Clarification about a Siu C. Fung paper on resistante and transom height

Greetings to everyone,

I'm working at the moment on the project of a semi-displacement fast yacht, and I need a bit of help on the following question:

As part of SNAME Transactions, I have the "Resistance and Powering Prediction for Transom Stern Hull Forms During Early Stage Ship Design" paper by Siu C. Fung.
The aforesaid paper is quite important for our actual project, but I have a small doubt about it and I hope to find a clarification.

In Figure 13 of the paper, there's a graph for Cp, Cx, Ta and Tw values based on the V/L^0.5 ratio, but it's not clear if the Ta curve is missing or if it's coincident with the Tw curve. And in the first case, how is the Ta curve shape?

Otherwise, can you point me to relevant articles about the ratio between transom section area and maximum section area, or about transom height, (related on Froude number or Speed/Lenght ratio, or anyway suitable to fast displacement hulls)?

Thanks in advance for your help

Best regards...

Paolo Lucchesi

 

Hello Paolo, sorry for the delay in responding.

The TA curve in Figure 13 is barely visible at the bottom of the figure. It comes in at V/L=1.1, and slowly rises to the right reaching about 0.35 at V/L=2.3

I don't see any line to the left of V/L=1.1, but it makes sense to me that the optimum transom area will continue to diminish as speed reduces, roughly parallel to the TW line.

I hope this helps.

Chris McKesson

 

You may note also that in 4.2.6 Siu talks about the relationship between TA, TW, and TT. Add to this the knowledge we get from Larry Doctors, which suggests that TT should be such that transom Froude number does not exceed 2.5. Thus:

FNT = V / [sqrt(g*TT)] <= 2.5

or

(V / 2.5 )^2 / g > TT [1]


You could combine the above Eq [1] with Siu's curve for TW and Siu's Eq [4] to get a value of TA.

 

Thanks for your help, Chris. Your suggestions are really precious and useful for my work. I'll look to Doctors papers.

May I ask one last great favour? In the pdf I purchased from sname, I still cannot see the TA curve. Could you please send an image of the curve or else a few couples of values (V/L^0.5, TA) so that I can rebuild it?

Thanks again in advance

Best regards

Paolo Lucchesi

 

Sure, let's see if this comes through... Note that I darkened the line with pencil.

 

That's perfect.
Thanks again for your help, Chris.

Best Regards
Paolo Lucchesi