2 aerate or not?????

[Wayne Pennell]

The slip is a measure of efficiency on plane. When talking about coming on to plane slip isn't really applicable. Aerating does however allow the props to slip or more accurately stated ventilate. When the prop ventilates it allows the engine to rev up. Years ago many boats would ventilate on their own while coming on and at times had a negative effect but, now days with modern propellers and ultra high speed set ups a controlled ventilating is a must. Many thru the hub exhaust propellers have holes[ some with adjustable sizes ] to allow you to adjust the ventilation to improve a hole shot. Speed master drives are obviously different and aerating tubes are the way to get air in behind the leading edge of the prop to get it to ventilate.

For example a 525 and #6 boat like Amsoil can swing { not sure exactly } like 34 inch propellers and can go 130 some miles an hour. Say 3000 rpm's is 75 mph and 5300 is 130 { just guessing }. The bottom half of the propeller is doing all the work. The boat is running on plane and has little drag. Now to get it there with the available power, gear ratio, prop selection, entire bottom and drive dragging, entire prop biting, in a rpm range well under the power curve you need to slip the props to allow the engine to gain rpm's and get into its significant power range.

So how would a vee hull and standard bravo drive react to a tube....if it's not set up near the surface? It seems in theory it will still introduce air at the leading edge of the prop causing it to rev higher thus being able to run a higher pitch prop which would create more speed? Or would it just make the slip be unmanagable?

[Ratickle]

I'll see who knows, but my gut feel is that an aeration system on any drive would only work on surface piercing types. They load up when they are fully submerged underwater, and once up and moving they aerate themselves automatically. I cannot imagine a scenario where the submerged style of a Bravo would need any aeration because it is designed to not aerate, ever.

Now, one of the new IMCO Bravo surface drive would be a different story...

[MOBILEMERCMAN]

It seems in theory it will still introduce air at the leading edge of the prop causing it to rev higher thus being able to run a higher pitch prop which would create more speed?

The tubes allow it to ventilate { slip } to get on plane. They do nothing once the boat is on plane.

A V with Bravos { any Bravo for that matter } is a completely different and unrelated situation.

[Wayne Pennell]

A V with Bravos { any Bravo for that matter } is a completely different and unrelated situation.

But how would a bravo react to one?

[Wrinkleface]

But how would a bravo react to one?

Don't know there's room on a Bravo cav plate, way 2 short!!!

[Wrinkleface]

starboard!!!!

[Bobcat]

Plenty of room in there for a small family.

[Wrinkleface]

Plenty of room in there for a small family.

When Connie kicks me out of the sack cuz she has gas, I'll go lay in the bilge w/ a VO & coke w/ some REO crank'n on the stereo!!!! The "Life"!!!!!!!

[Wrinkleface]

Hey Rat, how do ya like that pic ya punk!!!!!

[Ratickle]

Hey Rat, how do ya like that pic ya punk!!!!!

So who did it for you??????

[Wrinkleface]

So who did it for you??????

NOYFB!!!!!!

[MOBILEMERCMAN]

But how would a bravo react to one?

It will let the props free wheel as it trys to come on plane. It is possible they would prevent it from getting on plane. Once on plane props need clean water to work effectively.

Does it labor to get on plane now? If you push the throttles all the way forward while putting it on plane how high will the rpm's go? What props are you running now?

[Wayne Pennell]

Does it labor to get on plane now?

Mine, single engine, gets on plane fine

If you push the throttles all the way forward while putting it on plane how high will the rpm's go?

It will rev to ~3500 rpms during take off.......and that is full power to get it there

What props are you running now?

Unlabbed 28P B1.

My plan still is to labbed a prop..........but my question was more to how a bravo would act with one. You kind of answered my question when you said the prop needs clean water to perform properly....it probably would let it spin more RPMs but it would have a negative affect? I already have a stelling extension box in middle position..so raised 1"...and an IMCO 2" shortened lower.....so how far below the water is the cavatation plate while on plane? It is 3 1/2" below the bottom.

