Right propellor versus speed ??

[Dutchman]

Dear Catalina owners,
We have a C34MK2, with an Universal 35BC.
My experience:
1800 rmp/min : 5.9 knots (my cruising speed for long distance).....fuel 2.5 ltr/hr
1900 rpm/min: 6.0-6.1 knots
2100 rpm/min: 6.5 knots
2300 rpm = the maximum speed 7.1 knots and is  little below the hull speed ? The swimmingplatform surface is just in the water.

So my opnion.....do I have the right propellor/pitch ??

Please give me your information and experience with your boat.

Best regards,
Ton Eijsermans
Amuse

[Ken Juul]

The first step in this process is to ensure that the tachometer is reading correctly.  You can purchase a laser rpm gun or your local boat mechanic should have one.  There are instructions in the tech wiki for adjusting the tach.

The speed profile you presented looks about right, you are not going to get much more than about 7 knots.  If the tachometer is determined to be correct, then I would say you are over pitched, the engine should reach close to 3000 rpm under load.

[Joe Kern]

I agree with Ken.   The RPMs seem low across the entire range to me.   Even with a clean bottom and clean prop 7 knots at 2300 rpm is much different than my experience.

[Stu Jackson]

Uhmm, maybe I missed it, but what pitch do you have on your prop?  What prop do you have?  Otherwise, we're all in the dark on this one.

[Ron Hill]

Tom : Look at my Mainsheet Article a few issues back on "RPM & Boat Speed."  I also talk about prop pitch.  A thought!!

[Tom Clay]

Ton,

We also own a MK11. We have the standard 3 blade prop supplied by Catalina. Your numbers are exactly what we see on our boat, even the swim platform item is the same. We do occasionally cruise at 2500 RPMs which give's us a hull speed of 7.3 knots.The majority of our time is spent at 2300-2400 rpm at 7.1-7.2 knots and we gain very little beyond 2600 RPM. Folks that cruise together with us are very surprised at how well she cruises.

1800 rmp/min : 5.9 knots (my cruising speed for long distance).....fuel 2.5 ltr/hr
1900 rpm/min: 6.0-6.1 knots
2100 rpm/min: 6.5 knots
2300 rpm = the maximum speed 7.1 knots and is  little below the hull speed ? The swimmingplatform surface is just in the water.

[SeaFever]

One question I would have is whether you are able to achieve your engine's rated max RPM or close to it. If not, you are perhaps over-pitched already. If you are, then you proceed at looking at other parameters...I have a M25 and don't remember the rated max rpm for the 35.

[Ron Hill]

Guys : The entire thrust of my Mainsheet article is : The rpm that you are quoting it it the Tach gage numbers ? or the real engine RPM numbers?( from a laser tach gage) 
It sure makes a difference!!   

[horsemel]

Ron,
Is a laser tach gage expensive?  I assume you can get them at an auto parts store.  Do tool rental places rent them?
Mark Mueller

[Craig Illman]

Mark - I think about $35, for sure less than $50.

Craig

[prh77]

I picked up a new one on Ebay for $22. Put the reflective tape on the pulley and found my tach was reading 300 RPM low. That explained a lot of things...

[Ron Hill]

Guys : As Peyton mentioned, Ebay has laser tachs for the $20 to the $50 range.