My boat is slow under power...why?

[soulfinger]

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.

[Joesaila]

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?

[BristolJonny]

has it always been slow or is this a new thing? Your prop could be pitched wrong, or perhaps your transmission is slipping?

[scottyt]

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

[bubb2]

is the tide coming in and you are heading out when you see the slower GPS speeds?

[JSL3]

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

[scottyt]

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

[PalmettoSailor]

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,

[reillyjd]

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.

[soulfinger]

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.