Lister Blackstone diesel

In my large collection of boat related "stuff" I have a 26 ft. motor whaleboat hull, Capilano steering and a 1965 Lister Blackstone SL2M diesel engine. They're all in good shape, the engine still has all the original decals and starts and runs well. Here's the issue, the engine is rated at 8.5 hp @ 1800rpm continuous, I'm just a little leery of only 8.5 hp, calculations show that if I can keep it under 4000 lbs. it should do hull speed. It has a 2 to 1 gear and will turn a 16" prop. I have almost everything I need to put it together so it's a low dollar project and none of the components have a mission in life at present so I'm thinking of it as some kind of hobby/experiment that shouldn't take a tremendous amount of work if I keep it as an open boat to help keep weight down. Any advice/ideas/comments ?

 

These older motors are not about the Hp - they have the torque

Don't compare with a modern 10hp outboard - its a very different animal - you'll be pleasantly surprised.

There are many English canal boats with the Stuart Turner 4 horse motors 60' long 'bricks' and they'll do 4 knots all day long on idle.

 

Use the motor and see how you go. I've got a 3 cylinder Lister (SL3) in my collection, it's rated at 12HP@1800 rpm. Came out of a 36' fishing boat and the owner said he'd never had any problems with it. Not sure what I'll do with it but sooner or later I'll find the right project.

And yeah, they have a lot of torque. I've got a later model 3 cylinder one tucked away as well, supposed to produce 30HP@1800 rpm. Both air cooled with 3:1 reduction gearing.

PDW

 

Way back many engines were TAXED by hp , so calling an engine 8hp was done for the benefit of the customers, even if it was 3x more powerfull ..

It should be fine , a quick check is to use 1/3 the cubic inches of the engine displacement as long term cruise hp rating.

After its running , in neutral run it wide open for a few seconds to observe the max rpm.

Then when in gear and UNDERWAY ,not tied to a dock, open to full throttle , and observe the rpm ,operate 10% or more below the observed rpm and you should not be overloaded , blowing black smoke.

Most power boats do not operate at hull speed as pulling back a Knot can reduce fuel burn by half or more.

 

I'm going to go ahead with project, the engine is to nice not to be put to use and enjoyed.

 

I've imported Lister clones from Asia,and they are bloody heavy...something to keep in mind if you ever want to put it into another boat.

If it's water cooled look at about 1200 pounds,air cooled probably just under a 1000.

 

Thanks, I think mine is quite different from the clones, this one is a two cylinder air cooled engine, 56 cu. in., weighs 512 lbs. with gearbox and reduction.

 

Probably the LR2 here:

http://www.bluemoment.com/manuals/lister_man.pdf

 

Actually it's an earlier version, an SL2M.

 

this one is a two cylinder air cooled engine, 56 cu. in.,

Should make close to 20 hp,

 

I'm curious how much efficiency one gains from using a 16" 900 rpm prop over something like a 11" 1800 rpm on a high-thrust Yamaha T9.9. 10%?

It would also be interesting to compare BSFC numbers. I suspect about the same (old diesel vs new 4 stroke gas).

 

I am certainly no expert, but in Dave Gerr's Propeller Handbook he states "For the vast majority of installations, the larger the diameter the greater the efficiency". He goes on to point out that this doesn't apply to high speed vessels. I know from my own experience of replacing an 8hp four cycle outboard with a 9hp diesel inboard the amount of useable power went up and fuel usage went down, both by a considerable amount.

 

It's not so much the hp but the torque to spin the prop.

That 8.5 hp diesel at 1800 is about 25 lbft.
An 8 hp gas outboard at 5000 rom is about 8 lbft.

Yes you can gear the gas engine down to get the torque,but then you still have all the frictional and pumping losses with the higher engine speeds.Plus of course the diesel advantage in energy per gallon of fuel.

 

I understand that outboard HP is measured at the prop and an inboard engine is measured before the gearbox. So at the prop shaft, an OB has the advantage.

Energy per gallon doesn't matter if it's burned in an inefficient engine and you get less HP-hours per gallon.

 

Regardless of outboards being measured at the crank or prop- it matters little (gear loss 3-4%)-because after gearing down the hp remains the same but the torque goes up.