Bravo I - Any ideas on this?

[Havasu47]

Sorry if this sounds blunt, but...... a 26' Wellcraft, blown BBC, 3 BLADE PROP
Put a 4 blade Bravo 1 prop and the cavitation will go away. The blower creates large amounts of torque at low RPM'S. Just when the boat rolls over is when the torque curve comes on strong. If your trim system isn't working properly get it fixed of course, but it will still blow the prop away with a 3 blade.
just my .02 of course

[75spectra]

This sounds exactly like what is happening to me. I'll get a nice hole-shot and just as soon as the bow starts to bow down, the "blowout" occurs. I do have thru-hull exhaust.
Dumb question, but what exactly are the exhaust bellows? Those butterfly-looking valves that redirect the exhaust on my captain's call? We might be getting somewhere here.... Thanks for the idea'rs, guys...
Ok, if you have "captains call" exhaust then you need to replace the bellows with a exhaust tube. This is called for in Mercruisers service manual. The tube might be there if the captains call was installed at the factory. Tilt your drive up and look underneith of it, you should see a large bellows thats the u-joint bellows and the lower one is the exhaust. The small one on the right side has the shift cable going through it. If you see a "tube" that is open and seals off when the drive is down then you need to look at a diffrent prop that prevents blow-out?

[Speedin' Ian]

Sorry to hijack the thread but 75 Spectra has me thinking about my own boat. On my 25' Commander I have thru hull exhaust and I think my drive still has exhaust bellows installed on it. Is this bad? I haven't notices any problems getting on plane, and it has been set-up like this for almost ten years. How does having belows create a vaccum?

[75spectra]

Sorry to hijack the thread but 75 Spectra has me thinking about my own boat. On my 25' Commander I have thru hull exhaust and I think my drive still has exhaust bellows installed on it. Is this bad? I haven't notices any problems getting on plane, and it has been set-up like this for almost ten years. How does having belows create a vaccum?
If the "U"-pipe has been removed and blocked off then the prop will create a low pressure area inside the drive when you start moving water away from the prop. The Bravo drive has pressure reliefs just above the cavitation plate, feel for them they are there they go up into the drive. When these reliefs finaly break the vaccum some props will instantly "blow out".... NOT ALL BOATS HAVE THIS CONDITION! This info is in Mercruiser's service manual. I remove all exhaust bellows from any boat we put thru hull exhaust on. Silent choice is diffrent, for this you remove the bellows and replace it with a "exhaust tube" this tube is a Merc part.

[Rev. Williams]

Sorry if this sounds blunt, but...... a 26' Wellcraft, blown BBC, 3 BLADE PROP
Put a 4 blade Bravo 1 prop and the cavitation will go away. The blower creates large amounts of torque at low RPM'S. Just when the boat rolls over is when the torque curve comes on strong. If your trim system isn't working properly get it fixed of course, but it will still blow the prop away with a 3 blade.
just my .02 of course
I'd have to agree with this comment......... I run a 26p 4 blade B1 and I can blow it out when I come over on plane. It catches up quick once the boat lays down, but for that brief few seconds I get nothing from the prop.
In ***boat West there is a thread going about 28p props and within that thread someone posted a number to a place that lets you test/rent different props to see what works best. I'm gonna test the 28 on mine, I'd suggest a 24-4 or a 26-4 for what you have.
Good luck and have fun with it.....
BTW: when I was growing up we had a Wellcraft 21Nova. Talk about a smooth riding boat!!

[Shallow Minded]

Sorry if this sounds blunt, but...... a 26' Wellcraft, blown BBC, 3 BLADE PROP
Bluntness is ENCOURAGED. I just want to figure out how I can get a little better take-off and optimize the power I'm making. I've spoken to another guy who runs a very similar set-up and he's running a 24 pitch, 4-blade. My boat weighs about 6500 lbs which might have something to do a very tame pitch. Considering I'm only running 4800 RPM's at WOT, I'm a little gunshy about stepping up to a 24.
Also, as for the bellows, I'll take a good look at it tonight. I'm sure nothing has ever been altered here, just a standard Silent Choice set-up. I really appreciate the info.
And yes, these Nova's ride like a Caddy...

[Shallow Minded]

From the looks of things, the exhaust bellow has been removed. I compared my outdrive to the B1 on my brother's boat and I did NOT have the flexible, connecting tube from the transom to the actual outdrive. I'm assuming that is the "bellow."
Also, sounds like I need to put a 4-blade prop on my X-mas list. Anybody have a 4-blade, 22 or 23 pitch laying around? Thanks.

[superV]

I have owned thre Nova's 26,27 and a 23. With that set up you should be running a 26p clever.The nova's need the setern lift! And I would also look into your motor 4800 with a 23? That where mine would run wioth a 26P Just my .02

[spectras only]

I'm surprised you're only turning 4800 with 23p and a blown engine. I've got 6.2's , n/a [320HP at the prop] and turning 5000 with Bravo1 4 blade, 15X26p . My boat is ass heavy with the twins ,but no problem getting on plane with the K-planes.

[Havasu Hangin']

I'm surprised you're only turning 4800 with 23p and a blown engine. I've got 6.2's , n/a [320HP at the prop] and turning 5000 with Bravo1 4 blade, 15X26p . My boat is ass heavy with the twins ,but no problem getting on plane with the K-planes.
Off the subject...
...are you gonna change your screenname to "spectras sometimes"?