High speed craft design

hi

does anybody know of any program to calculate speed/resistance etc for a stepped hull?
also regarding stiffness hogging sagging etc what scantlings can i use?what is the min. pressure, long. strength etc.?

THANKS!

 

Regarding the scantlings of the ship, you can use the various regulations of Classification Societies. As it is difficult to know them all, each designer will tell you it is better that one he knows better. I like much the "Special Service Crafts Regulations" by Lloyd's Register but I think they are all good and I could not tell which one is the one that results in the minimum weight structure. With each of them, playing well with the separation of reinforcements, you can get optimize your structure. I think it depends more on this, that the rules chosen.
If your design is for a recreational craft, in Europe, you should use ISO 12215, which, of course, results in softer scantlings than with Cllasificación Societies. Only comment is limited to boats from 6 to 24 m in length, and for speeds less than 50 knots.

 

Thanks very much TANSL!

 

George,

predicting resistance of stepped planing craft seems to be some kind of black magic with lots of experience required to get it right.

However, there are some approaches using the Savitsky method, where the hull is devided into individual sections at the steps and each section is calculated on its own. Afterwards everything is put together again, so to speak.

Find attached a Masters Thesis by David Svahn on the development of such a method.

Regarding scantlings you may want to refer to the ABS High Speed Craft Code which only has a lower speed limit. However, if the speed exceeds 50 knots (and/or 50 m in length for FRP hulls and 61 m for metal hulls), you are required to demonstrate the mechanical properties of the main supporting members of the vessel by direct analysis.

 

thank you Olav!very helpful!

 

Olav one question:
if i dont want to use class scantlings and want to go above 50 knots...any clues? for example do you know what rules cigarette, nor tech and other american boat builders are using?they seem to go up to 100 knots or more. or for example Hunton XRS 43 is a 58 knot boat.

 

sorry above question is for tansl too....

 

I think you have no choice but to apply the direct calculation of structures. You have to talk to the government agency will certify the ship and negotiate with them the pressures to use and allowable stresses as well as explain the software or calculation method you want to use.

 

Agreed, there's no way around the engineering on high speed craft, the forces and consequences are just too great.

 

thanks!