Horsepower vs torque

"I am considering repowering m

"I am considering repowering my Carver. It currently has a 260 horsepower Merc in it. I have been told that it is torque that moves the boat. That being said, what would be the equivalent diesel that would move the boat the same as the 260?"

can't help you on the dies

can't help you on the diesel but I repowered my 1994 23' w/a. Went from a 1994 5.7 4 barrel to a 2006 5.7 vortec rated at 300hp. The differance was night and day. I am able to turn more prop and cruise went from 24mph @ 2.25mpg to 32mph @ 3.4mpg. Much more power out of the hole and in heavy seas too. All around performance was sluggish before and now it is very peppy.

"I think I can get my hole sho

"I think I can get my hole shot with a 4 blade prop. I am looking more for better ecconmy.
I am thinking that If I can get the same torque from a small diesel that I can get from the 350 (weighs in at around 500lbs) and maybe loose some weight at the same time, I might have a win-win situation.
Diesel fuel is cheaper than gas in Ontario. Furnace fuel is even cheaper."

"The problem with what you are

"The problem with what you are trying to do is the following:
1)Diesel marine engines are pretty darn expensive even with the lower horsepower engines.
2)They are also heavy (power/weight ratio)
3)They generally spin slower than a gasoline engine which would limit top end speed unless you could find the right ratio for drive system.
4)You would have to either buy brand new or buy rebuilt and the question is how much would it cost for heat exchanger,manifolds, and every other thing that will cost you to adapt to the particular engine type you are going with.
5)It would really depend on how heavy your boat is and what the minimum hp diesel you would want to put in and what your top end expectations would be.
6)The engine manufacturers of the diesel engines are now forced to comply with pollution controls and I know that alot of Industrial applications have alot of electrical issues. Its not the way it used to be unless you were to buy an older rebuilt motor before manufacturers were forced to comply with emissions. They can be expensive to diagnose and repair! If I had a choice I would say no to the diesel motor only because they made something fairly simple into something so complicated that you need diagnostic equipment to figure out what the heck is wrong with it. best of luck, Tom"

"Being it is a 1987 boat, I wa

"Being it is a 1987 boat, I was thinking along the lines of a 1987 motor or earlier.
I forgot about all the other stuff manifolds etc. and the adapter to attach it to the Alpha 1.
I think maybe I would be `money in the bank` to scrap that idea and just go with plan A.
4 or 5 blade prop and leave the power alone."

"[i]what would be the equivale

"what would be the equivalent diesel that would move the boat the same as the 260?
A 260HP diesel.

you are correct about torque. Your current engine has about 350 lb.ft. of torque; enough to make 260HP at around 4000rpm.

You need a diesel that has enough torque to make 260HP at a lower rpm, around 2500rpm. Diesels turn slower but make more torque. So a 260HP diesel would make about 525 lb.ft. of torque

Torque X RPM/5252=HP

Then, with the diesel outdrive's different gear ratios, your boat will have the same power and speed characteristics.

Mercruiser offered various diesels in the 250HP range. You would be best to look for a drop in Mercruiser drive package new or used. You need a marine diesel that comes with the outdrive so you have the proper gears, and the transom plate/gimbal/bellhousing/exhaust etc. etc.

would want to budget $10,000 for good used stuff. Your gasoline fuel tank is probably ok with diesel, but might want to read the tag on it.

you would have to save 4000 gallons of fuel to ever save money with the swap. Can't see that ever happening in a pleasure boat. If a charter boat or busy commercial boat might be economical.

Probably cheaper to sell what you got, and buy what you want."