Hi Scott
Martin Pascoe speaks well of Darglow Marine Engineers and the propeller they supplied for his new engine. [See 2017 Magazine. also http://www.darglow.co.uk ]
I don't have a folding prop and let the propeller trail. This reduces the drag by over 50% at 6 knots. [Source: Admiralty Manual of Seamanship; bollard pull required to tow an aircraft carrier with 4 screws is 20 tonnes; double that with locked screws. Sorry, I like that statistic.]
Martin has a 13 x 8 propeller with max revs of 3,600. Props are still measured in inches. 13 inches is about the maximum you can swing in the standard Twister rudder.
One thing about the Twister is that the water flow to the prop is not ideal; slip is quite high at speed. [Slip = the theoretical difference between the distance covered in one revolution and the actual.] I calculate that it is about 40% to 45% for VIVEZA at hull speed in flat water no wind.
To complicate the issue you can have wide chord and narrow chord props. [Chord = relationship between tip to centre length and blade width.] A narrow blade [think glider wings] will give less drag but give less 'push', especially against a headwind, in a Twister hull. I was strongly advised to have a wide chord prop.
As a cruising boat I chose the less expensive and possibly more reliable fixed blade prop. This is because the advantages of the folding prop are greatest when at less than hull speed; there any extra friction slows you. If you press a Twister hard in a good wind you will get to hull speed whatever prop you drag.
I know that you are at the other side of the World but I'm sure Darglow exports and they have experience of at least one Twister.
If I can help more; please ask. I offer this in open forum for any comments by anyone. When I changed the engine on VIVEZA I did get advice and do research. If you are interested and really want to get into the subject it's worth looking at how different types of ship and yacht mount their props.
Peter
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Chris Sinclair
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