Speed Forecast

[RANCHI OTTO]

I would appreciate our speed forecast for the following craft:

LWL > 13.7 m
Bmld > 4.0 m
Displ. Full load > 20.6 t
Deadrise > 18.5 deg.
LCG > 5.1 m from transom

Power > 2 x 700 Bkw
Propulsion > twin waterjets

Thanks,

RANCHI Otto

[DaveB]

Hi Ranchi,

I think we need some more info to make a good estimate... I've assumed a draft of 1m, but need sail area (superstructure and topsides areas) to estimate wind resistance... Information on wetted surface area would also be good... I used the empirical estimate built into NavCAD...

I've attached the NavCAD report and if you'd like to fill in the blanks (post values for what is left blank [zero]) I'd be happy to rerun the estimate... I think it would be best for us to give you resistance estimates and you can then use them to size waterjets and propellers...

Cheers,

Dave

[RANCHI OTTO]

Dear Dave, thank you very much for your kindness.

The additional informations are as follows:

Lcp > 14.2 m (projected chine length)
Aw > 12 m2 (frontal surface)
T > 0.85 m (static draft)
Ca > 0
Wind speed > 5 knots
Waves height > 0.250 m
Tother > + 5% (waterjet sog, waterducts inlets, etc.)
S > 52 m2 (static wetted surface)

What I'm looking for is to check with an existing craft if the speed of 40 knots for this boat is realistic or not.

RANCHI Otto

[hmattos]

We manufacture fast Rigid Inflatable Boats, both outboards and jets( see www.explorermarine.co.uk) and we find that the best source for jet performance data is going straight to the experts - Hamilton Jet in New Zealand. Try their site www.hamjet.co.nz and submit a full data query. Their calculations are pretty accurate.

Regards
Hugh Mattos
Explorer Marine Devon UK