Benthic2
Guru
4 minute video on the function of the bulbous bow:
Bulbous bow - A good thing or bad?
- Thread starter rawlitwn
- Start date
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sunchaser
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In answer to your question about improvement in efficiency, I'd guess the answer is maybe but only if one tracks fuel consumption accurately like commercial guys do. The internet is rife with naval architect explanations as to how it works on large ships and efficiency etc gains. But adding to one of our pleasure boats, it is not cheap nor benefits cut and dry.
CharlieO.
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I'm looking forward to Jim's tech talk on his installation and real world results once it hits their you tube channel. I can tell by his previous tech talks and installations that he very thoroughly researches any modifications or add ons to his vessel and follows up with the results honestly.
FF
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"But adding to one of our pleasure boats, it is not cheap nor benefits cut and dry."
Many of our cruisers travel at 6 or 7K on about 2 GPH.
Doing anything that might make even a 10% difference would not add up to much except on a world cruise.
Many of our cruisers travel at 6 or 7K on about 2 GPH.
Doing anything that might make even a 10% difference would not add up to much except on a world cruise.
Cruising Sea Venture
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Hi Everyone,
Great discussion here.
Our Bulbous Bow addition on Sea Venture has been an outstanding success, but first I think it would be important to understand how they work on trawlers vs. large ships.
Our primary goal was to reduce pitching - any efficiency gain would be a bonus.
We never considered a cost benefit re: efficiency gain. Here is Alaska where we are cruising this winter a lot of commercial fishing boats have added bulbs to gain efficiency, and they all report success. The cost benefit works for them because they are operating in the 2-3000 hours per year range.
Why bulbs work on large ships is entirely different then how they work on trawler yachts.
Here is a link to an article by Jim Leishman of Nordhavn that appeared in PassageMaker Magazine pointing out that tank testing shows all Nordhavn models gained efficiency when a bulb was added and why they don't put them on all Nordhavn's.
https://www.passagemaker.com/web-extras/blue-maxs-bulbous-bow
Here is also a link to Bray Yacht Design and Research, who has done a bunch of work on bulbs specific to trawler yachts:
Bray Yacht Design & Research Ltd - Bulbous Bows
As you will note in the Bray Design article they found the water over the top of the bulb was pushing the bow down, thus reducing the stern squat, and increasing efficiency by improving trim. Nothing to do with changing the bow wave pattern, like on big ships.
Now that we have installed a bulb here is what we have found:
1) When changing speed from 2 knots to 7.5 knots on Sea Venture, on average the bow , before bulb added, lifted 1.6 degrees (we have a Inclinoscope on board for testing the bulb), with an associated drop in the stern.
2) With the bulbous bow, when changing from 2 knots to 7.5 knots, the bow drops 1.2 degrees, with the associated pick up in the stern.
3) On average, sea trials indicate we have picked up .5 of a knot in speed. We will refine this number over time.
4) Pitching has been reduced approximately 50% - but more testing in larger seas is still needed. Note that in 2-3 foot seas pitching is under .4 of a degree. Decreased pitching also increases efficiency. Due to reduced pitching Sea Venture does not experience as significant of a deceleration at the bottom of the trough.
5) We have not yet encountered any slapping. Commercial fish boat owners here in SE report their bulbs make noise in seas over 8 feet with a period of less than 8 seconds. Maybe fishing weather, but not cruising weather. As indicated in the Bray article, they report a small change in speed and/or direction seems to resolve this issue. Some report when the bulb starts to slap its a good indication it's time to pull gear and head in.
6) We now have a really large crash bumper on the front of the boat. It's a different story but one of the 75 ton commercial fishing boats - (Delta 59) drove into a rocky beach at 9 knots with their new bulb - tore apart the bulb but no damage to the hull.
Our bulb has a hole drilled in the top and bottom, so it's full of sea water, which is part of why it reduces pitching as effectively as it does.
Ours was installed by a company here in SE Alaska who has done a lot of them, mostly on commercial fish boats. They work with the folks at the University of British Columbia where almost all modern tank testing has been completed.
The total cost was about $15,000 - compared to almost any other significant change we have made to Sea Venture it was not a large investment, so we went for it, thinking if it didn't work we could just cut it off - There were no penetrations in the hull during the installation. Total bulb length on the sides, where it goes the furthest back is 12'. Total addition to the water line length is 42".
We are working on a multi-part video series for our YouTube Channel on the bulb addition. Part 1 will most likely be published this coming Saturday.
At least for us it has been a great success so far. Happy to share any additional details for anyone that is interested. You can email me at CruisingSeaVenture@gmail.com or contact us though our website. It may take me a little bit to respond, since we only have internet when we are in port.
Note our YouTube Channel and Website are just a way of sharing and paying forward to all the boaters who took time to help us out over the almost 30 years we have spent cruising. There is no avenue to pay anything, we don't accept sponsorships, etc.
As we say at the end of every video, "Wishing you no wind and flat seas".
Jim Addington
M/V Sea Venture
www.CruisingSeaVenture.com
Great discussion here.
Our Bulbous Bow addition on Sea Venture has been an outstanding success, but first I think it would be important to understand how they work on trawlers vs. large ships.
Our primary goal was to reduce pitching - any efficiency gain would be a bonus.
We never considered a cost benefit re: efficiency gain. Here is Alaska where we are cruising this winter a lot of commercial fishing boats have added bulbs to gain efficiency, and they all report success. The cost benefit works for them because they are operating in the 2-3000 hours per year range.
