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Propeller and shaft problems (Read 8807 times)
Heber
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Carlingford Ireland
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Re: Propeller and shaft problems
Reply #15 - 04.03.2010 at 20:40:39
 
Hi   We replaced our Dolphin with a Nanni 2.40HE (10.6HP). which is bigger than the Yanmar GM10.  I don’t know if this is relevant to your question but my partner in the boat fitted sturdy angle irons to the outside of the original engine bearers and them set the Nanni on these.   We retained the original propeller shaft 19mm (?) and purchased a new 3 Bladed prop 11’’ diameter with a 10° pitch at least is states 11 10 on the prop.  Whether this is the correct one for the engine and boat combination, I do not know, but it appears to work very well.  We also had a Keyway milled into the original shaft.

We had to adjust (hack) the original bearers to allow for the wider engine housing / body.   One thing you need to be aware of is that you have sufficient clearance between the propeller and the hull. If this is insufficient it apparently can damage the hull.  If you read any of the engine user manuals it will most likely give you an indication of the required clearance.

We are currently trying to have the engine rebuilt or replaced but that is nothing to do with the installation.


Heber.
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Corsair
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Cardiff South Wales
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Re: Propeller and shaft problems
Reply #16 - 10.03.2010 at 09:15:33
 
Hi, thank you for your reply, the Yanmar GM10 is now installed on a very neat steel frame which was bolted on to the existing engine bearers, the prop information is useful and we currently await a reply from a prop company, so we can give them your figures, although I had hoped to avoid a three bladed prop.  When I collected the engine it came with a two bladed prop, but that is too big for the swing between the shaft & the hull!!  The engine fitted in fairly neatly with ample space around it although we are still connecting bits up and we still have to build a new casing around it.
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Heber
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Re: Propeller and shaft problems
Reply #17 - 11.03.2010 at 21:24:52
 
Hi again,  In relation to the propeller and the size 11’’ by 10° pitch I have been thinking about it and realise that our engine RPM was approximately 2400 and the gearbox reduction ratio is 2:1 this was giving us approximately 5 knots.    My concern would be that 2400 RPM would be on the high side of the RPM range that skippers like to run their engines at.  The RPM range that I perceive that skippers like to run their engines at is between 1800 and say top end 2200.

As before do not take any of the measurements for granted do your own calculations.

It would suggest that you would need a bigger propeller or/and a greater pitch to get additional drive at less RPM, presuming the engine can handle it. The clearance from the top of the propeller and the hull in 46mm. The Diameter of the prop is (11’’ x 25.4mm) 297.4mm with a required clearance of “say” 10% 28mm.

Diameter in Inches                  11’’            12’’
Diameter in MM            25.4      279.4            304.8
Half Prop diameter            0.5      139.7            152.4
                 
Current  Clearance                  46            33.3
Shaft Centre to Hull                  185.7            185.7
                 
Required Clearance            0.10      27.94            30.48
                 
Safety Margin mm                  18.06            2.82

In our case we would be able to gain an additional 5mm shaft length from the coupling which would increase the safety margin ??.   Please note that our shaft is mounted on the mid line of the hull not off set to port.

If any body has any experience regarding propeller sizing, gearbox ratios and Engine RPM and cruising speed achieved I would appreciate it.

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Heber
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Re: Propeller and shaft problems
Reply #18 - 16.03.2010 at 13:09:23
 
Hi Guys

Welcome to the witches cauldron of matching Propellers to engines!

There is an information that the Propeller we have 11in x 10in maybe OVER sized for the 10.6HP Nanni diesel in the boat. This may well account for some of the problems we have being having with the engine.

Again if you have any experience regarding engine size and propeller size in a trapper 28/400 your input would be appreciated.


Heber

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