Rebel_Heart

I measured from the bottom directly in front of the drive down to the center of the prop shaft today. That came in at 7.5 inches. Would I benefit from a shortie and if so, what prop is going to give my the best results? Thanks.

bbladesprops

Yes you could benifit from a shorter drive if you are indeed at 7.5" below. I would actually consider a 1" shorty instead of 2"

RaggedEdge

Could you explain why you would consider the - 1" vs. the -2" gearcase? I am also researching the shorter case on a single step 35 Fountain and would be interested in you input, as well as your input in regard to props for the boat with the shorter lowers.

jryan26

I think I would buy the -2 so that I could add spacers if needed.

bbladesprops

Agreed going to 2 inches up allows spacing down to achive the desired affect.

These hulls can go backwards occasionally with two much height (there is a reason why). After talking to Rebel and determining his efficiancy, 2 inches could be too much because his slip is a little high.

Each application is different and we have seen that with these boats. Be sure you are hooked up real well before you raise the drive. CG matters quite a bit. Cabin design and accesories can affect this. Rebel is at a 50/50 spot. It may work and it may not help over all. I believe lightly loaded in perfect water it will reap some rewards. !' inch may be the sweet spot.

Rebel_Heart

Thanks again. It was great to talk to you and listen to your reasoning. I am still trying to decide what to do. If I knew that I would pick up speed, and could still use a 4 blade - I would go ahead with the project. I just don't think that the drives can handle the additional blade and weight.

BBlades - what is your honest opinion of raising my drives and using a labbed Bravo?

RaggedEdge

Rebel,
You could check with Imco for sure, but I think you can do the internal parts change (yours) into their case and use their larger prop shaft, if your concern is the prop shaft not being strong enough. What did your prop slip come out at?

Rebel_Heart

Brett calculated the slippage at 14.5%. I am able to get on plane without any problems now. At speed, I run the trim down to the bottom of the indicators to get the last bit of speed out.

RaggedEdge

I did mine the low tech by hand method, and using the "prop slip calculator" on the Bam Marine site, just a computer program based on the mathematical formula. The results put my boat at 8 -10%, using my average speeds and RPM not the low / high ends. In other words not my cool fall day best nor the hot humid august day worst. Varies between the two prop styles, but the Merc Bravos are not always true to pitch, and sometimes the lab versions do slip a little more, so I've been told. What are you running for props? And are the engines in your boat stock or tweaked?

Rebel_Heart

I'm running 540s that dynoed at 710 hp at 5800 rpm. So I borrowed a set of 29 Hydromotives that seemed to get the boat into the right rpm range (5700-5800). I have been told that the slip problem is a result of the Hydromotives and trimming too far?

The hp that I am running is my main concern for upgrading my Bravos. I have another thread that is asking for help concerning drive up grades, what is needed? Since I have the OL drives, some have said that I need to upgrade the uppers. Others have said just to switch over the internals to shorties and run. Or, leave the uppers alone and upgrade the lowers with a larger prop shaft? At this point, not sure what direction I'm headed.