SCALE MODEL , Size?

[Guest625101138]

Alan
If you are only after 6 knots why not go for an optimised hull. If you give me your intended displacement and stabiltly (I could work on beam of 8ft) I could just do a Godzilla optimisation. It would be better than the Atkin hull.

Rick W.

[Guest625101138]

Alan
The attached shows a hull optimised for 6kts. It displaces 4.5 tonne and has a miniumum WL beam of 8ft. It is similar in concept to the Atkin but designed for a much lower speed. The underwater section is like a fat canoe.

It would take around 1kW to push it at 6kts in calm conditions.

Rick W.

[CaptainAB]

Originally Posted by Rick Willoughby

Alan
If you are only after 6 knots why not go for an optimised hull. If you give me your intended displacement and stabiltly (I could work on beam of 8ft) I could just do a Godzilla optimisation. It would be better than the Atkin hull.

Rick W.

Hi Rick - Thanks for your offer, I don't know how to specify the figures you mention, I can only tell you what I have in mind. I want to tour a significant part of the Murray river with my partner. I picked 35' as about the right size for comfort as live about for a couple of weeks at a time for two people. I'm not in a hurry, so about a cruising speed of about 10 Km/h would be ample. The Murray is very shallow in many places as you know and the less the draft the better. The Atkin design appealed to me because the draft figure includes the prop and rudder and if the hull is run aground, there is a sporting chance that the prop will survive. Other than that, I'm open to all suggestions!

Incidentally, would you be prepared to post the .FBM file for the River Belle calculations you did up for Fast Fred earlier in this thread ? I have been working on Free!Ship to try and create my own, but I'm struggling a bit ?

Many thanks

Alan

[Guest625101138]

Fred
I have attached some images of the Godzilla hull with the Atkin squared stern. This one is optimised for 17.5kts. Power required is 70HP with the 20" prop shown. You would like a bigger diameter for efficiency but the shaft would need to be angled to mount the box. Also the blades would require greater draft. They are already deeper than the keel.

The Atkin hull previously posted requires 86HP with a 20" prop. (I used the drag from the optimum hull when I made the post on the other thread.)

This one would not be as easy to transport. A two blade prop could be used and set horizontal for transport. Also two smaller rudders could be used and go no deeper than the keel.

This one has slightly better inherent stability than the early one. KMt is 1.39m compared with 1.26m for the earlier one.

Rick W.

[FAST FRED]

Thanks for all the help and work , and the difference between 70 and 86 hp could easily be one GPH.

The problem is I will expect the boat to be transported , stored resting flat on the box keel. Or something near , that could run on simple pipe rollers.

I do wonder tho how much of the boats displacement should be taken by the keel, and what percentage by the hull body?

I'm also hoping that there might be some veracity to the efficiency claims of the Atkin (reverse deadrise , box keel) design , which may not be computer recognizable , from lack of current data.

FF

[masalai]

Fred, Have a look at mine, similar concept in hull form but as a cat. I am aiming for better than 1 nautical mile per litre at 15 knots cruise (flat sea no wind) with a range of 2000 to 2500 NMi on tanks holding 2000kg of fuel. (near 2500 litres). Rick W has been helping me with underwater refinements. (Did it all). My published model is the initial concept idea development & now to further test that before building a model close to final result.