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S&S Swan General - Swan 40 ... Kiwi Prop Question for Lars
18 April 2020 - 14:41
Join Date: 03 March 2007
Posts: 241

Swan 40 ... Kiwi Prop Question for Lars

And for the message.. I have a 15.5 inch 3 blade Kiwi prop coupled to a Yanmar 4JHE 44 hp. There are 2cm between the prop tip and the hull.  I am under propped ... what are your thoughts on removing 1 cm of glass to increase the clearance to 3cm so I can go up to a 16 inch prop? 

Anybody do this "trimming" ???

all the best

Mike from StormSvale

18 April 2020 - 15:20
Join Date: 02 January 2008
Posts: 1547


If this area is accessible from the inside, you could consider removing even more, and building up additional thickness on the inside

Kind regards


19 April 2020 - 08:58
Join Date: 03 March 2007
Posts: 241

Hi Lars. 

Not much room in there... we call the area the Houdini hole. Anyway, so grinding out 1cm should not be an issue? I think that is all I will need. 

as always thanks for your great advice!

best wishes 


Mike from Stormsvale

19 April 2020 - 10:58
Join Date: 02 January 2008
Posts: 1547

1 cm is OK


20 April 2020 - 07:16
Join Date: 03 March 2007
Posts: 241

Thanks Lars and PLEASE take care!!!!!!


Best wishes



20 April 2020 - 19:04
Join Date: 14 May 2017
Posts: 66

Hi Mike,

Doing well? Maybe the longetudial position of the prop makes another cm. I noticed with my prop - and shaft installation the position matters.

Would be nice you some pictures. I am interested for sure!

Kind regards,


26 April 2020 - 09:04
Join Date: 03 March 2007
Posts: 241

Hi Both,

I have had a discussion with the folks at Kiwi prop and they feel that I will be Ok with just changing the pitch a bit. They do not believe a 1/2 jump in diameter is justified.. I have a 15.5 inch now and they say that the tip pushes it to 16 inches... I have been happy with the prop but thought I could get a bit more speed and maybe better fuel efficiency out of it... 

Anyway one less project.

Jolling here are some picks of the installation.

Kiwi prop 2

Kiwi prop 1

26 April 2020 - 17:52
Join Date: 02 January 2008
Posts: 1547

Dear Mike

Fuel consumption at cruising speeds interests many owners. It would be possible with fairly simple equipment to find out the actual numbers. A rpm meter, a speedometer, and a fuel consumption meter would be needed, all calibrated and accurate, as well as time to do a number of test runs in calm and deep water.
For diesel engines the difference between fuel feed and return needs to be measured, and two fuel flow meters are required. If you want to be accurate the air pressure, the air temperature and salinity of the water should be recorded also.
Even if you determine the numbers for your own boat, they usually do not refer for sisterships unless they are fully identical. If the keel, engine, reduction ratio, or propeller is different the numbers are not the same.
Generally it can be said that the slower you go, the lower the consumption, but at some stage the fuel required to keep the engine turning exceeds the amount of fuel used for developing propulsion power. 
The recommendation for continuous powering is to use at least 25% of the engine maximum output in order to keep its internals clean, otherwise there may be carbon build-up and glazing, which is very bad for the engine.
I can work out the 25% output rpm if you provide the maximum full throttle rpm with the present propeller setting.
Kind regards

28 April 2020 - 04:36
Join Date: 03 March 2007
Posts: 241

Thanks Lars!!!!! 
she goes in the water next week and I will do the test run and send you the data!!


Take care!!!



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