fire ball to the East. The captain of the fishing vessel describes the ball of fire as a new Sun rising to the East. Another fishing vessel (30 miles to the North) describes the fire as being visible with flames hundreds of feet in the air, and the explosion sending flames thousands of feet in the air.

Note to self: No smoking aloud on any of my boats!

Ted

 

[sunchaser]

Steve Dashew has reported that some think bulbous bows on smaller hulls present more of a tripping hazard in large following seas as the vessel will tend to bow steer. Hollywood raises a good point, no Nordhavn designs have incorporated them for over 16 years.

The most rigorous tank testing on smaller vessels has been in sailing fraternity. No bulbous bows there.

 

[Nomad Willy]

The efficiency of a vessel is measured by how much power it takes per ton of displacement to be driven and for a bulbous bow to even stay attached in rough going it must be very heavy. So to just break even it must overcome that large increase in weight PLUS the extra skin friction drag just not to be a loss. So it appears the benefit would need to be great just to break even and overcome it's own penalties. And their benefit is only available at a certain speed since their whole function is dependent on the length of the vessel's own wave starting at it's bow and becoming longer and shorter depending on speed.

Probably would work on Willy though as we almost always go 6.15 knots. The whales of McKay Reach may view it as a battering ram though.

I think it would be better and not any or much more trouble to just make the boat longer. And considering that a great deal to most BBs are fitted to vessel's with very raked bows so just a plumb stem like the Titanic should get much the same result. But the plumb stem would probably not fly in our "in w the new out w the old" mentality of our pop culture. New is always better even if it's not.

So the possibilities for a BB on small boats is limited at best and the only weak possibility exists almost exclusively for full disp boats. And there are VERY few of them in the powerboat world.

 

[Slowboat 37]

bow bulb

Not sure what the cargo is, could be grain or lumber products but it's heading downstream on the Columbia. Video taken last year while returning a 65ft feadship to Portland from San Juan Island for the owners.

 

[Nomad Willy]

Slowboat,
I've seen the BBs at work too and it's amazing how they lift all that water up and recoup all the energy it takes to do that. Notice also here that the WL is considerably below it's static line as can be seen to the right of the video arrow. Once all that water starts moving away from the hull it wants to keep going .. away from the hull and that inertia pulls the water away from the hull as seen here at the WL to the right. But perhaps they don't do so well after all but lots of vessels of this type have them. And you'd think if they didn't pay for themselves you wouldn't see them in numbers.

Feadship. Beautiful boats and partly because there's no bow pulpit. I remember them from Motor Boating magazines of the early 50s. Top class boats. My dad gave me a subscription to Motor Boating. I think they still make Feadships.