Propellers

[Robert Mann]

Currently my MK II is fitted with a Martec folding prop and a stainless steel shaft.  The prop is noisey, both at low engine speeds when running and during gear engagement.  On top of this it seems that the engine idle speed needs to be 500rpm, which is a little on the low side, judging by the engine movement at idle. On top of this my ability to back the boat is poor, could be operator error but I don't think the prop is on my side either.

I am considering moving back to a fixed 3 bladed prop, Ron if I read correctly you reccomend a 15 x 11 with the XP35 engine, is this still your thought?

Does anyone have a good reccomendation for a source for the prop?

We are considering doing the swap in the water, it seems from reviewing the current set up today, that the prop may not be completely tight, can't tell for sure but I'm wondering if the cotter pin holes failed to line up and the installer loosened the prop slightly to get a alignment rather than redrilling.  Has anyone tried an in water replacment and if so what are the issues (other than the 96' drop into Davy Jones' locker)?

Are prop drive shafts standard dimensions?  By this I mean the axial mounting dimensions for the prop.  Are there any spacers that may be required?  I presume the standard type props are secured with a castellated nut and cotter pin, is this correct?

I'd like to get this in one tank of air so any input is gratefully received.

[sail4dale]

I had a Martec two blade on my CAT 30 for years.  It was not too great backing up ... needed a hi RPM burst to start but after that OK.

I've replaced my 3 blade fixed prop on my MkII with a 3 blade folding from Flexofold.  Couldn't stand the 40 pound drag at 6 knots. I got a 15 x 10 and it pushes me along at 7 kts. plus if I want.  I wouildn't argue about a 9 pitch as it would get you to higher engine RPM's but I do get max torque and good speed without smoke.  I have to idla at about 700 rpm or it gets rough.

It backs up like a charm  I love it.

Check them out on line.  The price is reasonable also.

[Ron Hill]

Bob : Yes, I still recommend a fixed 3 bladed 15" prop.  My 15" Sailor style prop is pitched to 11" and I have a 23hp engine.  It does NOT lug down the engine. 
Most shafts are common at the threaded prop end, but the prop is made for a specific diameter shaft ie. 1" for your C34.  It's not unusual to have to cut some of the threaded shaft OFF to accommodate a feathering/folding prop.  This is done to accommodate the larger hub.  All props that I've seen have a castellated nut for a cotter pin to secure it to the shaft.  I've made a spacer out of a penny by hammering it to the desired thickness - when needed.
 
If your engine idle is only 500rpm (and not shaking your teeth out), I believe that your tach is off (too low) and needs to be checked against a calibrated engine driven tach.   

[Howard Armstrong]

I replaced mine in the water. yes they most likely have the castellated nut with a cotter pin. i have seen some with two nuts one was a jam nut with set screws in the nut. if your present nut has this be sure and loosen it first as not to strip off the threads. if you would like to talk about this more i would be glad to talk about the install.
howard

[sail4dale]

I would still investigate a folding prop.  After all most of your boating is sailing and would you want to be towing a bucket behind whenever you sail?  It is a LOT of drag (40# using a fixed prop).  Also it is more prone to collecting plastic bags, kelp, etc.

At least I feel you would do yourself a favor by investigating whats available. 

PS       I have my old 15 x9 3 blade fixed prop as surplus.    offers?