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Old 07-17-2017, 12:24 AM   #1
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Nordhavn 40

I was in Nanaimo, BC this afternoon dropping my son off at BC Ferries and decided to hop over to Stone's Boatyard to have a look around at some boats up on the hard. I came across a Nordhavn40 that had an unusual (I had never seen such a thing in almost 40 years of being around boats and boatyards) underwater configuration. It had a "belly" on its belly, symmetrical on either side. The "belly on the stbd side had keel cooler fitted in, while the one on the port side appeared directly below a wing engine. Just wondering if this modification to hull form was aftermarket or if Nordhavn offers it as an option. I have attached photos and would appreciate any info on this unusual feature.
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Old 07-17-2017, 12:55 AM   #2
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Post Maintenance strakes

On several of the Nordhavn boats in this mid-size range they do this from the factory.

It is OE.

They are called "maintenance Strakes as I recall or something like that.

On the inside it is a place for you to stand to work on engine.

They give you more head room in the boat engine room with these & I also heard they can also give you a little more speed too.

I like some of the Nordhavn models, but not others. Not due to maintenance strakes, but due to not all in the smaller sized having walk around side decks.

IMHO - The big draw back I see with some of the smaller Nordhavn line of boats is the lack of full walk around decks on some of their models. They opt for the wide body approach to give more interior room. Many like that, but I am not one of them.

I did like one I saw that was a Nordhavn 50 named "Marabel" that was a full walk around model, but it was a bit out of my price range at the time - in fact most of them are out of my price range. I do like the older 62's as I think they have classic lines.

Anyway I hope that answered your question.

Alfa Mike


Here is a quote from the official Nordhavn explanation about those items you saw.
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"Another modification of the full displacement hull was the addition of "maintenance strakes," or underwater bulges in the hull form in the vicinity of the main engine. Originally designed to provide extra headroom in the engine room by lowering the bilge or floor, tank testing revealed that these shapes also added slightly to the efficiency of the hull by reducing the wetted surface area. The result is not only a more spacious engine room that encourages routine maintenance and care of the vessel's main propulsion engine and operating systems, but an underwater hull form that is even more slippery than usual." and an even more surprising 2.5 percent reduction in drag from its initial design."
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Have fun.

M.
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Old 07-17-2017, 06:39 AM   #3
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Yes, part of the design, and one which the main KK dealer here in Florida derides. When I was in a conversation with the owner/broker he said something along the lines of "really, they have two bulges on the bottom of the boat and they are saying that it does not impact performance, come on!"
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Old 07-17-2017, 08:46 AM   #4
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Gotta love marketing/advertising speak.

Quote:
Originally designed to provide extra headroom in the engine room by lowering the bilge or floor, tank testing revealed that these shapes also added slightly to the efficiency of the hull by reducing the wetted surface area.
Say what? How can adding surface area reduce surface area?

Quote:
...an underwater hull form that is even more slippery than usual." and an even more surprising 2.5 percent reduction in drag from its initial design.".
If you start with a larger hull, then reduce it in size and add some belly bulges, I guess it sorta makes sense
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Old 07-17-2017, 10:04 AM   #5
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Post Hull Bulges - but less drag ?

Yea, I was thinking about that.

How can you have such obvious bulges like these & end up with less drag.

I guess the marketing guys got a little carried away.

But it does give more head room by dropping the floor in that area.

LOL !


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Old 07-17-2017, 10:11 AM   #6
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Thanks for the explanations. Guess the concept hasn't caught on yet as other builders have not yet adopted the idea.
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Old 07-17-2017, 10:25 AM   #7
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It's one of those designed in compromises that half the people hate and half the people love. I'm in the the love them camp.
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Old 07-17-2017, 10:51 AM   #8
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I suppose it doesn't cost more in materials but it begs the question, why not just widen the entire hull there? Its already displacement.
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Old 07-17-2017, 05:38 PM   #9
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They should call them Beluga Belly Bulge hulls
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Old 07-17-2017, 06:56 PM   #10
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Nordhavn is run by some classy professionals. If you called the HQ shop in Dana Point to ask, or sent them an email, I would be surprised if they were not willing to share their tank test and/or simulation data pertinent to the maintenance strakes.
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Old 07-17-2017, 11:03 PM   #11
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Unfortunately KK sales spends a lot of time dissing Nordhavn's. When we were boat shopping (and seriously considering a KK) we found it very unprofessional and a real turn off. They strike me as way too focused on chasing Nordhavn, and shouldn't. They are different boats with a different purpose, and they should focus on what they do well.
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Old 07-18-2017, 12:30 AM   #12
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Quote:
Originally Posted by twistedtree View Post
Unfortunately KK sales spends a lot of time dissing Nordhavn's. When we were boat shopping (and seriously considering a KK) we found it very unprofessional and a real turn off. They strike me as way too focused on chasing Nordhavn, and shouldn't. They are different boats with a different purpose, and they should focus on what they do well.
That would assume they know what they do well.
That insecurity you experienced is a sign they don't.
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Old 07-18-2017, 06:35 PM   #13
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That would assume they know what they do well.
That insecurity you experienced is a sign they don't.

I was trying to be nice.
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Old 07-18-2017, 08:15 PM   #14
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Quote:
Originally Posted by twistedtree View Post
Unfortunately KK sales spends a lot of time dissing Nordhavn's. When we were boat shopping (and seriously considering a KK) we found it very unprofessional and a real turn off. They strike me as way too focused on chasing Nordhavn, and shouldn't. They are different boats with a different purpose, and they should focus on what they do well.
Totally 100% agree. I ignored all further communication with him - which, once he had my email, was quite a lot!
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Old 07-18-2017, 08:32 PM   #15
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Originally Posted by MurrayM View Post
Gotta love marketing/advertising speak.

Say what? How can adding surface area reduce surface area?

If you start with a larger hull, then reduce it in size and add some belly bulges, I guess it sorta makes sense

Wetted surface is not the same as total surface area which is not the same as drag. In this case it could well be in an area; or increasing an area of lower pressure that does in fact reduce overall drag.

Not a naval architect and did not stay in holiday inn last night....
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Old 07-18-2017, 08:33 PM   #16
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Originally Posted by MRRiley View Post
Wetted surface is not the same as total surface area which is not the same as drag. In this case it could well be in an area; or increasing an area of lower pressure that does in fact reduce overall drag.

Not a naval architect and did not stay in holiday inn last night....
Express man, express....
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Old 07-18-2017, 08:36 PM   #17
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Hydrodynamics baby....
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