Why bulbs work on large ships is entirely different then how they work on trawler yachts.
Here is a link to an article by Jim Leishman of Nordhavn that appeared in PassageMaker Magazine pointing out that tank testing shows all Nordhavn models gained efficiency when a bulb was added and why they don't put them on all Nordhavn's.
https://www.passagemaker.com/web-extras/blue-maxs-bulbous-bow
Here is also a link to Bray Yacht Design and Research, who has done a bunch of work on bulbs specific to trawler yachts:
Bray Yacht Design & Research Ltd - Bulbous Bows
As you will note in the Bray Design article they found the water over the top of the bulb was pushing the bow down, thus reducing the stern squat, and increasing efficiency by improving trim. Nothing to do with changing the bow wave pattern, like on big ships.
Now that we have installed a bulb here is what we have found:
1) When changing speed from 2 knots to 7.5 knots on Sea Venture, on average the bow , before bulb added, lifted 1.6 degrees (we have a Inclinoscope on board for testing the bulb), with an associated drop in the stern.
2) With the bulbous bow, when changing from 2 knots to 7.5 knots, the bow drops 1.2 degrees, with the associated pick up in the stern.
3) On average, sea trials indicate we have picked up .5 of a knot in speed. We will refine this number over time.
4) Pitching has been reduced approximately 50% - but more testing in larger seas is still needed. Note that in 2-3 foot seas pitching is under .4 of a degree. Decreased pitching also increases efficiency. Due to reduced pitching Sea Venture does not experience as significant of a deceleration at the bottom of the trough.
5) We have not yet encountered any slapping. Commercial fish boat owners here in SE report their bulbs make noise in seas over 8 feet with a period of less than 8 seconds. Maybe fishing weather, but not cruising weather. As indicated in the Bray article, they report a small change in speed and/or direction seems to resolve this issue. Some report when the bulb starts to slap its a good indication it's time to pull gear and head in.
6) We now have a really large crash bumper on the front of the boat. It's a different story but one of the 75 ton commercial fishing boats - (Delta 59) drove into a rocky beach at 9 knots with their new bulb - tore apart the bulb but no damage to the hull.
Our bulb has a hole drilled in the top and bottom, so it's full of sea water, which is part of why it reduces pitching as effectively as it does.
Ours was installed by a company here in SE Alaska who has done a lot of them, mostly on commercial fish boats. They work with the folks at the University of British Columbia where almost all modern tank testing has been completed.
The total cost was about $15,000 - compared to almost any other significant change we have made to Sea Venture it was not a large investment, so we went for it, thinking if it didn't work we could just cut it off - There were no penetrations in the hull during the installation. Total bulb length on the sides, where it goes the furthest back is 12'. Total addition to the water line length is 42".
We are working on a multi-part video series for our YouTube Channel on the bulb addition. Part 1 will most likely be published this coming Saturday.
At least for us it has been a great success so far. Happy to share any additional details for anyone that is interested. You can email me at CruisingSeaVenture@gmail.com or contact us though our website. It may take me a little bit to respond, since we only have internet when we are in port.
Note our YouTube Channel and Website are just a way of sharing and paying forward to all the boaters who took time to help us out over the almost 30 years we have spent cruising. There is no avenue to pay anything, we don't accept sponsorships, etc.
As we say at the end of every video, "Wishing you no wind and flat seas".
Jim Addington
M/V Sea Venture
www.CruisingSeaVenture.com
Attachments
AboardAdventurer
Member
Absolutely love your channel Jim, and the latest two episodes highlighting the bulbous bow addition were especially good. If your experience doesn't put to rest the debate over the benefits of a bulbous bow on "small" trawlers, nothing will. I'd spend the money on one in a heartbeat if our trawler had a full displacement hull form. Keep up the great work, and the great channel.
rsn48
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If your experience doesn't put to rest the debate over the benefits of a bulbous bow on "small" trawlers, nothing will.
Come on, do you want to ruin it for the rest of us, of course the debate will never be put to bed.
PS: I watched the two Venture "big nose" videos, like'm a lot.
Come on, do you want to ruin it for the rest of us, of course the debate will never be put to bed.
PS: I watched the two Venture "big nose" videos, like'm a lot.
PennBruce
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My 35' Ta Chiao came from the builder with a bow bulb.
I've not had enough experience with her yet to have an opinion.
Bruce
I've not had enough experience with her yet to have an opinion.
Bruce
I take it there were no rough-sea tests, quick-turn performance maneuvers, speed trials and fuel use stats accumulated pre bow bulb installation. Then similar items undertaken after bow bulb in place... for comparison??
Nomad Willy
Guru
BB?
A waste of time and money.
Makes a good conversation platform tho.
Mako,
Maybe it was a torpedo tube and he changed his mind.
A waste of time and money.
Makes a good conversation platform tho.
Mako,
Maybe it was a torpedo tube and he changed his mind.
Last edited:
Gotwex
Veteran Member
Very interesting article about a 'DIY" bulbous bow. Have to read about 1/2 way into the article for the section on the bulb.
https://www.soundingsonline.com/boats/saving-sinbad
https://www.soundingsonline.com/boats/saving-sinbad
3rd time is charm!
Benthic2
Guru
They must have merit because a lot of companies are paying a lot of money to put them on their ships, however I think they only work at a specific speed. I would think this makes them a better fit for commercial ships than for pleasure boats.
just my two cents (and its probably overpriced!)
just my two cents (and its probably overpriced!)
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