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Old 01-26-2016, 09:53 PM   #1
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How about this bulbous bow?

2010 Independent Shipwrights Ltd LRC Pilothouse Trawler Power Boat For Sale -

I've seen this boat in YW several times and it looks like it needs another couple of hundred feet of anchor chain, or at least top off the tanks. She looks like she's riding high.

I have seen a few bulbous bows that you could see on the waterline, but it's usually at light loading. Is this normal?
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Old 01-27-2016, 10:51 AM   #2
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Looks like it is sitting right on its painted waterline. Looks like the bulb is high to me also. What about those roll chocks. Nice boat.
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Old 01-27-2016, 11:58 AM   #3
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I don't like it at all for 6 or 7 reasons or features.

What do you mean stubones99 by "how bout"? The way it looks or the bulb or what? Mark may like the green color. But I think it should be darker.

But rebel if the painted WL is correct that's a significant plus.
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Old 01-27-2016, 12:31 PM   #4
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If the bulb is underwater at cruise speed, then I guess it is not too high. Looks too high.
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Old 01-27-2016, 12:41 PM   #5
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The benefits of a bulbous bow on a 50' or so trawler are illusory. I recall that for one of the early Nordhavns a bulbous bow was tank tested and showed promise. But in full scale, almost no difference. They gave up on that idea.


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Old 01-27-2016, 12:46 PM   #6
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The benefits of a bulbous bow on a 50' or so trawler are illusory. I recall that for one of the early Nordhavns a bulbous bow was tank tested and showed promise. But in full scale, almost no difference. They gave up on that idea.


David

The bulb did reduce hobby horsing allegedly on the N50.

The "maintenance strakes" that they put in around the engine to give better headroom gave a boost to efficiency that surprised them. The bulges in the hull increased water flow somehow IIRC.
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Old 01-27-2016, 01:45 PM   #7
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All the books I've read say that bulbous bows have to be designed for a target speed and are ineffectual at other speeds. They also say that less than 60' length and you can't tell if it's there or not.

The how about thing... It looks like it's hobby horsing all the time. One of the images has the waterline painted coming up and around the bulb. I guess that was a test that didn't work out.
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Old 01-27-2016, 01:59 PM   #8
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Originally Posted by djmarchand View Post
The benefits of a bulbous bow on a 50' or so trawler are illusory. I recall that for one of the early Nordhavns a bulbous bow was tank tested and showed promise. But in full scale, almost no difference. They gave up on that idea.


David

Just another "I wanna be like the big boys" feature.
It's like extended OB brackets ... better to just extend the whole boat.
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Old 01-27-2016, 02:21 PM   #9
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The bulbous bow are usually hollow, so the can serve a number of function. Usually speed and range is what comes to mind. However they also protect the bow from damage, and can affect a quick raise fall of the bow, and allow addition weight in the bow.

Everett, Wa use to have a commercial yard, and many or the bulbous bows had gorgeous on damage, and most where empty so the bow did not sink down as far ans quicker recovery. Anyway speed is a factor but there are other benefits.
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Old 01-27-2016, 02:30 PM   #10
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Outboard brackets are designed to take into account for the rise in water after the transom when running. They allow for higher engine mounting allowing for shallower draft without tilting and less drag.


Outboard brackets have a lot of design in the good ones.
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Old 01-27-2016, 05:08 PM   #11
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Psneeld that's an advantage I had'nt thought of.
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Old 01-27-2016, 05:26 PM   #12
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Bulbous bows take many different forms, and are installed for various reasons, not limited to just reducing resistance. The different shaped bulbs work in different ways. Optimizing a bulb for a particular hull and speed is a complex series of tank tests, usually never worthwhile for a pleasure boat where saving 5-10% on fuel is a minor detail and won't affect the sale. I don't think any tank testing went on for the Independent Shipwrights boat and thus doubt the bulb does anything significant. It used to be that bulbs were smaller and out of sight below waterline. On modern beamier boats bulbs have become far larger and often extend well above the at rest waterline, see the new Danish trawler (a real trawler) in the photo.

Some earlier writing on the subject.

Bulbous Bows

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Old 01-27-2016, 06:59 PM   #13
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How about this bulbous bow?

Good grief. That bulb is huge.

It's interesting to see how much hull is below the waterline on a real offshore trawler. That boat looks like it draws 8-9' but looking at the markings on the bow maybe only 5-6'? Or am I looking at that wrong?
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Old 01-27-2016, 07:58 PM   #14
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Good grief. That bulb is huge.

It's interesting to see how much hull is below the waterline on a real offshore trawler. That boat looks like it draws 8-9' but looking at the markings on the bow maybe only 5-6'? Or am I looking at that wrong?
Draft marks are in metres, bottom one is 2.6, upper one 4.4. The white painted line is right at 3 metres. The boat is approximately 55' long with a beam of 20'.
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Old 01-27-2016, 08:13 PM   #15
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Well, I'm blind.
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Old 01-27-2016, 09:32 PM   #16
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That Danish trawler is one oddly ugly boat.
I'd call that a bow goiter.
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Old 01-27-2016, 09:34 PM   #17
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Looks like the trawl might have hung up.
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Old 01-27-2016, 09:41 PM   #18
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Looks like the trawl might have hung up.
Either that or that is one hobby horse of a ride. It sure does not look like rough enough water to create that kind of bow rise!
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Old 01-27-2016, 09:55 PM   #19
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Just another "I wanna be like the big boys" feature.
It's like extended OB brackets ... better to just extend the whole boat.

Have you ever been on a bulbous bow boat or run one for a time in various seas.

I disagree with your comments of keeping up with the big boys, the ones I have run have produced a softer ride with less hobby horsing than other designs with increased speeds from less power.

Just my 2cents worth based on personal experience
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Old 01-27-2016, 10:07 PM   #20
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gwkiwi,
Yes they do dampen pitch but that costs dearly in the ability for a boat to rise up to a sea .... something I think is important for a small boat to do.

And part of the "all chain rode" is also a "big boys" thing.
Speaking of big boys your bow line looks thke those on a ship.
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