My Martec two blade folder needed factory refurbishment twice in less than three seasons. They SLAM open and perform very poorly in reverse. It also had severe vibrations that Martec was never able to fix, even with refurbishment, to fix the bent pin and the slop.
I replaced it with a three blade wheel and the vibrations were totally gone, so I know it was the prop, because that was the only change.
If you are considering a folder I would give serious consideration to the geared models like the Flex-O-Fold as opposed to the non geared models.
If you are not racing it's a big expense to gain that extra .1-.2 knots..
My experience is not the same. I've never had the prop "slam" open. I cannot tell the difference between the Martec, Michigan Wheel, and Campbell Sailer when shifting into gear at idle.
The Martec and Michigan Wheel are both two bladed props and both have the same (too high) pitch, the Michigan Wheel motors slightly better than the Martec but not much, the Campbell Sailer is the best prop for motoring.
In reverse there is not much difference in the props, but the Martec seems to have less propwalk ... that is my only complaint ... I like having a decent amount of propwalk ... I had to relearn some skills.
Sailing in light air there is NO comparison. In light air the fixed blade props are speed killers. That .2 knot is 5% of upwind boat speed and a measurable loss in pointing ability on my boat. The folding prop means that I now sail when I used to motor upwind in light air. The 6 - 9 sec/mile credit in rating is not nearly enough to make up the difference in performance. That does not sound like much, but it is about 60-80 boat lengths in 15 miles. To give yourself some idea of what better motoring performance costs in sailing ability, compare sailing upwind at 3.8 knots and 48 degrees off the wind to sailing 4.0 knots at 45. It is huge, you lose more than a mile every 5 hours.
In SF I had the Michigan Wheel and did not notice the poor sailing performance so much in the 12-20 knots of wind. When I moved to Vancouver, I had to deal with huge currents and low average wind speeds, so the Campbell Sailer was a good choice. Now I'm in a variable wind, low current area and the boat is a positive joy to sail with the folding prop. I'll NEVER have a fixed prop on a sailboat again. I just wish that I could get the Martec at a lower pitch to get the same RPM I had with the Campbell Sailer ...
The Boat is a Catalina 30 with an Atomic 4. The props are limited in diameter by both the silly 1:1 drive ratio and the short strut. The boat does not motor well to begin with.
Other boats with decent sized props and reduction gears can make use of higher pitch, I am certain that they react to prop changes differently than the C30. A slightly larger diameter prop and higher pitch at lower RPM would be a more more efficient set-up. This also goes to the locked vs freewheeling debate where a freewheeling higher pitch prop does not hurt sailing performance as much as a lower pitched prop does.
I'd go with the Martec recommendation, I would not add 3 inches of pitch. If the 16D9P gives full RPM the prop is correct. 16D12P will overload the engine.
If the prop you are looking at is used, find out just how much pitch can be taken out before you buy it.
All two bladed props vibrate more than three bladed so if the vibration from your current two bladed prop does not bother you, you will not notice a difference with the folder ... unless there is something wrong with it.
