cruising speed??

[angie1015]

this may be a dumb question... my boat is a 1982 larson 25 cabin cruiser with a 350 and an omc stringer drive..... i can get it up to about 31 mph on a flat river pretty much wide open trottle...(if i hold it wide open it boggs out a little,prob a filter or something) and the rpms are about 37-3800. I can do about 19 mph at 28-2900 rpms and 23 mph at about 32-3300 rpms. my question is what speed is a good cruising speed. am i pushing the motor by holding it at 23mph 3300 rpms..i have an old drive (in great shape however) and even though my motor is a fresh rebuild I still want to baby the boat cause i dont want any problems... I also want to get the best gas mileage possible... any suggestions ...

 

[FreeBeeTony]

Re: cruising speed??

Think you want to go down in prop pitch...........your WOT should be about 4200-4500RPM's.

 

[angie1015]

Re: cruising speed??

if i go down in prop pitch will i plain out eaiser??? will that hurt my gas mileage. I am not really looking to get the rpms up to 4500. the motor is screaming enough at 3800.... i just want to cruise and have a happy motor while getting the best gas mileage...

 

[FreeBeeTony]

Re: cruising speed??

Others will join in here..........but.............

If your WOT is only 3800RPM then your "lugging" the engine which can cause serious damage and shorten the life of the engine.

Are you sure of the WOT RPM's? Is your tach accurate?

 

[angie1015]

Re: cruising speed??

actually if I try to give it wot it boggs out a little bit. not bad but i think i need to change the filters or something. like i said i am all about cruising in this boat so wot has not been a concern...

 

[QC]

Re: cruising speed??

FreeBeeAntonio is correct. Yes, you should:

A) Verify your tach is accurate
B) Get the engine running right
C) Verify your WOT RPM with the engine right

With the lower pitch prop it will absolutely plane easier. Yes, theoretically fuel economy might suffer, but it will be sooo slight you won't notice. None of this discussion may be necessary if the prop is correctly sized as is, but we can't know that without A, B and C . . .

 

[Limited-Time]

Re: cruising speed??

FreeBeeAntonio is correct. Yes, you should:

A) Verify your tach is accurate
B) Get the engine running right
C) Verify your WOT RPM with the engine right

With the lower pitch prop it will absolutely plane easier. Yes, theoretically fuel economy might suffer, but it will be sooo slight you won't notice. None of this discussion may be necessary if the prop is correctly sized as is, but we can't know that without A, B and C . . .

In this case A+B will give you C, but only if A and B are correct to begin with. If your not developing full power due to an ing. or fuel delivery issue, or your tach is 1000 RPM low. Your WOT cannot be verified.

 

[Don S]

Re: cruising speed??

And here are some reasons that will prevent you from getting that all important WOT rpm.

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel
• Propeller pitch or diameter, damaged blades
• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
• Marine growth on hull and outdrive
• Wrong gear ratio in outdrive
• Restricted carburetor air intake (clogged flame arrestor)
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Boat overloaded, improperly loaded, or improperly trimmed.
• Engine Overheating
• Engine timing and ignition system operation (Full tuneup done recently)
• Remote control cables and linkage for proper travel to open throttle plates fully.

 

[angie1015]

Re: cruising speed??

thanks for the great help..im pretty sure its a fuel problem. if i try to give it to much gas it boggs down cause its not getting enough fuel. i do have to check the timing however it sounds to me like a fuel problem....

 

[Limited-Time]

Re: cruising speed??

angie....if you suspect a fuel delivery issue check out this post, HOW TO: Testing Your Boats Fuel System. - iboats Boating Forums This will help you correctly ID the problem, or rule out the fuel systen as the issue.