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Old 03-14-2019, 12:48 AM   #21
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From my experience as an engineer on a container ship, I agree with FF and MarkPierce. In a 24 hour period, our ship (with a bulbous bow) would burn roughly 64 tons of fuel oil at 95 rpm. So on that ship, it may have helped fuel economy but by how much, nobody I bet could tell you? Because if we were fully loaded, that bulb would be completely under the water line, however, if we were not fully loaded, the bulb would be sticking halfway above the water line or somewhere in between. So, there may be more factors into it than just having one or not. Also, I dare anyone to find a bulbous bow on a ship that does not have anchor chain scratches across it. End the end, I think they give a “small boat” that big ship look and it does look cool but not sure it is worth the money. However, I wouldn’t cut one off a boat either if it had one.
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Old 03-14-2019, 02:41 AM   #22
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Hi


In this video, a new type of bulb designed for a fast pilot boat on a heavy track, the end of the video is an interesting comparison where the bow's bow motion is measured and the new bulbi reduces jumping quite well (can of course be due to other design


https://youtu.be/pqGVSn6saM8


An interesting article about bulbs...
http://www.brayyachtdesign.bc.ca/Sup...ient%20LRC.pdf


NBs
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Old 03-18-2019, 01:23 PM   #23
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I had a boat with a bulbous and had no problems with anchoring. It all depends on the overall design and the relationship of the bulbous bow and anchor placement.

I knew of one guy on a 76’ that added the bulbous bow for buoyancy. He cruised Alaska and wanted to add extra chain and an up-sized anchor.

Some bulbous bows where designed to hold water which you could fill or empty depending on sea conditions and whether you were in a following sea or heading into the seas.
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Old 03-18-2019, 01:59 PM   #24
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Some bulbous bows where designed to hold water which you could fill or empty depending on sea conditions and whether you were in a following sea or heading into the seas.

Very cool idea. A big bulb could hold several hundred gallons. That’s a lot of fresh water for local cruising (probably wouldn’t want to fill it during ocean passages).
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Old 03-18-2019, 02:00 PM   #25
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Bad for yachts/trawlers
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Old 03-18-2019, 02:38 PM   #26
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Good explanation here" https://nordhavnonly.com/nordhavn-mo...tails/bulbous/
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Old 03-18-2019, 03:44 PM   #27
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I had a boat with a bulbous and had no problems with anchoring. It all depends on the overall design and the relationship of the bulbous bow and anchor placement.

I knew of one guy on a 76’ that added the bulbous bow for buoyancy. He cruised Alaska and wanted to add extra chain and an up-sized anchor.

Some bulbous bows where designed to hold water which you could fill or empty depending on sea conditions and whether you were in a following sea or heading into the seas.
Interesting stuff, thanks!
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Old 03-18-2019, 07:22 PM   #28
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I was looking to put one on a past commercial fishing boat I owned. My objectives were to reduce my wake (which it seems to do on other vessels I saw retro-fitted), reduce the vertical leap while bucking, straighter tracking in heavy seas, and of course better fuel economy.

The marine engineer I spoke with on the project talked me out of doing it. He felt that a well designed hull does not benefit much if at all from retro-fitting a bulb?
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Old 03-18-2019, 07:59 PM   #29
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Marlow considered itand even built a boat with one, it must not have worked as I can’t seem to find it offered any longer.
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Old 03-18-2019, 08:22 PM   #30
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Quote:
Originally Posted by PacNW View Post
I had a boat with a bulbous and had no problems with anchoring. It all depends on the overall design and the relationship of the bulbous bow and anchor placement.

I knew of one guy on a 76’ that added the bulbous bow for buoyancy. He cruised Alaska and wanted to add extra chain and an up-sized anchor.

Some bulbous bows where designed to hold water which you could fill or empty depending on sea conditions and whether you were in a following sea or heading into the seas.
The bulb on our Selene has an open "hole" located on the underside that fills with sea water, thus, it adds weight and reduces buoyancy at the bow. We will be visiting the west side of Vancouver Island this summer, which is open to the Pacific swells, so it will be interesting to see how the Kika runs in both following and head seas. Btw, though the bulbous bow protrudes quite far forward, it has yet to interfere with either deploying or weighing the anchor.
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Old 03-18-2019, 08:32 PM   #31
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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.
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Old 03-19-2019, 09:28 AM   #32
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They do make for great pictures:






https://twistedsifter.files.wordpres...-marry-2-1.jpg

https://twistedsifter.files.wordpres...-marry-2-4.jpg
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Old 03-19-2019, 01:14 PM   #33
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And more fun with a bulb... named "Tigger"
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Old 03-19-2019, 10:44 PM   #34
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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).
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