Can i use an EMAX CF2805 on a 12inch boat? will it be enough power?
http://www.emaxmodel.com/views.asp?hw_id=156

Ya.... Of course you can use it.

Neil, if you use a 2840 Kv motor on a 12 inch boat, it will fly out of the water and become airborne unless your boat weighs around 1Kg. 

Jokes apart, what is AUW of your boat and what prop/cell combination are you thinking of using. Most importantly what kind of a boat are you planning to build?

P.s. It's good to see that Boat building is flourishing on the forum for the last few days. Keep going sailors, the pilots have been kings for too long.

+1 VC sir.....

Quote from: VC on June 23, 2013, 09:40:54 PM
Neil, if you use a 2840 Kv motor on a 12 inch boat, it will fly out of the water and become airborne unless your boat weighs around 1Kg.  

Jokes apart, what is AUW of your boat and what prop/cell combination are you thinking of using. Most importantly what kind of a boat are you planning to build?

P.s. It's good to see that Boat building is flourishing on the forum for the last few days. Keep going sailors, the pilots have been kings for too long.

A racer boat like the mini mosquito, 5.4 knots is the speed i want to get is this motor enough? battery will be 2s 800 mah, ESC 25A, total electronics weight 300 gm max
AUW 550gm, Prop 3 blade 25mm home made aluminum prop

Should i reduce the weight? to get that speed? i dont know of any calculations so if anyone could help me out i would be grateful

Make it and try it out. You could always upgrade later if needed

Which servo should i use for rudder? i have decided to build a 15" boat, will a HXT900 suffice for the rudder system or do i need a more powerful servo. If i do then what weight class  and torque should it be?

Will a 15 gm servo suffice? at 5.4 knots(10km) is it strong enough to handle such force?

yeah a 9g will suffice... unless your building a large boat, then use a servo greater than 15g or so.. look for high torque... and keep the rudder blade long vertically... the more horizontal area the rudder is, the more strength the servo requires to move it

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Thank you aniket, The HXT900 is okay for 15" right? rudder will be 3.5 x 2 cm

yeah... it should work... make it a parallelogram

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Neil, I've replied to your queries

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Will this Setup give me 10km on a 14" AUW 500 - 550gm? Mini Mosquito type speed boat?

Prop - http://www.hobbyking.com/hobbyking/store/__12695__Prop_Nylon_1_4_X_27.html - 1.4X27 prop
Batt - http://www.hobbyking.com/hobbyking/store/__9276__Turnigy_800mAh_2S_20C_Lipo_Pack.html
ESC - 30A will put up details soon
Receiver - http://www.hobbyking.com/hobbyking/store/__12901__Hobby_King_2_4Ghz_Receiver_6Ch_V2.html
Motor - http://www.brchobbies.co.uk/catalog/product_info.php?products_id=714 - EMAX CF2805
And HXT900 servo for rudder

yeah dude... it's not a plane... you can go for a higher mah battery.... receiver doesn't really matter, you can use any receiver... 30A esc is good, though it will work with a 20A also.. prop seems fine... 

How bout a 1500 mah batt? or 1300mah?
yeah i am seeing if anyone wants to sell their 20 ESC for cheap. I have someone so will get a 20A instead of 30A
will a CF2812 - http://www.emaxmodel.com/views.asp?hw_id=157 - motor also work? i can put a 3s pack then but even that will be 1000mah

Thanks for info Aniket i really appreciate it, i will need a bigger prop if i use the CF2812?

Which foam is best for making V hull boats?
foam board is too rigid EPP doesnt come in very huge thicknesses so which foam is best?

use sunboard

Sunboard? isnt that the same foam you built you neptune with sir?
Any other names for it?

yes

hey! buy a 30a esc... no point taking a lower power one... higher is okay

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Sunboard, Sunfoam, PVC foam board are different names for it. Cobblers, sometimes, use it for making shoe insoles. PM me your address and I will send you samples.

Thank you very much VC sir
and sanjay sir