GORI Two Blade Folding Propeller

[p_schurli]

GORI Propeller advise please
I want to change to a two bladed 18x12 Gori folding propeller. I have a Volvo MD2030 29HP with MS25S Saildrive (1:2,47 reduction). Does anyone have experience with that combination or with a similar 30HP engine? I am interested in your max rpm and speed with cruising rpm in the range of 1800 to 2500.

[Symphony]

No direct experience of a Gori, but extensive experience with a FlexoFold - which in my view is the best  folding prop on the market. I have had one on both a 2030 and a D1 30 and performance is superior to the standard fixed 2 blade. It is critical with any propeller and particularly folding props to take the recommendation of the supplier as size may not be exactly the same as for a fixed prop. For example for my D1 30 the standard size (for my B33) is 16*13 but the Flexofold is 16*11. Your 18*12 sounds on the large side for a 2030 - they usually have a 16" and I don't think you will achieve anywhere near maximum rpm with an 18*12 -  that is you will be "overpropped" - my (educated) guess is that you will achieve less than 2800 RPM which is unacceptable.   

If the prop is sized correctly you should with a 2030 achieve maximum revs of at least 3400 RPM and, depending on the size boat you have a speed of around 7.5 knots in flat water. This is the sort of performance that Volvo expect when commissioning a new engine. The cruising speed of a 2030 is 2400 RPM which gives a speed in the range of 5.5-5.8 knots depending on boat. This was what I achieved with my old 37 with a 2030.

If you are in the UK I suggest you talk to Darglow Engineering about a recommendation for a Flexofold for your boat or of course you can go to FlexoFold direct in Denmark.

Hope this helps

[p_schurli]

I have found an owner with a MD2030, Saildrive and GORI 2-bladed 18x12 who told me that he gets 3300rpm with full throttle. If that is true it seems to be the ideal propeller for me. GORI recommends a 2-bladed 16,5x13 for the 29HP Volvo 2030 but for 34HP engines they recommend the 18x12 already.

[Symphony]

Surprised at that, but as I suggested earlier, folding  (and feathering) props do not always follow sizing which is based on conventional fixed propellers, mainly because their blades follow a different shape and often have a smaller BAR (Blade/Area Ratio). That is why it is important to fit the size recommended by the manufacturer of the specific propeller as that will be based on their experience of what works for a particular boat/engine combination.

As a general rule, a change of 1" of pitch or diameter changes engine revs by between 200-250rpm at the shaft speed  (1500rpm) on a saildrive. That is how I arrived at the figure of approx 2800 for a 18*12 (compared with a 16*11 normally fitted to a 2030). That is 2" of diameter and 1" of pitch equals up to 750rpm, so 3600-750 = 2850. However now we know that the Gori recommendation for their design of prop is a 16.5*13 which will be based on achieving 3600rpm, the revs with an 18*12 could well be 3250 (3600 - (1.5*250)).

Having said all that there is no advantage in using the larger propeller - in fact a loss as you will only be able to extract around 90% of the available power by restricting the revs. So, if you are going for a Gori, then fit their recommended size.

[Salty]

I have found an owner with a MD2030, Saildrive and GORI 2-bladed 18x12 who told me that he gets 3300rpm with full throttle............

With respect, you haven’t mentioned what make of boat, it’s size, waterline length, hull shape etc., surely those factors will also have a bearing on the rpm achievable, just asking ?

[p_schurli]

The boat is a Bavaria 40 from 2002.
@Symphoni Thanks for your excellent explanation!

[Salty]

I have found an owner with a MD2030, Saildrive and GORI 2-bladed 18x12 who told me that he gets3300rpm with full throttle..........

The boat is a Bavaria 40 from 2002.......

Ok, so the other owners boat is identical to your own Bavaria 40 from 2002 except he has a Gori prop. That’s handy as it makes comparison so much easier than with a different hull form.