Re: [PSUBS-MAILIST] Calculating Hull Speeds

[MerlinSub@t-online.de (Carsten Standfuss)]

Hi Doug, 
in Metric the formular is 2,43 times the square root of the waterline. 

Sample for Euronaut : 
Length over all  : 16,0 meter (52,5 feet)
Length waterline : 15,8 meter (51,8 feet)
Surface speed : 
2,43 square root 15,8 m = 9,66 knots
or in your formular : 
1,34 square root 51,8 ft = 9,64 knots

Sample for Sgt.Peppers : 
Length waterline : 2,5 m 
2,43 sqroot 2,5 = 3,8 knots

With a lot of extra power you can increase this speeds for displacemnet
hulls about 10% . 

On subs the border is reach when the bow-wave climbed over the deck and
the sub starts to dive just dynamicly - which increase the need of power
to increase the speed dramatically.  On Euronaut this speed is reached
at about 9 knots. I can build the deck higher to increase the speed a
little for about 0,5-1,0 knots but this higher deck will reduce later
the max.underwater speed - live is a compromise. 

The figure of 4 HP per tons to reach this speed is 
probably not right for any sub. 

Euronaut will estimate run at 57 ts displacement 
this speed (9 knots) with about 95 HP. Thats 1,6 HP per t. 

A Hecht runs : 
with 11,83 t and 12 hp about 5,7 knots thats : 1 hp/t 
(but reach not the full waterlinespeed.)

A Biber runs : 
with 6,25 t and 32 hp about 6,5 knots thats : 5,1 hp/t

A Seehund runs : 
with 14,9 t and 60 hp about 7,7 knots : 4 hp/t 

A XE-craft runs : 
with 36 ts and 42 hp about 7,0 knots : 1,2 hp/t 
but reach not full waterlinespeed.

The Forelle of 1902 : 
with 15,5 t and 65 hp  about 8 knots : 4,2 hp/t

Seehund and Forelle have relative small diameter propellers with high
rpm and lower efficency. Euronaut and X-crafts have greater diameter
propellers at lower rpms with greater efficency.. 

If the propeller in the stern at the end of the hull you win about 
20% power against hull with propellers on the side or below the hull. 

An Power-optimized boat has the propeller at the stern 
and a maximize Propellerdiameter. Like some of the wet waterbike-subs.  

Teardrop hull subs runs faster underwater (with the same power) than at
the surface. VIIC style hulls run with the same poweer faster on the
surface. 

regards Carsten




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