Prop Swap

[kagallag]

Hi, I want to replace my Darglow folding 2 blade prop with a good old fixed one (2 or 3 blade) but I dont know how to select the required prop. My engine is Yanmar 1GM10 and boat is 8m sail boat of mid 70's vintage. The current prop has good clearance on a stainless 1inch shaft. Any ideas welcome. Thanks in advance.

 

[srp]

There are a few prop calculation programs around (use Google). One of them is an Excel spreadsheet, and the link is about half way down this page.
If you go to someone like Lancing Marine, they will take all your boat details and then recommend a suitable diameter and pitch. They were very helpful when I bought my last prop from them.

 

[bendyone]

14 x 10 should work well. ( assuming a 3:1 gearbox)

 

[charles_reed]

Any reputable supplier will do the calculations for you.

But be aware that any fixed prop is only fully efficient at a certain engine speed, hull speed and sea/wind state, so any recommendation will be a compromise.

How anyone has the temerity to offer a guess based on the minuscule information provided defeats me.

In hindsight a comment both sweeping and condemnatory.

To do the calculations your supplier will need, at least:-
1. Engine maker and type (to know the power-curve)
2. Gearbox ratio (to determine the pitch/diameter)
3. LWL and loaded weight of boat.
4. Prop shaft diameter, taper and key profile
5. Clearance for prop.

Additional information:-
6. Waters in which the boat will be used
7. Underwater profile of boat
8. deadwood shape, size and position

Prop design is something of a black-art, the calculations tend to only be a guide to the basics - rather as GRIB downloads only give pointers to weather developments.

 

[baltic]

i found a down load somewhere internet that works it out for you called PropCalc

 

[flaming]

Just out of interest, what has prompted you to ditch the folder in favour of a fixed prop?

 

[FullCircle]

Check the gearbox reduction ratio usually on the plate nailed to the side of the box, work out narmal max rpm from the engine plate, and you can work out the shaft rpm.
Then draw a line between engine HP and Shaft rpm, that will give you a prop size. Ish.


Talk to these people, they are very good...


http://www.sillette.co.uk/

 

[kagallag]

the pins that hold the blades have started to loosen due to wear and age. The replacement costs are very high and I now have doubts about a blade flying off. So a fixed blade will give me much more peace of mind.