Newbie needs help on Bravo issue

[Blackfinguy]

Hi all, I just discovered this forum and am looking for some guidance from the Bravo experts.

My 2 partners and I are in the middle phases of restoring a 24-0 1974 CC Blackfin. The boat had been modified by a previous owner removing the original gas motor and running gear and replacing it with a 300hp Yanmar LP6 Diesel coupled to a Bravo III outdrive via a jackshaft turning a 30" stainless duo-prop.
We stripped the boat COMPLETELY shortly after purchase to do a complete (not cap-off however) restore. We're about ready to reinstall, and have recently received some advice telling us the Bravo III is not strong enough for the 300hp diesel......that we will break outdrive (input?) shafts. I do know that the previous owner DID break a shaft! We were told that we really need the XR outdrive.

Is this correct, or is it BS?
If true, I have many more questions........
Many thanks for your time and input.

[PAST DUE]

it depends on which shaft you are talking about ...input shaft from engine ? drive shaft in lower unit ? prop shaft or shafts?i belive the lower unit on the b-3 is the same lower unit used on the b-3 xr. the difference is in the upper unit.

[Blackfinguy]

I'm not sure which shaft the previous owner broke and then replaced. It certainly was a shaft in the outdrive itself.
I'm not sure it matters which one, as my question is:

Are any of the components in the Bravo III too weak to routinely handle the 300hp diesel Yanmar and the associated torque? Should we look for an XR outdrive (or something else) to replace the Bravo III?

Thanks for any input!!

[PAST DUE]

the bravo x was put behind mercs diesels not sure up to what h.p. i guess you could use an bravo x upper and the bravo 3 lower.

[Mr Gadgets]

Blackfin,
The B3 has some weak points. I have only worked on a couple of B3's and do not have a great deal of info. The vertical shaft (the shaft that is in the top of the lower unit) was a weak point at one time. I think it was upgraded to the XR vertical shaft at one point to solve that problem.
Inherently the B3 upper is just a B1 upper with helical cut gears. At one point they have offered the XR upper to mate with the B3 lower. That would theoretically be your strongest B3 drive. But for the past few years the XR upper gears have been having a problem with the driven gear teeth breaking off at the root. I would suspect with the diesel motor, you would not be immune to that problem.
As far as other shafts, the input shaft has been upgraded a few years back. If it doesnt have grease fittings then it is the newer unit. There are two sizes of ujoints, B1 is smaller, than XR, on both the old and new styles.
I am not familar with the 24' Blackfin, but if it is a heavy boat, then you may well have problems with either the B3 or XR. If the reason for going to the B3 is blade area for bow lift, etc then the XR lower would not be a step in the right direction. So staying with a B3 for "out of the hole" and "bow lift" capabillities, then the XR upper should be a good fit, accept for the luck of the draw on good gears.
So it all depends on what you are trying to accomplish, and what amount of money you are willing to spend to either experiment with combinations or solve the problem.
One solution, if the single prop setup is a good option?, would be to go to an Imco SCX. Imco ran one behind a diesel motor in a boat at one time and had good luck with it I believe.

So depending on what your end goal is.. You might want to try the B3 you have and see how it holds up. If the boat isnt a heavy one.. it may just work. But with all that torque from the diesel.. it is a crap shoot.
Another item to discuss is the gear ratio that is used. I am not totally familar with the ratios the complement the diesel setup. But there are charts to help when you mix and match uppers, lowers, etc.
Maybe others can chime in on setups that are similar to yours.. Give us some details on what the boat is all about.

Hope this helps.
Dick