[MOBILEMERCMAN]

so how far below the water is the cavatation plate while on plane? It is 3 1/2" below the bottom.

The cavitation plate should be well clear of any water.

Parallel the prop shaft with the bottom and measure your height. That should be about 3 1/2 incahes below on a 80 mph boat.

Some propellers have the plastic plugs or holes in the prop near the leading edge. They are there to adjust the slip getting on plane. If you have them what ever size hole you have now a little larger will allow the R's to go up thus giving it a better hole shot. Not that it is really that important if it is not laboring now. If it was laboring adjusting the slip could be beneficial. The tubes on a surface speed master type drive are there because in some set ups it will only turn 2500 r's and it bogs and never comes up . The tubes allow it to rev up and get up on plane.

The thing is if the height is up and the set up is good usually it slips too much. If it isn't slipping at all the drive must be pretty low in the water. All the shorties and boxes raised do little when it starts out low. Sometimes the best thing to do is actually raise the cut out and re rig the engine to get the height where it needs to be.

[Wayne Pennell]

The cavitation plate should be well clear of any water.

Parallel the prop shaft with the bottom and measure your height. That should be about 3 1/2 incahes below on a 80 mph boat.

My prop shaft is 3 1/2" below the bottom of boat.

No pastic plugs on my Bravo 1 propeller, but the boat does not have an issue getting on plane.

[Ratickle]

Sounds like th perfect height. It looks as if you may have the same issue that I possibly have. The thick part of the lower is so close to the water it actually may come in contact as the water rises behind the transom.

[Ratickle]

My plan still is to labbed a prop..........but my question was more to how a bravo would act with one. You kind of answered my question when you said the prop needs clean water to perform properly....it probably would let it spin more RPMs but it would have a negative affect? I already have a stelling extension box in middle position..so raised 1"...and an IMCO 2" shortened lower.....so how far below the water is the cavatation plate while on plane? It is 3 1/2" below the bottom.

Surface piercing props are designed totally different from a normal Bravo prop. The surface pierce prop is cavitating all the time because it is leaving the water surface and re-entering the water surface as it rotates. Allows much larger pitch and diameter than a sub-surface prop like the Bravo.

So, I believe, to run a surface peirce prop on a Bravo, it would have to be a totally different design. Then , with the drive raised that high and the totally different design prop with the l;arge diameter and pitch, you may have to run n aerator to get the rpm's up into the range where the boat would come on plane.

I wonder what IMCO says with their new surface pierce drive Bravo design? Has anyone talked with them?

And last, am I all washed up in my thoughts?

[Wrinkleface]

Surface piercing props are designed totally different from a normal Bravo prop. The surface pierce prop is cavitating all the time because it is leaving the water surface and re-entering the water surface as it rotates. Allows much larger pitch and diameter than a sub-surface prop like the Bravo.

So, I believe, to run a surface peirce prop on a Bravo, it would have to be a totally different design. Then , with the drive raised that high and the totally different design prop with the l;arge diameter and pitch, you may have to run n aerator to get the rpm's up into the range where the boat would come on plane.

I wonder what IMCO says with their new surface pierce drive Bravo design? Has anyone talked with them?

And last, am I all washed up in my thoughts?

Washed up, yes!!!! Hey, a buddy of mine on this side of the state just put 2 of the brand new Scx4's on his 46 Black Thunder!!! testing will start soon!!!! can't wait!!! hope it works well 4 him!!

[Ratickle]

Yep, I cannot wait to hear how it performs and the differences in handling. One of the issues Doller had with my boat on the conversion to 3a's from Bravos was they had to set them deeper than they wanted due to the swim platform. A switch to 5's may change that if his BT shows really good improvement.

[Wrinkleface]

Yep, I cannot wait to hear how it performs and the differences in handling. One of the issues Doller had with my boat on the conversion to 3a's from Bravos was they had to set them deeper than they wanted due to the swim platform. A switch to 5's may change that if his BT shows really good improvement.

U have pix on your phone ya punk!!!