353 Fastech- difficulty getting on plane
 

I recently purchased a 2004 353 fastech with 525EFI's, XR drives with Stelling boxes, and lab finished 5 blade 30" maximus props. Problem is the props "blow out" when trying to get on plane, and I'm concerned that I will damage the drives. I have tried drives tucked in and out, K-planes up and down, but seem to have the same problem every time. Any suggestions for drive/tab trim settings? I am considering re-propping if I can't work this out. Boat handles great once on plane!

Standard lowers or shorties? If you have shorties it is a penalty for trading high x and speed for planing ability.

Start with the drives all the way down, and tabs 1/2 to 3/4 down. Roll on the throttle to about 2800 to 3000 and let the boat work it's self on plane, it may take longer than the boat you are used to. When the boat planes out start trimming up tabs and drives without adding throttle, rpms should rise up another 700-1000 just from trimming...now you can get on it :)

Unless you are on the limiters wide open I would not make a prop change, seems to me someone did their homework if you have 5 blades on there

try turning from left to right it sometimes help getting props to bit a little bit ... had this on a 2008 35 fountain staggered 525... ran 98 mph top but pita to plane...

Thanks for the advice. I've only taken this boat out twice, and couldn't figure out the right combination of trim and throttle. Last boat was 275 baja with stock 496- this is like learning to drive all over again!

The problem I had with my Fastech 271 and this problem turned out to be the dual pick-up drive shower I had on my drive. I switched to a single pick-up style drive shower and my prop no longer blows out. I have a single engine and you have twins, but you may want to take off your drive showers and see if it makes a diffference. Jeff Wurl

trim tabs @ 2,,drives all the way in put the sticks @ 3k and wait for the bow to start to roll over ,once you see the rear of the tail start to flatten trim out a bit then move sticks to 3500 rpm,,trim as needed..you have to be patient with a stepped hull..

Are the diffuser rings cut off the props?

I run IMCO boxes, 1" shorty IMCO lowers and labbed 36p Bravo props, and it would not plane on the 36's after I cut off the diffuser rings. It ran the fastest with no rings, but the props were useless without them. I had BBlades weld rings back on and the dont blow out at all.

Funny thing is, I also have a set of stock 34's with no diffusers and it planes fine. Very little blow out, but never an issue getting on plane with any kind of load. Maybe the lab has something to do with it??

Maximus props come with a huge diffuser ring, at least the set I tried did, but maybe someone trimmed yours down, or cut them off completely.

My 353 runs its best, and carries its nose better with as little diffuser as possible. Still playing with the 36's, I cut back around 1/4in of the 3/4in diffuser that they had, going to trim back a hair more, and see what happens.

LE

The diffuser rings appear to have been modified. Can't tell if lengthened or shortened.

Post a picture of the props....

How about the lowers? Stock or imco/ssm?

Drive showers?

We can't help you if you do not answer the questions :D :lolhit: hahah

stock XR's & no drive showers from memory when I saw the boat a few days ago.

Yes, correct. Stock lowers, no showers.

Apparently, some cavitation is normal with this setup. I have run the boat 5-6 times now, and am able to get on plane with minimal slippage by lowering tabs fully and tucking in drive. Tabs full up as soon as bow drops, then dive up to 2-3. Takes a long time to plane (compared to old 27 Baja), but runs great once up. Thanks for the help!

There is what has been refereed to as the "celery stick" at the mounting point of the trim rams to drives.
This can be rotated 180 around to the front of the pin which lets the drives tuck further under. Helped my friends 382 plane faster. Has showers also which i think add to the cavitation out of the hole.
Tabs at about 2 was about all it would like.

# 37... Ok the real name is "Trim Adjustment Insert".
:)

Any luck?

You really should not need to make mechanical trim/tab mods unless you are running a race boat. For some time, I ran the bravo 30p props which were stock on my 99 353 w/hp 500s / bravos / boxes and the tabs were not needed at all to get on plane. I have tested with 28p 3 blades and the nose ran higher but the blowout/planing became a problem. Once you move to a more top end prop you will use your tabs. As other members have suggested, your props may have been significantly altered so you could be running a very different profile than you think and the blowout indicates too much slip/air/turbulance around the props (or over throttling). As a matter of best efficiency, you should always launch with the drives fully in. See if you can get a set of stock props for your year and start from there. Then work with a respected prop shop or Merc racing for the necessary changes (if any are really needed). Some mods may only yield 1-2 mph but deliver all kinds of undesireable launch and midrange characteristics - your choice. Lastly, if you are planning on any significant horsepower upgrades, your modified props may no longer be optimal as it sounds like they are now. Good luck and keep us posted!