Design

[Nomad Willy]

FF,

Cruise at a speed/length ratio of .9 ? Rediculus. That is 4.7 knots for my 30' boat. Lots of large ships do that but not power yachts. SL of 1.1 to 1.15 is more like it. For a boat to equal the efficency of a FD boat at SL .9 at SL 2.4 it would need to be a freak in terms of displacement, B/L ratio, wetted surface ect ect. The boat would be useless except to perform the feat. As for the box keel .. the more weight it supported the less initial stability the boat would have and being a 50 year old design it's brobably quite narrow. I really liked the river boat you refered to with the John Atkin designs ( River Queen as I recall ) but it is a river boat and seaworthyness is not a strong point. Your'e barking up*the right tree with long narrow boats, however, and most*50 year old designs are narrow and more efficent because they didn't have much power then.

Eric Henning*

Eric Henning

-- Edited by nomadwilly at 14:28, 2008-12-29

 

[FF]

"Cruise at a speed/length ratio of .9 ? Rediculus."

The question was efficiency , not speed.

Most cruisers will pay more for speed so the SL of 1.15 is about as fast as most will pay for as getting to SL 1.4 may cost doubble again the fuel burn.

"As for the box keel .. the more weight it supported the less initial stability the boat would have and being a 50 year old design it's brobably quite narrow"

The actual hassle is the more displacement in the box keel , the less floor space may be* aviliable , a rough tradeoff on a cruiser.

Skinny is the ONLY (and light) way to get over SL 2.5 with a displacement fuel burn per mile.

The vessel were testing has a LOA of 39ft and a BOA of 7 ft 6 inches , to fit as shipping container.

BWL is about 5.5 ft , for an Lwl/Bwl of about 7, add that to a DL of under 100 (the boat will be under 8800lbs for easiest Euro Cert).

This is a boat to cruise a couple , and sleep 4 on occasion (2 in Concordia Bunks in salon) and be able to feed , party 8 at a table or underway.

The internal room is similar to about a Thunderbird a 27 ft sail boat.

A roomaran it isnt , hopefully a world useful cruiser (beachable shippable and really efficient) she will be.

" seaworthyness is not a strong point. Your'e barking up the right tree with long narrow boats, however, and most 50 year old designs are narrow and more efficent because they didn't have much power then."

This is a simple cruiser with no pretense at ocean voyaging , but she should be able to hold her own in a blow.With engine and batt bank in the box keel stability shouldnt be a problem, but it will have a "multihull ride" on top of the water.

Long and narrow was used because the engines were primitave and weak, but the use of minimum power on a skinny boat still works , the question then becomes how minimum can the fuel burn be ?

And that boils down to how heavily (with in mfg guidelines) the engine can be loaded at far less than max rpm.Hence CP prop and 2 speed.


-- Edited by FF at 05:17, 2008-12-30