Saildrive leg and props... Help!

Nostrodamus

New member
Joined
7 Mar 2011
Messages
3,659
www.cygnus3.com
I have a Volvo MD22 engine which was attached to a 120 saildrive leg.
The leg had to be replaced but it would appear that Volvo have changed the gear ratio’s on the leg making them difficult to find a prop that actually works. They no longer supply the 120 with the old gear ratio’s.
For the technical minded
Old leg gear ratio was 2.24:1
New leg ratio is 2.19:1

This does not seem a huge difference but in combination with the engine the specifications have caused huge problems in finding a prop that works anywhere near its optimum.
Several prop makers would not consider supplying a prop or I was told that they would perform badly.
One company did really try everything for me (Brunton’s). With their first prop the boat would not go in reverse.
They did exchange it for another prop design that has independent adjustments for pitch in forward and reverse. Now it is excellent in reverse but forward thrust is poor and I need to adjust the pitch. It is a compromise but it was the best solution at the time
Has anyone else heard of this problem or can anything else be done!
 

Tranona

Well-known member
Joined
10 Nov 2007
Messages
41,211
Visit site
Yes. I have just had a 130 leg fitted to my 2030 replacing a 120. No problem with a prop. I used the Propcalc programme and fitted a Volvo 2 blade fixed prop of 16*11 - 1" flatter pitch than the original because the shaft is spinning faster. Spot on. An MD22 would (I think) normally have a 17" 3 blade - you can check with a Volvo dealer who will have a chart. This is a good starting point, but you will probably need to go flatter on the pitch. The reason for the lower gear ratio is that the later engines max at 3200 rather than 3600.

The Propcalc programme can be found on www.castlemarine.co.uk
 

Nostrodamus

New member
Joined
7 Mar 2011
Messages
3,659
www.cygnus3.com
Thank you for your replies.
I cannot use a Kiwi prop as they do not make them for my size of boat.
I agree in that you do need a flatter prop and that is why I ended up with a Variprofile prop. It is similar to a Maxprop but the pitch in forward and reverse can be changed independantly.
The point is that there are a lot of 120 legs fitted to boats out there and if the owners have to change them their props may well not work with a new leg and only certain props will work.
Volo must have known this but is it a case that they are just not bothered about their customers.
 

Tranona

Well-known member
Joined
10 Nov 2007
Messages
41,211
Visit site
To be fair to Volvo, the number of legs that need changing is tiny and otherwise the 130 leg has real improvements, particularly the bigger anode and the ability to deal with larger hp.

I am really surprised that you are having problems as there is nothing difficult about dealing with the slightly higher shaft speed. There is plenty of choice of folding and feathering props available and I am sure you will be able to find one of a suitable size. Max Prop or Flexofold 3 blader would be high on my list. You could also do the sums and get a standard fixed Volvo 3 blader of the right size for a reference point - they are relatively cheap at about £300. You will then have a spare prop you know works. That is what I did on mine and am changing to a Flexofold next week now we know the optimum size.

Just run your details through Propcalc. As I suspected the old 120 leg would have a 17*10 3 blade. The new one would be 16*9. Both would give the same speeds.
 
Last edited:
Top