Twin bravos slipping Formula 311sr1
 

Hi all,

boat is a 1988 Formula sr1 w twin 330hp 454s and bravo drives.

The problem: at around 3k rpms on both motors the rpms shoot up and the boat stops accelerating. It feels like a spun hub on the props but I swapped out props to solid steel props with no hubs and the issue persists.

It buries the ass of the boat like it wants to get on plane but can’t manage and as you apply power when it hits 3k both sides lose their bite, and the engines rev up to over 4k.

Next guess would be engine coupling to the bravo drive?
Is it likely that both would react exactly the same at the same rpm on both motors?

A month or so ago I did manage to get it on plane and run WOT to 4.4krpms without but was only able to get to 28mph when this boat should be around 60mph at WOT 4.4k.

I have the bottom scrubbed every month by a diver so it shouldn’t be a barnacle issue from what I can tell.

Any help here is appreciated.

sounds like you have a couple hundred gallons of water in the boat.....:lolhit:..........so the boat have never ran correct ? 4400 revs @ 28 mph something is all wrong, what are the props

lol that’s about exactly what it feels like.

When I bought it the guys said it ran fine but had been sitting for a few years. It had a hole in the port side ex manifold.
I ran it home on the intercostal on one engine and was having the same issue (blowing the prop out over 3k) at that time with the one running engine but did manage to get on plane with one motor but never went above 3500 and it was a short run.

Since then it’s been on the water behind my house. Scrubbed monthly for barnacles. Put a new ex manifold on it and had to swap the port side raw water pump.

Since then I’ve only been able to use it a couple hours at a time cruising the canals around Fort Lauderdale at minimum wake.

Original props are 3 blade 14-5/8 23p. These have the rubber hub.

In an attempt to check if it was prop hubs, I bought a pair of 23p cleavers that are solid steel with no rubber hub.
Having the exact same issue with these which leads me to believe the issue is not the props.

coupler is slipping by the sounds of it or the cone clutch in the drives.ever smell any rubber burning?

I haven’t smelled any rubber that I’ve noticed. Any tips on diagnosing this or determining if it’s the drives vs the coupler?


And another request, does anyone know of a good shop around Fort Lauderdale that will work on I/O boats? Everywhere seems to be outboards only now days.

outboard only like in
you simply see them everywhere
or more like
They refuse to work on an inboard boat?

refuse to work on inboards. I’ve had the same trouble with my inboard Bertram 28.

But back to the main topic, any tips on diagnosing engine coupler vs drive clutches?
Id like to know the problem before bringing it in anywhere to avoid any confusion or issues.


This thread seems to indicate that if the engine coupler goes, it goes completely. Unlike my situation where I can still drive around.


any thoughts?
https://www.offshoreonly.com/forums/...ne-clutch.html

I find it hard to believe that both engines and drives are having the same problem at the same time.

Silly question, are the drives going all the way down? Could something be stuck or jammed not allowing them to go all the way down? Some boats will fight getting on plane with the drives trimmed up a tiny bit.

Agreed! I’m not sure what to think.

This is also something I’ve come across in my research. The drive indicators on the dash show that they are all the way down but I don’t have a good way to verify. The water behind my house is sketchy at best so I try to stay out of it.

I wonder if they could be going all the way down at idle speeds but lifting under power.

Anyone have any recommendations on diagnosing this, specifically.

I think you need to get it out of the water and push pull side to side and up and down on the drives, there should be no movement

Just thinking out loud here. When cone clutches fail, it causes a delay in shifting into forward or reverse. I have never seen one slip while under way. I would rule that out.
I don't believe the drives would be raising while under power. The force of forward thrust would push the drives down, not raise them. It this was happening, you would be able to see it on your drive indicators.
I don't think the engine couplers are stripped. When they fail, they fail. No movement at all.
I believe that you have some serious prop cavitation going on either from the drives not going down all of the way, some improperly installed drive showers or something of this nature. Another possibility would be the bottom of the hull is in worse condition than you think it is. Very dirty, algae or barnacles growing on it or something along those lines.
I am surprised that it has 3 blade props on it. What are others running on this hull?
Boat could be waterlogged and so heavy that it just can't go.

Did I read correctly that you had a Formula 311 on plane, with one engine? A 330 at that?

lol yes but to clarify, I had the second engine running as a booster. Just didn’t want to take it over 2k rpms because of an exhaust leak.


NOW, on to what I’ve discovered today. I had the boat hauled out to see if the drives were slipping in any way. They are not.

But I have found the source of the problem: the barnacle company that’s been diving every month has been scamming me.
Take a look:



https://cimg8.ibsrv.net/gimg/www.off...1b9720ca4.jpeg


So the drives are all right with no play. I spent a few hours pressure washing the barnacles off the hull and I’ve got a buddy who’s going to do the bottom in an ablative paint in the next week or so while she’s out of the water. Hoping that solves all the issues.

Omg

Whoa!!

Is there anyway to keep her out of the water when not being used?

Couple of observations, those props are not your friend. Get some Bravo props or Mirage 3 blades. Check the operation of the tabs and indicators. Painting the bottom will scrub 3 or 4 mph from you but at least you shouldn’t have this mess again for a while. Remember that frequent use of the boat is your friend and leaving it sit in the water has its disadvantages.

Bud - keeping that in the water is going to create the worst boating experience you could ever ask for. Before long you are going to be longing for the days when getting on plane was a concern. If you have to keep an I/O boat in salt water you need to sell it and get a boat that’s appropriate for your circumstances.

so, for my own instruction, having this bottom like that could be enough to stop a boat from planning? even though there is 640 hp pushing it ?

Is there a marina close by with in/out service? Wouldn't have to paint the bottom.

So the after a couple days of muriatic acid and pressure washing she’s finally clean!

https://cimg1.ibsrv.net/gimg/www.off...5eae87c4c.jpeg


Thursday the guys are going to start sanding and then it’s getting 2000e primer and the Pettit Black Widow bottom paint. The stuff isn’t cheap but it’s designed for racing boats to be very slick and apparently it’s polish able to get a gloss finish. We’ll see how that goes.
Also going to be priming and painting the outdrives.

Once that’s done, the original props will go back on and should be good to go.
This adventure has made me consider getting a trailer for the boat. I have a boat ramp into the canal on my property on the side yard. I may start storing it out of water, as inconvenient as that is compared to walking out back, untying ropes and going.

Storing it out of the water is the way to go, make sure all the mechanics work on the drives and tabs steering before dunking it.

Saw the vid on YouTube. Looks like you got it sorted out. 👍🏻

Link….