Speed
 

32ft Deep V Bravo 1 twin 650hp Repowered with more hp and the Boat runs the same speed empty as it does full on fuel. [ 180 gallons } 5200rpm The Boat seems to not have the lift in the bow as before. Tried propping from 28 to 26 got more rpm less speed. Props are turning inward. We feel top speed should be 87-90mph getting 80 and thats the speed we got with the old 500hp motors. any ideas??

yes.... without knowing what you started with for total drag numbers , my guess would be that you have underestimated how much more power you need to go that much faster... i have stock 502's in a 38 gun.... assuming the published numbers for power and working backwards from the observed top speed gave me the total drag... the using that number i calculated how much MORE power i needed for a 10 mph increase.... it was about 125 hp PER motor... and that was to go from 65 mph to 75 mph...

now remember that the drag is the CUBE of the speed.... your starting drag number at 80 mph is much greater than mine and looking for another 10 mph after that is a lot of power.

thats all the theory... if you search this forum youll find that thread where all this was discussed with the math and links to various sites that have speed vs power calculators which wern't bad...

bottom line.... you are going to need a HUGE increase in power to get the numbers you are looking for , i think...

speed
 

OK I will look for them threads but, answer me this about your boat. Does it run the same speed full of fuel and 7adults as it does empty and just you? At 65-70 the bow is up, when we acellerate past that the bow drops. We used to be able to trim up until the nose started bouncing but now it won't do that, the bow stays down. Its like the added power is pushing it down for some reason. Thanks for your help we will look for the threads

turning inward will usually give stern lift. try turning out. and a good number to go by is 100 perside for 8 to 10 up to 90. usually. hooks , actual power, props , drive height, etc,,, will make for variables.
i raised the x-dimension on a bullet with 600 h.p. boat went from 69 to 81 . only addition besides x change was imco's standard length. just went with the more hydrodynamically designed case.

good luck.

this is the thread
http://www.offshoreonly.com/forums/s...highlight=drag

and no... my boat is considerably faster empty then full... what you describe sounds like a trim issue altho i would assume that you know all that which is why you are asking...

so no, i can't explain your imbalance and inabilty to get the bow up

Sounds like a hook in the bottom of the hull.

My boat is also faster when full of fuel & people. My reason is I have a bow rider & when boat is light in the rear it wants to lift up & bow goes down due to weight of the bowrider.

Thanks for all your input guys, sooner or later I will get it figured out ..I already tried turning them out and it was not better, so put back like the Factory had them. This is driving us Crazy