Re hull shapes

[Matt.D]

Toying with the idea of building a 15m full displasment steel cat.
Powerd by 2x 80hp outboards mounted inboard as a cheap alt to saildrives.
Avg speed 10 kts aprox.
Aprox weight 23 tones

Ques. What shape is the best? Eg round chine or v ? canoe or square stern with a gragual point? or just a v point on the front?

R these speeds attainable?

Sorry i had some drawings but the failed to load!

Thanks for your input!

[Spiv]

Hi Matt,

have a read of this post http://boatdesign.net/forums/showthread.php?t=21267 and expecially follow the link to Malcolm Tennent article.

[Guest625101138]

I put your constraints to Godzilla and it came up with the attached for the minimum drag ship. It would take around 30kW to push it at 10kts.

The shape is not quite what I expected but Godzilla often gives surprises. I am reasonably certain that there were no other constraints that drove the shape.

Rick W.

[Matt.D]

Thanks mate ! What an awesome read !

[Matt.D]

Hi Rick , thanks for ur reply ,still a bit new but what is Godzilla? and u mentioned attachment ? cant seem to find any? and is that 30kw of trust or engine power? Full of questions arnt i!!! : )

[Guest625101138]

Godzilla is a hull optimising program.

The 30kW is power as in about 40HP. Roughly 1HP equals 750W and 1kW equals 1000W.

The attachement is a lineplan beneath post #3 on this thread. If you open the thread and click on the small image it will show up full size. Or to make it easier I will place a link here:
http://boatdesign.net/forums/attachm...2&d=1202978944

Rick W

[Matt.D]

Thanks Rick.

[yipster]

Rick, not an swift turner but allmost old fashioned keels, Rudy Choy ( and i ) would love to see those hulls sail boardless

[Guest625101138]

Yipster
The draft is over 1.6m on a 15m WL so not the ideal foil but a lot more efficient than the typical rounded hull.

I was surprised when Godzilla produced it so I checked that there were no other constraints unintentionally in play. I could not find any. Thinking about it and looking at current design trends for heavy displacement cats it seems reasonable.

It is a heavy boat for 15m but it would not take a huge sail to achieve design speed.

Rick W.

[Matt.D]

Hey guys im thinking of powered rather than sail and if i made the hulls 1600mm wide would this slow it to much?
Want to keep all accom. in the hulls and leave the wing deck for a large saloon area with a seprate dining aft and galley midship.
A little unconventional i know, but the salloon /dining area in standard cats just dosent seem inviting to me. whats ur thougts?

Matt

[Guest625101138]

Required power goes up to around 60HP.

Rick W.

[yipster]

Originally Posted by Matt.D

Hey guys im thinking of powered rather than sail and if i made the hulls 1600mm wide would this slow it to much?
Want to keep all accom. in the hulls and leave the wing deck for a large saloon area with a seprate dining aft and galley midship.
A little unconventional i know, but the salloon /dining area in standard cats just dosent seem inviting to me. whats ur thougts?

i tend to agree with that, think better interior design can make the difference