what can I do do improve planing and top speed

[sikz3]

I got a 1980 seaswirl w/ 140 omc. It takes along time to plane and is pretty slow once it gets out of the hole. I don't know what pitch the prop is cuz I can't read the numbers. I am at high elavation 3500' to 4500'. The boat rpms run at about 5000 rpm at wot maybe 5500. What size prop do you suggest?

 

[QC]

Re: what can I do do improve planing and top speed

Well . . . Everybody wants that, so don't feel alone.

Your RPM is too high for good top speed but your hole shot will truly suffer if you up the prop pitch. The only thing I can suggest would be some type of trim tabs, either adjustable or SmartTabs. Then you could go up two inches in pitch (if you don't know what you have now you'll have to find a shop that will allow you to test a few). The tabs will help with your hole shot even with more pitch and the pitch change should increase your top speed.

Has it ever run better? If yes, then your problem is probably not with the propeller . . .

P.S. You should repost this in Boat (not-engine) section.

 

[CaptAlfex]

Re: what can I do do improve planing and top speed

Top RPM speed for that motor is 4600 RPM. Unless you use boat for pulling skiers, I would suggest a higher pitch propeller. I have the same motor on a 3000 lb. boat and use a 15 or 17 inch pitch prop. I cruise at 3200 RPM at 23 MPH. You should never see 5000 RPM with the 3.0 liter engine. I agree with QC on the trim tabs addition. I have 8" ones on my 21' boat.

 

[Boatist]

Re: what can I do do improve planing and top speed

WOT RPM range for that motor is 4200 to 4600 rpms.
If your WOT RPMS are 5500 then You need to go up 4 to 6 inches in pitch. On average each inch in change reduces RPMS by 200. So if you go up 2 inches you would be at 5100 RPMS. Up 4 inches would be 4700 rpms. Up 6 inches would be 4300 rpms and your fasted top speed.
Your hole shot will take longer but you will get more speed and better gas mileages also.

My OMC 1980 140Hp on a 21 foot 2800 pound boat has two props. The 19 pitch 3 blade stainless turns 4200 WOT RPMS and has a top speed of 38 MPH. The 17 pitch 3 blade stainless turns 4600 WOT RPMS and has a top speed of 35 mph.

I always use the 19 pitch in ocean where we tend to make long trips. Often as much as 60 miles. Also in the ocean do not tend to do a lot of starts and stops. On a 60 mile round trip I will use 3 gallon less in fuel.

I use the 17 pitch mostly in river and lake where we tend to start and stop more. In river all the marinas or boat fishing. In lakes usually short runs 15 minutes or less.

My Motor has OMC select trim and Bennett 24 by 12 Hydraulic trim tabs so can get on plane very fast if I want to.