Boat Speed and Fuel Consumtion

[nvilleteacher]

I have a Catalina 380 that was built in 1999 that I purchased this past spring. The boat came with a self feathering propeller made by Autostream. I am wondering if the self feathering prop is in need of some adjustment. It if difficult to get the boat to motor much past 6 knots. I have been cruising at 2800 rpm and increasing the engine speed makes the boat sound over-revved. My fuel consumption is 1.5-1.75 gallons per hour. The engine is stock, Westerbeke 42 hp 4 cylinder. I draw 5.5 feet with the finned keel.

I am wondering if my prop has enough pitch.

What should my flat water cruising speed be?
How much fuel should I be consuming?

Any help/insight is appreciated.

Paul

 

[Claude L.-Auger]

Specs showing on site here talk about 7.9 knots for hull speed of your 38. Water line length is listed at 34'8". If your numbers differ, you can do your own maths with the theoretical formula everybody uses: 1.34 X Sq. root of LWL.

Others with same model can probably help you with fuel consumption figures. Obviously there is a relationship between your current speed (or lack of) and fuel usage since the 6+ speed is a real indication that the engine/tranny/prop system is not operating as efficiently as it should.

Whether it's your prop or something else, there are several things to consider before you can reach an answer:
1) Has the boat always been able to reach only 6+ kn or is it something new ? 2) What is the condition of the bottom ?
3) What is your transmission ratio ?
4) What is top RPM engine is rated for ?
5) Is your tach giving you the proper info ?
6) Is the engine able to reach and maintain top RPM while under load ?
7) Are you getting black smoke when pushing it ?
8) Have you compared the pitch and diameter of your prop with similar boats ?
9) Do you have access to the adjustment ratios for your prop ?

 

[nvilleteacher]

Claude,

Thanks for the response. You are correct to detail all of the variables that could effect my boat speed while under power. What I'm dealing with is a stock boat where the prop has been replaced. The engine and trans are original to the boat. What I was looking for is another boat, with a stock setup, to compare my boat to. I'm hoping to make the proper adjustments to my prop that will improve my performance.

Does anyone out there have a Catalina 380 with the Westerbeke 42 hp engine, standard trans and prop? If so, how fast can you cruise and what is your fuel consumption like? I'd like to know what my boat should be capable of while under power.

Paul

 

[Claude L.-Auger]

Paul, I do understand your need to compare, but specs for the boat talk about 7.9 knots hull speed. That is indeed a valid number. And your engine/tranny/prop system should get you close to that. You mention getting only a little over 6. That is more than 20% less than what you should be able to reach. It is way too much of a difference and there is definitely something wrong somewhere. Hopefully someone with the same set-up will chime in and be able to point you in the right direction. Why not give a call to Martec (Auto-Stream). If you provide the info re engine and tranny they might be able to help you in regards to the prop. http://www.martec-props.com/autostream.htm Good luck