Power/Speed issue

[srokag44]

Had my 10 meter out this evening and was only hitting around 14 knots at 3400 rpm. Engine temperatures and oil pressures looked good. Spark plugs are new. Bottom was cleaned by a diver 2 weeks ago. Didn't hear or feel anything unusual.

What should I be looking at as possible causes for the loss of power? What would you start with? Fuel filters? (I don't know when they were last replaced) Fuel pump? Carbs?

Thanks in advance for any advice!

[RWS]

Is this the early design (three port windows per side) or the later design (two port windows per side) ?

Otherwise the obvious question is what is your WOT RPM and KTS now and what were these data prior?

RWS

[prowlersfish]

Had my 10 meter out this evening and was only hitting around 14 knots at 3400 rpm. Engine temperatures and oil pressures looked good. Spark plugs are new. Bottom was cleaned by a diver 2 weeks ago. Didn't hear or feel anything unusual.

What should I be looking at as possible causes for the loss of power? What would you start with? Fuel filters? (I don't know when they were last replaced) Fuel pump? Carbs?

Thanks in advance for any advice!

Only hitting 14 knots at 3400 rpm ,. And I can assume you where a lot faster at 3400 rpm before ,correct ? If I am correct in this assumption then the engines are not the problem , its the boat . Meaning the bottom/running gear . Some divers don't do a good job , seen some just clean the wheels and skip the shafts etc. . And thats what you get. But in the divers defense growth happens fast in warm water . If its been a while since haul out and you have no antfouling left on the running gear like popp speed or zinc coat , Then you can expect to clean the running gear every few weeks .

Nothing you do to a engine will change the speed at a given rpm .

[Big D]

....what is your WOT RPM.....

+1
You need to get this out of the way first IMO. Don't worry about speed yet. Assuming hardware has not been changed, if the engines are spooling up to rated WOT, then it is not an engine problem.

Not that this may have a bearing yet but if you don't know when your fuel filters were replaced then it's time to replace them!! Habbit for me is to replace at the end of every season as part of my winterizing proceedure, so at least once a season in my books.

[prowlersfish]

But if he is not hitting full rpm it can still be a running gear bottom issue . the speed vs RPM change is what will answer the question . If there in a big change in the speed at a given rpm then its not the engine . If the speed at that rpm is the same as before and the engine won't turn up then it can be a engine issue . But if the speed has dropped at 3400 then its NOT a engine issue . I wish I had all the money waste fixing engines when the boat bottom was the problem .

Remember this boat is in FLA waters . And there are some divers that are not doing a good job ( and some that are great ) I seen a few clean the areas you can see and thats it .


What was your speed before at 3400rpm ? I see boats lose half their rpm and not get on plane and the issue is the running gear all the time .

[Big D]

But if he is not hitting full rpm it can still be a running gear bottom issue . the speed vs RPM change is what will answer the question . If there in a big change in the speed at a given rpm then its not the engine . If the speed at that rpm is the same as before and the engine won't turn up then it can be a engine issue . But if the speed has dropped at 3400 then its NOT a engine issue . I wish i had all the money waste fixing engines when the boat bottom was the problem .

Remember this boat is in FLA waters . And there are some divers that are not doing a good job ( and some that are great ) I seen a few clean the areas you can see and thats it .


What was your speed before at 3400rpm ?

Absolutely correct Paul, just suggesting something else as he does not mention prior numbers at that rpm or whether 3400 is all he's getting; re "loss of power".

[prowlersfish]

Good info & complete info gives better answers . a few weeks of growth can easly cause drop in rpm and speed arond here , and Fla has a bigger growth issue .

[prowlersfish]

one other thing "power loss" is it both engines ? growth will effect both , but not always the same , I have more of a issue on my port.

[srokag44]

Thanks for all the responses!

The boat is a two window per side Sedan.

Each engine will reach about 3800-3900 rpm at WOT. This has always been the case. I seem to remember getting up to around 18 knots at 3400 about a year ago. Bottom job hasn't been done in about 2 years so perhaps it's time? I will dive under there today when I'm out in clearer water to take a look for myself.

Still got up on plane last night at 3400 rpm with full tabs down, just felt a bit sluggish and GPS confirmed slower than it should be.

[Big D]

....Bottom was cleaned by a diver 2 weeks ago.....

....Bottom job hasn't been done in about 2 years so perhaps it's time?....

Huh?
I think you found your problem!

[prowlersfish]

Even the best divers can only do so much , shafts props and rudders need to be as clean as possible . Wear glove barnacles will cut the heck out of you ,I have the scars to prove it .

[goros]

Good morning. I own a F32 of 78 with two yanmar engines of 240 hp each. Do not run over 3400 rpm 14 n maxima. I modified the boat by extending the swim platform. I have no flaps stabilizers. I have very dirty diesel with mucus bacteria. Whenever the sea is angry and turns my diesel engine is for closing the filters. It may be that the problem of lack of speed?

thanks and greetings from Spain

[bigrgh]

changed my spark plugs this year...(twin 454's) boat would only pull 3400 rpm at wide open throttle.(both engines).... one spark plug wire was accidently left off a plug,(on starbord engine)... when found and replaced on the spark plug, the boat ran perfect 4200 rpm at 33 mph...damn Captain Morgans!!! lol

[sehord]

My 10 meter 454's run 4400 max. I cruise with tabs down at 3000 getting 18knts.... Cool her off to 2500 with tabs still planing at 14kts. The engine does not have any idea how fast it makes the boat go just rpm. Ill bet you've got some potatoes on your props....

[srokag44]

Sure enough there were a couple barnacles on the props and a lot of white squiggly looking growth. I'll post pictures I took with my underwater camera later tonight.