Change pitch on stainless steel prop?

[proline2]

I've got a l984 23' Proline walkaround cuddy with 3.8 v6 OMC I/O. I recently put on a stainless prop with the same 15" diameter by 17" pitch as me aluminum prop. Since then the rpms have dropped to a max of 3900-4000, instead of the 4200-4600 they should be. My speed has also dropped. Can I have the prop repitched down an inch or so to bring up the rpms, and how much of a job is this? Also, what about keeping the 17" pitch and having the diameter reduced? Anybody out there have a prop that perfoems well with this type boat? My top speed right now is around 29 mph. Thanks

 

[Bondo]

Re: Change pitch on stainless steel prop?

Any Good prop shop can beat it down a inch or two.... They would know best if the dia. should be changed....

 

[ufm82]

Re: Change pitch on stainless steel prop?

That's just the opposite of what should have happened. Usually an SS prop will bring up your speed by a few miles an hour and raise your RPMs just because of the smoother surface and less drag. I would check to be certain that the prop really is the same. A prop shop can measure the prop and determine the true pitch. You can usually replace an aluminum prop with a SS of 1 pitch range higher and expect the same RPM with a slight increase in speed. The SS prop will have some cupping on the blades that the aluminum prop won't have but this just helps the prop bite better- it shouldn't kill your rpm that bad. <br /><br /> You can have the shop remove some pitch if you want. Doesn't cost too much to do that either. <br /><br />UFM82

 

[Doug Durako]

Re: Change pitch on stainless steel prop?

I'm with UF---You need a pitch guage or advice from a prop shop. One of the props has been reworked to a different spec. than what you've been told. My guess is the aluminum one is not what you thought it was.

 

[proline2]

Re: Change pitch on stainless steel prop?

Actually, I had a 135 Evinrude that did the same thing when I went to a stainless prop, the rpms on that dropped from 5600 to 4400, and the speed went down slightly. I have two aluminum props I've used on my current boat and they perform the same, each with 17" pitch. The stainless prop is marked 17", but other than a visual inpection I have no way to actually measure it. I will definitely check into it with a prop shop I know of. Thanks for the replies.

 

[cobra 3.0]

Re: Change pitch on stainless steel prop?

I just went out today to test my standard 14 dia. x 17" pitch aluminum prop against a recently purchased (used) 13"dia x 19" stainless prop that I purchased off ebay. I have a 16 ft Peterborough open deck boat with a cobra 3.0 and here are my results:<br /><br />The Aluminum 17" prop had much better hole shot and grabbed really well in tight turns with superior acceleration and maintained speed in curves.(maximum rpms 4750)<br /><br />The stainless was slightly faster by 1-2 miles per hour . In tight turns, it would actually spin in its own wash and feel like it lost all grab in the water and then suddenly slowly grab and accelerate moderately.(mawximum rpms 4200)<br /><br />All in all I think I'm going to have the stainless prop repitched to either 18" or maybe even 17" pitch. I'll talk to my prop shop guy for his advice.

 

[proline2]

Re: Change pitch on stainless steel prop?

Cobra, it's interesting that you mentioned getting cavitation with the stainless prop. I forgot to mention it, but I seem to get it with the stainless prop I'm running whereas I don't remember getting it with the aluminum. This has only happened in a relatively tight turn. HMMMM.

 

[loadnet]

Re: Change pitch on stainless steel prop?

Something to stick in your head..<br /><br />This may sound corny to you but if I were in your shoes, I'd put the old prop back on the boat and see if the RPM's return to what they were before.<br /><br />It would kill you later if you found out all you had was a minor tuneup problem causing the loss in RPM which just happen to occur at the same time you installed the SS prop. It happens.<br /><br />If the RPM's return with the old prop on there, by all means...head for the prop shop pros.. for sure!

 

[rodbolt]

Re: Change pitch on stainless steel prop?

Hello<br /> most prop shops wont attempt to repitch a stainless wheel. they can play with the cup at the trailing edge. even with aluminium they wont usually try more than a 2" change in pitch. sounds like you went from an uncupped AL. wheel to a cupped SS one. they may try to take some of the cup out. I agree with the advice to retry the AL wheel then have it measured. there should be a whole subject just on props. seems with the new 4 strokes all the dealers are trying to prop it like a 2 stroke. prop technology is very confusing and what works on one rig wont work well on a similar rig.<br />good luck and keep posting

 

[proline2]

Re: Change pitch on stainless steel prop?

I checked both props and even though the stainless one is not a cupped prop per se, it seems to have a little more cup in it than the aluminum does. The reason for going to stainless was to replace the aluminum prop which was damaged by a lobster pot rope. The engine runs as smooth now as it did before but because of the damage to the aluminum prop I can't put it back on right now to check it against the stainless. I will be checking in with a prop shop to see what can be done with it. By the way, I checked in my OMC manual this morning and it recommended either stanless or aluminum in 15 x 17. Max speed for my size boat with that prop was listed at 28-32 mph, so I'm really not out of line with my present speed situation, I'm just running too few rpm's for the engine. Keeps the posts coming, this is helpful. Thanks