Prop blowout. Any sugestions
 

Ok I made my first run today in my older boat project, and am fairly new to this boat ,its a 32 baja, 496 ho, trs, bravo 1, 4 blade 26 p. problem is on take off drives down, if I go any faster than 4 sec. idle to full , the props blow out, same thing in a full throttle turn, slight up drive. Dose the drive angle (toe in - toe out) have any thing to do with this, or altitude ( I am at 5,400 elevation) any help would be greatly appreciated, Thanks.

force320
 

it all has to do with set up ,conditions and the props as well,

give me a call and we can TALK PROPS AND ALL your concerns.

we can get you dialed in ,will be more than glad to help ,

Thanks Darin:)

Are your props lab finished? Sounds like they are. If so you are right about where you should be for a top end set-up. Did you raise the X dimension of the out-drive? I would be surprised if you could blow-out a stock Bravo 1 with TRS drives at a normal drive height.

Try some toe-in. Start with 1/8" toe-in and see if you notice a difference, especially in turns.

Do the props blow-out in high speed turns at WOT or only at low speeds?

Matt

Altitude will definetly have something to do with it. If you don't have a diffuser ring on your props, adding one will help. So will adding some cup near the root of the blade.

cord
 

we are hiring :D you the man!!!!!!!!!!;) and add a little on the tips.

hey darin sent you a private message about prop work. let me know...

these are brand new bravo 1 solid hubs. the trs drives are in stock location, I dont know much about x dem. and what is a defuser ring.( ai know ..beginer), the drives are set at 0 toe ( strait ahead).

Now that's real interesting. Bravo 1's are amoung the best (if not the best) planing prop out there. It will have a diffuser ring built in. My thinking is that you have some other issue...

how about switching drives and turn props in.

I had a 26' cat with a high x, and ran into the same problem running a labbed 32 4 blade. We added some cup to the prop and it helped.

I eventually went to a 1.35 gear ration and dropped a couple inches in pitch. That was a cure to the problem, but lost some mid range acceleration.

I would try adding a little cup, it might be your cure.

let me know if I scared you off:eek: :D

I just saw a report in Poker Runs America that says you should run 3/16 of an inch "toe out". go figure......... I ran my boat with a tiny amount of toe in. Who knows any more?

Reed,

We have done a lot of testing with race teams and changed the drive alignment both in and out. Sometimes as much as 5/8". Very interesting results.

It comes down to trying different alignments and note how the handling of the boat changes. With different alignments we would sometimes get better top end, sometimes better acceleration and other times get better handling. With the information we learned the boats would be set up for a race depending on the prop, course and water conditions.

Matt

toe in are toe out also matters which way you spin the props, in are out, this will affect the drive a little,

Check and see if you are running the exhaust baffle connector hose from the gimbel to the drive. You will find it with the drive in the trailer position.

If you aren't running silent choice you will (should) have it capped on the inside transom gimble plate. If the baffle hose that connects the gimble to the drive is off or has a crack in it, it will allow air to run through the drive and out the back of the prop creating blow out.

Some hulls will run faster with them off because it reduces prop drag but can also create blowout.

Interestingly enough, on our race boat (28 saber, small blocks, bravos) we used to run them off in fresh water and had no problems. In salt water we had blowout and had to seal the exhaust inlet on the back of the drive. It solved the problem immediately.

Whirlygig

Oh , interesting, I am full time through transom exhaust and the drives don't have the exhaust hose on them. but what would be the difference if air got sucked down and out compared to exhaust gases, or would the amount of water mixed with the exhaust make any diff.

i had an older 280 baja years ago, and it would always blow out the props when you try to take off if you went to full throttle before you planed the boat. I didn't have to go to full power to get on plane only about half throttle, so my fix was i never went to WOT when i was trying to plane. a 320 is not a drag boat, ease into the throttles and get the nose and props biting before you throttle up to WOT.

Don

Force,

It wouldn't make a difference if you were running your exhaust through the drive with or without water. Since you are running staight out the transom and don't have the gimble exhaust hose connected I would suggest plugging them.

Take a piece of plastic. Cut it slightly larger than the exhaust port on the drive side. Duct tape it to the port, it sticks out a little so you should have adequate access though it's tight. Run some zip ties around the outside, over the tape, for insurance. This should do a fine job of sealing the port (much cheaper than purchasing the hose and easier to put on).

In your current setup, as the propeller travels through the water it creates drag. The water that travels over the prop is pulling air from the exhaust port that is open, through the drive and out the prop. You now have a solid stream of pressurized air running out the back of the prop lifting the water away from the prop hub. This is even more dramatic if you are running diffuser rings.

BTW, Chromecat is also on the money. Most manufacturers run their X dimension as high as possible to maximize boat performance. It is not uncommon for many high performance powerboats to break loose a little when you hammer them from the start. They also dial the boats in with particular props which over time get replaced by owners with something different. Looking for more top speed they sacrifice holeshot. Look at comparisons between bravo and hydromotive props, you'll see what I mean. The 320 is not a light weight and the amount of torque and pressure you are putting on your drives and motors during a full throttle start is agonizing. Your drives will last a season or two longer by taking it easy getting on plane.

The exhaust plug isn't a fix all as the race boat blew out getting on plane even with the exhuast hole plugged but it helped tremendously, especially upon re-entry. There is also quite a bit of prop technology that exist that will help the problem if this doesn't. This is just a quick and inexpensive way to try and help the problem, if it doesn't help, call the guys at Houston Prop, they will hook you up.

Whirly

spoke with a merc. mech. today, ( had the boat in the shop for a warranty oil filter hose leak) and he said that a possible cause could be at the drive drain plug on my TRS drive , the plug is recessed and creates a start piont for a bubble of air to travel back to the prop, I gess they fixed this problem with the bravo 1 by putting the drain plug in behind the prop. any one here of this?