boat speed

hellow guys, i am new over here and this is my first post
These are my specifications of the boat
Cummins engine:NTA855
HP :325
Rpm :1800
Loa :16.23m
Lbp :13.18m
Beam :4.70m
Draft :2.44m

Now my question is this that how much speed(knots)will i get with these specifications?????

 

What is the full up weight of the boat; full fuel, water, max crew and stores?

 

There will be a very large difference between "top" speed and cruising speed.

At least if reducing the fuel burn by 1/2 or 2/3 is of use .

 

fuel capacity:1600 ltr
water:750ltr
engine weight:1296 kg
max crew 6-8 person
stores: 2
full weight of boat:15 tons

 

Assuming a moderate V bottom with a fair bit of running gear hanging, you'll be lucky to muster 15 knots (17 MPH). There are a lot of assumptions in this speed estimate, such as hull shape, long tons, deadrise, drive type, slip, etc. This speed suggests you'll be at the higher end of semi plane mode (2.6 S/L), so the hull should be optimized for this speed (tabs, hook, etc.) or trim could be an issue.

 

I don't think you'll go much beyond 9.0 kts. Your boat is not exceptionally slender, both in terms of L/B and in terms of L/D. One last question: is it canoe-stern or transom-stern?

P.S.
PAr was quicker. However, I sincerely doubt it will manage to get up to 15 kts at full weight. I might as well be wrong there, but I've seen similarily sized and powered semi-disp. boats barely get over 11 kts, and only after several props have been tried and the best one choosen.

 

Again Slavi, I was making several assumptions, particularly in hull form and agree it would be difficult to get up on her wave train with the weight, available power and 2.8 B/L ratio. Assuming she could claw her way up, she'd max out around 17 MPH in flat water, with no contrary currents winds, compensation for drag or sea state. I'm with you in that I don't think she'd be able to manage much more then hull speed (about 9 knots) with the available power.

 

what should i do to increase the speed(atleast 20 knots)???
should i use water-jet or what should be the gear ratio???

 

You'll need something like 1000 HP (without any weight increase) to get to around 20 knots.

Water jets or gear ratio won't do it. You use gear/propeller specs to get you engine to max revs only. With your current engine, about 13 knots is the best you can hope for. You might get 15 knots if you could reduce weight to 10 tons, but that is likely impossible.

Size, shape and weight determine whats possible, and with enough HP the possible can actually happen. If you need 20 knots then you need a different boat.

 

Using the same spec's as I did previously, I got 780 HP for 20 knots, but again, this included lots of assumptions about hull shape, of which we haven't a clue. It may be very likely that this boat just could do 20 knots, so without an idea of what this hull form looks like, it's really just a bunch of very loose guess work. I suspect it's a semi displacement hull and couldn't see 20 knots in it's wildest dreams, but this too is just a guess.

 

PAR
Yes of course, we are all guessing for some parameters, so there are a range of outcomes. But hopefully getting fairly consistent theme to the OP that his expectations are very likely too high.

 

well guys this is the photo of hull...

 

Information related to the thread

Dear Sprayed,

Could you please send two photos of the Hull's Astern by side and aft view?
It will be helpful.

 

And yes i forget to mention we have twin engine...

 

Few corrections

Dear,

I suppose that the total Power is 2 x 325 HP = 650 HP.......