Prop Pitch and Size

Ross · Feb 17, 2008

Horse power and gear ratio will help.

You have told us about the boat but not about the engine and transmission.

Ross · Feb 17, 2008

The best i can tell you is the I believe that you are under proped

I turn a 13x13 3 blade now I am having it repitched from 13x15 and I have 10 HP with a 3:1 gear. The 15 inch pitch was a little much. Repitching here costs about 100 dollars.

Maine Sail · Feb 17, 2008

Some things to consider first

Here are some things to consider before you address the props pitch or size.1) Are the bottom and the prop perfectly clean no barnacles and no slime or growth?2) Have you checked your tach against the actual crank shaft rpm with a photo electric tachometer? Many, many times these tachometers can be of by more than 300-800 RPM. These tachometers also do not always react in a linear fashion. By that I mean you could be off at idle by 150 RPM and a wide open by 500 RPM. Just like you have a compass deviation card you can also have a tachometer deviation card for what can't be adjusted out.3) Do you know for sure that the throttle cable is moving the engines throttle arm to it's max open throttle position.4) Have you confirmed with Catalina tech support what the correct prop size is?5) Are your fuel filters clean?6) Is your air filter clean?P.S. The standard factory supplied prop with the M-25 in 1982 was a two blade 13" X 12 pitch RH. You have a 1990 so I'd call Catalina to confirm the size of yours is correct.I think the 13X9 is the correct size and going up to a 10 pitch would only make your problem worse if you can't get to max RPM.

Stu Jackson · Feb 17, 2008

How about going to the SOURCE?

The C30 Association?Kinda basic, Maine Sail hit on most of it, but the prop on the C34 is DIFFERENT than a C30 because of the length of the strut and the clearance from the hull.Check your tach, too.

Jadedcrew · Feb 17, 2008

Prop (er) Pitch

Read Mainesail's post carefully. Correct me if I am wrong Mainesail, but you would need a tip clearance of 15% of the props diameter between the tip of the prop and the hull. That means you need 2 inches (1.95) for a 13 inch prop.A fixed (Michigan Wheel Propeller) 3 blade prop for my C36 with a 30hp is a 15X9. It came with a 2 blade 15X11.

Dave from Mi. · Feb 17, 2008

Hi Bad Obsession;I have a 96 Catalina30 with the Universal 25XP (23hp) I had the factory 3 blade 13X10 and was not happy with the performance. My engine turns 3200RPM WOT, with a Hurst 2:1 Tranny.I wrote to Michigan Wheel and another prop company, and ask for their recommendations. they both recommended that 13" diameter was the max to allow for proper hull clearance, (15% of prop diameter) and that a 13 pitch would be the best combination. They would sell me one for around 400$. I had my original repitched from 10 to 12 inches and I am very happy with the results. I can still turn 3200 rpm and I cruise at just over 6K (confirmed via GPS) in flat water at 2500. I was told that the max they could repitch a prop was about 2 inches.As others have said, check your tach, that engine should turn that prop to max rpm unless cover in barnacles or crap. My handbook says 3200 is max and cruise from 2100-2600 rpm.Hope this helps.Fair windsDave

ITMaster · Feb 23, 2008

I'm not a nautical or marine engineer

But maybe one of the folks like Maine Sail could elaborate on this. My understanding about theoretical hull speed is that it is a function of the square root of the length at the water line times 1.33. Therefore, a 30 footer should not run as fast as a 34 or 36 footer. Even with the same size engine or even with an engine larger than that on a longer boat. I have been told that you can put a larger engine on a boat, yet with a displacing hull, the boat is still going to have limited hull speed based upon the function cited above.I have noticed that the most critical factor of speed for my boat, is how clean the prop is kept. If growth is allowed to accumulate on the prop and the hull, the boat is going to go slower than it will with a clean prop and hull.I have a friend that allowed his catalina 36 mk II to sit to the point that one day they went to take the boat out and it wouldn't go. They made arrangements to get the boat repowered, since they were convinced that the engine was shot, only to find out that the prop was covered in barnacles, so bad the boat wouldn't go. Fortunately, I am not in as much need of being educated as my friend. My advice to you would be to copy down the list that Main Sail has given you and do exactly what is said in the order it is said. Good luck.

All U Get · Feb 23, 2008

Oh oh

I've writen the same question after reading similar threads for three years. Although a bigger boat is supported with facts, the first mate is threatening a general inquiry if I proceed. Therefore I am creating a portfolio of supporting facts for the upgrade. Presently i'm doing some research on design that may provide better thrust for my 81 Catilina 30.

Jim S. · Feb 26, 2008

Prop

I have a C30 mkIII with a 25XP emgine and a 14x14 Martec folding prop. That is the size they recommended five years ago. I don't know what rpm or knots I run, but I have the fastest sail boat in the marina. I usually cruise at 2100 rpm. I would run more but my auto pilot can't take the prop wash into current.

Dave from Mi. · Feb 26, 2008

Laser Tachometer

Hi Bad Obsession;Go to EBAY, search for "laser Tachometer" you will get about 100 "hits" with prices ranging from $25 and up.It is a small hand held battery powered unit. Simply put some of the refelective tape provide with the unit on the main pully of your engine and "shoot it" with the laser tachometer for a rpm reading. You can adjust your tach with the small adjustment screw on the back of your boat tach. I would check it over the whole range of operating RPM, as it can differ at various speeds.You will be the most popular guy in the marina when word gets out that you own one!Fair windsDave

Prop Pitch and Size

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