Mbam

In addition to the drive height you would be better off with 1.5 ratio. In the mean time you should really try some larger diameter props.

Do you have an idea what the top speed will/should be? Unless you are anticipating 80 mph 26/27 is way too much pitch. If you run mid 60's the 22's should be just about right, For sure try some Revolutions if you can get your hands on them.

kubcat

Tony was the importer of Cigarette at the time Don passed away. He couldn’t get stock as the factory was a mess and he decided to built a new class 2 race boat hence it was built pretty light and set up for a single big block.

The story I have been told by Simon that was working with Tony was:

During construction a ski boat customer of his wanted the boat and kept offering more money till he sold it to him. The ski boat customer also saw the V8 Evinrudes in the shop and wanted them so it was completed as a cruiser and sold.

When I finally had enough of 8 hours maximum without melting a piston I decided to repower. 12 years ago outboards were nowhere near as powerful, or as quiet, or as fuel efficient. That’s how long it has taken to get to this stage.

kubcat

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As for top speed, not sure. It did just over 60mph with twin 275hp outboards. Guessing maybe 70mph with twin 420hp as per the Bam speed calculator. Then using the prop slip calculator set about 10% I need 24’s.

Unfortunately I just ordered and paid for a pair of Bravo 26’s

IGetWet

Have you calculated slip at cruise or wot? 10% would be low slip if you’re having problems getting putt of the hole, so with higher slip 26s may be closer to what you need. Bravos are actually shorter than what they’re advertised as well, a 26 should be put in as 25.3 into a slip calculator.

kubcat

The slip I am guessing on where it might be when dialled in. It is all theory so far, spent way too much time with google.

It is reassuring to know the Bravos will be a bit less pitch than advertised.

The Bravo 26’s should arrive early next week and the Chopper 24’s are at a local prop shop getting a once over. The prop shop showed me how the chopper props rock when placed facedown on a flat surface so the blades are not even which could be some of my problem. Looking at the Machs they have much smaller blade area and less diameter so with my relatively high x-dimension that makes sense that they wouldn’t push the boat.

All I have to do now is get some time off work to test the new props mid week when the waterways and boat ramps are not too busy.

Crude Intentions

I think 10% is a wet dream with that hull. Big heavy straight bottoms aren't very efficient. 10% is something you see in stepped hulls that have been played with to get props right. Avg slip is usually in the 15-18% range. Don't try to estimate slip you have to get on plane test wot and find your exact slip and then go from there.

kubcat

My Bravo 26 props arrived today, except that they are Lexor 26’s by Solas. Looks like we mis communicated.

Guess I better send them back.

MikeScarab28XLT

2021 what was the end of the story ??

kubcat

My lounge room had about 5 sets of props as I tried quite a few.

In the end the original 24 props that were on the V8 Evinrudes were given some love by a local prop shop and they have been the best props so far.

Takes a little while to get on the plane, probably need to go deeper with the drives but gets to just over 65mph and close to the rev limit.

It is incredibly quiet, smooth, effortless once on the plane and super economical. On par with my twin diesel 30ft RIB.

The centre of gravity has moved forward a bit with the sterndrive configuration making it even better when we head into the ocean.

As far as I am concerned it is a success and would like to thank everyone for their input.

Unfortunately I don't have much time to play with it as I now spend most of my time on our Sunseeker.

I think the engines are up to about 30 hours from new.

I guess I am just getting old.