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Jackett

Member Since 27 Mar 2011
Offline Last Active Yesterday, 04:38 PM
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Posts I've Made

In Topic: Tumblehome?

14 November 2016 - 01:05 PM

French warship designers of the late XIX and early XX centuries seemed to love the tumble-home design... I think they expected it to be more efficient at deflecting enemy shells than a vertical side. Here you have some pictures of the pre-dreadnought battleship Tsesarevich, from the Imperial Russian Navy, but designed and built in France:

 

https://en.wikipedia...h1903France.jpg

 

1904_08_00_tsesarevich_at_port_arthur.jp

 

a6dabe84312c80804890a28d85e7ca30.jpg

 

 

 

Its commonly stated that the tumblehome was to help deflect shells up. This isn't the reason, or at least no the primary reason.

 

The limitations of the guns at the time (and the targeting apparatus) meant that the shells likely to hit the hull would be fired at fairly short range and so would have a fairly flat trajectory. 

 

If you had, say, 2 inches of armour and vertical topsides, the shell had to penetrate 2 inches of armour. But if that armour was raked at 45 degrees, the shell had to travel further to penetrate the armour as its travelling at an angle through the armour- just over 2.8 inches. So raking the armour has the effect of increasing the thickness of the armour (from the point of view of the shell) without any weight penalty (a weight saving potentially, as for a given waterline beam you ended up with less deck, which is itself more weight).

 

Its the same reason as armoured vehicles tend to have raked sides. The rake may help deflect the shell up, but that's not the primary reason for the rake.


In Topic: Coolboats to admire

07 October 2016 - 12:46 PM

That dinky mizzen does very little, if anything, for boat speed.

 

Probably slows it down - apparently the class rules for the Salcombe Yawl now state that the mizzen must be flown when racing, after some owners realised they did better if they didn't bother hoisting the sail.


In Topic: Surfing, bar crossings and boat shape

14 September 2016 - 07:56 AM

Assuming you're corssing the bar under motor, a single rudder is actually better than a twin rudder. Coming in, the waves will be overtaking you. As the wave crest comes under the stern, the water in the crest will be travelling forwards faster than the boat is (particularly if its beginning to break), so you loose water flow over the rudder and so loose steerage.

 

If you have a single rudder and an inboard motor, the rudder is positioned in the flow of water from the prop, allowing you to maintain a modicum of steerage as the wave crest passes under the stern. You don't get that with twin rudders.

 

Nearest we have to your bar in this part of the world is Chichester bar, which can get hairy in a southerly. Done it with young kids - as long as they're clipped on, and you're not trying to do it in stupid conditions, they think its great fun - better than a theme park!


In Topic: Olympic Classes

10 August 2016 - 11:48 AM

 The idea that adding a hot boat like the 49er sounded good in theory.  It would go fast and would be exciting to watch.  But really, I can't seem to find coverage of Olympic sailing despite having cable and other subscriptions.  It seems to me that adding the 49er did zero for viewership.

 

Maybe the lack of TV coverage has more do do with how well (or badly) your sailors are doing, rather than the class they're racing? Here in the UK there is always plenty of coverage of the Olympic sailing - is this because we normally win a handful of medals in the sailing?