Unpleasant bulbous bow

muckypup

muckypup

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From the Nordhavn website....


"Another choice that the buyer of an N76 is given is whether or not to have a bulbous bow or conventional bow. The N76 hull mold has two different bow configurations (conventional and bulbous) which are interchangeable and set up prior to hull lamination. The bulbous bow provides benefits but also has an unpleasant side to it and thus has become somewhat controversial in recent years. We will discuss with you your intended use of your Nordhavn 76 and help you decide which bow configuration is right for you."

What is the unpleasant side to a bulbous bow?

S.
 
I think you're right, Brendan. There is a report on the Selene website (sorry there's so much on the site that I can't be arsed to look for it) on a passage undertaken by a Selene with a traditional bow and another larger boat with a bulbous bow during which the larger boat had to slow down because of the uncomfortable motion. Not surprising really that sticking a sodding great big blob on the bow of your boat causes it to pitch uncomfortably in certain sea conditions
 
That's a very interesting question - and I concur with other posters on this thread...
But I wondered whether another 'unpleasant' aspect of a bulbous bow (for small vessels, rather than large ships, that is), is maybe the hazard of running over warps/nets, floating or otherwise, and getting entangled? A 'normal' bow on a vessel like a Nordhavn with protected sterngear, would just run over the rope unnoticed? Err, maybe?
Best wishes
 
Looking at the advantages instead, the principal positive aspect of a bulbous bow is (so I understand) that it fools the ship into thinking that it is longer than it actually is, by modifying the wave pattern (ie where the 'humps' and 'hollows' are) and hence the wave-making resistance.

And a longer ship in displacement mode will always have a slightly higher maximum hull speed than a geometrically similar shorter vessel, all else being equal. The total wetted surface area has not increased significantly with a bulbous bow, hence if the overall resistance is assumed to be the same for both bulbed and unbulbed bows (but it will not necessarily be), then the bulbed bow vessel should go a bit faster for the same fuel consumption. Or she can ease back a bit on the speed and enjoy improved fuel economy.

But I am no hydrodynamics expert, and this is just my simplistic way of looking at it - am sure someone else can come up with a better explanation! /forums/images/graemlins/confused.gif
 
that works on large commercial ships, we are talking about much smaller boats

One of the sites I looked at said that a huge US ship still suffered bulb slamming in heavy seas
 
Re: Bulb slap.........

Bit like this then..........

Nordhavn62.jpg
 
Have a look at the Dashew's new 'Unsailboat' at http://www.setsail.com/dashew/do_PARADIGM.html.

No bulbous bows in sight anywhere, and she apparently has wonderful sea-keeping, excellent fuel economy, and a very comfortable motion at sea - they (just 2 crew) drove her home from New Zealand to California, and most of this passage was upwind.

I guess you will ever love Wind Horse or hate her - especially as the styling (reminiscent of a pocket battleship?) is so totally different to just about any other motor yacht in existence today.

But I think she is lovely, and if I was ever in the market for an ocean going power boat, and had the necessary funds and enthusiasm to build a vessel of this calibre, she would be top of my list by far.

PS - Be warned, if you have never been on Setsail before, it is very addictive - most first timers spend hours glued to their computers. So much useful info there, about almost every conceivable topic re cruising under power and sail - rather like this forum!
 
That site quite spoiled my day (so far) with views on Proper Yachts.

I did notice, however, that the Unsailboat appears to be owned by a well-known Forumite, making concessions to Flag rules.


cg1.jpg
 
Fair point about the effect of boat size. I would think that a bulb on a mobo would work well only in mild swell. Otherwise out of the water to much of the time. Also, many superyachts with bulb bows might better be called blade bows. Their bulbs are not circular in section, much thinner across. I see from the photo posted that Nordy sticks with the circular style.

Kelly
 
I was wondering about that myself and also the fact that the bulb is in a very exposed position. Say you run into a submerged container at sea. With a normal bow, there is a chance that the container is pushed to one side whereas with a bulb IMHO there is a chance the bulb gets ripped off putting the boat at riak
Another question. Why don't you see bulbs on sailboats? You would think that extending the waterline length would make a significant difference to performance
 
Conventional thought is that to be effective the bulb travels just under the surface at ballast draft on deep sea ships - this breaks a hole for the hull to ease through. In loaded condition ie when deep draught, unsure if there is huge advantage.

Cruise ships and car carriers travel as roughly the same draft year round so effective all the time.

The problem with shallow draft boats (as opposed to ships) is the bulb comes out of the water, which it ought not to do on big commercial stuff. I've seen substancial damage caused by slamming, and by water slapping under the bulb when very light ship.
 
‘Bulb’ on a sailing vessel? Interesting question; Yes, I agree. Like most things, it’s probably been done! Though a proper ‘big ship’ bulbous bow on a small sailing boat maybe increases wetted area/increases drag/etc/etc; and is perhaps of no use. You’d have to ask someone a lot more qualified in naval architecture than I.

I just like the (bigger) Nordhavn's though - lovely... a 57 maybe?

Best wishes.
 
Re the "bulb slap" that has been mentioned, I discussed this with the president of the company when onboard and he told me that he was in the process of re-designing the bulb so a better exit and entry would be experienced without any serious reduction in performance gain. I dont know if they were successfull or not though!
 
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