Sailboat-shaped Powerboats?

and I get 7.5 miles per gallon

 

7.5 miles to the gallon at what speed?
That's good for the wallet.

The 38 gets 2 miles to the gallon at 18 knots cruise speed.

 

Going back to the original post-A motor sailor fills the slot. It often has a full disp. hull somewhere between sail and power and still has a rig for sailing steadying and to help with economy. If you observe sail boats cruising in the summer in many locations they power or motor sail 90% of time. So while they qualify as sailboats what ever that means they function just fine as motor boats.

 

Hi BPL,
The answer is in post #10 - http://www.boatdesign.net/forums/boat-design/sailboat-shaped-powerboats-41441.html#post522583 - My boat is a Bob Oram 39C sailing cat without mast and sails and under power alone does 10.1 knots on both engines but I cruise on one engine and using the autopilot as that steers better... On one engine at 3000rpm at the engine http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-121.html#post499727 has data on the most recent brief run to assess performance...

6.7 knots at 3000 burning 3 Litres/hour... = 8.45nm/gal - - - on 2 engines at 3000rpm, same fuel burn (6litres/hour) and 10.1knots = 6.37nm/gal - - - - I made a mistake calculating conversions... I think this is correct now...

I learnt to "think outside the box", and realise that, though mono-hulls have a certain BEAUTY, - - practicality demands certain compromises, and the wallet also forces other considerations, and a 40 ft x 21.5ft CAT is the best compromise I could imagine and the Bob Oram design met most NECESSARY criteria...

I still have the opportunity to put a mast (12m stick - where the radar stands), and rig for a genoa to each bow, giving up to 90 sq metres (968 sq ft) of sail to carry in most slightly downwind and broad reach situations... The chain-plates, deck reinforcing are all in place to effect the rig... Displacement varies between 4,500kg and almost 6,000kg depending on fuel and 'cargo'...

 

I have no argument with the ultimate preformance edge of the multihull power or sail over the mono. I believe the key issues for those considering both are related to loading and how much time one spends at docks. I have lived with both formats and there are definete trade offs. It all comes down to how you use your boat. A fat cat kept light and on the hook makes for an attractive package. A fat cat overloaded and in need of hard to find dock space can be a pain in the butt.

 

Mat-C, Mr. Briand knows what you mean.
Luxury powerboat having a sailboat-like linesplan: Picchiotti 50 Exuma, from Perini Navi Group.
Phillipe Briand design (one of the biggest specialist in luxury sailboats) . Displacement hull, 13.6 lt/nm at 12 knots.

http://www.perininavi.it/it/flotta/motor-yachts/picchiotti-vitruvius®-exuma

 

I see your point Tad but of course we should not generalize some people do have good taste, they are just struggling with the 4 million
Peter
www.passagemaker.co.za

https://picasaweb.google.com/105852014649751428903/Ataraxia#5056550756183331586

 

Thanks all...
I don't really see the Pichiotti as being anything other than a displacement monohull that was designed by a sailboat designer... similar to the Dashew boats. Sure they have a passing resemblance to a sailboat hull, with finer fwd sections than you might otherwise find...

Besides they operate at lower speeds than I was thinking of. Irens LDL boats are closer to the mark....

 

First I have seen Nigel Irens' LDL hulls. Thanks for the link Michael.

 

Mat - Daiquiri and Tad have both given what I would consider to be the predominant reasons....
The sailboat hull is compromised by the fact that it has an unfortunate habit of leaning over, so it's shape is dictated to some extent by this. Faster, more modern yots are held more upright than their predecessors ever were, which is why they do (to some extent) more closely resemble some mid-speed powerboats.
But, as Tad pointed out, few powerboats are designed or built without taking interior volume into consideration. Would they be more 'sailboat-like' if it wasn't? To some extent yes, as the designs of Irens and others demonstrate.

 

About "Exuma", it has a sailboat-like underwater body, optimized for low Fn. It seems like Briand has a registered patent on this issue, I should search for it. I think no other reason to shape a powerboat as a sailboat but low speed regime and low fuel consumption.

 

Pretty good reasons, a couple more.

To be able to Sail when your engine breaks downs

To be able to Motor when the winds are gone, or way too adverse.

The standard marketing talk at http://www.macgregor26.com/

and I will have to start spruiking the same thing soon as I try to flog another version of the 'hybrid' motor-sailer
http://schoolroad.weebly.com/project-2.html

 

Exuma is an admirable design but I see nothing that I would consider Patentable or unique. She is a narrow and lightly loaded displacement hull, that's all......I believe Briand has trademarked the name BOS (Briand Optimized Stretched Hull).

Length is 164' and beam 31.15', so B/L = .19
LWL = 160' and cruising speed is 12 knots while top speed is 17. So S/L at cruising is 0.95 and at top speed is 1.34 (So called displacement hull speed).
D/L = 97.6 at full load (400 tons)

The equivalent 50' will have a beam of 9.5', displacement of 27,300 lbs at full load, cruising speed of 7 knots and full speed of 9.5 knots.

 

Indeed... though we can no doubt all think of examples of where patents have been granted where perhaps they ought not to have been...
Exuma is one of my favourite's of the current crop of superyachts... perhaps because Briand has followed the very same fundamentals that I have in the design of a similar sized motoryacht that I've been working on for some time, which shares very similar stats...

http://www.charterworld.com/news/47...acht-tender-cway-pty-imaginocean-yacht-design

Perhaps I ought to trademark an acronym of my own... WOSH perhaps (Will's Optimised Stretched Hull) or maybe SQUISH (Super QUiet Stretch Hull)..

 

Will.......yes, get those catchy phrases trademarked right away before they're all taken.....

I would note that Exuma's owner's accepted minimal accommodation for the ship's length.......Nice to see that Will was able to resist the 4th and 5th decks on his 47m....