Fitting the right stern drive to my boat

[Giles Mellor]

Hi, I am looking for advise as which stern drive to fit to my boat an Alpha or Bravo, she is a Fairline Sunfury 26ft which now has a Ford Transit Diesel engine 2.5 litre 70hp fitted replacing the two Volvo Penta engines, the engine now sits in the middle of the engine compartment which means that the stern drive would almost be total submerged to keep my trust is that ok to do this? Please note I purchased the boat with no engines or drives. Thank you.
To all of you for your time thank you very much, I have had a good long think about what you guys have said and I will be going for the Alphe stern drive, i don't need speed as on the rivers on the UK we can only go 8 knots, my engine is not to old built in 2001 by ford simple but solid and not too many miles when it was in a van only 52k it's been fully marinised and ready for work again, if there is anything else you guys think of please do tell me and I will take it on board!

 

[alldodge]

Hi, I am looking for advise as which stern drive to fit to my boat an Alpha or Bravo, she is a Fairline Sunfury 26ft which now has a Ford Transit Diesel engine 2.5 litre 70hp fitted replacing the two Volvo Penta engines, the engine now sits in the middle of the engine compartment which means that the stern drive would almost be total submerged to keep my trust is that ok to do this? Please note I purchased the boat with no engines or drives. Thank you

Howdy

IMO being totally submerged is an increased maintenance issue over time only. There is a seal in the top for the steering pin and arm. This seal will keep the water out but over time it will start to leak. Most are setup to where when the boat is not moving this seal is out of the water. My boat sits real low and the seal is under the water by about 1 inch. If yours is more then that, this might just cause a leak sooner. Also if your in salt water this will increase the issue.

That size diesel would work with either alpha or bravo, but the bravo work easier, handle more power and has a belt driven water pump. The pump not being in the outdrive I think is a plus

 

[thumpar]

If you are willing to pay the extra money go Bravo. It can handle more power and has smoother shifting.

 

[Mischief Managed]

With only 70 HP on tap, I'd want as little drag as possible and would go with the Alpha drive. There's a huge cost savings too.
Don't sweat the shifting, Alphas shift the same way as every shiftable outboard and nearly every motorcycle and it's a perfectly fine way to shift gears.

 

[thumpar]

The diesel will have a lot more torque than a gas engine. I have never seen a motorcycle with a clutch dog shift system and I have been riding since the age of 6.

 

[Bondo]

Ayuh,.... Welcome Aboard,..... I agree that a Bravo is what ya need,....

Makin' the diesel stumble to shift an Alpha could be a problem,.....

A Volvo might be another option that might be more plentiful where you live too,....

The depth the drive runs is determined by gettin' the cav-plate even with or slightly above the runnin' surface of the hull,....

 

[Mischief Managed]

The diesel will have a lot more torque than a gas engine. I have never seen a motorcycle with a clutch dog shift system and I have been riding since the age of 6.

Motorcycle transmissions don't have syncros, they use shift dogs to change gears, just like an alpha drive. They aren't ramp shaped though, because they need to work loaded under power and while engine braking.

A 70 HP diesel engine capable of operating at RPM needed to use a stern drive properly (say 2500) won't make more than 150 ft-lbs of torque.

 

[Mischief Managed]

Ayuh,.... Welcome Aboard,..... I agree that a Bravo is what ya need,....

Makin' the diesel stumble to shift an Alpha could be a problem,.....

A Volvo might be another option that might be more plentiful where you live too,....

The depth the drive runs is determined by gettin' the cav-plate even with or slightly above the runnin' surface of the hull,....

The same shift interrupt circuit that interrupts the ignition on a gas engine could be used to interrupt the fuel supply solenoid power on a mechanical injection diesel. There's gotta be a simple way to electrically cut the power on a common rail diesel, but if not, I would start by interrupting power to one injector wire and see if that's enough, if not, do it to two or more of them.

 

[thumpar]

Motorcycle transmissions don't have syncros, they use shift dogs to change gears, just like an alpha drive. They aren't ramp shaped though, because they need to work loaded under power and while engine braking.

A 70 HP diesel engine capable of operating at RPM needed to use a stern drive properly (say 2500) won't make more than 150 ft-lbs of torque.

Motorcycles have a clutch. The Alphas don't. That is why the need the shift interrupt on them.

 

[Bondo]

The same shift interrupt circuit that interrupts the ignition on a gas engine could be used to interrupt the fuel supply solenoid power on a mechanical injection diesel.

Ayuh,.... I donno what his diesel motor is, so I'm assumin' the worst, that is a fully mechanical diesel, that ya pull a cable to shut-down, like an old Mack,....

 

[alldodge]

I don't see how to make a diesel stumble and not shut down at idle, not that it cannot be done, but must agree it would be much easier with a bravo

 

[Mischief Managed]

Motorcycles have a clutch. The Alphas don't. That is why the need the shift interrupt on them.

Not sure why that's relevant, but I was referring to changing gears, not clutching, and motorcycles can be shifted very easily without touching the clutch by just reducing the load on the transmission momentarily (this is exactly what the shift interrupt circuit does).

To upshift, apply slight upward pressure on the shifter and roll OFF the gas a little bit, the transmission will snick right into the next gear up effortlessly. To downshift (it is assumed that you are trying to slow down, clutchless downshifting is not a good idea if you are trying to accelerate hard), apply a little downward pressure on the shifter and roll ON the gas a little. It will snick right into the next gear down effortlessly.

 

[thumpar]

Not sure why that's relevant, but I was referring to changing gears, not clutching, and motorcycles can be shifted very easily without touching the clutch by just reducing the load on the transmission momentarily (this is exactly what the shift interrupt circuit does).

To upshift, apply slight upward pressure on the shifter and roll OFF the gas a little bit, the transmission will snick right into the next gear up effortlessly. To downshift (it is assumed that you are trying to slow down, clutchless downshifting is not a good idea if you are trying to accelerate hard), apply a little downward pressure on the shifter and roll ON the gas a little. It will snick right into the next gear down effortlessly.

Try shifting from forward to reverse like that.