I'm nearly there as far as a decision about gearboxes etc.
Crowthers got back to me:
Have now carried out calculations for you and have the following recommendation:-
Based on a direct drive gearbox 1:1 the propeller would be 21" diameter.
1:5:1 the correct propeller would be 28" diameter but we note you would be unable to swing this and therefore put forward one of our compensated range of propellers which would be 24" but with a larger blade area ratio to give the equivalent of the 28" required.
Obviously it would not be possible for you to have 2:1 reduction as even with our compensated range you would not be able to accommodate a big enough diameter.
That leaves me with two options for a prm gearbox:
A prm 500 or prm 750 with 1.5:1 reduction throwing a 24" compensated prop
A prm 750 with a 1:1 reduction throwing a 21" standard prop
Both gearboxes are an expensive choice! About par for the course
I now hunt for a gearbox. There's not much call for the bigger prm units on the inland waterways. I'll have trawl the marine breakers on the coast.
The positive side is that the mounting dimensions for both the 500 & the 750 are identical, which means that I can make a mounting plate up ready for the gearbox to connect to the engine.
If any of you have a 500 or 750 at the back of the garage - let me know!
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2 comments:
I would have thought a PRM 260D would have been suitable for your engine
Sanssouci,
A prm 260 would be just the right size. Unfortunately, the smallest reduction they do (currently) is 2:1. Even with a 1.5:1 reduction, my theoretical prop diameter is 28". I need 1.5 or 1:1. That said, see my post today
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