OMC Cobra 140 hp low top speed..

[Dennis OMC]

hello,<br /><br />I'm new on this forum and i have a question..<br />I recently bought a boat with a 140 hp OMC cobra inboard (1991) this boat is about 5,5 meters long and weighs about 1000 kg.<br /><br />At full throttle te engine makes about 6000 rev's but the speed stalls at about 55 km/h (35 <br />mph)<br /><br />now i know somebody who ownes a Renken 1700 Classic whitch is about the same boat in size and weight and with the same engine.. this boat runs about 80 km/h (55 mph)on GPS on full throttle with the same prop!!<br /><br />Can anybody tell me what can be wrong with my boat?<br /><br />Thank you!!<br /><br />Best regards,<br />Dennis freom Holland

 

[tommays]

Re: OMC Cobra 140 hp low top speed..

you max rpm should be about 4400 to 4800 rpm but boat tacks are pretty bad so you need to test it against a shop tack<br /><br />35 mph is not a bad speed it really depends on the hull type once you no the correct RPM you can see if you can use a different prop<br /><br />nobody is going to go 55 mph with a 3.0 if you make it 40-42 mph your doing REAL GOOD<br /><br />tommays

 

[Dennis OMC]

Re: OMC Cobra 140 hp low top speed..

Thank you for your reply tommays!!<br /><br />So you say i need to connect an other tack to see if the rpm is really 6000?<br /><br />Ok i can do that very easy... <br /><br />Here is the adress to see a picture of my boat.<br />I don't think the hull has a bad shape... <br /><br /> http://www.mijnalbum.nl/Foto=ZHPYI3OB <br /><br /> http://www.mijnalbum.nl/Foto=N4TTSLXW <br /><br />thank you!