I just thought I'd chime in to report my recent experience upgrading my C30 from the original two-blade prop to a Martec folding prop.
Since buying this boat November 2015, I have always been a little put out by the low top speed under motor. It took 9 months, but I finally figured out that the original prop was intended for the 1:1 ratio of the Atomic4 while the boat actually has the Universal M25. Upon calling Martec, they told me that it was at least 50% underpowered and installing a new prop would fix it. My diver also warned that the under powering could cause the M25 to carbon up.
Luckily the guys at Martec had some spare parts and put together a refurbished 14x12 MKIII Eliptec folding prop for a little over half-price, and had it to me within a week. The diver had it on early the following week.
The prop made a huge difference. The top speed under power is about 6 knots and it reverses well. I am very careful to let the engine spin down to idle before shifting to reverse. I picked up about 1 knot under sail, and the prop doesn't rotate and vibrate the hull. Also, my M25 with 750 hours never actually gets up to 180F at cruising speed anymore, which baffles me since it is pushing more load. Now it cruises around 165-170F.
The only thing I'm a little worried about is a persistent tapping sound on the shaft at higher RPMs. It's one tap per revolution. I think my dad's J35 has done the same thing for the last 30 years but I can't remember exactly. I bet it's nothing, but I'll call Martec to check.
I hope that's informative for someone!
Since buying this boat November 2015, I have always been a little put out by the low top speed under motor. It took 9 months, but I finally figured out that the original prop was intended for the 1:1 ratio of the Atomic4 while the boat actually has the Universal M25. Upon calling Martec, they told me that it was at least 50% underpowered and installing a new prop would fix it. My diver also warned that the under powering could cause the M25 to carbon up.
Luckily the guys at Martec had some spare parts and put together a refurbished 14x12 MKIII Eliptec folding prop for a little over half-price, and had it to me within a week. The diver had it on early the following week.
The prop made a huge difference. The top speed under power is about 6 knots and it reverses well. I am very careful to let the engine spin down to idle before shifting to reverse. I picked up about 1 knot under sail, and the prop doesn't rotate and vibrate the hull. Also, my M25 with 750 hours never actually gets up to 180F at cruising speed anymore, which baffles me since it is pushing more load. Now it cruises around 165-170F.
The only thing I'm a little worried about is a persistent tapping sound on the shaft at higher RPMs. It's one tap per revolution. I think my dad's J35 has done the same thing for the last 30 years but I can't remember exactly. I bet it's nothing, but I'll call Martec to check.
I hope that's informative for someone!
