Boat won't stay on plane

[adamk523]

I have a LArson Cabrio 280 with twin 4.3 Mercs. The boat looses plane at less than 3500 rpms and only does about 20 MPH at 3500 rpms. I noticed that the rpms rev high and slowly drop down when I first take off. Seems like I am catching a lot of air when I go full throttle. THe boat tops out at 40 MPH at 4500 RPMS which is normal. I know someone with a 29 searay running the same engines and his boat planes better and runs faster. Any ideas?

 

[tommays]

Re: Boat won't stay on plane

do you have trim tabs ??<br /><br />tommays

 

[QC]

Re: Boat won't stay on plane

This sounds more like prop blowout, although I always recommend tabs, especially for a boat that size. Seems like the props just lose their bite at a couple of key spots. I would start talking to some local prop gurus myself.<br /><br />Good luck!! If that boat truly runs 40 at 4500 it should be able to hold a plane below 3500 IMHO. BTW, I just got my 23 footer to hold plane with tabs full down at 12 MPH and 1800 RPM . . . Just braggin', not suggesting your boat could or should do that.

 

[Jdeagro]

Re: Boat won't stay on plane

I think your top speed indicates that the props are about correct. On a boat of that size without trim tabs I am not surprised that you can not hold plane at 20 MPH. You will realize a termendous difference with the addition of trim tabs.

 

[adamk523]

Re: Boat won't stay on plane

I have trim tabs. When they are down, The boat will plane, but they put a tremendous drag on the boat slowing it down. The boat has a duo delta conic hull. It is a stepped hull which I think is designed to help the boat plane, but I was told that this might cause a lot of air. This would explain why the tachs go from 4500 down to 3500 when I start to take off. The bottom was just painted and is clean.

 

[Jdeagro]

Re: Boat won't stay on plane

Once you are on plane you should bring them up. If not, you will drive the bow in the water. You should Trim as needed to keep the boat on plane. At running speeds - you most likely do not need any trim.