mdb2/md11 propellers,change needed? newbie

[friday]

Thanks to all for help on previous mdb2/md11 question.

Having changed the mdb2 for the md11 I realise that I'll have to change the prop shaft as its too short, but will i have to change the prop as well ?

 

[spannerman]

Very probably, if you have more horsepower it will over rev at full throttle.

 

[Stemar]

It seems the MD11 develops 17HP and the 2B developed 25HP, both at 2500. Some variants of the 11 rev higher and produce 25HP at 3000 rpm.

I assume you'rre changing the engine 'cos the 2B reached the end of its life. If so, it's probably been running somewhat below par for a while, in which case, you may not find a great deal of difference.

If you can dry out to change a prop so changing it later doesn't cost a fortune, I'd be incline to try it with the old one. Props aren't cheap and you may well get away with it. Black smoke at full throttle and the engine unable to reach peak revs would mean you're overpropped. Full revs and not much happening over the back would mean you're underpropped.

I'd download Castle Marine's prop calculator and plug some numbers in. If the answer's not far off what you've got, it's worth a try. If the result isn't satifactory, you may be able to have your prop adjusted to change the pitch, which is a hellava lot cheaper than a new one. You may be able to find a second hand job. I did, but it took several months for the right one to come along.

BTW, I have a 15X10 (diameter X pitch) 2-bladed prop and a 13X8 3-blader, both left handed and for a 25mm shaft if either are any good to you, availavble from N London or Gosport. PM me if interested.

 

[garvellachs]

23HP for theMD11C at 2500, 25HP for the MD11D at 3000 I think?