Subject: Re: [harryproa] Re: Design your proa HUll exercise
From: Rick Willoughby
Date: 5/16/2011, 12:48 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Todd

The V hull will produce lift but nowhere near as efficiently as a cambered centreboard.  I also doubt that it will be more efficient than a flat bottom hull.  Using your numbers you have increased the wetted surface more than 30% just to increase the lateral surface area.  There is a huge cost in terms of extra hull drag.  The lift coefficient for a deep V section could easily be half that of a flat panel.  So 18sq.ft V may not be any better than 7sq.ft flat.  

I have some reasonable models for flat panel planing and Savisky for planing V hulls but it stops at 35 degrees deadrise for vertical lift.  I know anything steeper than 45 degrees deadrise will dig in rather than slip sideways.  So if the deadrise is greater than 45 degrees it should be good at preventing leeway but still not as good as a slab side.  

Rick


On 16/05/2011, at 2:11 PM, tsstproa wrote:

 

Hull length for length. Hull displacement for displacement.

Say on a 20 foot hull with a 400lb displacement.

V hull with a 13'' draft and Square bottom hull with a 6'' draft.

V hull 38sqft wetted surface area, square bottom hull 28sqft wetted surface area.

V hull with 18 sqft lateral area and Square bottom hull 7 sqft lateral area.

V hull skidding out and not producing lift I doubt it!!!

V hull with more than double the area how do you figure it would and not produce lift?

Also at high angles of heel do you see the difference in under water plane shape? The wider the square bottom hull becomes the more defined is becomes.

Placement of rudders on beam is more about convenience for the models. The rudder placement on the model in this clip is to close to the hull. If you look at the end of the clip. The same model with the reverse flow sail design on it you might see what looks like rudder ventilation. I use rudders to test balance of hull to sail. Not to test foil designs. Except of course the large leefoil and windward foil design models.

Todd


Rick Willoughby
03 9796 2415
0419 104 821

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