Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-12-2019, 11:55 PM   #1
Member
 
City: Wilton, CT
Country: USA
Join Date: Oct 2014
Posts: 14
Bulbous bow - A good thing or bad?

Hi All,

Is having a bulbous bow on a 50_60' trawler a good thing? I've read that having one in calm waters is ok, but in rougher waters, makes the bow slap.... any opinions?

Thanks,

T.G.
CT
__________________
Advertisement

rawlitwn is offline   Reply With Quote
Old 03-12-2019, 11:58 PM   #2
Guru
 
Comodave's Avatar
 
City: Au Gres, MI
Country: US
Vessel Name: Never Say Never
Vessel Model: President 41 DC
Join Date: Jul 2015
Posts: 5,979
I think it would depend on how well it was designed. It should enhance fuel economy.
__________________

Comodave is offline   Reply With Quote
Old 03-13-2019, 12:21 AM   #3
Senior Member
 
Sabre602's Avatar
 
City: NW Washington State
Country: United States
Vessel Name: Kingfisher
Vessel Model: 37' converted gillnetter/crabber
Join Date: Oct 2017
Posts: 346
It's not a simple answer. Properly designed, it may improve fuel economy. But...yeah, it's not a simple answer. Here are what a couple of naval architects have to say on the matter:

Bray Yacht Design & Research Ltd - Bulbous Bows

George Buehler's thoughts on bulb bows
__________________
Anson & Donna

Be kind whenever possible. It is always possible. ~The Dalai Lama
Sabre602 is offline   Reply With Quote
Old 03-13-2019, 01:09 AM   #4
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Country: USA
Vessel Name: Carquinez Coot
Vessel Model: penultimate Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 11,452
Less than a ship, doubt a boat can ever recover the investment (cost of new bow) compared to any possible fuel savings. Leastwise, it has never been demonstrated to me. As a "fashion statement" it could be a worthwhile investment for someone.
__________________
Kar-KEEN-ez Koot
markpierce is offline   Reply With Quote
Old 03-13-2019, 01:28 AM   #5
Guru
 
City: Canaveral
Country: USA
Join Date: Jun 2012
Posts: 1,389
Good articles above.

I doubt the cost of retrofitting a small boat would ever be recaptured. However for a new construction it would be different. Two shipyards that I have been discussing with have bulbs in their designs. In one case the boat is very front-heavy and the added buoyancy is a benefit and pitching is slightly reduced. In both cases the waterline length is extended about 4-5 feet, so LWL is almost the same as LOA. The naval architect told me he estimates about 5% efficiency increase, which coincides with the longer LWL.

Regarding to negative motion, articles indicate bulbs can act like a deep forefoot, and when running downwind in heavy seas there may be a slight tendency to drag, but how significant this risk is to you is debatable.

In general T.G. I would say that if the 40-60 ft boat you're buying comes with a bulb, then great. And if it doesn't, then great. But if you want to learn more from actual naval architects, and some experts, then head on over to boatdesign.net/forums

Oh BTW you need to be careful about anchor roller/hawsepipe placement.
makobuilders is online now   Reply With Quote
Old 03-13-2019, 02:54 AM   #6
Senior Member
 
dirtdoc1's Avatar
 
City: Palo Alto
Country: United States
Vessel Name: Ann-Elyse II
Vessel Model: North Pacific 45
Join Date: Apr 2016
Posts: 370
I would think that if you spend much time on the hook a bulb could be problematic. Personally I would look in to that potential problem with great interest.

There was a Nordhavn 46 for sale recently that had a bulb. It was painted like an Orca. It looked great!
__________________
Dirtdoc1
dirtdoc1 is offline   Reply With Quote
Old 03-13-2019, 07:10 AM   #7
Guru
 
djmarchand's Avatar
 
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Vessel Model: Atlas Pompano 23
Join Date: Aug 2012
Posts: 4,895
Nordhavn tried one on an early boat and it didn't do any good.


David
djmarchand is online now   Reply With Quote
Old 03-13-2019, 07:30 AM   #8
Guru
 
O C Diver's Avatar
 
City: Fort Myers, FL... Summers in Crisfield, MD
Country: USA
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 7,717
While there is nothing wrong with a little more efficiency, I was under the impression that on smaller boats, the purpose was to improve wave entry going into seas. Obviously beyond a certain size wave, they would loose their effectiveness. Just curious if anyone has cruised on a <80' boat and can comment on the effectiveness of it improving the ride.

Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
O C Diver is online now   Reply With Quote
Old 03-13-2019, 07:36 AM   #9
TF Site Team
 
Insequent's Avatar
 
City: Brisbane
Country: Australia
Vessel Name: Insequent
Vessel Model: Ocean Alexander 50 Mk I
Join Date: Mar 2012
Posts: 2,371
I understand bulbous bows are tricky to get right to gain efficiency. Usually it involves testing of a model in a towing tank facility to get size and position correct. More often they are likely to be there to offset bow-down trim.
__________________
Brian
Insequent is offline   Reply With Quote
Old 03-13-2019, 07:51 AM   #10
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 19,844
On ships it was found the bulbs were built for long term operation at one cruise speed.

Change the cruise speed and you need to remove and redesign the bulb.

Big bucks unless you measure fuel burn in tons per day.
FF is offline   Reply With Quote
Old 03-13-2019, 08:20 AM   #11
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 4,967
Quote:
Originally Posted by Sabre602 View Post
It's not a simple answer. Properly designed, it may improve fuel economy. But...yeah, it's not a simple answer. Here are what a couple of naval architects have to say on the matter:

Bray Yacht Design & Research Ltd - Bulbous Bows

George Buehler's thoughts on bulb bows

I wish these articles (all articles) had dates. We are always learning and evolving. My guess is that both are pretty old.


