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Discussion Starter · #1 ·
My boat (Catalina 350) doesn't go as fast as it should under power. I get about 4.2 knots (GPS) at 2100 rpm, and get only 5.0 knots at 2600 rpm. I should be getting better than 6, even 7 knots at this speed. Where can I start diagnosing this?

My boat isn't loaded with junk, so it's not too heavy. The hull is clean. The prop is good. What gives? I don't even know where to start.
 

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1977 Morgan OI 30
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what size engine?

I have a 30' Morgan with a 27 hp Yanmar and get 6 knots ave. It only weighs 9,500 and I'm pretty sure your boat is heavier. How big is your engine?
 

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i would check the prop again, you might have picked up a line or a trash bag or something. then double check the bottom while under water

this is depending if it just lost speed, ie it was going faster
 

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thinking of this...
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Any smoke in the exhaust at high rpms? In addtion to the smoke, I couldn't get close to hull speed.

I just went through this and found a prop covered in barnacles. Easy fix.

see this thread
 

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jim after seeing your thread i dove on my boat, it was not as bad as yours. i am up by the inner harbor where are you on the chessy ( edit just saw south river ), it might be interesting to see the difference from where you are to where i am.

to answer your question that never got answered i held my breath. you did not ask me but i will answer any way. i found if i anchored in just enough water to keep the boat off the bottom is was easy to "sit" on the bottom and hold my hand on the hull to stay in place, that way no energy was used to stay in place
 

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It sounds like you've checked the usual suspects if the prop is clear and the bottom is clean. Will the engine turn higher RPMS or is 2600 wide open?

If it will turn more RPM's it might be that your tach is off. Other than that I can't think of anything else it might be.

Good Luck,
 

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Could you have barnacles on the prop

I need to dive on the prop every June to scrape a colony of small barnacles from the prop. In Annapolis they seem to be a regular visitor to my Pearson Vanguard, and I know its time to dive when I see my speed fall 2 knots from one weekend to the next when under power.

Good luck, and let us know what you find.
 

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Discussion Starter · #10 ·
I had the boat out of the water a few months ago. Hull was fresh then, and prop was clean. Engine is a Universal M35B, not making any smoke. I've had the boat about a year; this is how it's always been. The throttle is not maxed out....could a tachometer really get out of whack? How do you check that? Other people with the same boat/prop get a lot more speed.
 

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soul finger the prop can be fouled with barnacles in a month if the conditions are right. go look at the thread jsl3 linked to and see what 10 weeks did to his prop
 

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I had the boat out of the water a few months ago. Hull was fresh then, and prop was clean. Engine is a Universal M35B, not making any smoke. I've had the boat about a year; this is how it's always been. The throttle is not maxed out....could a tachometer really get out of whack? How do you check that? Other people with the same boat/prop get a lot more speed.
First a few months can make a huge difference. Here on the Chesapeake I got an encrustation an inch thick on each side of the prop in a two week period. The boat was fine one week, we came back two weeks later and the boat wouldn't back up worth a hoot and we noticed a marked decrease in speed and RPM. I'd suggest taking a swim with a mask and have a peek at the prop.

If it really is clean, you can check the RPM with an optical tachometer. The Catalina 36 owners group has one members can borrow so perhaps the 350 group does as well. One member reported a 350 RPM error which might well explain what you are seeing.
 

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Telstar 28
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Was the performance of the boat ever what you're expecting?

If not, the prop size/pitch could be wrong. That would result in not being able to make 3000 RPM and a lower than normal speed for the boat.
 

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Discussion Starter · #15 ·
That's why this is weird. This performance is not new, it has been that way since I bought the boat about a year ago. Originally, this model had some cavitation issues with the prop. Catalinia, in conjunction with Michigan Propellers and several 350 owners designed and tested a new prop for this boat.....the previous owner of my boat changed out to the new prop, so this shouldn't be a prop problem. I'll be going down to the boat tomorrow; I"ll try juicing the throttle and see what happens. I've never brought it over 2600 rpm on the tachometer.
 

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Don't assume correct prop

Even Catalina will not prop correctly for everyone, do you want power/speed or less drag? The two aren't always possible with the same prop. If it wont go well then it probably wont stop/back down well either.
I sent my last prop back to be repitched 3 times before I got max rpms at WOT. You need to get this figured out, you will be much happier, I know I was.
TJ
 

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Soul - Hey have you never tried to rev it past 2600 rpm? I don't know that engine, but most diesels ( my old Yanmar 2GM, for example) is designed to run continously at around 3200 rpms. Try opening up the throttle and see how many rpms you get in gear (full throttle!!!) And do you then get any smoke???? Then try revving it as high as possbile in neutral! How many rpms do you get, full throttle in neutral??

Joesaila- Just curious, but you have alot of HP for a 30 ft boat! At what rpms do you get 6kts??

I have a 30' boat, fin keel, book disp says 8600lbs, but the crane says closer to 10,000 loaded. I have a 15hp (peak) 13hp (continous) 1982 Yanmar 2GM. Last year (and likely for many years b4 I bought her), it would only reach 2200rpms and aboutr 6kts before black smoke, and no speed increase.
I had the 3 blade fixed prop taken down this spring from 15X10 to 14x9, and I am now able to run all day at 3200 rpms, and cruise at 6.4 kts. Even in a 15-20 kt headwind, I only lose a knot or so.

In hindsight, since it was previously overpropped, and I could only reach 2200 rpm, the engine wasonly producing about 8hp, or so. Now that I can run at 3200 rpm, I have about 13hp to puch the boat. Last year, a headwind would knock me back to 2.5 kts or so, as I couldn't rev higher, and use all available HP!
 

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That's why this is weird. This performance is not new, it has been that way since I bought the boat about a year ago.
Sounds like she's over-propped, to me. (Assuming the bottom and prop are clean and the drive train is all in order.)

the previous owner of my boat changed out to the new prop, so this shouldn't be a prop problem.
Have you asked the PO about his experiences, before and after the prop change?

Jim
 

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i have a perfect pitch 2 blade 15 by 11 pitch propeller. engine is a yanmar 2GM20F. transmission is a kanzaki 2.62 ratio. this will get up to 6.9 kn at 3,600 RPM, shaft RPM 1374. boat is a 1994 nimble 30 express. canoe stern. WL length is 27ft. WL beam is 8' 8 '' . the boat weighs a little over 7,000 lbs. this is the ideal setup for this vessel. i did research to get the correct prop and anyone who wants to check if their prop is correct should do this also. there is a lot of information online to help
 

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I'll second the advice to have to tach checked with an optical tach. It's common for the tach to read incorrectly.

Also, after completely warming up the engine (cruise for a solid 10-15 minutes), run it up to max rpm - wide open. After a few minutes read the tach. Compare this number to the max rated rpm, which is probably on the serial number plate of the motor. You should be able to get near the max rated rpm. You should cruise at 80% of your max achievable rpm. If you can't get near the max rated rpm you've got a problem.
 
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