Re: New Hudson 'Great White' 1X

Jonny wrote:
On Mar 16, 12:51 am, vet...@xxxxxxxxxxx wrote:

Seehttp://www.hudsonboatworks.com/breakingNews.aspx.

The sales pitch says 'Hull volume moved toward bow, creating a more
stable platform from finish' (sic)


Sounds like a great way to avoid improving your technique (ie
dumping!).

I do like the look of the wider rails - i've got calves that stick out
and I am forever donating chunks of myself to particular boats.

Can anyone say from theory or experience whether this actually works,
and if so is this better or worse that the Stampfli shape where (I
would say) the hull volume has been moved towards the stern ?


Carl!?!?!?!
I think it would.
Sort of off topic - Question for Carl...
I was having a good look at one of your doubles, first I've seen up
close, and it is rather 'thick' through the bows, almost blunt,
compared to many other boats that taper over a longer distance. It had
just won a head race in rough conditions and it certainly looked like
it would have had an advantage.

I have noticed a number of newer designs (Resolute comes to mind) that
are much longer in the bow than the stern - much more so than many
other designs (all/most singles are longer in the bow). Perhaps they
are trying to find a similar outcome?


I know nowt of the actual design of the new Hudson single, so would be in no position to comment even if I'd wanted to.

But I can respond to questions on our own designs:

It is easy to misjudge the actual shape of a boat from its appearance. Yes, ours do look relatively broad in the bow and fine in the stern, but that's because, unlike every (?) other shell, ours incorporates a significant amount of flare towards the bow. In other words, a cross-section taken well to the bow shows as a deep V rather than the more usual U.

The U-shape is a hang-over from traditional shell building. Boats were built inverted & the main timbers (keelson & 2 inwales) set up on stocks together with mould boards & ribs which defined the shape over which the single-plank skin would then be formed. It was normal, & convenient, to keep the inwales square with the horizontal & to bring the hull sides vertically onto their outer faces. Otherwise the inwales (the long timbers running at deck level inside the sheerline) would have to be twisted or machined with progressively increasing bevel along the full length of the boat - which complicates life.

There are good fluid-dynamic arguments for a distinctly V cross-section to the bow, giving a deep but fine entry into the oncoming water, & blending this out to a U as you move astern. And there are good arguments for continuing this V section up above the normal waterline. A fine entry is a good way for a hull to start split the oncoming water flow, & a deep entry maximises effective hull length (which has a strong influence on maximum speed potential). A deep bow also improves the boat's directional stability in cross-winds or a cross-chop.

Contrary to appearances, our bow is rather fine (=narrow) at & below the waterline. However, the flare to which I referred at the beginning leads all the way up to the sheer-line (=deck edge), making the bow look wider than other boats. Why do that? We do it because, while volume above the waterline does little & costs nothing in flat conditions, it is valuable when you hit the rough.

In theory you could scull a boat whose sheer-line stood just at the waterline, but in practice it would be unrowable. As the boat tended to pitch during the stroke, first one end then the other would completely submerge. When an end submerges, a boat immediately loses much of its pitch (longitudinal) stability because this depends on the available uplift continually increasing as you depress that end. Uplift being directly proportional to the amount of water displaced, it cannot increase where no more hull volume remains above water.

[As an aside, this consideration seriously limits the rescue capacity of some low-volume catamaran launches. If a person climbs onto a bow it may submerge &, unless they then let go, the boat could even roll diagonally over, so rapidly does it lose stability in that direction - especially if those aboard have moved towards that corner to assist a rescue. So a cat that is ill-designed for such use & can bury a bow can go from apparently dead stable to inverted in a trice].

A low-volume (non-flared) bow tends to pierce waves due to its low rate of increase of displacement & uplift with degree of immersion. A hull of our shape, with a better entry angle than the U hull, handles waves better: by its shape it generates dynamic uplift to gently raise the bow to the waves; & its greater available volume well forward provides buoyant uplift to keep water from flowing along the deck. Water over the deck is a weight depressing the bow &, since it greatly enlarges the wetted surface, increases fluid drag & slows the boat. So a hull form which minimises that possibility while in no way impairing the flat-water entry characteristics gives benefits in all conditions.

I think that's what you were indicating, wasn't it? And I guess that boat was the Stampers' CD-X double? In which case, well done, Mark & Co.!

Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: carl@xxxxxxxxxxxxxxxxx Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)
.

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