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Message board > Miscellaneous topics > Prop size for Suzuki DF 70 and Bosun

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Message 1 of 6
Posted by member David Freeman on Tuesday 15 August 2017

I had to have a new gearbox and prop fitted earlier this year due to fouling with some rope. Fortunately my insurance company were very good and this was deemed a legitimate claim so with an excess payable all the rest all was covered.
My boat is a Hardy Bosun and the engine is a Suzuki DF 70 (2004). prior to the new prop I could achieve reasonable speeds and boat handled well, since the new prop has been fitted I have lost power and struggle to get to 8/9 knots and handling is difficult against tides/currents. I do not have the specifications for the new/replaced prop (I am awaiting these) but suspect it was a standard one that was re-fitted. My thoughts are that the loss of power is down to to the wrong prop size being fitted.
Does anyone know what size props are best for this combination of boat and engine??
All and any suggestion welcome !!!

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Message 2 of 6
Posted by member David Freeman on Tuesday 15 August 2017

my current props are PROPELLER 3X13X19

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Message 3 of 6
Posted by member robert sneddon on Wednesday 16 August 2017

Hi David
I have a Family pilot and also have a 2004 DF70 on the stern.
The engine is rated for max rpm of 5500. With the prop that was on the engine when I purchased it I could only get approx 4400 rpm and like you only getting single figure knots.
Changed prop ( 3 blade X 13.75 Diam X 13 Pitch) all is well. Engine will achieve max revs and I can get onto the plane pretty quickly if I want to when conditions permit.
Trim tabs fitted.
Hope this helps
Kind regards, Robert.

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Message 4 of 6
Posted by member David Freeman on Monday 21 August 2017

thanks Robert, very useful.

Steel Developments have said:


if you are getting 4000 rpm and should be 5200-5800 then we would suggest a 13 pitch

if you are getting 3000 rpm and should be 5200-5800 then we would suggest a 9 pitch

So I reckon I will go for the 13" pitch. will let you know how it goes.

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Message 5 of 6
Posted by member David Freeman on Wednesday 30 August 2017

The Boat is only getting max 3000 revs so do you think perhaps the 9" pitch....

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Message 6 of 6
Posted by member robert sneddon on Thursday 7 September 2017

Hi David.
The prop on my engine was 17" which I changed to a 13"
I believe you lose approx 500 revs for every inch in pitch.
Assuming your engine is running correctly I would probably fit the 13.
This should allow your engine to achieve the recommend revs.
Just be careful of the possibility over revving if you are lightly loaded.
If you haven't already, have a look in the forum under engines. The last entry which has some very good info of other members prop changes.
I also phoned Hardy at the time and they also recommend a 13".
Give Hardy a call they are very helpful.

Hope this helps
Robert.

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