convert sea ray express bridge to diesel

[holdingfirm2]

i have a 1991 searay expressbridge with mercruiser 7.4 bluewater series inboards connected to hurth v drive. i want to repower with diesel as this boat is used for charters. i would like to use the existing gearbox if possible. im not worried about top end speed mainly fuel economy.
any suggestions would be greatly appreciated.

 

[Skybolt]

Re-powering with diesels would require a different transmission to handle the torque as well as larger shaft and different props. Which also means struts and new shaft logs for the larger diameter shaft.

That year boat may not be worth re-powering.

Welcome!

 

[Blueone]

I’m not sure how you get a ROI on the diesels alone ….let alone what @SKybolt said

 

[bobeast]

Optimistically, that boat may be worth 35k. The cost of two engines, the entire fuel system, the generator if it has one, the transmissions, the running gear, etc. would likely exceed the value of the boat. And we haven't even started talking about labor yet.

 

[dtfeld]

Hardware wise, each engine is likely $35K-$50k each. Transmissions $4k-$8k each Shafts and Props $5k each Engineering and labor? Well...a lot. Its easily a $75k-$100k project.

Sell that boat and buy what you need.

 

[PlayDate]

https://www.boats.com/how-to/ready-to-switch-from-gas-to-diesel/

 

[dtfeld]

https://www.boats.com/how-to/ready-to-switch-from-gas-to-diesel/

This is a good article!! $40k (2018 $) is a much more reasonable and the devil is in the details as the article says they don't have to upsize the shafts or props in 80% of cases. Knowing how Sea Ray built boats, the components were probably spec'ed right at their max, so I would get some hard numbers before commiting.

Still that's a lot of work and $$$ for a 1991 Sea Ray.

 

[ttmott]

If I were to do this it would Cat C7.1's ordered with the ZF gears. That engine comes in three specs 400, 450, and 500 HP. I'd stay with the 400 or 450 spec especially with a charter boat. It's a small compact engine which would probably work well with the smaller boat like the 350EB. The harder things here would be the exhaust system design - for that DiAngelo in FT Lauderdale would be the source.

 

[dtfeld]

If I were to do this it would Cat C7.1's ordered with the ZF gears. That engine comes in three specs 400, 450, and 500 HP. I'd stay with the 400 or 450 spec especially with a charter boat. It's a small compact engine which would probably work well with the smaller boat like the 350EB. The harder things here would be the exhaust system design - for that DiAngelo in FT Lauderdale would be the source.

Now that's a $100k upgrade!

 

[holdingfirm2]

https://www.boats.com/how-to/ready-to-switch-from-gas-to-diesel/

Thank you very informative article i was wondering if the yanmar 4 cyl wld be a good fit with the least amount of modification

 

[holdingfirm2]

This is a good article!! $40k (2018 $) is a much more reasonable and the devil is in the details as the article says they don't have to upsize the shafts or props in 80% of cases. Knowing how Sea Ray built boats, the components were probably spec'ed right at their max, so I would get some hard numbers before commiting.

Still that's a lot of work and $$$ for a 1991 Sea Ray.

Re-powering with diesels would require a different transmission to handle the torque as well as larger shaft and different props. Which also means struts and new shaft logs for the larger diameter shaft.

That year boat may not be worth re-powering.

Welcome!

Thank you for your advice

 

[holdingfirm2]

I’m not sure how you get a ROI on the diesels alone ….let alone what @SKybolt said

Im located in bermuda gas is $10 avg per gal vs about $7 gal diesel . As i do charters and this boat is layed out for what i do i dnt plan on getting rid of it .

 

[Blueone]

Im located in bermuda gas is $10 avg per gal vs about $7 gal diesel . As i do charters and this boat is layed out for what i do i dnt plan on getting rid of it .

On the internet you never know the background…. For most of us it wouldn’t make sense but you do your thing…. Please share your progress