High Speed Aluminum Hull

[RANCHI OTTO]

Do you have any comments?

[StianM]

This was not easy to understand.
My Italian is far from perfect.
3 engines is not that mutch off a option since it's 2 engines we are asked to deliver.
I can't see why annybody even want a outboard.
2xsteyr with kamewa waterjets would be more fuel economical and reabile than anny outboard configuration and would manuver mutch bether.
surface drive and it would be superior at speed.
Outboard is for hobby use.

[RANCHI OTTO]

Not at all...I've designed military boats for Gulf country equipped with 4 outboard engines and speed over 50 knots.

If you have a mechanical problem it is much easyer to change an OB than an inboard diesel. Did you estimate the weight of the steyr + kamewa if compared to 2 OB engines ?

There is nothing to understand in my diagram, you calculate the KR coeff (left axis) KR=(BHP)^0.551/(DISPL)^0.476 where (^ means power) and down you read the corresponding speed...that's all, nothing more. The title is "Outboard engines).

[StianM]

Originally Posted by RANCHI OTTO

Not at all...I've designed military boats for Gulf country equipped with 4 outboard engines and speed over 50 knots.

If you have a mechanical problem it is much easyer to change an OB than an inboard diesel. Did you estimate the weight of the steyr + kamewa if compared to 2 OB engines ?

There is nothing to understand in my diagram, you calculate the KR coeff (left axis) KR=(BHP)^0.551/(DISPL)^0.476 where (^ means power) and down you read the corresponding speed...that's all, nothing more. The title is "Outboard engines).

Where is the weight?

A waterjet from hamilton and a Steyr would weight about 292kg withc is a aceptable weight. Inboard diesels has more reabilety than a gasoline aout board and the increase in weight can be compensated with smaler fuel tank because off the lover fuel consumtion.

Miletery boat with outboards??
The reason there was developed diesels for MTB's in the first place was because gasoline is mutch more flamable and potential more dangarous than diesel in a combat situation.

Using more than 2 outboards are really a last option. It will increase the cost and decrease the milage and the customer has spesefyed 2 engines.

[RANCHI OTTO]

I would prefer such high speed boats that a boat equipped with diesel + waterjet for craft up to 12 meters.
Price isn't a problem for such boats...

NAJA ASD 12
Hull ASD
Aluminum
4 x 300 hp
Displacement 7500 kg
1 x 20 mm gun
2 x 12.7 mm lightgun

sold in 40 units to Gulf Area country

Capability to shoot against target at 50 knots while manoeuvring....!

[RANCHI OTTO]

TOM CAT

Length 7.5 m
2 x 225 hp
Speed 40 knots
1 x 12.7 mm
Grp

[RANCHI OTTO]

It's enough....?

[StianM]

LOA 9-11m
Max. Breadth 3-4m
980 littres off fuel.
Crew and effects 950kg
Aluminium hull
Navigation equitment
50kn with TWO(not 1,3 or 4) outboards.
Vesel is to be open and not with anny sort off cabin.
Hull not to be steped.

Than RANCHI OTTO, but it's just not what I look for.
Please feel free to inform me on how to acheve this.

[RANCHI OTTO]

I've rushly checked the craft weight, and I find :

aluminum hull+console+mast+windscreen 1400 kg
gasoline 823
crew+effect 950
OB engines 540
electronic+nav. equipm. 25
starting battery+cables 50
extinguishers+lifesaving equipm. 20
outfittings (fender, seats..) 50
mooring equipm. (anchor,ropes,chain,...) 40

displacement fully loaded > 3898 + 2 (rounding) = 3900 kg

bhp = 2 x 250 ----> speed = 38/39 knots

To reach 50 knots the corresponding displacement would be 2700 kg abt.

[RANCHI OTTO]

the fixed starting weights are :

gasoline 823
engines 540
crew+eff. 950

total > 2313 kg !

...and the alu weight ?....

your boat is a 40 knots design, not more or you put 1 engine more....

[dougfrolich]

Nice boats R.O.!!!

[RANCHI OTTO]

Thanks dougfrolich....!

[yipster]

nice boats and figgers are rite Otto yet i'm pleased to see that TOMCAT took down his TATATATA your dead thing

[StianM]

Outboards is actualy 504kg, but that is no big diference.
I was looking at some yamaha 300hp.
So I have a power increase off 20%
The speed increase neaded is 20% identical to the hp, but a 1% speed increase require a 3-4% power increase.

What if I lover the bow to increase airflow over the hull and lower the stern to get a earodynamical lift to reduce water resistance? How mutch diference would this make?

Thanx for your answer

[RANCHI OTTO]

with a couple of engines developping 600 hp, the top speed would be of 45 knots abt. The OB engines have the possibility to change while running the inclination of the thrust and therefore the dynamic trim.
Good luck with your design !
if you reach the 50 knots, let me know how...!