I also suspect there is much more understanding of the exact dynamics of a bow and hull form. Good computer modeling should have removed all the mystery from this, but who knows. Certainly not me.
__________________
www.MVTanglewood.com
twistedtree is online now   Reply With Quote
Old 03-13-2019, 09:39 AM   #12
Senior Member
 
BIG CAT's Avatar
 
City: Kiln,MS
Country: USA
Join Date: May 2016
Posts: 457
I talked to a engineer that I used to work with. He basically said most pleasure boat are too small to get any benefit from them.
BIG CAT is offline   Reply With Quote
Old 03-13-2019, 11:29 AM   #13
Senior Member
 
nwboater's Avatar
 
City: Whidbey Island WA
Country: USA
Vessel Name: MV Kika
Vessel Model: Selene 47 Ocean Trawler
Join Date: Oct 2008
Posts: 284
My Selene 47 has a bulbous bow that was added by the previous owner. I suspect he did this because the boat lived in Oregon and was cruised up the coast each summer to B.C. and Alaska. Thus, the bulb might have reduced pitching when running against our prevailing NW winds and currents. Since owning the boat, Iíve not noticed any particular advantage or problems.

Click image for larger version

Name:	IMG_3753.jpg
Views:	96
Size:	76.5 KB
ID:	86378
__________________
Richard S.
MV Kika, Selene 47 Ocean Trawler
nwboater is offline   Reply With Quote
Old 03-13-2019, 12:22 PM   #14
Guru
 
Woodland Hills's Avatar
 
City: Jacksonville
Country: USA
Vessel Name: Alzero
Vessel Model: Hatteras 63' CPMY
Join Date: Apr 2017
Posts: 845
I’ve always been curious how a bulbous bow affects anchoring. Does it interfere with the anchor as it comes up?
Woodland Hills is offline   Reply With Quote
Old 03-13-2019, 12:40 PM   #15
Senior Member
 
Flybull's Avatar
 
City: USA
Country: USA
Vessel Model: 1983 Trojan F44 FBMY
Join Date: Dec 2018
Posts: 154
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...
Flybull is offline   Reply With Quote
Old 03-13-2019, 01:07 PM   #16
Senior Member
 
Civilitas's Avatar
 
City: PNW/Seattle-ish
Country: Air
Vessel Name: M/V Peter Iredale ;)
Vessel Model: rusting hulk
Join Date: Feb 2018
Posts: 128
Quote:
Originally Posted by FF View Post
On ships it was found the bulbs were built for long term operation at one cruise speed.

Change the cruise speed and you need to remove and redesign the bulb.

Big bucks unless you measure fuel burn in tons per day.
I have read this in relation to smaller yachts, too.

Particularly, I was reading about the bulb design on the Nordhavn 62. The bulb offered advantages in fuel burn at full cruise. But if one throttled back slightly to extend range for a long passage, the savings evaporated.
Civilitas is offline   Reply With Quote
Old 03-13-2019, 01:12 PM   #17
Guru
 
Codger2's Avatar
 
City: San Diego
Country: US
Vessel Name: "Sandpiper"
Vessel Model: 2006 42' Ocean Alexander Sedan
Join Date: Oct 2007
Posts: 5,936
Quote:
Originally Posted by Sabre602 View Post
Here are what a couple of naval architects have to say on the matter:

Bray Yacht Design & Research Ltd - Bulbous Bows

George Buehler's thoughts on bulb bows
Thanks for the links! Although they are two guy's opinions....their credentials have more weight than TFers with no design experience weighing in.
__________________
Codger 1941.. Constant pursuit of the ultimate SoCal Cruising boat.
Codger2 is offline   Reply With Quote
Old 03-13-2019, 01:31 PM   #18
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 4,967
This is all anecdotal and/or second hand, but this is what I know from Nordhavns.


- The fastest and most efficient hulls they have made are the 50 and 57, both of which have bulbs. How much of that comes from the bulb I don't know.



- A common complaint was/is the slapping when in heavy head seas.


- The slapping is not the bulb hitting the water surface, but rather the water coming together over the top of the bulb as it submerges. The water coming back together "claps" as you would clap your hands.


- Bulbs are now only offered on the 76 and larger boats, and have a flattened top surface that reduces the water clapping.
__________________
www.MVTanglewood.com
twistedtree is online now   Reply With Quote
Old 03-13-2019, 02:01 PM   #19
Senior Member
 
City: SW Alberta
Country: Canada
Join Date: Oct 2016
Posts: 111
Quote:
Originally Posted by FF View Post
On ships it was found the bulbs were built for long term operation at one cruise speed.

Change the cruise speed and you need to remove and redesign the bulb.

Big bucks unless you measure fuel burn in tons per day.
Fleming initially offered a bulb option on their new 58 but that has disappeared from their literature. If I remember correctly they stated that it was designed for a steady cruising speed. There didn't appear to be that much of a fuel savings though.
leeman is offline   Reply With Quote
Old 03-13-2019, 10:52 PM   #20
Member
 
City: Wilton, CT
Country: USA
Join Date: Oct 2014
Posts: 14
Thanks everyone, a lot of great feedback....seems the biggest concern is when anchoring or when docking bow in.....
__________________

rawlitwn is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 08:11 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×