offshoredrillin

bingo Steve, therein lies your problem, as you are getting up on plane trim your drives out you should run an easy 65. keep your tabs up, start out with drives at 2 ease up on plane and trim them out...as you are going out you will pick up speed, when you stop gaining speed or it slows down, trim back in, it will take you some time to find the sweet spot, but have at it man...

thisistank

Show some pics of the boat!

stevesxm

ding ding ding

tried two trim positions.... numbers meaningless i guess but tried some and then some more. one drive pump too weak to move the drive at speed so have to stop to make adjustments... either way, difference exactly what you predict... boat just took off . now 4900 and 62 mph easy in not great conditions... lots of flying involved.... went right past where i normally turn for home and was some miles around the island before i could focus on the gps and see where is was... oh well...

so ... 'problem" clearly identified as pilot error. will erbuild the one pump so adjustments possible at speed and report back...

and to all that offered suggestions i thank you and wish you good holidays and if you ever get to sint maarten, look me up

am sure there will be more questions coming and appreciate the opportunity to participate.

MrCIG

iTrader: (1)

A little trick I learned when you have a weak pump, is to pull the trottle back on the motor with the weak pump and hit the trim button the drive will go out. Not a fix but it does make it drivable for the time being. Trim makes a big difference on these boats.
Have fun.

Mark

stevesxm

seems so.... am i to assume that by kicking the drives out a bit it picks the nose up out of the water and simly makes less hydrodynamic drag ? horsepower required is a cubed factor to overcome drag so can clearly see how reduced drag would make huge dif but would have thought that nose up aero drag just as bad.... but guess not.... at anyrate am immensly pleased and now have place to start to start dialing it all in... thx again

GLH

Trim out till you blowout!

Get a GPS and finetune your trim till you max out on speed then mark your trim indicators.

I had that exact engine combo on a Cafe. a gun should be close in speeds if not fater from what I heard and it ran 67 with labbed 4 blades 24" at 5000 RPM

With the 3 blade 23" it came with it ran 65

PM Otis he had close to that set up on his Gun a few years back and was close to 70.

Hope this helps.

Panic Button

The fastest I've gotten in my Cafe on GPS (502 Mags, with 0 hours) is in the upper 50's. Running 23p Mirage's and maxing it at 5200 rpm's & trimmed out. How you guys doing it?

stevesxm

dear panic...
if you read the thread complete youll see that i am certainly no expert on these matters...had to be instructed in the most basic sense... but i think your answer is self evident. prop pitch is essentially the same as rear end gearing in a car... you run less pitch and you need more revs to go the same speed if everything else remains the same. you have to remember that speed is STRICTLY a function of drag and ( as mentioned) the hp required to overcome drag is the cube of the extra drag... so .... what happens when you do less prop is you get more revs , which gets you more power ( assuming not out of power band) which gets you a by a little drag which makes you go a bit faster... in your case, if you look at your numbers, they are essentially what mine WOULD have been BEFORE the trim adjustments and if i had simply done 23 p props.

bottom line in my best engineering opinion and based on the most recent experience, asuming the motors run well ...and sounds like they do... you need to get 24's on the thing and get the drag down substantially somehow...either by trim etc ( like my issue was ) or whatever your boat needs specific to its manufacture. we KNOW that the 502 mags will pull the 24's on a 38 ft 9500 lb boat. thats a fact... so if your mags won't and they run ok then the only answer can be that there is a drag problem that you have to address... just like i had to. drag is the enemy and it never sleeps

my case CLEARLY illustrates the need to have the PACKAGE correct... no single magic bean element...

MikaylaHunterCig

I owned the same boat - a 96 TG W/ 502 efi...
It would run 65 at about 5000 rpm w/ bravo 24p .
I tried 26 labbed bravos and it slowed down as the RPM was not high enough.
Everyone is right with the trim- if the motors are fine and nothing has been modified with your bravo drive height/length then trim out more .

Dave

BTW- The same boat went 78-80 once i installed procharged 500efi's- besides the top speed the boat handled much better with the needed power increase.

stevesxm

funny you should say that ... tuned in today to say that am now at 65 on the gps at 5000 ...maybe 5100 due a bit more screwing around.... not certain there is anymore but will poke at it a bit and report back.... conditions better today but still on full tanks so carrying 15 or 1600 lbs of fuel while doing this testing...

prev owner says they never got over 62 with 650 hp 454's .... which means one of two things.... ( or both) my rant about dyno numbers has another case history or those guys wern't smart enough to ask YOU guys what the problem was...

had my first official run in w/ the coastguard today.... was out testing and went by this zodiac looking thing with a couple big outboards and he started after me... THOUGHT was just a couple local guys wanted to race... only after i turned around and headed home that realized they were CHASING me... no tickets ..no fines... the locals here ( caribbean) are pretty cool once they realized there were no drugs or illegal immgrants involved...