Low Length/Displacement Hulls

Dear All,

Regarding the prime stages of this thread and the following posts and according to the base rules that Ad-Hoc described, please see the Lurssen's 1953's generation that was superseded the II War's S-boot.

The "Lurssen's effect" stern-design was then modified and also the Engine room's Installation Coordinates moved to the bow. The propellers number increased to four (4) and the power at 14.600 HP total -(Maybach engines edition) and the sides Propellers' shafts were installed related to Center Line, by angle.
LOA: 42.6m
Beam: 7.10 m
Draught: 1.90 m
Max.Tonage: 190 t
Speed: 39 knots
Escape Speed: 43 Knots

I think that there all a lot of subjects to be discussed on that.....

 

Alder

That hull has an L/D (length displacment) ratio of 7

The videos, in my other post, showing several high speed catamarans, their L/D ratios are 8-9.

So, that Lurssen's L/D is not as high as the cats, but still good. The effects of increasing L/D can be seen again here in the first graph.
http://www.boatdesign.net/forums/boat-design/dare-say-no-30261-9.html#post318285

 

"and the power at 14.600 HP total"

divide that by 16 (great for the era) and the fuel burn is over 900 GPH!

What a cruiser!

 

FF,

What a warship!

 

Latest edition of ProBoat contains an article by Reuel B. Parker about his design of Commuter Powerboat, so amuse yourselves carefully, whilst I read, mark, learn & inwardly digest. I'll be back.

 

Perry, this is a good list of beautiful boats. Thanks for sharing!

 

Fuel Consumption

Dear FAST FRED,

Lets as say that this hull has a fuel cost per hour at 22 Kts speed, around of 485 Lt and at 40 kts speed, reaches a quantity of 2830 Lt. (Specific Fuel Consumption around 195ml/hp.h).
Regarding the service range see please the attached diagram.
I think, not bad comparing to the most of the known type of cruisers/yachts with similar performances.

 

Fuel Consumption 2

Dear FAST FRED,

I forgot to note that according to Lurssen the Fuel's tanks Capacity is 30.000Lt.

 

On the River Thames at Hurley is the yard of Peter Freebody & Co. The Download Library contains real gems and the beauty of the watercraft described will delight the eye and tickle the fancy.

http://www.peterfreebody.com/about_us.php

Start from the bottom up; the restoration of "Herring Gull".

 

Perry, thanks for sharing these links. The Gelcye tenders (Herring Gull, Mavourneen,...) are indeed an exceptional beautiful and efficient example of the forced-displacement concept.
Really sad that Peter Freebody passed away last year. He was one of the few people who are on earth to teach us the difference between just working for money and being motivated by passion.

 

Here´s some fotos of the boat I did after this concept.

 

I must have been asleep for a while but have never heard the term forced-displacement before. Where did it come from and who coined it? The meaning is kind of intuitive but is it the same as semi-displacement or semi-planing?

 

Good question Tom. Try this on Wikipedia. http://en.wikipedia.org/wiki/Forced_displacement

Back to practical subjects.

Probably the first boat to express the principle must have been Turbinia. http://en.wikipedia.org/wiki/Turbinia

Torpedo boat destroyers. http://en.wikipedia.org/wiki/Destroyer

Fastest of them all. http://en.wikipedia.org/wiki/Le_Fantasque_(1935)

I think the horsepower requirements are greater for forced displacement than for planing (as witnessed by your Bluejackets) for a given hull weight and a stipulated speed above conventional waterline calculations. But, catamarans are the exceptions that prove the rule. C'mon Lottery, All I want is £6 million......

http://www.youtube.com/watch?v=vdqXoIhg0dA

 

Well, concerning the term "forced-displacement": I googled it and was surprised that I´m practically almost the only one using that term. I read it several times in pretty old articles (around 1925 to 1940) about the commuter yachts of the 1920´s and their typical hull characteritics. The term "forced-displacement-hull" was used for fast lightweight displacement boats that exceeded what was considered a nature-given hullspeed without climbing up the bow wave but istead keeping the bow wave extremely small by extremely stretched lines and therefor without producing excessive wave resistance.
I allways considered it a common term, never realized that I might be more or less the only one using it today.

Depending on special details of the hull shape concerning even distribution (a soft curve when shown as a graph) of change of displaced volume and a L/B higher than 6 a good forced-displacement hull will allways be superiour to a planing boat in terms of economy up to 1,6x the speed resulting of conventional waterline calculations (don´t want to upset some fellows by using the term hull speed )

 

Glad I asked guys. I liked the link to the Fantastique Pericles. I served on a destroyer for 2 1/2 years that fit this definition although we did not press the speed very often. At half power, we ran at S/L 1.5 during aircraft launch operations and could do 1.87 or so in a pinch at full power. Not so fast as either Fantastique or some of the WW2 Japanese destroyers though. I can accept that a forced displacement hull would be more fuel efficient than a planing boat if they were both restricted to the same displacement but not otherwise. Too many variables for any direct comparison anyway.

In all my reading, which has been considerable, I never before ran across the forced-displacement term so the intuitive guess of its meaning was wrong. There aught to be a better term for the phenomena since the practice is widespread, especially in multihulls.