Prop slipping and not getting on plane
 

Not sure if this is a rigging or prop question but here goes.

I converted my 35 ft monohull from twin V8 2 stroke Evinrudes to two 496’s.

Took the boat out for her first run and it took a long time to get on the plane as the props were slipping (cavitating?). She cruised beautifully at about 50mph (guess as no speedo) and then the props would slip over that and hit the redline with hardly any increase in speed.

As it was the first run ever I used the props that had originally come with the boat, some 4 blade 24p cleavers. As the exhaust flows over the blades I thought that was the problem so put on some Mach Stern Drivers 4 blade 26p that I had purchased years ago of a fellow Offshoreonly member.

Could not get on the plane with the engines bouncing on the rev limiters. Lots of what appeared to be steam from the props. Couldn’t believe they were worse even though the exhaust went through the hub now instead of over the blades.

The boat is not stepped and there is no pad. She weighed just over 3000Kg dry with the V8 Evinrudes and pods so now probably 3500kg or 7700 lbs. Bravo diesel drives 1.36 ratio, the prop shafts are about 5inches below the hull.

Just a little edit.

The Mach Stern Drivers are 14 x 27p, not 26’s as previously thought.

So any suggestions at all on what’s wrong?

some of the possibilities are:

Too much pitch;

Not enough diameter;

Not enough cup;

Drive height too high;

Engines not producing enough power;

Need trim tabs;

Any other suggestions?

Summer is approaching here and would love to get the boat going.

Here are a bunch of options:

See if you can get your hands on a set of Bravo 1 26 pitch 4 blade. I think they will bite more than the Mach and will probably get more bow lift. Even though you are at 5 inches that is very conservative on an older hull. My V hull is at 4.5 inches with extension boxes and its tough to get on plane. The Bravo 1 is probably your "go to" universal prop for a mid age deep V.

You could also try spinning the props in just to see what happens. Right now you are spinning out. Reverse the propellers from side to side and swap the cables. The two lifting strakes exit into the prop area arent helping you so this might help.

You could try a set of 5 blade Maximus at about a 22 pitch.... They will work but might be a little rough on the drives.

If none of these work, buy a 1 inch drive spacers and it will space your lower DOWN 1 more inch. Then you start all over again to find the best prop.

Keep trying, you are close!

Your drives are not deep enough, the vent plate should be right at the bottom of the hull. IMO your way high

Drives do appear to be mounted high. Spacers will quickly verify if that is the case.

I gotta agree. The drives appear too high. Before you add spacers I would try some Bravo 1 props and some Rev 4 propellers. They have a lot of blade area and might hold the water a little better.

I would also concur with trying a spacer after experimenting with props to lower the drive.

Thanks for the replies.

Being in Sydney Australia parts are hard to come by. Just about everything has to be sourced overseas.

I guess trying the props the other way is very doable. Can I just leave the cables as they are and put the gear shift lever in the opposite direction?

No idea where I can borrow a set of 26 Bravos as the prop shops I have rang in Sydney go to about 22. Also no idea where to find spacers.

I guess today’s job is to work the phones and see if anyone has 26 Bravos and/or some spacers.

Thank you very much for giving me a direction.

Yes, you can swap props side to side and then use reverse as forward and forward as reverse leaving the cables as is.

LOL, yeah, it makes docking VERY interesting!

Off topic but........
I went out in that boat with Tony Lowe many years ago. Launched at Patterson River (Melbourne) on a snotty day. The V-8's were damn noisy and not very fast but she rode beautifully in the slop. Overall, I was pretty impressed.

I've often wondered what became of the boat because I'm an outboard fan. I'm also curious "Why the inboard conversion rather than just update to to more efficient outboards?" I see quite a few people converting boats to outboards but not the other way round....

Cheers mate!
RR

P.S. The OP has glossed over the fact that this is an awesome boat. As I understand, it was built by Tony Lowe and his race team (Trident engineering) and is a Cig 35' hull. I think it was built under licence from Cigarette but he could not use the name.