blow out?

[need4speed2]

i ve got a 91 bullet 20 vee 2.5 245,ive been playing with,it has factory cle im going to send ot titus this winter for mods but i have been steady raising the motor a little.last time i run it i had it 1 inch over pad,now i got it a 1.5 i was just wondering am i getting to high for stock case?any chances of blow out?i am running a 3 blade 29 spinelli.thanks bobby

[Frank Molé]

my stock cle blew out at about 91-92:cool:

[need4speed2]

frank how high was propshaft? thanks bobby

[chris_lacey]

Normally blow out is an issue with substantially submerged gear cases. At 1.5 above, blow out shouldn't be an issue into the 90's. A skeg mounted Torque tab (your CLE may come with one) helps raise blowout speeds beacuse it prevents crabbing. A gearcase running straight won't blow out.

[whipper]

:eek: If your at the top end of a run and you bump the trim for some more mph and your RPM increases but your speed does not you are at the max speed. Bump that one back down because if ya hit a little wave at that trim angle who knows what will happen! Better safe than sorry.Some hulls are more forgiving than others in a blow out but why tempt it. Another way to tell if your over trimmed {that is what causes blowout} Is when you bump the trim and your bow starts dipping to the starboard , port for others. When this happens carfully back off because your on the cusp if its not to late. I run say to 88 mph which is faily regular weather permiting and have gone 90.7 once. Every time since that cool day in spring that I bump the trim at 88 to get to 90 again the rpm went up 50 and the gps never mooved a point. So to be safe I leave well enough alone. In the fall as water and air temps decrease Im sure that 88 will be 90 again.Engine hight even or above is a set up isue but combined with the trim angle is what will blow ya out. If at a lower prop shaft hight than 1.5 you needed less trim to achieve the same top speed than you dont need to be that high. Hope this helps. James

[chris_lacey]

:eek: Another way to tell if your over trimmed {that is what causes blowout} James

I beg to differ.

Blow out is caused by a crabbing gearcase. At speed a vacuum is formed on the low pressure side. When it gets to the point that the vacuum bubble becomes big enough to hit the exhaust, the exhaust floods into the vacuum bubble and then floods back into the prop blades. The sudden lack of traction (blade slip) and the crabbing gearcase make the boat suddenly turn right. How fast you are going when this occurs determines how bad the loss of control.
A gear case that is substantially out of the water doesn't have a low pressure side.

The prop ventiation that you were describing is similar, but not blow out.

[Jay R.]

There are many different causes and types of a "blow out". the standard deffination is the blow out cris described, but it can also happen with a gearcase that is not crabbing. when you loose traction from being over trimmed and lossing the bow the same effect happens for a different reason. the first thing you have to do is determine whats happenings, then go from there. since your just asking hypotheticly cause of what your running.
you need to fiquare out if you gained any speed when you went up, most boats like to be about even with the pad, you may stand to come down a little. with out enough set back my vector would drop the bow and kit to the side. if you experense that then your close to having an issue.