engine size

[fattysboat]

hi to all could you help me find the hp,needed for my boat ,sounds easy but having spoken to four engine supply company,s and got totaly different answers ranging from two 40 hp,to two,160 hp well there,s a big difference as you can see yet when i use a prop size program these hp,s give simlar through water speeds .the boat is 12 metres long full displacement 13 ton,s twin engine thats about the same info i gave engine suppliers.........manythanks fatts

[sailaweigh]

Go with the ones who quoted 40 HP. The others don't know what they're doing and will cause you nothing but grief.

[RANCHI OTTO]

according to my estimations based on sea trial results with previous designs are as follows for twin engines + submerged screws :


Vk (knots) / BHPtotal (metric)
------------------------
25 / 600
30 / 771
35 / 1005
40 / 1295

[sailaweigh]

"the boat is 12 metres long full displacement 13 ton,s"
Otto - being a displacement boat it is never going to achieve those speeds. A simple calculation for displacement hulls would indicate 40 HP Total would be enough, and if you go with 2 engines of 40 HP each, more than enough.

[RANCHI OTTO]

sailaweigh, you are right...I don't have undertood that the boat was a displacement one...my apologies !

[Vega]

.

Originally Posted by sailaweigh

Go with the ones who quoted 40 HP. The others don't know what they're doing and will cause you nothing but grief.

Of course, unless you want to run the boat occasionally only with one engine (in settled weather and for economic reasons) then you can chose 60 hp. With 2x60 hp, if you chose to cruise with the two motors, you will do it in a more silent way (less rpm).

[fattysboat]

thanks to all for taking the time to reply..the boat is of heavy displacement type so about 8/9 knots max no matter what engine type..the confusion lies in the hp of the two units i choose.i thought it would be a set rule a simple case of ask and find out ,,,,but the answer seems to swing from supplier to supplier depending on what they sell,,,,,but for me this is a big *spend*.i can get two 40hp,engine,s for the price of one 100,hp,engine but the boat must be sea safe in all respect,s?engine wise. i have space to turn ,from 18 to 26inch blades manythanks fatts